Gammaray Bursts GRBs Definition Bursts of gammarays from
Gamma-ray Bursts (GRBs) Definition: Bursts of gamma-rays from the universe. They are named by year-month-day: GRB 090610 (the second one on the same day) GRB 090610 B Distribution : Isotropic on the sky. Duration: T= 10 ms - 1000 s. Distance: Cosmological distance (highest known z = 8. 2). Isotropic energy: 10^50 – 10^54 erg.
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
FERMI ERA FOR GRBs PROMT EMISSION: Energy range : 8 ke. V-300 Ge. V Spectrum: Physics Do we need an extra component? ar. Xiv: 0906. 0991 v 1 AFTERGLOW: High energy delayed component? Decay as a function of time and spectrum (First time with Fermi)
FERMI GRB ANALYSIS GBM • Data from GBM burst Catalog • Long burst: cspec • Short burst: tte • Different detectors • rmfit LAT • Data from LAT server • Transient class • Diffuse class for the afterglow • Background: Iso tropic+source • gtlike GBM+LAT data rsp by rspgen
Fermi GRB Sample GRB T 90 (sec. ) class Ep (ke. V) z Energy Flux (8 ke. V-100 Me. V) (erg/s cm 2) LAT Boresight (deg. ) LAT Swift GRB 080916 C 66 L 424 4. 3 2 E-05 52 Y Y GRB 090510 0. 3 S 4400 0. 9 4. 0528 E-06 10 Y Y GRB 090902 B 21 L 798 1. 78 E-05 51 Y Y GRB 091221 68. 5 L 207 2. 8849 E-07 53 N Y GRB 100116 A 110 L 1240 9. 4648 E-07 29 Y No GRB 100131 A 6. 25 L 132. 1 1. 31 E-06 51 N Suzak u GRB 100206 A 0. 128 S 506 7. 1671 E-06 44. 7 N Y
To+80 -140 sec : LAT emission started late
Band ruled out! Extra component First Time!!!!
LAT analysis is consistent with GBM extra component
GRB 090902 B: Prompt Lightcurve 10 -100 ke. V 500 -1000 ke. V 100 Me. V -200 Ge. V Delayed Emission from LAT
GRB 090902 B : GBM+LAT Bright GBM and LAT burst LAT extended emission upto 1000 s Time averaged spectral fit shown ( upto T 0+65 sec) GBM (4 detectors) and LAT data (8 ke. V to 100 Ge. V) 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 -5 s, 5 -12 s, 12 -20 s, 20 -30 s, 30 -65 s] are determined to probe spectral evolution At early time (t< 6 s) only Band component seen. At late time (t >30 s) only PL component is present (LAT emission dominates) Intermediate: - Band in addn. to PL extending to lower and higher energies
LAT Extended Emission (up to 800 s) Bright Extended emission upto 800 s (data until earth occultation) Extra-galactic isotropic background derived from likelihood analysis of 2 weeks of preburst data. LAT emission spectral index (time averaged) 1. 94 +/- 0. 07 LAT Lightcurve Averaged over 100 Me. V to 300 Ge. V Max. Likelihood analysis for eight time intervals Flux increases and drops off as t^{-1. 5} around 10 days A spectral index change around the lightcurve turn over ? , Not siginificant enough
GRB 090902 B LAT Time averaged spectrum (gtlike) Model PL Index: 1. 9794 +/- 0. 0702152 Lower. Limit: 100 Upper. Limit: 300000 TS value: 1321. 03
LAT Extended Emission Bright Extended emission upto 800 s (data until earth occultation) EG Isotropic BG derived from 2 week data before burst Spectral index (time averaged) 1. 94028 +/- 0. 0740288 Max. Likelihood analysis for five time intervals tmid flux (E-06) TS 0. 22 539. 33 +/- 317. 384 58. 4648 8. 66 1000+/-0. 00254887 547. 562 56. 23 273. 692+/-45. 6465 497. 867 316. 23 22. 94+/- 4. 67975 E-06 192. 089
0. 128 sec
No extra components No significant evolution.
GRB 080916 C Na. I 3 8 -900 kev BGO 0 200 -4 e 4 kev LAT 100 Mev-100 Ge. V
GRB 080916 C GBM spectrum T 0+0 : T 0+90 Band+PL GBM 1. 2. 3. 4. PL SBPL Band+PL C-stat=2335 Dof=361 C-stat=557 359 C-stat=579 359 C-stat=527 r-chisq=1. 08/357
GBM+LAT spectrum GRB 080916 C T 0+0 : T 0+90 1. 2. 3. 4. 5. PL PL 2 SBPL Band+Eff C-stat=7882 Dof=461 C-stat=615 457 C-stat=627 459 C-stat=649 r-chisq=1. 02/459
GRB 080916 C Time-resolved spectra--Changing u Spectra are Changing u Alpha seems consistent u Epeak changes very little u Beta changes a lot These results imply that the higher-energy emission changes larger steeply than the low-energy one. u
GRB 080916 C LAT light curve & spectral index Light curve 1. 2 ØWith gtlike method ØThe first four data seems from the background like the last one ØThe others follow a power-law when we exclude two data. ØThe onset of afterglow is about 6 sec. For spectral index Øchanging
GRB 100131 A Na. I 6 BGO 1 Different profile between different energy range
GRB 100131 A GBM spectrum with Band function fitting [ T 0 : T 0+4 ] 1. 2. 3. 4. 5. 6. 7. PL C-stat=1461 DOF=350 Band C-stat=1150 348 SBPL C-stat=1151 348 PL 2 C-stat=1136 346 Comt C-stat=1222 349 Band+PL C-stat=1148 346 Band +Eff reduced chisq=1. 09/348 Epeak=106 alpha=0. 46 beta=2. 00
GRB 100131 A Time-resolved spectra [ T 0 : T 0+4 ] sec Slightly changes but not too much
Analysis on GRB 090510 BGO detector 200 ke. V – 40 Me. V Na. I detector 8 ke. V 900 ke. V Higher Energy photon <900 ke. V Taking part in the Gamma Ray Outburst
Prompt Emission Band+PL Ep=4029. +/- 134. ke. V Band Fit: C-STAT = 708. 71, DOF = 694 Power Law + Band's GRB Peak : CSTAT 412. 1 DOF 462 LAT spectrum = Power Law P. I = 2. 04 CSTAT 78. 3 DOF 93
1 st Peak LAT+GBM 2 nd Peak LAT+GBM Band Fit 1 st Peak (-0. 1 s to 0. 2 s w. r. t the Trig. Time): C-STAT = 628. 70, DOF = 599 2 nd Peak (1 s to 6 s w. r. t the Trig. Time): C-STAT = 710. 33, DOF = 601
Studying Spectral Evolution of Afterglow Emission XRT
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 (090510 -080916 C)
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