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GCN Circular 22909

GRB 180706A: Swift detection of a burst with optical counterpart
2018-07-06T08:43:15Z (6 years ago)
Scott Barthelmy at NASA/GSFC <>
M. Stamatikos (OSU/NASA/GSFC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), A. D'Ai (INAF-IASFPA),
V. D'Elia (ASDC), P. A. Evans (U Leicester), J.D. Gropp (PSU),
J. A. Kennea (PSU) and K. L. Page (U Leicester) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 08:24:40 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180706A (trigger=846395).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 181.665, +66.035, which is 
   RA(J2000)  =  12h 06m 40s
   Dec(J2000) = +66d 02' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two main peaks
with a total duration of about 40 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~28 sec after the trigger. 

The XRT began observing the field at 08:26:08.0 UT, 87.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 181.6428,
66.0366 which is equivalent to:
   RA(J2000)  = 12h 06m 34.28s
   Dec(J2000) = +66d 02' 11.6"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 32 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  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.44
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 7.91e-10 erg cm^-2 s^-1 (0.2-10

UVOT took a finding chart exposure of 250 seconds with the U filter starting
307 seconds after the BAT trigger. There is a candidate afterglow in the
rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	12:06:34.34 = 181.64308
  DEC(J2000) = +66:02:13.6  =  66.03712
with a 90%-confidence error radius of about 0.77 arc sec. This position is 2.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.74 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02. 

Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT 
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:
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