Manifestation of the jet photosphere
during the prompt phase in GRBs

Felix Ryde
KTH Royal Institute of Technology
Stockholm

On behalf of the Fermi GBM and LAT teams

Wednesday, 13 November 13

Bottom Line
1. Band crisis
The Band function is not the universal GRB
spectrum. What does it mean?
2. Appearance of the photosphereBlackbody, BB+nonthermal, broadened functions

3. GRB jet properties are variable.
Lorentz factor decreases over individual
pulses while the flow nozzle increase

Wednesday, 13 November 13

Bottom Line
1. Band crisis
The Band function is not the universal GRB
spectrum. What does it mean?
2. Appearance of the photosphereBlackbody, BB+nonthermal, broadened functions

3. GRB jet properties are variable.
Lorentz factor decreases over individual
pulses while the flow nozzle increase

Wednesday, 13 November 13

Spectral shapes of Fermi GRBs

The most well-observed bursts, i.e. most fluent and within the LAT FoV
Exponential cut off

Additional power law

GRB100724B

Additional p-l with cut off
GRB110731

GRB090510A

Double humped spectra
GRB110721

Statistically highly significant deviations from the Band function

Wednesday, 13 November 13

Spectral shapes of Fermi GRBs

The most well-observed bursts, i.e. most fluent and within the LAT FoV
Exponential cut off

Additional power law

GRB100724B

Additional p-l with cut off

GRB090510A

Double humped spectra

GRB110731

GRB110721

Statistically highly significant deviations from the Band function“Band Model Crisis”
Wednesday, 13 November 13

GBM+LAT joint spectral fits during “GBM” time window

Tetsted models:•Band function•Comptonized (cutoff p-l)
•Additional power laws
•Cut-offs(Possible photosphericcomponent not includedin the catalogue)

Ackermann et al. 2013, ApJS, 209, 11

The phenomenological Band model, implemented for BATSE GRB observations up to a few MeV,
does not seem to describe bright or well-observed LAT-detected GRBs sufficiently.

McEnery’s talkWednesday, 13 November 13

GBM+LAT joint spectral fits during “GBM” time window

Tetsted models:•Band function•Comptonized (cutoff p-l)
•Additional power laws
•Cut-offs(Possible photosphericcomponent not includedin the catalogue)

Ackermann et al. 2013, ApJS, 209, 11

The phenomenological Band model, implemented for BATSE GRB observations up to a few MeV,
does not seem to describe bright or well-observed LAT-detected GRBs sufficiently.

Band function is not a universal form of GRB spectra

Wednesday, 13 November 13

McEnery’s talkGBM+LAT joint spectral fits during “GBM” time window

Tetsted models:•Band function•Comptonized (cutoff p-l)
•Additional power laws
•Cut-offs(Possible photosphericcomponent not includedin the catalogue)

Ackermann et al. 2013, ApJS, 209, 11

The phenomenological Band model, implemented for BATSE GRB observations up to a few MeV,
does not seem to describe bright or well-observed LAT-detected GRBs sufficiently.

Band function is not a universal form of GRB spectra

McEnery’s talk

Extrapolating the Band function from LOW to HIGH energy is really a BAD idea!
Wednesday, 13 November 13

Which spectral fit is the correct one?
GRB080916c•Single emission zone?
•Multiple emission zones?
•Emission mechanism?

Guiriec et al. (2012; Marcel Grossman)
Wednesday, 13 November 13

Band function is not a universal form of GRB spectra

Solution: Fit theoretical models directly to the data!
Examples: Titarchuck et al. 2012, Burgess et al. 2013
A theoretical model should, after convolution with the response,
fit a Band function. Model deviations from a
Band function is thus possible!
In Burgess et al. 2013 it was showed that synchrotron emission
spectra that are fitted with a Band function has  values centeredaroundand not the expected -2/3.

Wednesday, 13 November 13

Bottom Line
1. Band crisis
The band function is not the universal GRB
spectrum. What does it mean?
2. Appearance of the photosphereBlackbody, BB+nonthermal, broadened functions

3. GRB jet properties are variable.
Lorentz factor decreases over individual
pulses while the flow nozzle increase

Wednesday, 13 November 13

Basic framework: the fireball model

Wednesday, 13 November 13

I. Single Planck function bursts

GRB930214

Ryde 2004
Spectra from temporally resolved pulses observedby BATSE over the energy range 20-2000 keV.

CGRO BATSE: 6 observed bursts
Wednesday, 13 November 13

Ryde (2004): Blackbody through out the pulse
Ghirlanda et al. (2003): Blackbody in initial
phase of burst

I. Single Planck function bursts

GRB930214
Rayleigh Jeans’ slope

Ryde 2004
Spectra from temporally resolved pulses observedby BATSE over the energy range 20-2000 keV.

CGRO BATSE: 6 observed bursts
Wednesday, 13 November 13

Ryde (2004): Blackbody through out the pulse
Ghirlanda et al. (2003): Blackbody in initial
phase of burst

I. Single Planck function bursts

GRB930214
Rayleigh Jeans’ slope

Ryde 2004
Spectra from temporally resolved pulses observedby BATSE over the energy range 20-2000 keV.

Void of photons

CGRO BATSE: 6 observed bursts
Wednesday, 13 November 13

Ryde (2004): Blackbody through out the pulse
Ghirlanda et al. (2003): Blackbody in initial
phase of burst

I. Single Planck function bursts
Fermi Gamma Ray Space Telescope
GRB100507

Ghirlanda et al. 2013

Wednesday, 13 November 13

I. Single Planck function bursts
Fermi Gamma Ray Space Telescope
GRB100507
Rayleigh Jeans’ slope

Ghirlanda et al. 2013
Void of photons
Wednesday, 13 November 13

GRB090902B Abdo et al. (2009), Ryde et al. (2010) Zhang et al. (2010)
Time resolved spectrum (11.608-11.880 s)= 0.55 +/- 0.16

CGRO BATSE
FWHM < 1 dex

15.9-16.4 s

Q FQ [keV cm-2 s-1]

LATb
LATf

Energy [keV]

Synchrotron emission excluded. likely photospheric emission

Wednesday, 13 November 13

GRB090902B Abdo et al. (2009), Ryde et al. (2010) Zhang et al. (2010)
Time resolved spectrum (11.608-11.880 s)= 0.55 +/- 0.16

CGRO BATSE
FWHM < 1 dex

15.9-16.4 s

Q FQ [keV cm-2 s-1]

LATb
LATf

Energy [keV]

Synchrotron emission excluded. likely photospheric emission

Wednesday, 13 November 13

GRB090902B Abdo et al. (2009), Ryde et al. (2010) Zhang et al. (2010)
Time resolved spectrum (11.608-11.880 s)= 0.55 +/- 0.16

CGRO BATSE
FWHM < 1 dex

15.9-16.4 s

Q FQ [keV cm-2 s-1]

LATb
LATf

Energy [keV]

Synchrotron emission excluded. likely photospheric emission

Observations of a Planck spectrum means that the spectrum was formed while
the outflow was photon dominated (below the saturation radius) or thatdissipation ended during the Planck or Wien part of the flow (Beloborodov 2011)
Wednesday, 13 November 13

II. Blackbody + additional component
Band only

Wednesday, 13 November 13

BB+plII. Blackbody + additional component
Band only

BB+pl

Ryde 2005

Wednesday, 13 November 13

II. Blackbody + additional component
Band only

BB+pl

Ryde 2005

Wednesday, 13 November 13

GRB 960530

Photosphere in GRB100724B

Guiriec+10

Limiting the band width to 8 keV - 1500 keV (Comparing the BATSE fits)
Band model

CGRO BATSE fits of GRB981021(Ryde & Pe’er 2009)

NaI
Band

GRB981021

Additional
non-thermal
emission
GAMMA-RAY BURST
SPECTRAL CORRELATIONS

Fig. 6.— Spectrum from GRB 960530 (trigger 5478; 6 s after the trigger) fitted with the Band et al. (1993with the two-component model ( Ryde 2004), with a power-law slope of s ¼ #0:62 " 0:27 (right). Note140
theSchaefer 1999).
GRB 960530

