Current Status andRecent Improvements ofFermi/GBM
Adam Goldstein
on behalf of the GBM Science & Ops TeamThe Fermi Spacecraft
Large AreaTelescope (LAT)
30 MeV - >300 GeV

Gamma-ray Burst Monitor (GBM)
NaI and BGO Detectors
8 keV - 40 MeV

KEY FEATURES• Huge field of view
–LAT: 20% of the sky at any
instant; in sky survey mode,
expose all parts of sky for ~30
minutes every 3 hours. GBM:
whole unocculted sky at anytime.
–Decreased detection deadtime 2.6 µs• Huge energy range, including
largely unexplored band 10 GeV 100 GeV. Total of >7 energy
decades!
• Large leap in all key capabilities.
Great discovery potential.

Current GBM Public Data
• Trigger data
• Continuous/daily data
• GRB trigger and spectral catalogs• GRB lightcurves• Earth occultation lightcurves, pulsar spin histories, etc.
• Spectral analysis software - RMfit
http://fermi.gsfc.nasa.gov/ssc/data/access/Continuous TTE
Data TypeTime Resolution

Energy Resolution

TRIGDAT1024/256/64 ms

8 channels

CTIME

256/64 ms

8 channels

CSPEC

4096/1024 ms

128 channels

TTE

2 μs128 channels• Initially TTE was available ~30 s pre-trigger - ~300 s
post-trigger• Implemented on November 26, 2012

Continuous TTE

Latitude30.

0.

Pre-Continuous
Post-Continuous
-30.
-120.

-90.

-60.

-30.

Longitude•10x improvement in TGF detections•

Less improvement for GRB candidates, but useful for ground search,precursors, fine-temporal lightcurve analysis, etc.

•Currently working on ground search software for un-triggered short GRBs/
GW followups

Briggs et al. JGR: Space Physics 2013

Introduction

SearchResults

Extended emission in individual GRBs

Orbital
Background
Background determination in GBM
Subtraction
Polynomial Interpolation
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3500

Estimation from offset orbits  

2500

2000

Search1500

Results

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1000

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

2000

1000

0

1000

Time since trigger (s)

2000

3000

•

Ger Fitzpatrick (University College Dublin)

 

2500

2000

Extended emission in individual GRBs

Long GRBs



3000

 3000

Introduction

3500

R ate (c ounts /s )R ate (c ounts /s )

3000

500

Conclusion

Conclusion

1500

1000

500

30

20

100

Orb its

102030Accurate alternative for polynomial-fitting,• 10-25 keV:
esp.• inlong-lasting
emission
Emission
extends to ∼640s @ 3 σ scenarios• Decay well described by a power law
of index −0.8 ± 0.2
Search for extended
in 4 yrs of GBM GRBs used to study
October22, 2012
3 / 20 gamma-ray•emissionPotentiallyextended• 25-300 keV:emission.
Lightcurve stacking suggests a PL
• Emission extends to ∼835 s @ 3 σ• Decay
welllightcurve.
described by a power law
decayof theof index −1.0 ± 0.12
• But sample includes many ‘long’ GRBs

Fitzpatrick et al. arXiv:1111.3779

GBM Localization Systematics
No. 1, 2009

FERMI GAMMA-RAY BURST MONITOR•

203 GBM GRBs also localized by Swift or IPN annulus•

Systematic model of core+tail Fisher distribution•

Model is azimuthally-dependent in spacecraft coordinates (by x-y quadrant)•

1-sigma systematic has 2.6-4.5 deg. radius•More details in Connaughton et al., submitted & poster

Figure 2. Functional block diagram of GBM.

30+/ïX
+/ïY

26.6

20

Dec (°)

1011.00

4.5
2.6
11.9

ï1024.0
Figure 3. NaI(Tl)-detector flight unit, consisting of a 5!! by 0.!! 5 NaI(Tl) crystal
viewed by a PMT.
(A color version of this figure is available in the online journal.)

ï20
ï30
150

160

170

1180
190
200 Table
NaI Detector
Measured Orientations
in210
Spacecraft Coordinates (see Figure 4)
RA (°)Detector ID No.
Azimuth (deg)Zenith (deg)
012

45.9
45.1
58.4

20.6
45.3
90.2

Figure 4. Locations and orientations of the GBM detectors.

