GCN Circular 13836
Subject
Swift Trigger 535026 is GRB 121001A: Swift-BAT refined analysis
Date
2012-10-02T01:14:20Z (12 years ago)
From
Craig Markwardt at NASA/GSFC <craigm@milkyway.gsfc.nasa.gov>
T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
V. D'Elia (ASDC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
Using the data set from T-60 to T+243 sec from the recent telemetry
downlink, we report that Swift trigger #535026 (D'Elia, et al., GCN
Circ. #13831) is consistent with being a GRB. We follow the designation
of previous authors for the trigger as GRB 121001A (Zheng et al. GCN
Circ. #13832; Andreev et al. GCN Circ. #13833; Gorbovskoy et al. GCN
Circ. #13834).
Based on the analysis below, the burst has strong emission up to 100
keV, and a FRED-like light curve profile with duration longer than
100sec. Neither of these is consistent with a neutron star
thermonuclear X-ray burst (which would be blackbody emission with
temperature kT ~ few keV). The soft emission we reported in GCN Circ.
#535026 is associated with an X-ray burst from HETE J1900.1-2455,
another active X-ray binary in the BAT field of view. Thus, we conclude
that trigger #535026 is consistent with a GRB interpretation.
We report further BAT analysis of GRB 121001A (trigger #535026).
The BAT ground-calculated position is
RA, Dec = 276.029, -5.667 deg which is
RA(J2000) = 18h 24m 06.9s
Dec(J2000) = -05d 40' 01.0"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
The light curve shows a FRED-like profile, starting near T-25sec, rising
to maximum at T-15sec, and gradually decaying to background near
T+130sec. T90 (15-350 keV) is 147 +- 24 sec (estimated error including
systematics).
The time-averaged spectrum from T-30 to T+143 sec is best fit by a
simple power-law model. The power law index of the time-averaged
spectrum is 1.34 +- 0.15. The fluence in the 15-150 keV band is 1.7 +-
0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+3.27
sec in the 15-150 keV band is 0.5 +- 0.1 ph/cm2/sec. All the quoted
errors are at the 90% confidence level.
The BAT results for this circular represent a limited time window. The
results may be revised if additional downlinked data show more emission.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/535026/BA/