No. 2, 2006

V

E FE

in the flux beyond 600 keV. This component should be mostimportant at energies beyond the BATSE window studied here.
Interestingly, a few super-MeV detections have been made todate that indicate the presence of a possible, additional emission
component at these energies (Hurley et al. 1994; Atkins et al.
2000; González et al. 2003). In comparing the two plots in Figure 6,
it is important to note the property known as ‘‘obliging’’; thatis, for models that fit the data badly, the data points tend to be incorrectly depicted. This is a well-known property of the forwardfolding technique used for the deconvolution (Fenimore et al.
1983; Bromm & Schaefer 1999). The observed quantity is thephoton counts, while the physically interesting photon flux or en-

BB+pl model

NaI
BB+pl

ergy flux are derfore a plot show
trusted fully if th
fitting is made o
GRB 960530 is

The choice o
distinctly differe
served, spectral
shows the spect
Band et al. (19

GRB981021

Fig. 6.— Spectrum from GRB 960530 (trigger 5478; 6 s after the trigger) fitted with the Band et al. (1993) model with " ¼ 1:7 " 1:5 and # ¼ #2:4 " 0:3 (left), awith the two-component model ( Ryde 2004), with a power-law slope of s ¼ #0:62 " 0:27 (right). Note the obliging of the data points (Fenimore et al. 1983; Bromm
Schaefer 1999).

V

E FE

in the flux beyond 600 keV. This component should be mostimportant at energies beyond the BATSE window studied here.
Interestingly, a few super-MeV detections have been made todate that indicate the presence of a possible, additional emission
component at these energies (Hurley et al. 1994; Atkins et al.
2000; González et al. 2003). In comparing the two plots in Figure 6,
it is important to note the property known as ‘‘obliging’’; thatis, for models that fit the data badly, the data points tend to be incorrectly depicted. This is a well-known property of the forwardfolding technique used for the deconvolution (Fenimore et al.
1983; Bromm & Schaefer 1999). The observed quantity is thephoton counts, while the physically interesting photon flux or en-

ergy flux are derived quantities that are model dependent. Ther
fore a plot showing the photon or the energy flux can only b
trusted fully if the model fits the data well. However, the statistic
fitting is made on the count data and is independent of this effec
GRB 960530 is further discussed in the following section.
2.3. Spectral Evolution

The choice of the model used to fit the !-ray data will lead
distinctly different interpretations of the cause of the apparent, oserved, spectral evolution. This is illustrated in Figure 7, whic
shows the spectral evolution of GRB 910927 (trigger 829). Th
Band et al. (1993) model is used for the fits in the top pane

EGRET TASC data available
for this burst; peak energy = 1600 keV

Fig. 7.— Spectral evolution of GRB 910927 (trigger 829), represented by time bins at 1, 6, and 10 s after tusing the Band model results in evolution of " and Ep. In particular, the "-evolution is noteworthy. Bottom
becomes very typical, in particular in the evolutions of kT and s. The data points have been rebinned to S/

Wednesday, 13 November 13

GRB 960530

Photosphere in GRB100724B

Guiriec+10

Limiting the band width to 8 keV - 1500 keV (Comparing the BATSE fits)
Band model

CGRO BATSE fits of GRB981021(Ryde & Pe’er 2009)

NaI
Band

GRB981021

Additional
non-thermal
emission
GAMMA-RAY BURST
SPECTRAL CORRELATIONS

Fig. 6.— Spectrum from GRB 960530 (trigger 5478; 6 s after the trigger) fitted with the Band et al. (1993with the two-component model ( Ryde 2004), with a power-law slope of s ¼ #0:62 " 0:27 (right). Note140
theSchaefer 1999).
GRB 960530

No. 2, 2006

V

E FE

in the flux beyond 600 keV. This component should be mostimportant at energies beyond the BATSE window studied here.
Interestingly, a few super-MeV detections have been made todate that indicate the presence of a possible, additional emission
component at these energies (Hurley et al. 1994; Atkins et al.
2000; González et al. 2003). In comparing the two plots in Figure 6,
it is important to note the property known as ‘‘obliging’’; thatis, for models that fit the data badly, the data points tend to be incorrectly depicted. This is a well-known property of the forwardfolding technique used for the deconvolution (Fenimore et al.
1983; Bromm & Schaefer 1999). The observed quantity is thephoton counts, while the physically interesting photon flux or en-

BB+pl model

NaI
BB+pl

ergy flux are derfore a plot show
trusted fully if th
fitting is made o
GRB 960530 is

The choice o
distinctly differe
served, spectral
shows the spect
Band et al. (19

GRB981021

Fig. 6.— Spectrum from GRB 960530 (trigger 5478; 6 s after the trigger) fitted with the Band et al. (1993) model with " ¼ 1:7 " 1:5 and # ¼ #2:4 " 0:3 (left), awith the two-component model ( Ryde 2004), with a power-law slope of s ¼ #0:62 " 0:27 (right). Note the obliging of the data points (Fenimore et al. 1983; Bromm
Schaefer 1999).

V

E FE

in the flux beyond 600 keV. This component should be mostimportant at energies beyond the BATSE window studied here.
Interestingly, a few super-MeV detections have been made todate that indicate the presence of a possible, additional emission
component at these energies (Hurley et al. 1994; Atkins et al.
2000; González et al. 2003). In comparing the two plots in Figure 6,
it is important to note the property known as ‘‘obliging’’; thatis, for models that fit the data badly, the data points tend to be incorrectly depicted. This is a well-known property of the forwardfolding technique used for the deconvolution (Fenimore et al.
1983; Bromm & Schaefer 1999). The observed quantity is thephoton counts, while the physically interesting photon flux or en-

ergy flux are derived quantities that are model dependent. Ther
fore a plot showing the photon or the energy flux can only b
trusted fully if the model fits the data well. However, the statistic
fitting is made on the count data and is independent of this effec
GRB 960530 is further discussed in the following section.
2.3. Spectral Evolution

The choice of the model used to fit the !-ray data will lead
distinctly different interpretations of the cause of the apparent, oserved, spectral evolution. This is illustrated in Figure 7, whic
shows the spectral evolution of GRB 910927 (trigger 829). Th
Band et al. (1993) model is used for the fits in the top pane

EGRET TASC data available
for this burst; peak energy = 1600 keV

Fig. 7.— Spectral evolution of GRB 910927 (trigger 829), represented by time bins at 1, 6, and 10 s after tusing the Band model results in evolution of " and Ep. In particular, the "-evolution is noteworthy. Bottom
becomes very typical, in particular in the evolutions of kT and s. The data points have been rebinned to S/

Wednesday, 13 November 13

GRB 960530

Photosphere in GRB100724B

Guiriec+10

Limiting the band width to 8 keV - 1500 keV (Comparing the BATSE fits)
Band modelaI + BGO
B+BandCGRO BATSE fits of GRB981021(Ryde & Pe’er 2009)

NaI Two components needed; a Band function
Bandand a BB (see Guiriec+10, Ryde+10, 11,
Burgess+11, McGlynn+12)

GRB981021

Additional
non-thermal
emission
GAMMA-RAY BURST
SPECTRAL CORRELATIONS

Fig. 6.— Spectrum from GRB 960530 (trigger 5478; 6 s after the trigger) fitted with the Band et al. (1993with the two-component model ( Ryde 2004), with a power-law slope of s ¼ #0:62 " 0:27 (right). Note140
theSchaefer 1999).
GRB 960530

No. 2, 2006

V

E FE

in the flux beyond 600 keV. This component should be mostimportant at energies beyond the BATSE window studied here.
Interestingly, a few super-MeV detections have been made todate that indicate the presence of a possible, additional emission
component at these energies (Hurley et al. 1994; Atkins et al.
2000; González et al. 2003). In comparing the two plots in Figure 6,
it is important to note the property known as ‘‘obliging’’; thatis, for models that fit the data badly, the data points tend to be incorrectly depicted. This is a well-known property of the forwardfolding technique used for the deconvolution (Fenimore et al.
1983; Bromm & Schaefer 1999). The observed quantity is thephoton counts, while the physically interesting photon flux or en-

BB+pl model

NaI
BB+pl

ergy flux are derfore a plot show
trusted fully if th
fitting is made o
GRB 960530 is

The choice o
distinctly differe
served, spectral
shows the spect
Band et al. (19

GRB981021

Fig. 6.— Spectrum from GRB 960530 (trigger 5478; 6 s after the trigger) fitted with the Band et al. (1993) model with " ¼ 1:7 " 1:5 and # ¼ #2:4 " 0:3 (left), awith the two-component model ( Ryde 2004), with a power-law slope of s ¼ #0:62 " 0:27 (right). Note the obliging of the data points (Fenimore et al. 1983; Bromm
Schaefer 1999).

