[vsnet-grb-info 9040] Swift-BAT refined analysis of the probable new SGR 1833-0832

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10528
SUBJECT: Swift-BAT refined analysis of the probable new SGR 1833-0832
DATE:    10/03/19 22:55:16 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), T. Sakamoto (GSFC/UMBC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), J. M. Gelbord (PSU),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+303 sec from the recent telemetry downlink,
we report further analysis of BAT trigger #416485 (Gelbord, et al., GCN Circ.
10526).  The BAT ground-calculated position is RA, Dec = 278.446, -8.533 deg,
which is 
   RA(J2000)  =  18h 33m 47.1s 
   Dec(J2000) = -08d 32' 00.2" 
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 87%.
 
The mask-weighted light curve shows two resolved peaks with a total duration
of ~16 millisec.  T90 (15-350 keV) is 0.012 +- 0.009 sec (estimated error
including systematics).
 
The time-averaged spectrum from T+0.000 to T+0.016 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index -1.02 +- 1.35, 
and Epeak of 38.2 +- 5.0 keV (chi squared 43.5 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.3 +- 0.2 x 10^-8 erg/cm2
and the 1-sec peak flux measured from T-0.49 sec in the 15-150 keV band is
0.2 +- 0.1 ph/cm2/sec.  Similarly, a blackbody fit yields kT= 10.0 +-1.2 keV
(chi squared 43.8 for 57 d.o.f).  A fit to a simple power law gives a photon index
of 2.58 +- 0.23 (chi squared 74.2 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/416485/BA/
 
Given (a) the low galactic lattitude (0.01 deg), (b) the short duration
of the event, and (c) the spectral softness (Epeak=38.2 and photon index
of -1.02), we believe this to be an event from a new probable SGR
which we are calling SGR 1833-0832.