GCN Circular 10524
Subject
GRB 100316D: Pre-burst emission measured by BAT
Date
2010-03-18T21:13:59Z (15 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori@milkyway.gsfc.nasa.gov>
T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), C. B. Markwardt (GSFC/UMD),
D. M. Palmer (LANL), M. Stamatikos (GSFC/OSU)
(i.e. the Swift-BAT team):
Using the BAT hard X-ray survey data (Detector Plane Histogram data), we have
processed the BAT survey data for pre- and post-trigger periods using the batsurvey
script and have extracted the flux at the location of the GRB. While Swift was pointing at
GRB 100316C from T-2650 s to T-80 s, the GRB 100316D location was in the FOV of BAT.
At 12:43, Swift slewed to a pre-planned target (1E 1048.1-5937), and triggered on GRB 100316D.
After re-pointing to the location of GRB 100316D, Swift slewed away from GRB 100316D
at T+750 s due to an observational constraint. GRB 100316D came back into the FOV of BAT
at T+5050 s (a pre-planned observation of 1E 1048.1-5937).
The BAT light curve in the 14-195 keV band around the trigger time is available at:
-Light curve from T-6000 sec to T+6000 sec:
http://gcn.gsfc.nasa.gov/other/GRB100316D_bat_lc.gif
-Zoom-in light curve from T-2000 sec to T+1000 sec:
http://gcn.gsfc.nasa.gov/other/GRB100316D_bat_lc_zoomin.gif
The light curve produced by the BAT event-by-event data is overlaid with the survey light
curve in the figure. There is a probable early low-level emission starting from T-1500 s.
The emission then rises at T-500 s, peaks at T-100 s, and decays with an exponential
decay constant of ~750 s. The emission continues through the slew at T+750 s.
The emission is no longer detected by BAT after T+5050 s.
As pointed out in Sakamoto et al. (GCN Circ. 10511), the BAT light curve profile of
GRB 100316D is very similar to the GRB 060218-SN2006aj burst
(Camapana, et al.; Nature, v224, p1008). The BAT light curve of GRB 060218 shows
a rise at T-300 s, a peak at T+450 s, and an exponential decay constant of ~500 s,
with a duration of ~2000 sec. GRB 100316D was detected in Swift-BAT from ~T-500 sec
to at least ~T+800 sec, hence the lower limit on the duration of GRB 100316D is ~1300 sec.
The fluence in the 15-150 keV band measured with the available 955 seconds of event data
is 3.4 x 10^-6 erg/cm2. This corresponds to an isotropic equivalent
energy (Eiso) of 3.1x10^49 ergs in the 15.88 keV - 158.85 keV band at the GRB rest frame
assuming a redshift z=0.059 of a potential source and a galaxy inside the XRT error
circle (Vergani et al. GCN Circ. 10512, 10513). This unusually long duration in
concert with a soft spectrum and a low Eiso (Eiso of GRB 060218 was
6.2x10^49 ergs) strengthens the similarity between GRBs 100316D and 060218. Although
the lack of a clear optical counterpart to GRB 100316D at this stage is distinctly
different than GRB 060218, the prompt emission characteristics are very much like
supernova-associated GRB 060218. Hence, we suggest additional follow-up observations
especially in the IR that may confirm the presence of a host supernova.