V

E FE

in the flux beyond 600 keV. This component should be mostimportant at energies beyond the BATSE window studied here.
Interestingly, a few super-MeV detections have been made todate that indicate the presence of a possible, additional emission
component at these energies (Hurley et al. 1994; Atkins et al.
2000; González et al. 2003). In comparing the two plots in Figure 6,
it is important to note the property known as ‘‘obliging’’; thatis, for models that fit the data badly, the data points tend to be incorrectly depicted. This is a well-known property of the forwardfolding technique used for the deconvolution (Fenimore et al.
1983; Bromm & Schaefer 1999). The observed quantity is thephoton counts, while the physically interesting photon flux or en-

ergy flux are derived quantities that are model dependent. Ther
fore a plot showing the photon or the energy flux can only b
trusted fully if the model fits the data well. However, the statistic
fitting is made on the count data and is independent of this effec
GRB 960530 is further discussed in the following section.
2.3. Spectral Evolution

The choice of the model used to fit the !-ray data will lead
distinctly different interpretations of the cause of the apparent, oserved, spectral evolution. This is illustrated in Figure 7, whic
shows the spectral evolution of GRB 910927 (trigger 829). Th
Band et al. (1993) model is used for the fits in the top pane

EGRET TASC data available
for this burst; peak energy = 1600 keV

Fig. 7.— Spectral evolution of GRB 910927 (trigger 829), represented by time bins at 1, 6, and 10 s after tusing the Band model results in evolution of " and Ep. In particular, the "-evolution is noteworthy. Bottom
becomes very typical, in particular in the evolutions of kT and s. The data points have been rebinned to S/

Wednesday, 13 November 13

GRB 960530

Photosphere in GRB100724B

Guiriec+10

Limiting the band width to 8 keV - 1500 keV (Comparing the BATSE fits)
Band modelaI + BGO
B+BandCGRO BATSE fits of GRB981021(Ryde & Pe’er 2009)

NaI Two components needed; a Band function
Bandand a BB (see Guiriec+10, Ryde+10, 11,
Burgess+11, McGlynn+12)

GRB981021

Additional
non-thermal
emission
GAMMA-RAY BURST
SPECTRAL CORRELATIONS

Fig. 6.— Spectrum from GRB 960530 (trigger 5478; 6 s after the trigger) fitted with the Band et al. (1993with the two-component model ( Ryde 2004), with a power-law slope of s ¼ #0:62 " 0:27 (right). Note140
theSchaefer 1999).
GRB 960530

No. 2, 2006

V

E FE

in the flux beyond 600 keV. This component should be mostimportant at energies beyond the BATSE window studied here.
Interestingly, a few super-MeV detections have been made todate that indicate the presence of a possible, additional emission
component at these energies (Hurley et al. 1994; Atkins et al.
2000; González et al. 2003). In comparing the two plots in Figure 6,
it is important to note the property known as ‘‘obliging’’; thatis, for models that fit the data badly, the data points tend to be incorrectly depicted. This is a well-known property of the forwardfolding technique used for the deconvolution (Fenimore et al.
1983; Bromm & Schaefer 1999). The observed quantity is thephoton counts, while the physically interesting photon flux or en-

BB+pl model

NaI
BB+pl

ergy flux are derfore a plot show
trusted fully if th
fitting is made o
GRB 960530 is

The choice o
distinctly differe
served, spectral
shows the spect
Band et al. (19

GRB981021

Fig. 6.— Spectrum from GRB 960530 (trigger 5478; 6 s after the trigger) fitted with the Band et al. (1993) model with " ¼ 1:7 " 1:5 and # ¼ #2:4 " 0:3 (left), awith the two-component model ( Ryde 2004), with a power-law slope of s ¼ #0:62 " 0:27 (right). Note the obliging of the data points (Fenimore et al. 1983; Bromm
Schaefer 1999).

V

E FE

in the flux beyond 600 keV. This component should be mostimportant at energies beyond the BATSE window studied here.
Interestingly, a few super-MeV detections have been made todate that indicate the presence of a possible, additional emission
component at these energies (Hurley et al. 1994; Atkins et al.
2000; González et al. 2003). In comparing the two plots in Figure 6,
it is important to note the property known as ‘‘obliging’’; thatis, for models that fit the data badly, the data points tend to be incorrectly depicted. This is a well-known property of the forwardfolding technique used for the deconvolution (Fenimore et al.
1983; Bromm & Schaefer 1999). The observed quantity is thephoton counts, while the physically interesting photon flux or en-

ergy flux are derived quantities that are model dependent. Ther
fore a plot showing the photon or the energy flux can only b
trusted fully if the model fits the data well. However, the statistic
fitting is made on the count data and is independent of this effec
GRB 960530 is further discussed in the following section.
2.3. Spectral Evolution

The choice of the model used to fit the !-ray data will lead
distinctly different interpretations of the cause of the apparent, oserved, spectral evolution. This is illustrated in Figure 7, whic
shows the spectral evolution of GRB 910927 (trigger 829). Th
Band et al. (1993) model is used for the fits in the top pane

EGRET TASC data available
for this burst; peak energy = 1600 keV

Fig. 7.— Spectral evolution of GRB 910927 (trigger 829), represented by time bins at 1, 6, and 10 s after t. In particular, the "-evolution is noteworthy. Bottom
using theof
Band themodel resultsin evolution of" and Eits
Having identified the photospheric emission allows the determination of the physical properties
outflowandbecomes very typical, in particular in the evolutions of kT and s. The data points have been rebinned to S/
photosphere Pe’er+07), Daigne+07.
p

In this case we find that the bulk Lorentz factor
Wednesday, 13 November 13

Examples of multi-peaked spectra observed by Fermi:
The photospheric component is modelled by a Planck function.
Is expected to be broadened to some extent.

NaI + BGO
BB+Band100724B

110721A

Guiriec et al. 2011
Axelsson et al. 2012

120323A

100
10
1
0.1

keV2 (Photons cmï2 sï1 keVï1)

1000

11092010

McGlynn et al. 2012

Guiriec et al. 2013

100

1000
Energy (keV)

Iyyani et al. 2014

Two component spectra: Blackbody component typically 5-10% of total flux.
But many cases with 40-60 %.
Wednesday, 13 November 13

104

Examples of multi-peaked spectra observed by Fermi:

PHEBUS/Fregate

Barat et al. 2000

Wednesday, 13 November 13

Multiple components in the short burst GRB120323A
One of the strongest bursts seen in the GBM
Low energy spectral index of the Band function
Rayleigh-Jeans1
0.5Band only

_

0
−0.5
−1
−1.5

0

0.1

0.2

0.3
0.4
Time from T0 (s)

0.5

0.6

0.7

Guiriec et al. 2013

Wednesday, 13 November 13

Multiple components in the short burst GRB120323A
One of the strongest bursts seen in the GBM
Low energy spectral index of the Band function
Rayleigh-Jeans1
0.5Band only

_

0
−0.5
−1

Band+BB

−1.5

0

0.1

0.2

0.3
0.4
Time from T0 (s)

0.5

0.6

0.7

Guiriec et al. 2013

Wednesday, 13 November 13

Multiple components in the short burst GRB120323A
One of the strongest bursts seen in the GBM
Low energy spectral index of the Band function
Rayleigh-Jeans1
0.5Band only_0

Statistically significant
improvement of the fits

−0.5
−1

Band+BB

−1.5

0

0.1

0.2

0.3
0.4
Time from T0 (s)

