GCN Circular 5686
Subject
GRB 060928: Swift observations
Date
2006-10-03T21:37:56Z (18 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L. Page (U. Leicester), J. Cummings (GSFC/UMBC), K. Hurley
(UCBerkeley/SSL), D.N. Burrows, D.C. Morris, J.A. Kennea, P. Brown (PSU)
and D.M. Palmer (LANL) report on behalf of the Swift team:
Swift-BAT serendipitously observed the location of the IPN localised burst
GRB 060928 (GCN Circ. 5684, Hurley et al.; GCN Circ. 5685, Bellm et al.),
which was out of the BAT field of view when the burst itself happened,
during a 28-minute observation beginning 11 minutes after the burst
trigger. Ground analysis of BAT data shows a weak source at RA, Dec
127.613, -42.739 (J2000) with a 90% confidence error circle of 2.5 arcmin
radius. BAT detects emission for many minutes in the 15-50 keV energy
range starting 11 minutes after the original burst and 8 minutes after the
larger second burst. This is unusual, and, in fact, such late high energy
emission has been seen by BAT only in one previous burst, the extremely
energetic very high redshift GRB 050904.
Swift-XRT performed a Target of Opportunity observation, starting
approximately 5.5 days after the burst. UVOT could not observe the
position because of a bright star in the field.
Using 7.2 ks of XRT Photon Counting mode data, we detect an uncatalogued
source within the IPN error box and close to the weak BAT detection at a
position of:
RA(J2000) = 08 30 29.90
Dec(J2000) = -42 44 58.5
with an estimated radial uncertainty of 6 arcsec (90% containment,
including boresight uncertainties). This is 49 arcsec from the
ground-calculated BAT position.
The mean count rate of the X-ray source is (4.9 +/- 1.5)e-3 count s^-1
which, assuming a photon index of 2.1 and a Galactic absorbing column of
1.1e22 cm^-2, corresponds to an observed (unabsorbed) flux of 3.5e-13
(8.0e-13) erg cm^-2 s^-1.
At the present time it is not possible to determine whether the source is
fading. Further observations are needed to verify whether or not this
source is, indeed, the afterglow of GRB 060928.
This circular is an official product of the Swift team.