Thermal emission in blackbody dominated GRBs
Miguel A. Aloy
ERC Fellow
Departamento de Astronomía y Astrofísica
collaborators
C. F. Cuesta-Martínez, M. Obergaulinger, P. Mimica

Supernovae and GRBs in Kyoto

Kyoto, 13 – 11 - 2013

Thermal emission inBB-dominated GRBs

107 cm1010 cm

1013 cm

Meszaros (2002)

1017 cm

GRB 101225A: A Christmas puzzle
Thöne+ (2011)• It has no classical afterglow: the X-ray

emission following the GRB (0.38 h < t< 18 days) is best fitted with BB + PL.

• During the first 2 h, there is aa
Flux density (Jy)Why is it unusual?
• Its -ray emission was exceptionallylong-lived (T90 > 2.000 s).

b

persistent X-ray source, seemingly
different from the “afterglow” emission.
the LC, suggestive of an associatedSN.

• Prototype of a class? Among nearby GRBSNe without a classical afterglow, there is aclass (BB-dominated) of very long GRBs withvery low Epeak, all of them showing a thermal
component in X-rays.

10–6
10–7
10–8
10–9
10–10
X (10 keV)W2 (1,928 Å)M2 (2,246 Å)
W1 (2,600 Å)U (3,465 Å)
B (4,390 Å)
g (4,815 Å)
r (6,400 Å)i (7,700 Å)z (9,050 Å)

10–6

UVOIR
10–7

Black body + supernova
Black bodySupernova

10–8

3XRT

10–5

cc

10–5

Flux density (Jy)

• After 10 days there is a flattening of

10–4

OSIRIS/GTC

0.1

1.0

10

Time since burst (days)

100(,lishX
cila(,coan
coan

cop
com
th
co
an
sem
fow

Forensic analysis“When all possibilities have been eliminated, whatever remains, however improbable, must be the truth."(Sir Arthur Conan Doyle)

What is GRB 101225A?

• A stellar murder on Christmas day (Thöne, et al. 2011, Nat, 480, 72):

A neutron star (likely material author of this crime) in a binary system undergoes acommon envelope phase (the system must survive the SN explosion giving birth to themain suspect) with a massive He-star companion. The NS merges with the core of theHe-star and induces its dead as a faint SN. Just a bit before the murder, a centralcompact object is born, probably a massive/hypermassive NS, which eventuallycollapses to a BH, producing a collapsar-like jet, whose propagation through thepreviously ejected hydrogen mantle of the secondary gives rise to the observed
phenomenology.

• An induced cometary suicide on Christmas day (Campana, et al. 2011, Nat, 480, 70):

A wandering neutron star (again, likely inductor of this event) captures a minor body (acomet) and disrupts it because of the tidal forces. If the comet has a relatively small
tensile strength, the captured body breaks down into gas, and forms a relatively thinannulus around the NS. The process can be chaotic and eventually the annulus turns
into an extended accretion disk with flares coincident with the periastron passages, andthe bolometric light curve is expected to decay, in the long term, as t-5/3.

4

Unveiling the murder“Get your facts first, and then you can distort them as much as you please." (Mark Twain)

In order to reconstruct the crime scene, we have to pay attention to the following
elements:• Prompt GRB emission.
• Early X-ray signature (unusual because of the BB component and the standing
X-ray source).

• Late UVOIR signature (also unusual because of the BB and the LC flattening).
• Do we see a SN?
• Do we see the host galaxy? (key to estimate the distance to the event, and settle
whether it is local or cosmological).

• Do we see a periodic behavior? (important element to give credit to the cometarysuicide interpretation).

5

Spectral fit of the BAT dataset• The burst started before the beginning of the BAT data at ~ T − T0 = −100 s andprobably continued while the source was not in the BAT field of view in T − T0 ∈[+1091 s, +1372 s].
RESEARCH SUPPLEMENTARY INFORMATION• Because of the low SNR, the BAT spectrum can be fitted by:
1. PL with photon index  ~ 1.9.

