GCN Circular 45930

S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha
(GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss
(GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T.
Sakamoto (AGU) (i.e. the Swift-BAT team):

Using the data set from T-179 to T+723 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 261011A (trigger #1516664)
(Cenko et al., GCN Circ. 45896
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 ).  The BAT ground-calculated position is
RA, Dec = 21.911, -21.550 deg which is
   RA(J2000)  =  01h 27m 38.7s
   Dec(J2000) = -21d 33' 00.7"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The
partial coding was 29%.

The mask-weighted light curve shows a multi-peaked structure that starts
~T+100 s and ends at ~T+210 s. T90 (15-350 keV) is 78.90 +- 18.49 sec
(estimated error including systematics). Note that the particularly unusual
light curve mentioned in the original circular (Cenko et al., GCN Circ.
45896
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 ) is no longer visible in the ground analysis. Further investigation
shows that there were some noisy detectors producing coincidental
pulse-like structures around the GRB time, and thus those pulses seen in
the raw light curve prior to ~T+100 s are not astrophysical.

The time-averaged spectrum from T+103.61 to T+208.74 sec is best fit by a
simple power-law model.  The power law index of the time-averaged spectrum
is 1.50 +- 0.07.  The fluence in the 15-150 keV band is 6.3 +- 0.3 x 10^-06
erg/cm2. The 1-sec peak photon flux measured from T+171.74 sec in the
15-150 keV band is 3.0 +- 0.4 ph/cm2/sec.  All the quoted errors are at the
90% confidence level.

The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1516664