793

– 12 –

GBM Localization Systematics– 15 –

Fig. 3.— The histograms show the fraction of GBM localizations lying within a given oﬀset(degrees) from the true positions for HitL (top) and Ground-automated (bottom) positions.
The solid vertical lines indicate a 68% containment radius of 5.3◦ [7.6◦ ], the dashed verticallines the 90% radius of 10.1◦ [17.2◦ ].

Fig. 1.— The histograms show the fraction of GBM FSW localizations lying within a given•

68% containment: 15 (1st FSW), 11.5o (last FSW), 7.5o (GA), 5o (HitL)

ooﬀset (degrees) from the true positions for the initial (top) and final (bottom)
FSW locations.

The solid vertical lines indicate the 68% containment radius of 14.9◦ and 11.6◦ , the dashed•

90% containment: 32o (1st FSW), 25o (last FSW), 17o (GA) 10o (HitL)•Main factors in improvement: More accurate background modeling andlonger, more accurate source selection.

vertical lines the 90% containment radius of 31.9◦ and 25.1◦ .

Fig. 3.— The histograms show the fraction of GBM localizations lying within a given oﬀset(degrees) from the true positions for HitL (top) and Ground-automated (bottom) positions.
◦◦Total Localization Uncertainty• Convolving the statistical probability map with thesystematic model, a total uncertainty map can beproduced• Currently 1,2,3-sigma contours are calculated. A png
and ascii file displaying coordinates of the contours areprovided• Special requests from observers will be considered.

Total Localization Uncertainty
Contours
Statistical Uncertainty

Total Uncertainty•

Files to be created when a final position
GCN notice is sent•

Contour files will be available at FSSC
website as an official data product•Already two successful follow-ups withiPTF using the contour files (130702A &131011A)

Current GRB Trigger Timeline

GRBTrigger~few secs

FSWLocalization

10-45 secs

Ground AutoLocalization~30-60 mins

Science Data
Received

Final Location~few hours Notice Sent

Tiled Followups

Burst Advocate
Localization

Contour Files
Createdblock diagram of GBM.

Investigation to Improve Speed &Accuracy of Localizations
NaI 0

Low Rates Spacecraft Blockage
Figure 4. Locations and orientations of the GBM detectors.
(A color version of this figure is available in the online journal.)

wrapping provides light tightness and guarantees the mechanicalstability of the BGO units. The two rings serve also as holdingstructures for the two PMTs which are mounted on both sidesof the crystals. The use of two PMTs results in better lightcollection and provides redundancy. The BGO detectors aremounted to a shell-type titanium holding structure. A picture ofa BGO detector is shown in Figure 5.

High Rates•

Localization is performed by comparing the relative observed rates from theGRB in each detector compared to the expected rates given the GRB isemanating from any of equally spaced 41,168 points on the sky in spacecraft
coordinates.

2.3. Photomultiplier Tubes (PMTs) and Front-End
Electronics (FEE)In order to transform the scintillation light into an electronic
signal the crystals are viewed by PMTs. For both crystal types,
PMTs of the type R877-MOD from Hamamatsu Corporation•

This requires an assumption of the spectrum, and the sky grid limits to astatistical minimum uncertainty of 1 degree.

Investigation to Improve Speed &Accuracy of Localizations•Primary delay in final localization is the Human-in-the-Loop (HitL).

•

Currently the Ground Auto (GA) localization is done using a single bin that
contains the peak count rate flux at 1024, 256, or 64 ms timescale.

•To improve the statistics of the localization, use a fluence-based source
selection that selects all of the signal over a certain time interval (e.g. 20 s).

•The background is given as the average of the background bins before thetrigger. This can be improved by implementing an algorithm to identify thesource and fit the background so that more accurate background-subtraction
can be performed.

GBM Triggers First 4 years• 954 GRBs
• 410 SolarFlares• 273 TGFs
• 201 ChargedParticles• 192 SGRs
Fig. 1.— The monthly trigger statistics over the first four years of the mission. For 2008 July and2012 July only the number of triggers in the time period from 2008 July 12 to 31 and 2012 July 1
to 11 are shown.

von Kienlin et al. submitted to ApJSPrompt GRB Observations Synergy
Through October 2013:• 1254 GRBs
• ~200 Swift+GBM• ~35 LAT+GBM• >300 GBM+other• 442 GRBs resulting in3124 GCN Circulars

GBM 4-year GRB Catalog(07/2008 - 07/2012)– 19 –– 18 –100.0•Fermi GBM GRBs in first four years of operation+90

