GCN Circular 13836

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/