0.5

0.6

0.7

Guiriec et al. 2013

Wednesday, 13 November 13

Multiple components in the short burst GRB120323A

Changes theinterpretations!
1. Change in Epeak
2. Change in alpha (synchrotron?)
3. Change in emission zones

Guiriec et al. 2013

Wednesday, 13 November 13

Omitting the Band function
The best procedure is to fit a physical model directly to the data:
Burgess et al. (2013) fit a synchrotron spectrum from a distribution ofelectrons in addition to a Planck spectrum (modelling the photosphere)in 8 well separated pulses.
In all cases the fits are the same of better than the Band function.
In 5 of these a BB is statistically required.
GRB081224A

Temporal behaviour of BB and synch are
different
Slow-cooling synchrotron spectrum: theelectrons must undergo continuous
acceleration (magnetic reconnection events or
second-order stochastic acceleration, MHD).
Burgess et al. (2013)
Wednesday, 13 November 13

Bottom Line
1. Band crisis
The band function is not the universal GRB
spectrum. What does it mean?
2. Appearance of the photosphereBlackbody, BB+nonthermal, broadened functions

3. GRB jet properties are variable.
Lorentz factor decreases over individual
pulses while the flow nozzle increase

Wednesday, 13 November 13

1

INTRODUCTION

flue
how
GRB110721A is one of the brightest bursts observed byvar
the Fermi Gamma-ray Space Telescope and had a fluencetoOne of the ten strongest bursts:
of 876 ± 28 ⇥ 10 7 erg/cm 2 in the energy range 10 keV - 10
agi
2
peaks
at
low
energies
Best model BB+Band: < 5 sigma
detection
of
an
extra
component
GeV (?). The prompt emission spectrum exhibits significant
todeviations from a single Band spectrum. The time-resolvedmoTime resolvedspectrum
spectrum:is characterised by two spectral peaks (Fig. 1): oneet acan be modelled by a blackbody while the second one is given
8-100 keV in G
Axelsson et al. 2012by a Band function, whose spectral peak is at higher photon energies (Axelsson et al. 2012). The timescale of the flux
variations is much longer than the timescale required to 100-250
per- keVter
whform time-resolved spectral analysis. This suggests that any
Arspectral variations can be followed with sufficient tempo-aryn&Rito
ral detail. GRB110721A is therefore the archetype burst
m
i
l
e
r
250-10jetstudy the characteristics of the blackbody componentp and its 000 keV
is ibehaviour. We note that a similar deviation from the Bandit ifunction was also found in the most fluent Fermi burst to>30 MeV madate, GRB100724B (Guiriec et al. (2011); 10 keV - 10 GeVeming? email: shabuiyyani@particle.kth.se
Ho

GRB110721A

c 2013 RAS

The thermal and nonthermal emission do not track each other.
Wednesday, 13 November 13

Flux ratio

FBB
=
FNT

10

(FBB/ σSB T4)1/2

kT (keV)⇣ r ⌘ 2/3

-18

-19

F[keV
cm -2 s -1]phe coasting phase the ratio
10
✏ad =
(1)
rs
the amount of adiabatic
10
e photosphere. As these
1
10
CGRO
BATSE typically constant:observed thermal and theTime (s)Therefore, in the absence
iabatic cooling, the ther10
where
r
is
the
saturation
radiusafter which theof thesves
are expected
to track
increasesfrom approximately
1%
to
10%
and
1

10
1
10 FBB is the blackbody enflow
coastswithaconstant
value,
onsin thelumi-circles correspond to. 2012).
The fireballsolid (open)2
ergy flux,and(s)FNT is the non-thermal, kinetic energy flux.
its normalisation,blue),and Timeits, where rNT R
is (squares/theTt:/2cEnergy [keV]
(Ryde
et
al.
2006).
An
estimationoftheadiabatic
parameR parameterincreases theas a single power law,ever,in GRB110721A
1. Timeresolved
for the time bin flux,
2.2 2.7 Fs afterter (eq. 1) is given Figure
by theratio
of spectrum
the blackbody
BB ,the GBM tr
ses
clearlyhave
di↵erent(kT ⇠ 100 keV)1%
and the1 MeV).
flux, FBBmodel;/F .solidTheratio initially increases
from approximately
to Band
10%functionand (Ep ⇠Rydeh the two-component
line is the Planck function and the dashedline isthe&. Pe’er
2009
to
-ray
flux
in
the
observedenergy
band,
F
This
is
the
residuals
in
units
of
the
standard
deviation,σ.
The
spectraarerebinned
to
have
on
even
peaks
earlier.
A
resolution
used
inevery(Axelsson
et byal.
2012). The solid (open) circles correspond toever kept for the residual
panels. For
burst, which is identified
its BATSE
apulsegood estimation as long as the efficiency of the radiative
663 has a complex light curve, while the other three bursts consist of a distinct
diabatic
lossesvaries
with
But
in
GRB
110721A
Right
panel:
component:
its normalisation, R (squares/ blue), and its
as well as withinbursts. InBlackbody
the rightmost column, thetemporal variation of the ratio
the burst whose spectra are presented to the left (time bins marked by largedots).
processof thepromptasemission
is 110721A
highlaw,
and the blackbody
3
Fermi
betweenthethermalandcaysabroken
power
law,
the
R
parameter
increases
a single power
rmal
fluxF
isas
calculatedbyintegratingovertheenergyband∼25–1900
keV.
BB
has a distinct pulse shape=(1)
is subdominant
in the spectrum. In general, these requireatic parameter
is
given
by
FNT
ments are met, see further equation (6) and discussion in• Varying adiabatic losses §4.4.1.
-19

0.1

kT (keV)

FBB/ F⇣ r ⌘ 2/3

10

F
he ratio
✏ =
=
(1)
r
F
diabatic
saturation radius after which theof theAs thesephoton(Beloborodov• Varyingvalue,
a constantF starvationis the blackbody
en-2012)and theNT is the non-thermal, kinetic energy flux.
absenceradiative
efficiency• Varying
6). Anestimationof theadiabatic parameTime (s)he ther- (Should though be high since luminous burst;
en by the ratiowhereof thersblackbody
flux, FBBradius,isthesaturationof theIyyani et al. 2013
to track Cenko et al. 2010, Nemmen et al. 2012) after which the
Figure 2. Left panel: Fraction of thermal flux to total flux, FBB /F . The ratio
x in the observed
energyband,a constant
F . This iscoastswithvalue,F
BB is the blackbody enllWednesday,lumi-13 Novemberflow
then decreases. The grey points correspond to the time resolution used in (Axel
13BB
phwith the two-component model;
es of time resolved E FE spectra, observed by BATSE, fitted
solid line is the Planck function and the dashed line isower-law) model. The small panels beneatheachspectrumshowtheresiduals
in
units
of
the
standard
deviation, σ . The spectra are rebinned to haveadatio of unity to make the plots clearer. The full resolution is however kept for the residual panels. For every burst, which is identified by its BATSEsNTo time bins are shown in the first two columns. BATSE trigger 1663 has a complex light curve, while the other three bursts consist of a distinct pulse
e cases illustrate the variation of spectral shapes among bursts, as well as within bursts. In the rightmost column, the temporal variation of the ratio
al and the total fluxes (in the ∼25–1900 keV band) is shown for the burst whose spectra are presented to the left (time bins marked by large dots).
calculated by integrating the Planck function, while
BBthe nonthermal flux is calculated by integrating over the energy band ∼25–1900 keV. 0.01

1

10

1

Flux ratio

FBB
=
FNT

10

(FBB/ σSB T4)1/2

kT (keV)⇣ r ⌘ 2/3

-18

-19

F[keV
cm -2 s -1]phe coasting phase the ratio
10
✏ad =
(1)
rs
the amount of adiabatic
10
e photosphere. As these
1
10
CGRO
BATSE typically constant:observed thermal and theTime (s)Therefore, in the absence
iabatic cooling, the ther10
where
r
is
the
saturation
radiusafter which theof thesves
are expected
to track
increasesfrom approximately
1%
to
10%
and
1

