GCN Circular 20220

S. D. Barthelmy (GSFC), J. R. Cummings (CPI),

N. Gehrels (GSFC), H. A. Krimm (NSF/USRA),

D. Kocevski (NASA/MSFC), A. Y. Lien (GSFC/UMBC),

C. B. Markwardt (GSFC), J. P. Norris (BSU),

D. M. Palmer (LANL), T. Sakamoto (AGU),

M. Stamatikos (OSU), T. N. Ukwatta (LANL)

(i.e. the Swift-BAT team):


Using the data set from T-239 to T+963 sec from the recent telemetry downlink,

we report further analysis of BAT GRB 161129A (trigger #724438)

(Kocevski, et al., GCN Circ. 20210
Not found
 
 
).  The BAT ground-calculated position is

RA, Dec = 316.221, 32.137 deg which is

  RA(J2000)  =  21h 04m 53.1s

  Dec(J2000) = +32d 08' 11.9"

with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).

The partial coding was 69%.


The mask-weighted light curve shows a short spike from ~T0 to ~T+0.2 s,

followed by several overlapping pulses that last until ~T+45 s.

T90 (15-350 keV) is 35.53 +- 2.09 sec (estimated error including systematics).


The time-averaged spectrum from T+0.06 to T+44.58 sec is best fit by a simple

power-law model.  The power law index of the time-averaged spectrum is

1.57 +- 0.06.  The fluence in the 15-150 keV band is 3.6 +- 0.1 x 10^-6 erg/cm2.

The 1-sec peak photon flux measured from T+26.64 sec in the 15-150 keV band

is 3.4 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence

level.


Because the light curve seems to resemble that of a short GRB with

extended emission (Norris et al. 2010), we perform further analysis of the

short spike. Using a 4-ms binned light curve, the lag analysis finds a lag of

4 +/- 3 ms for the 50-100 keV to 15-25 keV band, which is consistent with

that of a short GRB. However, the spectral fit of the short spike

using a simple power-law model gives a power-law index of 1.9 +/- 0.3.

This value is on the softer end of short GRBs, and also softer than all the

initial pulses of those short GRBs with extended emission (Lien et al. 2016).

The power-law index of the spectrum for the rest of the light curve

is 1.53 +/- 0.06, which is harder than the initial spike and thus

unexpected from a short GRB with extended emission.


The results of the batgrbproduct analysis are available at

http://gcn.gsfc.nasa.gov/notices_s/724438/BA/