• E,iso > 1.4 x 1051 erg (if z=0.33)

NO DETECTION

2. Cut-off PL (Epeak ~ 38 ± 20 keV)
3. BB (TBB ~ 10.1 ± 1.1 keV).

Out offield ofview

Out offield of view

T90,min

BAT -ray LC[15-150 keV]6 

Spectral fit of the 1st XRT dataset
phot, PL ~ 1.83

____ _ PL

BB+PL

TBB ~ 1.1x107 K ~ 1 keV~20% contribution
.... BB

7 

Evidence#2: Spectral fit of the 1st XRT dataset
Supplementary Figure 2 | Fit to the X-ray spectrum. a: X-ray spectrum from XRT during the first snapshot. The solidline is the spectral fit, the dashed line indicates the contribution of the power-law component, the dotted line the contributionof the black body component. b: Ratio between the observed data and the fitted model.

data after the second snapshot, no black body component is required and a simple absorbed power-law provides anacceptable
likely due
the lower signal-to-noise ratio at later times.
Otherfit,possible
fitstotried:

ModelPL
PL+BB
PL+diskBB
PL+comptΓ
1.72±0.03
1.83+0.13−0.10
1.79+0.36−0.22
1.79±0.04

kT (keV)0.96±0.13
1.64±0.35<22

NH (1022 cm−2 )0.24±0.02
0.22±0.03
0.18±0.04
0.31+0.03−0.02

χ2 /d.o.f. (F-test)
468/381421/379 (1.95×10−9 )417/379 (3.19×10−10 )424/377 (1.55×10−7 )Supplementary Table 1 | Result of different model fits to the X-ray data of the first snapshot. PL is a pure power-law
model, PL+black body (BB) a combination of a simple PL and a black body with one temperature while a PL+diskBB
includes emission from black bodys with different temperatures, PL+compt includes a comptonized component in addition
to the power-law. Γ is the photon index of the power-law, kT the black body temperature, the column density is the totaldensity, including the Galactic absorption. The last column shows the χ2 of the different fits and the F-test value comparedto the simple absorbed PL model.
8Evidence #2:

RESEARCH SUPPLEMENTARY INFORMATION

Spectral evolution (1st XRT dataset)


"



Little time evolution of phot, PL ~ 1.83

Little time evolution of TBB ~ 1 keV





Absorbing column density in X-rays (galacticcontribution in the line-of-sight: 7.9×1020 cm−2)
9!

BB size (RBB ~ 2R⦿) constant$
$ 20% average BB contribution

#      !" "! "  !

The motive for the stellar murder:1) A dense, toroidal CE-shellNo. 1, 2001

• Suggestion: the progenitor system is a He-star / NS merger.
• Existing theoretical possibility(e.g., Fryer & Woosley 1998; Zhang & Fryer 2001; Barkov & Komissarov 2011).
• When the secondary star leaves the main sequence and expands, it engulfs the NS,
MERGER OF HELIUM STAR AND BLACK HOLE

363

leading to a CE phase and the ejection of the hydrogen envelope and part of the He coreas the remnant spirals into the centre of the second star.

Orbital plane

4M⨀

Plane perpendicular to the orbital motion

2M⨀(from Taam & Ricker 2010)

The ejecta forms a broad torus with a narrow,
low-density funnel along the rotation axis.
(from Zhang & Fryer 2001)

10

The motive for the stellar murder:
2) The central engine• When the neutron star reaches the centre, after ~ 5 orbits (TCE ~ 1.5 yr), angular momentum
forms a disk around the remnant of the merger, allowing for the formation of:••

11GRB-like jet. (looks like a “collapsar-induced” jet; a stellar mass BH forms).
Magnetar remnant, (though not insurmountable, this is important to explain the very long duration of the GRB).

The motive for the stellar murder:3) The jet breaks the stellar jail through a hole!
• By the time of merger (TCE ~ 1.5 yr), the CE-shell may have traveled (close to the escapevelocity) to a distanceRdebris⇡(3⇡few ⇥ 1014 cm

3/25) ⇥ torbit vescape = (32⇡Rorbit (2GM )1/25) ⇥⇡ (27(GM )1/2 R1/2orbit• Stage 1: The jet propagates until it hits the CE-shell

External
mediumCE-shell

About 80 sec
after the GRB

12funnelrelativistic
jet hits the innerboundary of theCE-shell45) ⇥ Rorbit

The motive for the stellar murder:3) The jet breaks the stellar jail through a hole!
• By the time of merger (TCE ~ 1.5 yr), the CE-shell may have traveled (close to the escapevelocity) to a distanceRdebris⇡(3⇡few ⇥ 1014 cm

3/25) ⇥ torbit vescape = (32⇡Rorbit (2GM )1/25) ⇥⇡ (27(GM )1/2 R1/2orbit• Stage 2: Jet-shell interaction resulting in the formation of areverse shocksubrelativistic
jet breaking out ofthe CE-shellwings of therelativistic jet
penetrating theCE-shell

