Gamma-ray Burst 080405
(All information courtesy of the instrument teams.)
Previous IAU Circulars
Results of Observations
- 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
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,
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
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.
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Jochen Greiner, last update: 07-Apr-2008