GRB 071028B
GCN Circular 7019
Subject
GRB 071028B Swift-BAT detection of a burst
Date
2007-10-30T13:19:51Z (18 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <jayc@milkyway.gsfc.nasa.gov>
J. R. Cummings (CRESST/NASA/GSFC) and J. Greiner (MPE) for the Swift team
At 02:43:46 UT on October 28, the Swift Burst Alert Telescope (BAT)
triggered on GRB 071028B (trigger #295492). The burst was on the edge
of the field of view (4.1% coded) and no source was found automatically
onboard. A source was found during later ground analysis at a location
RA, Dec 354.163, -31.630 which is
RA(J2000) = 23h 36m 39s
Dec(J2000) = -31d 37' 47"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows two FRED peaks,
the first at T+1 sec about 4 seconds long, the second at T+48 sec about
9 seconds long. The peak count rate was about 1500 counts/sec
(15-350 keV), at ~1 sec after the trigger.
Because the burst was detected on the ground, there are no prompt
XRT or UVOT data. A Swift TOO has been scheduled for October 30,
at approximately 1400 UT.
There have been several ground-detected Swift-BAT bursts lately:
GRB 071006 (GCN circ #6858), GRB 071010C (GCN circ #6906) and
this one. We have not changed our procedures substantially, and
we do not believe that we have missed many such bursts in the past.
It apparently is merely an odd statistical fluctuation of rare
events: Two weak bursts on the edge of the BAT field of view and
another immediately before a preplanned slew maneuver.
Five such bursts have been noted before, one occurring just before
a preplanned slew, GRB 051012 (GCN circ #4093), one combining both
factors, GRB 070227 (GCN circ #6156), and the other three being very
weak/short, GRB 051114 (GCN circ #4272), GRB 060505 (GCN circ #5076),
and GRB 070406 (GCN circ #6247). A fifth nearly similar case was a
very long and weak burst, GRB 060123 (GCN circ #4608), producing a
significant detection onboard though automatic long-image triggers
were not enabled at that time.
GCN Circular 7040
Subject
Swift XRT and UVOT observations of GRB071028B
Date
2007-11-03T03:33:32Z (18 years ago)
From
Dirk Grupe at PSU/Swift-XRT <grupe@astro.psu.edu>
Dirk Grupe (PSU) and Patricia Schady (MSSL/UCL) report on behalf of the
Swift
team:
The Swift XRT began observing the field of GRB 071028B (GCN 7019; Cummings
2007) on 2007 October 30 13:36 UT approximately 212 ks after the burst.
Note that this burst was discovered in ground processing of the BAT data.
Therefore no immediate
observations after the burst were performed. There are clearly three sources
within the 3' BAT error circle. The brightest of these (0.01 counts/s)
coincides with a known source listed in the USNO catalogue.
There is one source nearly at the center of the BAT error circle at RA-2000,
Dec-2000 354.16300, -31.62050 which corresponds to
RA-2000 = 23 36 39.1
Dec-2000 = -31 37 13.8
with a 4.8" XRT error circle. The second source is located at
354.11579, -31.63948 corresponding to
RA-2000: 23 36 27.8
Dec-2000: -31 38 22.1
with a 4.8" XRT error circle.
UVOT observed the field of GRB 071028B for a total of 6443s in the
V-filter.
There is no optical counterpart within the XRT error circles of the
first and
second source. The
3-sigma upper limits are V > 21.3mag and V >21.6 mag, respectively.
These values are not corrected for the expected
Galactic extinction corresponding to a reddening of E(B-V) = 0.02 mag in
the
direction of the burst (Schlegel et al. 1998). There are no counterparts at
either of the source positions in the USNO catalogue within the XRT error
radius (90% containment).
This circular is an official product of the Swift team
GCN Circular 7064
Subject
Swift XRT follow-up observations of GRB071028B
Date
2007-11-12T20:25:48Z (18 years ago)
From
Dirk Grupe at PSU/Swift-XRT <grupe@astro.psu.edu>
Dirk Grupe (PSU) reports on behalf of the Swift XRT
team:
The Swift XRT re-observed the field of GRB 071028B (GCN 7019; Cummings
2007) on 2007 November 07 for 9 ks and 2007 November 10 for 11ks.
Clearly the first source listed in GCN Circ 7040 (Grupe & Schady, 2007)
had faded while the second source is still visible at a similar level as
reported in GCN 7040. It is therefore clear that this first source
was the X-ray afterglow
of GRB 070128, since its flux decreased.
The position of the X-ray afterglow of GRB 071028B is
RA-2000, Dec-2000 354.16300, -31.62050 which corresponds to
RA-2000 = 23 36 39.1
Dec-2000 = -31 37 13.8
with a 4.8" XRT error circle.
The 3-sigma upper limit at the position of the burst combining both data
sets
(20ks) is 6.7e-4 counts/s which converts roughly to 3e-14 ergs/s/cm2.
This circular is an official product of the Swift team