10
1
10 FBB is the blackbody enflow
coastswithaconstant
value,
onsin thelumi-circles correspond to. 2012).
The fireballsolid (open)2
ergy flux,and(s)FNT is the non-thermal, kinetic energy flux.
its normalisation,blue),and Timeits, where rNT R
is (squares/theTt:/2cEnergy [keV]
(Ryde
et
al.
2006).
An
estimationoftheadiabatic
parameR parameterincreases theas a single power law,ever,in GRB110721A
1. Timeresolved
for the time bin flux,
2.2 2.7 Fs afterter (eq. 1) is given Figure
by theratio
of spectrum
the blackbody
BB ,the GBM tr
ses
clearlyhave
di↵erent(kT ⇠ 100 keV)1%
and the1 MeV).
flux, FBBmodel;/F .solidTheratio initially increases
from approximately
to Band
10%functionand (Ep ⇠Rydeh the two-component
line is the Planck function and the dashedline isthe&. Pe’er
2009
to
-ray
flux
in
the
observedenergy
band,
F
This
is
the
residuals
in
units
of
the
standard
deviation,σ.
The
spectraarerebinned
to
have
on
even
peaks
earlier.
A
resolution
used
inevery(Axelsson
et byal.
2012). The solid (open) circles correspond toever kept for the residual
panels. For
burst, which is identified
its BATSE
apulsegood estimation as long as the efficiency of the radiative
663 has a complex light curve, while the other three bursts consist of a distinct
diabatic
lossesvaries
with
But
in
GRB
110721A
Right
panel:
component:
its normalisation, R (squares/ blue), and its
as well as withinbursts. InBlackbody
the rightmost column, thetemporal variation of the ratio
the burst whose spectra are presented to the left (time bins marked by largedots).
processof thepromptasemission
is 110721A
highlaw,
and the blackbody
3
Fermi
betweenthethermalandcaysabroken
power
law,
the
R
parameter
increases
a single power
rmal
fluxF
isas
calculatedbyintegratingovertheenergyband∼25–1900
keV.
BB
has a distinct pulse shape=(1)
is subdominant
in the spectrum. In general, these requireatic parameter
is
given
by
FNT
ments are met, see further equation (6) and discussion in• Varying adiabatic losses §4.4.1.
-19

0.1

kT (keV)

FBB/ F⇣ r ⌘ 2/3

10

F
he ratio
✏ =
=
(1)
r
F
diabatic
saturation radius after which theof theAs thesephoton(Beloborodov• Varyingvalue,
a constantF starvationis the blackbody
en-2012)and theNT is the non-thermal, kinetic energy flux.
absenceradiative
efficiency• Varying
6). Anestimationof theadiabatic parameTime (s)he ther- (Should though be high since luminous burst;
en by the ratiowhereof thersblackbody
flux, FBBradius,isthesaturationof theIyyani et al. 2013
to track Cenko et al. 2010, Nemmen et al. 2012) after which the
Figure 2. Left panel: Fraction of thermal flux to total flux, FBB /F . The ratio
x in the observed
energyband,a constant
F . This iscoastswithvalue,F
BB is the blackbody enllWednesday,lumi-13 Novemberflow
then decreases. The grey points correspond to the time resolution used in (Axel
13BB
phwith the two-component model;
es of time resolved E FE spectra, observed by BATSE, fitted
solid line is the Planck function and the dashed line isower-law) model. The small panels beneatheachspectrumshowtheresiduals
in
units
of
the
standard
deviation, σ . The spectra are rebinned to haveadatio of unity to make the plots clearer. The full resolution is however kept for the residual panels. For every burst, which is identified by its BATSEsNTo time bins are shown in the first two columns. BATSE trigger 1663 has a complex light curve, while the other three bursts consist of a distinct pulse
e cases illustrate the variation of spectral shapes among bursts, as well as within bursts. In the rightmost column, the temporal variation of the ratio
al and the total fluxes (in the ∼25–1900 keV band) is shown for the burst whose spectra are presented to the left (time bins marked by large dots).
calculated by integrating the Planck function, while
BBthe nonthermal flux is calculated by integrating over the energy band ∼25–1900 keV. 0.01

1

10

1

2740 S. Iyyani et al.
Photosphere model: 2 Emission
zone - model

Photosphere

Non-thermal emission

Photosphere(No dissipation below)
Above photosphere(Optically thin)

Figure 1. Time-resolved spectrum for the time bin 2.2–2.7 s after the GBM
trigger. The spectrum is best modelled using a blackbody (kT ∼ 100 keV)and the Band function (Ep ∼ 1 MeV).

Thermal andcomponent- Planck
function(BB)
therefore photosphericemission is inevitable.
The questionisonly how strong it is and if it is detectable. In 1986, both Paczyński(1986) and Goodman (1986) suggested a strong contribution ofphotospheric emission in GRB spectra. But these models were notappealing since the observed spectra appeared purely non-thermal.
However, later it was envisaged that the photospheric component
can also be accompanied by non-thermal, optically thin emission(Mészáros et al. 2002). Thus, the Band component in bursts like
GRB 110721A is typically interpreted as being produced by a nonthermal radiation process taking place in a separate zone in the flow,
typically at large distances from the photosphere (Mészáros et al.
2002; however, see Section 5).
An important consequence of −2/3
having identified the photospherein the burst spectrum is thatph the properties of the
BBflow at the photosphere canadbe determined (Pe’er et al. 2007; Ryde et al. 2010;s
NT
Guiriec et al. 2011, 2012; Hascoët,
Daigne & Mochkovitch
2013).
As the properties of the flow, e.g. the burst luminosity and baryon
loading, vary during thes burst the observed properties of the photo-observed
bled befo
GRBs, su
the magn
factors.
Likewithe jet, r0
The radiu
fireball stof the out
is assume
black holthe size o
109–10 cm
are sugge
shocks fr
sion andthat r0 ca
the energ
In thisGRB 110
duration.
and preseare prese
the non-t
conclusio

Non-thermal component - Band function
Variable jetin GRB 1
synchrotron,
ICMART...

e, Axelsson et al. (2012) showed that the light curve
varies with time, thereby changing the
rati
2 BA
SI
GAMM
es photons above ∼100 keV 2areconsistent
with
a
and
the
non-thermal
fluxes.
The
adiabaticpzone emission, various realisations
The Fer
However, if one includes photons with energies be! "GRB 110rF
If belowthehassaturation
radius- strong
GCN121
V the lightcurve
two clearpulses.
Thisblackshowsbody
that
=
=
,
$
et al. 201
If above saturation radius - adiabatic coolingrFrecord brlse in the light curve is dominated by a narrow discontrast t
ft photons, which has a different temporal behaviour
nent deca
where r is the saturation radius after which
Wednesday, 13 November 13

Assumptions• The shortest observable variability time is given by rph/2Γc2 ∼ 0.2 ms(rph = 1012 cm & Γ= 300). But, the observed variation timescale is much longer
than the time bins ( 0.1 s) used in spectral analysis. Light curve traces the activityof the central engine. In each time bin, the flow is assumed to be quasi- static.

• Flow is thermally and adiabatically accelerated beyond r0: rph > rs
• What we see is the baryonic photosphere (no subphotospheric dissipation, andno photon starvation).

• Emission is dominanted by the line-of-sight emission.
• Observed part of the flow is approximately spherical.

