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Prompt Emission Properties of Swift GRBs

Prompt Emission Properties of Swift GRBs. T. Sakamoto (CRESST/UMBC/GSFC) On behalf of Swift/BAT team. 101029. Breaking News!!. 101029. Name: Yuiko Sakamoto Gender: Girl DOB: Oct 29, 2010 8:54AM Weight: 5 lbs 8 oz (2490g) Length: 19” (48cm). Content.

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Prompt Emission Properties of Swift GRBs

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  1. Prompt Emission Properties of Swift GRBs T. Sakamoto (CRESST/UMBC/GSFC) On behalf of Swift/BAT team 2010 Annapolis GRB Conference

  2. 101029 Breaking News!! 2010 Annapolis GRB Conference

  3. 101029 Name: Yuiko Sakamoto Gender: Girl DOB: Oct 29, 2010 8:54AM Weight: 5 lbs 8 oz (2490g) Length: 19” (48cm) 2010 Annapolis GRB Conference

  4. Content • Highlight on Swift’s discovery on 2010 • BAT2 GRB catalog • Duration distribution (short GRBs) • Epeak distribution • Line of Death Problem • Extra power-law component in the BAT data? • Pre-/post-burst hard X-ray emission 2010 Annapolis GRB Conference

  5. Discovery on 2010 2010 Annapolis GRB Conference

  6. GRB 100316D/SN 2010bh: SN-GRB Association New SGR 1833-0832 BAT light curve Prompt emission (Starling et al. 2010) Slew away from the GRB Time since BAT trigger [s] Optical spectrum (Chornock et al. 2010) X-ray pulse profile (XRT and RXTE) • BAT Position • (l, b) = (23.325d, 0.009d) • Pulsating new X-ray source: • P=7.56 s, Pdot = 4 x 10-12s/s • (XRT and RXTE) • B = 1.8 x 1014 G (lower end) (Gogus et al. 2010) 2010 Annapolis GRB Conference

  7. BAT2 GRB Catalog (Submitted to ApJS, under the revision…) 2010 Annapolis GRB Conference

  8. BAT2 GRB Catalog • 476 GRBs (from GRB 041219 to GRB 091221) - including 25 GRBs found in ground processing • 3323 time-resolved spectra • 146 known-z GRBs 426 Long-duration GRBs (L-GRBs) (89%) (9%) 41 Short-duration GRBs (S-GRBs) 476 GRBs 9 Short-duration GRBs with extended emissions (S-GRBs w/ E.E.) (2%) Working definition of L-GRB vs. S-GRB: L-GRB: T902 s S-GRB: T90 < 2 s 2010 Annapolis GRB Conference

  9. T90 Duration (15-150 keV) 70 s S-GRBs: 9% (50 - 350 keV) 32 s S-GRBs: 25% 0.5 s 2010 Annapolis GRB Conference

  10. Discussion: Duration BATSE Log Pulse width [s] Log Energy [keV] BAT GRB 050525A 15-25 keV 25-50 keV Counts/sec/det (Fenimore et al. 1995) 50-100 keV BAT BATSE/LAD 100-200 keV Effective Area [cm2] Time since the trigger [s] Energy [keV] 2010 Annapolis GRB Conference

  11. Preliminary BAT: 10% S-GRBs (90% L-GRBs) Discussion: Short on S-GRBs in BAT BATSE: 25% S-GRBs (75% L-GRBs) Factor of 2.5 small # on S-GRBs in BAT BATSE - Rate trigger • BAT • Rate trigger • Imaging vs. 306 BATSE short GRBs 36 BAT short GRBs BATSE complete spectral catalog (Goldstein, Preece & Mallozzi) SNR > 10: 62 BATSE short GRBs BATSE short GRBs Band spectral parameters 4% of total BATSE GRBs 20% of BATSE short GRBs BAT energy response (30d) + background Majority of the BATSE short GRBs is too faint in BAT SNR Simulate BAT fg/bg spectrum 2010 Annapolis GRB Conference

  12. Time-averaged Epeak distribution CPL 79 keV 320 keV 65 keV 2010 Annapolis GRB Conference

  13. Discussion: Epeak (1) Epeak distribution (2) What is Epeak? Epeak : Peak of the Synchrotron spectrum BATSE BAT Effective area [cm2] HETE/FREGATE HETE/WXM - Broad single Epeak distribution (Racusin et al. 2008) Open questions: Epeak : Inverse Compton peak? - Where is a lower/upper limit of Epeak? Broad-band observation (from radio to gamma-ray) of the prompt emission is a key! 2010 Annapolis GRB Conference

  14. Discussion: Epeak (1) Epeak distribution (2) What is Epeak? Epeak : Peak of the Synchrotron spectrum BATSE BAT Effective area [cm2] HETE/FREGATE HETE/WXM - Broad single Epeak distribution (Racusin et al. 2008) Open questions: Epeak : Inverse Compton peak? - What is the intrinsic distribution of Epeak? Broad-band observation (from radio to gamma-ray) of the prompt emission is a key! 2010 Annapolis GRB Conference

