2. Gamma-ray Bursts (GRBs)
Definition: Bursts of gamma-rays from the universe.
They are named by year-month-day: GRB090610
(the second one on the same day) GRB090610B
Distribution : Isotropic on the sky.
Duration: T= 10ms s.
Distance: Cosmological distance (highest known z = 8.2).
Isotropic energy: 10^50 – 10^54 erg.

3. Fireball Shock Model
Ultra-relativistic expanding fireball-shock model synchrotron spectrum
Shocks: sudden change in density, pressure that decelerates supersonic flow
Particles are scattered back and forth across the shock, and gain energy

4. Do we need an extra component?
FERMI ERA FOR GRBs
PROMT EMISSION: Energy range : 8 keV-300GeV
Spectrum: Physics
AFTERGLOW: High energy delayed component?
Decay as a function of time and spectrum (First time with Fermi)
Do we need an extra component?
arXiv: v1

5. FERMI GRB ANALYSIS LAT Transient class Background:Isotropic+source
Data from LAT server
Transient class
Diffuse class for the afterglow
Background:Isotropic+source
gtlike
GBM+LAT
LAT data rsp by rspgen
GBM
Data from GBM burst Catalog
Long burst:cspec
Short burst:tte
Different detectors
rmfit

6. Energy Flux (8keV-100MeV) (erg/s cm2)
Fermi GRB Sample
Swift
LAT
LAT Boresight (deg.)
Energy Flux (8keV-100MeV) (erg/s cm2) z
Ep (keV)
class
T90 (sec.)
GRB Y 52
2E-05
4.3
424 L 66
GRB080916C 10
4.0528E-06
0.9
4400 S
0.3
GRB090510 51
1.78E-05
1.8
798 21
GRB090902B N 53
2.8849E-07
207
68.5
GRB091221 No 29
9.4648E-07
1240
110
GRB100116A
Suzaku
1.31E-06
132.1
6.25
GRB100131A
44.7
7.1671E-06
506
0.128
GRB100206A

7. To+80-140 sec : LAT emission started late

8. Band ruled out!!!
Extra component
First Time!!!!
ExpCutoff+PL

9. LAT analysis is consistent with GBM extra component

10. GRB090902B: Prompt Lightcurve
10-100keV
keV
100MeV -200GeV
Delayed Emission from LAT

11. GRB090902B : GBM+LAT Bright GBM and LAT burst
LAT extended emission upto 1000s
Time averaged spectral fit shown ( upto T0+65sec) GBM (4 detectors) and LAT data (8keV to 100GeV) using rmfit
PL component in addition to Band Fn. required
BB+PL (photosheric emission reported for this burst) is not a good fit for time averaged spectrum .
Spectral Evolution of prompt emission
Five time bins [0-5s, 5-12s, 12-20s,20-30s,30-65s] are determined to probe spectral evolution
At early time (t< 6s) only Band component seen.
At late time (t >30s) only PL component is present (LAT emission dominates)
Intermediate:- Band in addn. to PL extending to lower and higher energies

12. LAT Extended Emission (up to 800s)
Bright Extended emission upto 800s (data until earth occultation)
Extra-galactic isotropic background derived from likelihood analysis of 2 weeks of pre-burst data.
LAT emission spectral index (time averaged) /- 0.07
LAT Lightcurve
Averaged over 100MeV to 300GeV
Max. Likelihood analysis for eight time intervals
Flux increases and drops off as t^{-1.5} around 10days
A spectral index change around the lightcurve turn over ?, Not siginificant enough

13. GRB 090902B LAT Time averaged spectrum (gtlike)
Model PL
Index: /
LowerLimit: 100
UpperLimit:
TS value:

14. LAT Extended Emission tmid flux (E-06) TS
Bright Extended emission upto 800s (data until earth occultation)
EG Isotropic BG derived from 2 week data before burst
Spectral index (time averaged) /
Max. Likelihood analysis for five time intervals
tmid flux (E-06) TS / / /
/ E

15. 0.128sec

16. No significant evolution.
No extra components
No significant evolution.

17. GRB C
NaI kev
BGO e4 kev
LAT 100Mev-100GeV

18. GRB 080916C GBM spectrum PL C-stat=2335 Dof=361 SBPL C-stat=557 359
T0+0 : T0+90
Band+PL GBM
PL C-stat= Dof=361
SBPL C-stat=
Band C-stat=
Band+PL C-stat=527 r-chisq=1.08/357

19. GRB 080916C GBM+LAT spectrum PL C-stat=7882 Dof=461 PL2 C-stat=615 457
T0+0 : T0+90
PL C-stat= Dof=461
PL C-stat=
SBPL C-stat=
Band C-stat=
Band+Eff C-stat= r-chisq=1.02/459

20. Time-resolved spectra--Changing
GRB C
Time-resolved spectra--Changing
Spectra are Changing
Alpha seems consistent
Epeak changes very little
Beta changes a lot
These results imply that the higher-energy emission changes larger steeply than the low-energy one.

21. LAT light curve & spectral index
GRB C
Light curve
With gtlike method
The first four data seems from the background like the last one
The others follow a power-law when we exclude two data.
The onset of afterglow is about 6 sec.
For spectral index
changing
1.2

22. GRB 100131A Different profile between different energy range NaI 6
BGO 1
Different profile between different energy range

23. GBM spectrum with Band function fitting
GRB A
GBM spectrum with Band function fitting
[ T0 : T0+4 ]
PL C-stat= DOF=350
Band C-stat=
SBPL C-stat=
PL C-stat=
Comt C-stat=
Band+PL C-stat=
Band +Eff reduced chisq=1.09/348
Epeak=106 alpha= beta=2.00

24. GRB 100131A Time-resolved spectra
[ T0 : T0+4 ] sec
Slightly changes but not too much

25. Analysis on GRB090510 BGO detector 200 keV – 40 MeV
NaI detector 8 keV 900 keV
Higher Energy photon <900 keV Taking part in the Gamma Ray Outburst

26. Prompt Emission Ep=4029. +/- 134. keV
Band
Band+PL
Ep= / keV
Band Fit: C-STAT = , DOF = 694
Power Law + Band's GRB Peak : CSTAT DOF 462
LAT spectrum = Power Law P.I = CSTAT 78.3 DOF 93

27. 2nd Peak (1s to 6s w.r.t the Trig. Time): C-STAT = 710.33, DOF = 601
1st Peak LAT+GBM
2nd Peak LAT+GBM
Band Fit
1st Peak (-0.1s to 0.2s w.r.t the Trig. Time): C-STAT = , DOF = 599
2nd Peak (1s to 6s w.r.t the Trig. Time): C-STAT = , DOF = 601

28. Studying Spectral Evolution of Afterglow Emission
XRT
XRT

29. Conclusions:
LAT emission started later in all burst in our sample.
Band model represents most of the GRBs but in the Fermi ERA extra components can be determined by LAT!
LAT upper limits can help to feel extra components in case of only GBM detection.
High energy afterglows decay in time ( C)

30. THANK YOU