Wednesday, 13 November 13

jj

Downloaded fr

by the blackbody component.
For GRB
E2
Using BB: Outflow parameters= A(t) have been identifi,
NE (E, t) peakof thecalculations
thermalexp[E/kT (t)] − 1
F = astotal
observedpower
flux law, and second
cays
awherebrokenTranslation of the observables to jet quantities
E is the photon energy and k is the
F
=
BB
flux
BB
Pe’er, Ryde et al. (2007)
theindependent
discussion belowof
wethe
represent
the nowithtime,temperatT=
temperature
See also e.g.
parameterF
Fan et al. (2011)
Ryde
&
Pe’er
2009;
Axelsson
et
al.
20
"
!
Guiriecetal.
(2012)
FBB
rph
1/2
F
BB
Hascoet et al. (2013)
The increase in R ∝, rph / # is mainTro (rs)BB normalisation, R ≡ σSB T 4
Daigne’s talkcrease in Lorentz factor. This causes t(Unknowns efficiencies, magnetisation, distance)
where σ SB is the Stefan–Boltzmann
2dependAlso
on unknowns
since
the
relativistic∼R to increase
A(t)1/2, where! is the redua
R = 2π c !3/2
In
panel
in
the obse
The
increase
Y = inverse of becomesthe fractionweaker.
ofthe
theright-handtotalenergyofFig.
the2observ
burst
et al.
blackbodyisplotted on top of the temperatinobserved
γrays.
also strengthens
the increase
R. H
shows that normalization
variesof
independ
εBB = fraction of the fireball luminosity thermalised at r0.
increases
with smaller
time as R
are typicallyvariationsin rphmonotonically
0.15. Both the broken power law of the te2010; Guiriec
et al. 2011).
increase in R are similar to the results f
The observed
temperatureis risegive
bursts in Ryde
(2004, 2005). The
in
Iflawtheindex
flowρ,iswas
magnetised:found function
in Ryde & Pe’e
Since RWeak
is adependencesmonotonicwi
onthelarge spread, centred around an averaged
in temperature
be ofduebreamagnetisation
parameterσthea standardmust
deviation
0.25.toThe
value
fou
thus
among
rises observed.
(Hascöet
al.2013).
Such a breakcantheetbesteepest
dominantly
caus
The measured parameter R can be founcases with $ ad ∼ 2constant (Ryde & P(1 + z) rph∼
in=the dcase #of GRB 110721A.
$ ad , like R
L
Furthermore,
the temperature is obwith a numerical coefficient of the orderconstant,sumption
or decaying
weakly,of sphericalsymmetrybefore(Pe’er etFigure 3. Schematic figure illustrating the distances referred to in the text.
2
luminosity
distanceand dL is theinis due toredshift
the emitting
surface∼Rthe effective transverse size of the emitter if # % 1/θ , where θ is
ger than the dynamical time indicating that
thermalflux(L
0 $ ad ) which causes thonalongertime-scale.
Inaddition,
the
time
the
jet
opening
angle.
Wednesday, 13 November 13

discussion on possible magnetisation of the flow).
In ad4Equations
(4)
and
(5)
thus
show
that
R
/
Y
F/
and
round
Results:is thereby fully
Lorentz
factor,Γ
determined by the observables F , R, Y ,e light
1/4
1/4
andredshift
z:
/
(F/R)
Y
. An estimate of rph now
sed in1/4
3/4
1/4
follows giving: rph / F
R Y.
. ThisThese
estimations are robustz =and
3.512 depend only on the1000
z=2
3 assumptions (i) that the flow is baryonicdominated (rph is10
z = 0.382
the baryon photosphere), (ii) rph > rs , (iii) that the observed
part of the flow is approximately spherical, and (iv) that the
resentemission is dominated by line-of-sight emission, (v) that theoutflow is thermally and adiabatically accelerated beyondATSE
r0 (there is no internal energy dissipation; classical fireball(Rydemodel).
e of F
Furthermore the nozzle radius r0 , can be determined.
range
We assumethat a fraction ✏BB of the fireball luminosity,100

Γ Y -1/4

Γ Y -1/4•

110Time (s)102c 2013RAS,
MNRAS 000, 1–??
Γ decreases monotonously
with
time
1

Γ ∾ 1000 Time (s)Wednesday, 13 November 13

10

100

and the normalizatio

Implications
NE (E, t) = A(t)expwhere E is the photo✴ Challenge for simplest internal shock model.
the discussion below
parameter"!
1/2
Challengeforthemagnetar
model
of
GRB
centralengine.
✴
FBB,R≡
σSB T 4asaccretion
disk✴ Decreasing Γ : Increase in baryon pollution
where σ SB is thstabilises.

Wednesday, 13 November 13

3/2

1/

R = 2π c ! A(t)In the right-hand p
blackbody is plottedshows that normalizincreases monotonic

at BIBSAM on September 9, 2013

magnetization of the flow).
]−1
Equations (4) and (5) thus show that R ∝ Y F
4
ow that R ∝ Y F / # and # istherebyfully determinedby the observables F, R
Photosphericradius,
r
ph
and
k
is
the
Boltzmann
constant.
Inobservables F, R, Y and redshift z: # ∝ (F /R)1/4 Y 1/4 . An estimate of rph now follo
sent the normalization, A(t), by thete of rph now follows giving rph ∝ F 1/4 R3/4 Y 1/4 .
These estimations are robust and depend only
tions (i) that the flow is baryonic dominated (rp10and depend only on the assump(3)photosphere), (ii) rph > rs , (iii) that the observed
ic dominated (rph is the baryon is approximately spherical, (iv) that the emission i–Boltzmann
constant.
hat the observed
partTherefore,of the flow line-of-sight emission and (v) that the outflow is! is the reduced Planck constant.
hat the emission is dominated by adiabatically accelerated beyond r0 (there is no inte
. 2 the observed normalization of thesipation; classical fireball model).
hat
the outflow
is thermally
he temperature
evolution.
The figure andFurthermore, the nozzle radius r0 can be determi(there is no ofinternal
rs0 independently
temperatureand dis- that a fraction & BB of the fireball luminosity, Lb ,10energy
time as R ∝ t ρ , with ρ = 1.14 ±to the burst luminosity, L0 , in the case of a non-m
aw of the temperature decay and thethermalized at r0 . Therefore, from equation (1) wecanbedetermined.
We
assumer0
he results found for CGRO BATSE
1
10l luminosity,
Lb , bywhichis equal Time (s)Therise in R, given
the powerFBB
FBB
−1
(&
&
=
≈
Y
)
,
BB
yde
& Pe’erto have a very
caseof a (2009)non-magnetized
jet, is ad &BB Y F − FBB
Faveraged valueof
0.51
andthathavingmn equation
(1)
we
have
increases
time
variation in comparison
he valuerph
foundfor GRB with
110721A
is but moderate
where F is the total flux and the last step is valid if
to otherparameters
bserved.
is thecase in GRB 110721A. Furthermore, & BB Y ≥can −1
be found to be (for rph > rs )equations (1), (4) and (6) with the fact that r = (#
(2)

,

•

rph Y

-1/4

(cm)

13

12

Y) ,

Wednesday, 13 November 13

(6)

s

in

e et al. (2010) and

For GRB110721A, both R (Fig. 2, left panel) and ✏ad(Fig. 2, right panel) vary. At the time of the thermal emission
0
peak:
100

r0

8

= 10 cm0orders of magnitude
a broken power law• Nozzle ✓radius,◆ r
⇣

R
10 18

⌘ 1 F /FBB
Time (s)
0.07

3/2

10

(✏BB Y )

1

3/2

.

(8)

This estimate is similar to the one made by Thompson et al.
(2007) who used the Amati et al. (2002) relation and as10

10

8

11

10

5

0.1

εBB3/2 (cm)

6

10

5/4

10

At t = 2.6 s the value
10
reaches its peak.

rs Y

3/2

10

7

r0 / Γ0 (Y εBB)(cm)

c 2013 RAS, MNRAS 000, 1–??

1

10

10

9

10

8

0.1

Time (s)Figure 4. Evolution of the flow parameters in GRB110721A for redshift z = 2 (diamonds). For credshifts z = 0.382 (blue/ star) and z = 3.512 (red/ circle) are indicated for time bin around 2.5 s.
monotonously with time. (b). The photospheric radius, rph has a weak increase and lies around 101
increases and reaches a peak at about 2.5 s and then decreases weakly. (d) The evolution of the saof r0 . See the text for estimation of the parameters 0 , , ✏BB , and Y .

Wednesday, 13 November 13

e et al. (2010) and

For GRB110721A, both R (Fig. 2, left panel) and ✏ad(Fig. 2, right panel) vary. At the time of the thermal emission
0
peak:
100

r0

8

= 10 cm0orders of magnitude
a broken power law• Nozzle ✓radius,◆ r
⇣

R
10 18

⌘ 1 F /FBB
Time (s)
0.07

3/2

10

(✏BB Y )

1

3/2

.