About 4700 sec
after the GRB

13Supernova
Shock

X-ray
hot spot45) ⇥ Rorbit

As the jet passes through the funnel, it
decelerates owing to the increased baryon loadand shear with the funnel walls:

afterglow suppressed

The motive for the stellar murder:3) The jet breaks the stellar jail through a hole!
• By the time of merger (TCE ~ 1.5 yr), the CE-shell may have traveled (close to the escapevelocity) to a distanceRdebris•⇡(33/25) ⇥ torbit vescape = (32⇡Rorbit (2GM )1/25) ⇥⇡ (27(GM )1/2 R1/2orbit⇡ few ⇥ 1014 cm
Stage 3: Small fraction of the jet breaks out of the shell
producing an expanding bubble.
UVOT
emission

Supernova
Shock

Few hours
after the GRB

14wings of therelativistic jet
penetrating theCE-shell45) ⇥ Rorbit

The motive for the stellar murder:3) The jet breaks the stellar jail through a hole!
• By the time of merger (TCE ~ 1.5 yr), the CE-shell may have traveled (close to the escapevelocity) to a distanceRdebris⇡(3⇡few ⇥ 1014 cm

3/25) ⇥ torbit vescape = (32⇡Rorbit (2GM )1/25) ⇥⇡ (27(GM )1/2 R1/2
orbit45) ⇥ Rorbit• Stage 4: As the SN shock expands beyond the CE-shell, we observe a small bump in thelight curve at ~30 d.

Supernova
Shock

This He/NS merger scenario naturally
assumes the production of a relatively
small amount of radioactive Ni, leading
to a weak SNcompactremnant

15

Few days after theGRBUVOTemission
wings of therelativistic jet
penetrating theCE-shellA detailed model for the jet “breakout”
25º• Using the MRGENESIS code (Mimicaet al. 2009) we can compute 2D RHDmodels (>50 models explored withtypical resolutions of 50000x900 cells close to AMR models-).

1. Third-order finite-volume code.
2. Explicit RK3 + PPM + Marquina.
3. Method of lines.
4. MPI/OpenMP hybrid parallelization (scalingup to ~10.000 CPUs).

14º

16

A detailed model for the jet “breakout”

1725º

20º

14º

10º

A detailed model for the jet “breakout”

18

25º

20º

14º

10º

3.2.
Electromagneticemission
along thepath, s, of the photon.
Here are considered straight lines.

A detailed model for the jet “breakout”• Using a radiative transport code

(Mimica et al. 2009) we can computesynthetic multifrequency LCs for ourmodels using for the emission/
absorption the recipes of Anderson etal. (2009):