10.0Hardness

Number of bursts

150100-180+180 RA

953 GBM
0 GRBs789 Long
0.10
1590.01Short
5 No measured duration

1.00

10.00

100.00•Locations/Localizing Instrument•

T50/T90 (50-300 keV)•Peak flux (64/256/1024 ms;
50-300 & 10-1000 keV)

1.0

50

0.1
0.01

1000.00

T50-90[s]Dec

953 GRBs

•

0.10

1.00

10.00

100.001000.00

T50[s]

Fluence (50-300 & 10-1000 keV)

10.0Hardness

Number of bursts

100.0
Fig. 4.— Sky distribution of GBM triggered GRBs in celestial coordinates. Crosses indicate longGRBs (T90 > 2 s); asterisks indicate short GRBs.
150100

1.0

50

00.01

0.10

1.00

10.00

100.00T90 [s]von Kienlin et al. submitted to ApJS

1000.00

0.1
0.01

0.10

1.00

10.00

100.001000.00

T90[s]

Fig. 5.— Distribution of GRB durations in the 50–300 keV energy range. The upper plot shows Fig. 6.— Scatter plots of spectral hardness vs. duration are shown for the two duration measureGBM 4-year GRB Spectral
Catalog (07/2008 - 07/2012)– 38 –500•••943 GRBs

60100

2 types of spectra: 3.5 sigma S/N duration-integrated & (1024/64 ms) peak
4 spectral models

405020•>7500 spectral fits-2•-1
Low-energy index

00-51-4-3High-energy index-2010-1100

Well-constrained parameters and preferential models presented
(a)

(a)

2001000
Epeak [keV]

10000

(a)

40
PL
COMP
BAND
SBPL

150

BAND
SBPL

150

COMP
BAND
SBPL

30

# of bursts# of bursts

COMP
BAND
SBPL

80

100

0-3150BAND
SBPL# of bursts

200100

PLCOMPBAND
SBPL100# of bursts

300– 39 –# of bursts# of bursts

400– 42 –

20100

50500-310-2-1
Low-energy index

01(b)Gruber et al. submitted to ApJS

0-5-4-3High-energy index

(b)

-2-10
10100

1000
Epeak [keV]

10000(b)Distribution of the low-energy indices obtained
fromthe GOOD
fits indices obtained
Fig. 4.—
Distributionof F
thespectral
high-energy
fromDistribution
the GOODofF thespectral
Fig. 7.—
Epeak fitsobtained from the GOOD F spectral fit

GBM GRB Spectral Catalog Redshift Bursts– 49– 65– –10 12•

48 GRBs with redshift (42 long, 6 short)543# of bursts

6# of bursts

8# of bursts•108# of bursts•43

Rest-frame energetics calculated: Epeak, Eiso, Liso
64

2

2

4

Sufficient sample size to start studying correlations andconsistency with samples from other instruments
12

20 0
10 10– 49 –1000
100 100
1000
peak,[keV]
rest [keV]
Epeak,Erest

10 0
10 10

10000
10000

1000
100 100
1000
Ebreak,[keV]
[keV]
rest
Ebreak,rest(a) (a)12(b) (b)8 581063# of bursts# of bursts# of bursts

66# of bursts# of bursts

84265# of bursts

4844344222100

1000
Epeak, rest [keV]

10000

22

1

100 0 4953
5455
4910 10 501050
10000
1051 10521052 1000
10101051100
105310 105410
105510Ebreak,rest [keV]
iso [erg]
Eiso E
[erg]

(a)
8

7
6

100
10

10000
10000

(c) (c)(b)7001050 1050

1051

5210511052
101053
Liso [erg/s]
Liso [erg/s]

5453
1010

(d) (d)Gruber et al. submitted toFig.
ApJSFig.
14.—
distributionof theF spectra
fromBEST
samplelong30.—(a)(a)
E E distributionof theP spectra
fitsfits
fromthetheBEST
sampleforforlongandand6
rest rest
peakpeak10551054

Conclusions• Continuous TTE - Fine time res/Fine spectral res - Always on• New background estimation using orbital rate subtraction
technique to study extended emission• Understanding of Localization Systematics - New contour maps
• Continuing to improve localization speed and accuracy• Great synergy with prompt and follow-up communities afterglow, GW searches, cosmic-ray/neutrino searches• New GRB trigger and spectral catalogs out soon
See Rob Preece’s talk next week on GRB 130427ABACKUP