Gamma-ray Burst 080405

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #7564
  J. R. Cummings (NASA/GSFC/UMBC) on behalf of the Swift-BAT team K. Hurley on behalf of the Mars Odyssey GRS team
  At 09:18:55.6 UTC on April 5, 2008, BAT triggered on GRB 080405 (trigger #308549). Automated attempts onboard to find a significant source in an image were prematurely terminated by a Swift preplanned slew manuver.
  Mars Oddyssey GRS detected a ~10 s long event at 33236 s Mars time (09:13:56 +/- 700 s Earth time), and the team informed the IPN. The BAT team searched the BAT data for a corresponding event and found the failed onboard trigger and a large peak in the count rates.
  Ground analysis of BAT data found a strong source at RA, Dec 162.597, -4.250, which is:
  10h 50m 23.3s, -4d 15' 00" (J2000),
  2.0 arcmin error radius (estimated 90% confidence). This is 0.4 arcmin from [BTW2002] J105021.50-041505.9, the host galaxy of 2002AL (see Becker et al. IAUC #7804).
  The BAT light curve shows a slow-rise and slow-decay Gaussian-like envelope with multiple peaks. T90 is approximately 40 +- 5 seconds. The peak countrate was about 9000 counts/sec at T+25 sec (15-350 keV). The source was 37% coded in the BAT field of view. Because the burst was not detected onboard, the full burst response was not collected. Partial BAT data products will be available.
  Swift will execute a TOO on April 6 for the narrow-field instruments to observe this burst.
• GCN Circular #7565
  V. La Parola, B. Sbarufatti, V. Mangano (INAF-IASF PA) and D.N. Burrows (PSU) report on behalf of the Swift XRT team.
  The XRT began observing GRB 080405 (Cummings et al., GCN 7564) on 2008-04-07 at 04:25:49, ~43 hours after the trigger. The observation is in PC mode and consists of 1.5 ksec split over two orbits. A single uncatalogued source is detected in the whole XRT field of view, with coordinates:

  RA  = 10:50:23.64  (162.59850)
  Dec = -04:17:18.5  (-4.288476)
  

  with an uncertainty of 7.1 arcsec (radius, 90% containment). This position lies 2.3 arcmin from the BAT position (slightly outside the BAT error circle). The source has a count rate of 1.029E-02 2.9E-03 c/s,y corresponding to an unabsorbed flux of 4.63e-13 ergs/s/cm-2 (assuming a standard powerlaw spectrum with index 2.0 and a Galactic line of sight absorbing column of 3.8e20 cm-2). With these data we cannot assess if the source is decaying.
  This circular is an official product of the Swift-XRT team.
• GCN Circular #7566
  T. Sakamoto (GSFC/ORAU), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), M. Stamatikos (GSFC/ORAU), T. Ukwatta (GWU), K. McLean (GSFC/UMD), W. Baumgartner (GSFC/UMBC), E. Fenimore (LANL), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), G. Sato (GSFC/ISAS), J. Tueller (GSFC) (i. e. the Swift-BAT team)
  We report further results on GRB 080405 (Cummings et al. GCN circ #7564) based on the BAT event data from T-1.3 to T+8.7 seconds. This interval covers only about the first fifth of the event, and not the interval of peak flux.
  The best BAT position remains the same: RA, Dec 162.597, -4.250 deg which is:

  RA(J2000)  = 10h 50m 23.3s,
  Dec(J2000) = -4d 15' 00" (J2000)
  

  with an uncertainty of 2.0 arcmin (radius, sys+stat, 90% containment).
  The burst was 36% coded at T0. A Swift preplanned slew began at about T+4 sec, and the burst left BAT's coded field of view entirely at about T+45 sec. The unweighted counting rates are still somewhat sensitive to photons entering through the side of the instrument.
  These rates show a slow rise becoming detectable beginning about T-4 seconds, rising to a series of overlapping peaks at T+12, T+20, T+27, T+32, T+36, T+44, and T+47 seconds, with the peak at T+27 appearing the highest. The burst seems to follow an approximately Gaussian envelope (though as noted, the profile is modulated by the slew and by scattering and transmission through the side of the instrument). T90 is 40 +-5 seconds. It fades below detectability at about T+52 seconds.
  The spectrum from T-1.3 to T+8.7 sec is well fit by a single power-law function with a photon index of 1.28 +- 0.07. The fluence is (1.2 +- 0.1) x 10^-6 ergs/cm2. We estimate that the total fluence of the entire burst is ~5 x 10-5 ergs/cm2; i. e. we caught only a small fraction of the burst in our detailed data.