(8)

This estimate is similar to the one made by Thompson et al.
(2007) who used the Amati et al. (2002) relation and as10

10

8

11

10

5

0.1

εBB3/2 (cm)

6

10

5/4

10

At t = 2.6 s the value
10
reaches its peak.

rs Y

3/2

10

7

r0 / Γ0 (Y εBB)(cm)

c 2013 RAS, MNRAS 000, 1–??

1

10

10

9

10

8

0.1

Time (s)9 cm.
Considering Figurea moderately
magnetised
flow,
r0 increases
from 106 tofor10redshift
4. Evolutionof the flow
parametersin GRB110721A
z = 2 (diamonds). For credshifts z = 0.382 (blue/ star) and z = 3.512 (red/ circle) are indicated for time bin around 2.5 s.
monotonously with time. (b). The photospheric radius, rph has a weak increase and lies around 101
increases and reaches a peak at about 2.5 s and then decreases weakly. (d) The evolution of the saof r0 . See the text for estimation of the parameters 0 , , ✏BB , and Y .

Wednesday, 13 November 13

e et al. (2010) and

For GRB110721A, both R (Fig. 2, left panel) and ✏ad(Fig. 2, right panel) vary. At the time of the thermal emission
0
peak:
100

r0

8

= 10 cm0orders of magnitude
a broken power law• Nozzle ✓radius,◆ r
⇣

R
10 18

⌘ 1 F /FBB
Time (s)
0.07

3/2

10

(✏BB Y )

1

3/2

.

(8)

This estimate is similar to the one made by Thompson et al.
(2007) who used the Amati et al. (2002) relation and as10

10

8

11

At t = 2.6 s the value
10
reaches its peak.
10

6

10

5

εBB3/2 (cm)

10

5/4

10

rs Y

3/2

7

r0 / Γ0 (Y εBB)(cm)

c 2013 RAS, MNRAS 000, 1–??

106cm
0.1

1

10

10

9

10

8

0.1

Time (s)9 cm.
Considering Figurea moderately
magnetised
flow,
r0 increases
from 106 tofor10redshift
4. Evolutionof the flow
parametersin GRB110721A
z = 2 (diamonds). For credshifts z = 0.382 (blue/ star) and z = 3.512 (red/ circle) are indicated for time bin around 2.5 s.
monotonously with time. (b). The photospheric radius, rph has a weak increase and lies around 101
increases and reaches a peak at about 2.5 s and then decreases weakly. (d) The evolution of the saof r0 . See the text for estimation of the parameters 0 , , ✏BB , and Y .

Wednesday, 13 November 13

e et al. (2010) and

For GRB110721A, both R (Fig. 2, left panel) and ✏ad(Fig. 2, right panel) vary. At the time of the thermal emission
0
peak:
100

r0

8

= 10 cm0orders of magnitude
a broken power law• Nozzle ✓radius,◆ r
⇣

R
10 18

⌘ 1 F /FBB
Time (s)
0.07

3/2

10

(✏BB Y )

1

3/2

.

(8)

This estimate is similar to the one made by Thompson et al.
(2007) who used the Amati et al. (2002) relation and as1010109 cmc 2013 RAS, MNRAS 000, 1–??

At t = 2.6 s the value
10
reaches its peak.
10

6

10

5

εBB3/2 (cm)

10

5/4

10

rs Y

3/2

7

r0 / Γ0 (Y εBB)

(cm)

8

106cm
0.1

11

1

10

10

9

10

8

0.1

Time (s)9 cm.
Considering Figurea moderately
magnetised
flow,
r0 increases
from 106 tofor10redshift
4. Evolutionof the flow
parametersin GRB110721A
z = 2 (diamonds). For credshifts z = 0.382 (blue/ star) and z = 3.512 (red/ circle) are indicated for time bin around 2.5 s.
monotonously with time. (b). The photospheric radius, rph has a weak increase and lies around 101
increases and reaches a peak at about 2.5 s and then decreases weakly. (d) The evolution of the saof r0 . See the text for estimation of the parameters 0 , , ✏BB , and Y .

Wednesday, 13 November 13

e et al. (2010) and

For GRB110721A, both R (Fig. 2, left panel) and ✏ad(Fig. 2, right panel) vary. At the time of the thermal emission
0
peak:
100

r0

8

= 10 cm0orders of magnitude
a broken power law• Nozzle ✓radius,◆ r
⇣

R
10 18

⌘ 1 F /FBB
Time (s)
0.07

3/2

10

(✏BB Y )

1

3/2

.

(8)

This estimate is similar to the one made by Thompson et al.
(2007) who used the Amati et al. (2002) relation and as1010109 cmc 2013 RAS, MNRAS 000, 1–??

At t = 2.6 s the value
10
reaches its peak.
10

6

10

5

εBB3/2 (cm)

10

5/4

10

rs Y

3/2

7

r0 / Γ0 (Y εBB)

(cm)

8

106cm
0.1

11

1

10

10

9

10

8

0.1

Time (s)9 cm.
Considering Figurea moderately
magnetised
flow,
r0 increases
from 106 tofor10redshift
4. Evolutionof the flow
parametersin GRB110721A
z = 2 (diamonds). For credshifts z = 0.382 (blue/ star) and z = 3.512 (red/ circle) are indicated for time bin around 2.5 s.
monotonously with time. (b). The photospheric radius, rph has a weak increase and lies around 101
increases and reaches a peak at about 2.5 s and then decreases weakly. (d) The evolution of the saof r0 . See the text for estimation of the parameters 0 , , ✏BB , and Y .

The core of
the Wolf- Rayet progenitor star

(Woosley & Weaver 1995,Thompson et al. 2007).
Wednesday, 13 November 13

e et al. (2010) and

For GRB110721A, both R (Fig. 2, left panel) and ✏ad(Fig. 2, right panel) vary. At the time of the thermal emission
0
peak:
100

r0

8

= 10 cm0orders of magnitude
a broken power law• Nozzle ✓radius,◆ r
⇣

R
10 18

⌘ 1 F /FBB
Time (s)
0.07

3/2

10

(✏BB Y )

1

3/2

.

(8)

This estimate is similar to the one made by Thompson et al.
(2007) who used the Amati et al. (2002) relation and as1010109 cmc 2013 RAS, MNRAS 000, 1–??

At t = 2.6 s the value
10
reaches its peak.
10

6

10

5

εBB3/2 (cm)

10

5/4

10

rs Y

3/2

7

r0 / Γ0 (Y εBB)

(cm)

8

106cm
0.1

11

1

10

10

9

10

8

0.1

Time (s)9 cm.
Considering Figurea moderately
magnetised
flow,
r0 increases
from 106 tofor10redshift
4. Evolutionof the flow
parametersin GRB110721A
z = 2 (diamonds). For credshifts z = 0.382 (blue/ star) and z = 3.512 (red/ circle) are indicated for time bin around 2.5 s.
monotonously with time. (b). The photospheric radius, rph has a weak increase and lies around 101
thethenjet drills
throughthe(d)progenitor
star of the sa
increases and reaches a peak at about 2.5As
s anddecreases
weakly.
The evolutionof r0 . See the text for estimation of the parameters. from accelerating
oblique shocks
0 , , ✏prevents
BB , and Y it

The core of
the Wolf- Rayet progenitor star

(Woosley & Weaver 1995,Thompson et al. 2007).
Wednesday, 13 November 13

strongly• Saturation radius, rs
1

10Time (s)rs = Γ r0
Photospheric radius, rph

10

11

rs Y

5/4

(cm)

10

-1/4

10

13

rph Y

εBB3/2 (cm)

10

10

10

9

12

1

10

Time (s)

10

8

0.1

1

10

Time (s)redshift z = 2 (diamonds). For comparison the parameters values for
dicated for time bin around 2.5 s. (a) The Lorentz factor, , decreases
weak increase and lies around 1012 cm. The nozzle radius, r0 , initiallyweakly. (d) The evolution of the saturation radius, rs is similar to thatnd Y .

gives the power law indices 3.0 ± 1.8 and 1.0 ± 0.9, before
Wednesday,
Novemberand 13after
the13 break, which is at t = 2.6 ± 0.7. We note