1. Emission: bremsstrahlung-BB.
2. Absorption: (modified) Kramers.

19

We have performed a new version of the radiative transport code SPEV.
3.2.1. emission
ThermalThermal
hasemission
been implemented for this work, owing to the observationsof GRB 101225A.
The theoretical emission and absorption coe⇤cients (Rybicki & Lightman
The radiation transport equation states the intensity of the radiation in1979)
ofthe
thermal-bremsstrahlung(free-free), emission
are described in this secterms ofemission, j , and absorption,coe⇤cientstion. First of all we define the variable
dI=Ih⌅+ j .
(1)
x=(2)
dskT
along the path, s, of the photon. Here are considered straight lines.
where h is the Planck constant, ⌅ is the frequency of the radiation, k is theBoltzmann constant and T is the temperature of the fluid in the rest frame.
3.2.1. Thermal emission
Then, for a plasma with a Maxwellian distribution of velocities the emission
The theoreticaland absorptioncoe⇤cients(Rybicki & Lightmancoe⇤cient
per unitemissionof frequency,⌅, takes theform1979) of thermal-bremsstrahlung 2(free-free) emission are described in this sec1⌃
38 variabletion. First
we8definej of= all 6,⇥ 10 theZ 2 2 T 1/2 e x ḡff (⌅, T ) erg s 1 cm 3 Hz 1 .
(3)
4⇧
mph⌅
x=(2)
Following the Kramer’s law for opacity
the absorption coe⇤cient, whichkT
depends
alsofrequency,
is determinedby the relation= j /B k, where
where
h is
theonPlanck
constant,⌅ is the frequencyof the radiation,is the B
istheblackbody
intensity.
In
thisway
Boltzmann constant and T is the temperature of the fluid in the rest frame.
2
Then, for a plasma with a Maxwellian
distribution of velocities the emission
23 2 ⌃
7/2
⇧
4.1
⇥10Z
Tx 3form(1 e x )ḡff (⌅, T ) cm 1 .
(4)coe⇤cient per unit of frequency, ⌅,2takes themp2
138 2 ⌃
13j equations=6, 8 ⇥⌃ 10
Zrest2 mass
T 1/2density,e x ḡff (⌅,mTp) erg
cm mass,
Hz 1ḡ.ff the(3)In theseis thethe sproton
tem4⇧
mp
perature averaged Gaunt factor for free-free transitions and Z = µi /µe , where
theandKramer’s
law+for
opacity
the absorption
whichµe Following= 2/(1 + X)
µi = 4/(13X).
The variable
X is thecoe⇤cient,
relative abundance
dependsalso
onfrequency,
isdeterminedbythe
relation=j/B,
whereBof hydrogen and we have chosen the typical value X = 0.71.
is theblackbody
intensity.
In this wayTheMaxwellian,temperature
averaged free-free Gaunt factor has been ob2
tained by interpolation of23thecomputedby Sutherland (1998;
see Table⌃values7/2
1⇧ 4.1⇥ 10 onZ 2the2 variables
Tx 3 (1e x )ḡff (⌅,Tu) cm. article)(4)and2 within), that
dependx(definedasinthemp⇥ 2 = Z 2 Ry/kT , where Ry is the Rydberg energy. In our range of temperatures
Intheseequationsthe⌃ isGaunt
the rest
massisdensity,
mpthetheunity,protonsomass,
tem- apff theandfrequencies
factorclose toit is ḡnota badperature
averagedGauntfree-freetransitions
andtakeZ =theµi /µe , whereproximation
to takeḡff (⌅,factorT ) ⇤for
1. Otherchoicecould beunity
for lowµtemperaturesandtakeµi =the4/(1+3X).
ThevariableX
istherelativeabundance
e = 2/(1 + X)andexpression proposed by Anderson et al. 2010 for highof hydrogen and we havechosen the typical value X = 0.71.
temperatures (T > 105 K).
The Maxwellian, temperature averaged free-free Gaunt factor has been obThe temperature has been calculated considering that the total pressure istained by interpolation of the values computed by Sutherland (1998; see Table
given by adding the gas pressure and the radiation pressure,2 within), that depend on the variables x (defined as u in the article) and⇥ 2 = Z 2 Ry/kT , where Ry is the Rydberg
energy.
k1 In4 our range of temperatures
P = is close⌃Tto+theaTunity,and frequencies the Gaunt factor
so it is not a bad ap- (5)µmH
3proximation to take ḡff (⌅, T ) ⇤ 1. Other choice could be take the unity for low1
where mH (⌅andmptake) is theof theproposedhydrogenbyatom
and µet=al.
(1/µ1/µhigh⌅e +fori)temperatures
themass
expression
Anderson2010
4/(3 + 5X) theweight in units of mH .
temperatures(T mean> 105 molecularK).
The temperature has been calculated considering that the total pressure isA detailed model for the jet “breakout”• Using a radiative transport code

(Mimica et al. 2009) we can computesynthetic multifrequency LCs for ourmodels using for the emission/
absorption the recipes of Anderson etal. (2009):

1. Emission: bremsstrahlung-BB.
2. Absorption: (modified) Kramers.

• Shell is hot enough (T>104 K,n~7x10-13 cm-3), that it is fully ionized,(note differences with, e.g., Badjin,
Blinnikov, Postnov’13).

• Parametric study favors:
1. Wider jets (q >20º).
2. Massive shells (M>0.15M⊙).

20

A detailed model for the jet “breakout”
jet = 25ºintensity

21

absorptionemission

A detailed model for the jet “breakout”
jet = 25º22

Conclusions• GRB 101225A seems to be a rather unusual LGRB associated to a SN without classicalafterglow and with a BB component (class defining event, but not the only one!).

• In favor of our model:
Existing progenitor model.
Consistency with numerical simulations.
Simple explanation of the X-ray hot spot and UVOIR evolution.
Explains faint SN (fainter than any other observed).
Numerical models reveal a generic way of preventing an standard afterglow (jet/CE-shellinteraction). Work on going.

• Against our model:
Need of specific CE-geometry and high density, though justify from numerical models.
More elaborated modeling required: RMHD, non-thermal emission (Newtonian shocks),Comptonization of X-rays in the dense CE-shell, ionization (if the shell is cool), etc.

• The Christmas burst is likely the result of a stellar murder: stars may have found newways to die!.

23