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GCN Circular 25552

Subject
GRB 190829A: Swift detection of a burst consistent with a galaxy at z=0.08
Date
2019-08-29T20:25:37Z (4 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
S. Dichiara (NASA/GSFC/UMCP), M. G. Bernardini (INAF-OAB),
D. N. Burrows (PSU), P. D'Avanzo (INAF-OAB), C. Gronwall (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (PSU),
H. A. Krimm (NSF), N. P. M. Kuin (UCL-MSSL), S. J. LaPorte (PSU),
A. Melandri (INAF-OAB), K. L. Page (U Leicester), D. M. Palmer (LANL),
M. H. Siegel (PSU), K. K. Simpson (PSU) and A. Tohuvavohu (Toronto)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 19:56:44.60 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190829A (trigger=922968).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 44.540, -8.968 which is 
  RA(J2000) = 02h 58m 10s
  Dec(J2000) = -08d 58' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a smaller peak
at ~T-50 seconds followed by the main peak around T~0 with a 
duration of about 15 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 19:58:21.9 UT, 97.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 44.5440,
-8.9579 which is equivalent to:
   RA(J2000)  = 02h 58m 10.57s
   Dec(J2000) = -08d 57' 28.6"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This
location is 39 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data does not constrain the column density. 

The initial flux in the 2.5 s image was 7.75e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 106 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.05. 

This GRB was also reported by the Fermi GBM Team (GCN #25551), 
at the time of the first peak. 

We note the presence of a galaxy SDSS J025810.28-085719.2 with z=0.07914 
centered at a distance of 10 arcseconds from the XRT location. 
http://skyserver.sdss.org/dr14/en/tools/explore/Summary.aspx?id=1237652899156721762

Burst Advocate for this burst is S. Dichiara (dichiara AT umd.edu). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)
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