Energy [keV]• Saturation radius, rs

Figure 1. Time resolved spectrum for the time bin 2.2
1
kT ⇠ 100 keV) and the Band function(Ep ⇠ 1 MeV).
Time (s)2.7 s after the GBM trigger. The spectrum is best modelled using a blackb10

rs = Γ r0

The Astrophysical Journal Letters, 757:L31 (6pp), 2012 October 1

200
400

10

300

Counts/Bin

0

5

10

Energy [MeV]

8

0.1

1

1

300

250 keV -- 10 MeV
BGO 1

200

40

10

Time
Time
(s) (s)

10

-18

10

-19

12

30 MeV -- 130 MeV
LATLLE20
1> 100 MeV
LAT

3

10

10

Time (s)

1

10 10

20

100

0

10

15

200

9

0.01

13

-17

100 keV -- 250 keV
NaI 6, 7, 9, 11

100

Counts/Bin

10

10

10

5

400

kT (keV)

5/4

rs Y

400

(FBB/ σSB T4)1/2

10

Photospheric radius, rph

(cm)

10

Counts/Bin

100

BB

εBBF3/2 /(cm)
F

0.1

600

-1/4

11

GRB110721200
8 keV -- 100 keV
NaI 6, 7, 9, 11

800

rph Y

10

Counts/Bin

1000

1

2

10

-5

0

10
5
Time
(s)

10

Time since T0 [s]15

20

Figure 1. Composite light curve of GRB110721A. (a)–(d) Count light curves from different energy ranges (NaI 6, 7, 9, 11, and BGO 1
photons. Time intervals are indicated by green lines; the red line shows the trigger time. Filled circles in (e) indicate >90% probability
The time is relative to the GBM trigger.
(ABB
color version of this figure is available in the online journal.)

Axelsson et al.2012

redshift2.zLeft= 2 panel:(diamonds).
For
FigureFractionof comparison
thermal fluxthe
to parameters
total flux, Fvalues/F .for
The ratio initially increases from approximately 1% to 10%
dicatedfor time
bingreyaround2.5corresponds. (a) The to
Lorentz
factor,, decreases
hen decreases.
The
pointsthe time
resolution
used in (Axelsson et al. 2012). The solid (open) circles correspon(dof). Based on the earlier detection of
The peak of the energy flux over the energy range>
increaseofandaround1012 cm. ofTher0received.
, initiallyaweak
significancethe lies
thermalcomponent(3 ).radius,
Right
Blackbodycomponent:its
R (squares/ blue), ans panel:BBnormalisation,⇠ 5nozzle
in other Fermi bursts (Ryde et al. 20
8 keV–1 GeV occurs at 0.3ph
s relative to the GBM
trigger with
−2
Burgess et asal. 2011),
we testpower
whether
0.2)
× 10−5powererg s−1 cm. the R parameter increases
emperature(circles/black).
While
the temperatureas(5.7a±brokenlaw,
a single
weakly.
(d) Theevolutionof thesaturation
radius, rsdecays
is similartothat
by including a blackbody. The fit im
In Figure 1 we also present the light curve of the LAT
withoutnd Y . any obvious breaks.
C-stat/dof = 901/616 (corresponding
Low Energy events (LLE, 30–130 MeV). The LLE data are

Adiabatic loss is minimum when r is closest to r and F
resulting in a thermal pulse.

becomes dominant

produced from a non-standard LAT analysis which for brightsources provides large effective area at low energies, joining the
LAT and GBM energy ranges (Pelassa 2011). An observationspecific response matrix is generated for each time range of data
2/3
using a Monte Carlo simulation
LAT, which
rph of the
FBBincreases
energygives
part theof theflow.law
Duringthe3.0coasting
phase 1.0
the±ratio
power
indices± 1.8 and
0.9,
beforethe spectral capabilities✏ad = of the Fermi data.=We note that thersis peculiar since itFpeaks
13afterNovembercurve for this burstofWednesday,
these
parts
depends
mainlyon theamountof adiabatic
NT before,
andthe13 break,
which
is at
t = 2.6± 0.7. LLE
Welightnote⇣⌘

Compared to the Band-only fit, the pintegrated Band function shifts from E
2400 ± 170 keV. Since the blackbody
to evolve (see analysis below and Ry
time-integrated spectrum is expected toby a multicolor blackbody (mBB; Pe’esuch a component instead of the blackMore Fermi bursts:

GRB 130427A

Preece’s talkAckermann et al. 2013

Wednesday, 13 November 13

More Fermi bursts:

GRB 130427A

Preece’s talkMore Fermi bursts Ackermann et al. 2013

102
10

1

100

101

Time (s)

1010
102

102
100

1011

101

102

Time (s)1010
103

GRB081224A

103

102

101
10

1011

1010

2

10

1

100

101

Rph (cm)

103

1012

Gamma

1011

GRB110920A

Rph (cm)

Gamma

1012

104

Gamma

1013

Rph (cm)

GRB100707A

103

109
102

Time (s)Burgess in prep. (2013)
Wednesday, 13 November 13

Jet parameters for BATSE bursts and for GRB 100507

ro generally increases
and lies in between
107 and 1010cm
 typicallydecreases
Ghirlanda et al. 2013

Wednesday, 13 November 13

Jet parameters for BATSE bursts and for GRB 100507

ro generally increases
and lies in between
107 and 1010cm
 typicallydecreases
Ghirlanda et al. 2013

• Alternative interpretations:
Wednesday, 13 November 13(i) Varying efficiency(ii) High latitude emission(iii) Varying photon starvation

Conlusions
1. Band function is not the universal spectral shape.
More complex spectra are needed with multiple components:
photospheric emission, cut offs, and additional power laws

2. Observational appearance of the photosphere:
Planck spectrum-

Broadened functions

-

2740

BB+nonthermal
S. Iyyani et al.

Figure 1. Time-resolved spectrum for the time bin 2.2–2.7 s after the GBM
trigger. The spectrum is best modelled using a blackbody (kT ∼ 100 keV)and the Band function (Ep ∼ 1 MeV).

and therefore photospheric emission is inevitable. The question is
only how strong it is and if it is detectable. In 1986, both Paczyński(1986) and Goodman (1986) suggested a strong contribution ofphotospheric emission in GRB spectra. But these models were notappealing since the observed spectra appeared purely non-thermal.
However, later it was envisaged that the photospheric component
can also be accompanied by non-thermal, optically thin emission(Mészáros et al. 2002). Thus, the Band component in bursts like
GRB 110721A is typically interpreted as being produced by a nonthermal radiation process taking place in a separate zone in the flow,
typically at large distances from the photosphere (Mészáros et al.
2002; however, see Section 5).
An important consequence of having identified the photospherein the burst spectrum is that the properties of the flow at the photosphere can be determined (Pe’er et al. 2007; Ryde et al. 2010;
Guiriec et al. 2011, 2012; Hascoët, Daigne & Mochkovitch 2013).
As the properties of the flow, e.g. the burst luminosity and baryon
loading, vary during the burst the observed properties of the photosphere will also vary. For instance, a varying Lorentz factor, !, wasobserved in GRB 090
bled before decreasin
GRBs, such as the in
the magnetar model
factors.
Likewise, the dista
the jet, r0 , can vary (The radius r0 represe
fireball starts expandof the outflow increas
is assumed to have a
black hole (e.g. ∼106
the size of the core o
109–10 cm (Thompson
are suggested to be ashocks from the coresion and accelerationthat r0 can vary with t
the energy dissipation
In this paper, theGRB 110721A show
duration. We discussand present the modeare presented and dis
the non-thermal, Banconclusions are given

3. GRB jet properties are variable. Over individual pulses 
decreases, while r0, and rsat increase. This causes the FBB and
Ftot to have different temporal profiles

Wednesday, 13 November 13

2 BA S I C C O N S
G A M M A - R AY O

The Fermi Gamm
GRB 110721A are
GCN12187 and GCN
et al. 2011). The Ba
record breaking 15 ±contrast to this behav
nent decayed as a bro
and Fig. 2 below).