[vsnet-grb-info 15040] Swift Trigger 600114: Preliminary BAT analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16334
SUBJECT: Swift Trigger 600114: Preliminary BAT analysis
DATE:    14/05/28 05:58:06 GMT
FROM:    Craig Markwardt at NASA/GSFC  <craigm at milkyway.gsfc.nasa.gov>

W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (NASA/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):

Using the data set from T-120 to T+180 sec from a recent telemetry
downlink, we report preliminary analysis of BAT trigger 600114,
tentatively associated with the M31 galaxy (Barthelmy, et al., GCN
Circ. 16332).  The BAT ground-calculated position is
RA, Dec = 10.371, 41.520 deg which is
    RA(J2000)  =  00h 41m 29.0s
    Dec(J2000) = +41d 31' 11.7"
with an uncertainty of 3.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 50%.

The mask-weighted light curve is consistent with a sharp rise
(~10 sec rise time) near T+0sec, followed by a ~60 sec decay.  The
excess counts are primarily in the 15-50 keV band.
T90 (15-350 keV) is 55.2 +- 15.9 sec (estimated error including 
systematics).

The time-averaged spectrum from T-4 to T+55 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.35 +- 0.57.  The fluence in the 15-150 keV band is (3.1 +- 1.1) x
10^-7 erg/cm2. The 1-sec peak photon flux measured from T+22.42 sec in
the 15-150 keV band is 0.6 +- 0.2 ph/cm2/sec.  All the quoted errors
are at the 90% confidence level.

We caution that this is a faint BAT transient and the significance is
lower than typical for GRBs.  We urge confirmation at other wavelengths.
Significance, light curve and spectral properties may be revised after
further refined analysis.  If confirmed as real and associated with
the M31 galaxy at a distance of 778 kpc, the mean luminosity averaged
over the T90 duration in the 15-150 keV band would be 2-6 x 10^41
erg/s.

Such a luminosity, if isotropic, would be highly super Eddington for a
1 solar mass object (by a factor in the 2000-5000 range).
Alternatively, the source could be highly beamed in our observer
direction.  Although either interpretation suggests a tantalizingly
energetic event as the progenitor, we again urge caution until the
presence of a bright source at this location is confirmed
independently.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/600114/BA/