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GCN Circular 4780

Subject
Preliminary refined analysis of the Swift-BAT trigger 191157
Date
2006-02-18T21:12:56Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC),
G. Cusumano (IASF-Pa INAF), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (GSFC/UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), 
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:

Using a partial data set from T-60 to T+116 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 060218 (trigger #191157)
(Cusumano, et al., GCN 4775).  The BAT ground-calculated position is
RA,Dec = 50.380,+16.904 deg {03h 21m 31.1s, 16d 54' 14.8"} (J2000)
+- 2.6 arcmin, (radius, sys+stat, 90% containment).  The partial coding was 88%.
 
The mask-weighted lightcurve is weak and flat from T-60 to T+120 sec
(all the data we have so far).  Nothing can be said about T90.
Since there is obvious emission prior to T-60 and after T+116,
we are not quoting the usual spectral fit values at this time.
We note that Swift completed a Pre-Planned Slew 8 sec prior to the beginning
of the image trigger integration which resulted in trigger 191157,
and therefore BAT was unable to trigger prior to this slew on this source.
We also note that all the emission is in the 15-50 keV band.

There is also a detection at this location at the same flux level at T+900 sec.
And there is a possible 5.6-sigma detection at the same location on Jan 17, 2006
(a month earlier).  While we can rule out that this is a chance fluctuation,
it does call into question the GRB nature of the event (trigger 191157).
At this stage in the analysis, it is equally likely that this trigger
is a GRB or hard x-ray transient.  We expect the full data set by Feb 20,
and so will be able make a better assessment.
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