  15. Line of Death Problem Synchrotron Shock Model (SSM) N(e) dee-p de (e m) Fast cooling  p-/2  • n a : self-absorption frequency • n c : cooling frequency • m : synchrotron frequency of the minimum-energy electrons  BATSE time-resolved spectra (Preece et al. 1998) 23% LoD    p/2  -2/3 -3/2 acm Energy (e.g. Sari et al. 1996, 1998) Epeak 2010 Annapolis GRB Conference

  16. BAT Time-resolved Spectra- PL fit - -2/3 Exceed LoD: 18/2968 spectra (=0.6%) 2010 Annapolis GRB Conference

  17. BAT Time-resolved Spectra - CPL fit - -2/3 -3/2 Exceed LoD: 23/234 spectra (=10%) 2010 Annapolis GRB Conference

  18. >1.6  Examples of LoD intervals 2010 Annapolis GRB Conference

  19. >1.6  Examples of LoD intervals • 0.6%(PL fit) and 10% (CPL fit) of BAT spectra exceed LoD • LoD intervals: Either bright spikes or a rising part of a peak 2010 Annapolis GRB Conference

  20. Extra power-law component in the BAT spectra? F spectrum of region b Fermi GRB 090902B (Abdo et al. 2009)   Epeak = 908 keV dN/dE Band   ~50 keV Energy 2010 Annapolis GRB Conference

  21. Extra power-law component in the BAT spectra? BAT spectral simulation of region b Reduced 2 distribution • 30 deg off-axis BAT energy response • including real background data • xspec fakeit 10,000 simulations • fit by PL and CPL Simulated spectra (PL) Time-resolved spectra (PL or CPL) Example of BAT simulated spectrum of reg b PL fit - 99.97% of the simulated spectra  - 2/3284 (0.06%) of the BAT time-resolved spectra  BAT hasn’t seen such a spectral feature… 2010 Annapolis GRB Conference

  22. Summary • Duration: long GRB T90 ~ 70 s •  longer duration at softer energy band • : lack of short GRBs •  localizing bright end of BATSE short GRBs • Epeak: Strong instrumental selection bias •  broad-band observation of the prompt emission • Line of Death: ~1% (PL) and ~10% (CPL) violate LoD limit •  Either bright or rising part of the peak • Extra power-law component: No 2010 Annapolis GRB Conference

  23. 2010 Annapolis GRB Conference

  24. GRB 100316D/SN 2010bh: SN-GRB Association X-ray afterglow Optical spectrum Prompt emission GRB 100316D Slew away from the GRB GRB 060218 Time since BAT trigger [s] (Starling et al. 2010) c.f. GRB 060218 c.f. GRB 030329/SN 2003dh HETE-2 • z = 0.0593 • Type Ic • v ~ 26,000 km/s@21 days • (2x SN 1998bw) • No evidence of helium • Low metallicity host (Campana et al. 2006) (Chornock et al. 2010) (Vanderspek et al. 2004) 2010 Annapolis GRB Conference

  25. New SGR 1833-0832 (Gogus et al. 2010) BAT light curve • March 19, 2010 18:34:50.78 UT • BAT Position (18h33m46s, -8d32m13s) • (l, b) = (23.325d, 0.009d) • BAT spectrum fit well with BB (kT=10 keV) instead of PL • Very faint X-ray source by XRT • (Issue GCN Circ. “Possible new SGR”) • Pulsating new X-ray source: P=7.56 s, Pdot = 4 x 10-12s/s (XRT and RXTE) • Sub-arcsec position by Chandra • No burst detection by Fermi/GBM; four weak bursts detected by RXTE/PCA • No obvious IR (UKIRT) and radio (WSRT) counterpart • B = 1.8 x 1014 G (lower end) X-ray pulse profile (XRT) 2010 Annapolis GRB Conference

  26. Interpretation of BAT PL index (1) EBAT < Epeak (2) EBAT < Epeak < EBAT (3) Epeak > EBAT dN dE  Epeak BAT PL ~ 1 BAT PL ~ 2.5 BAT PL ~ 1.7  BAT BAT BAT Energy • BAT PL photon index does inform about Epeak. • ~75 % of BAT GRBs: Epeak is very likely located inside the BAT energy range (Sakamoto et al. 2009). 2010 Annapolis GRB Conference

  27. Anti-Sun Pointing Matters! known-z GRBs unknown-z GRBs Redshift determination rate by different Sun hour angle (GRBSun) of GRBs GRBSun 9 hr: 45% 6 hr  GRBSun  9 hr: 47% 3 hr  GRBSun 6 hr: 34% 0 hr  GRBSun 3 hr: 10% Anti-Sun pointing has a strong effect in redshift determination of Swift GRBs 2010 Annapolis GRB Conference

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