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GCN Circular 17946

Subject
Swift triggers again on V404 Cyg
Date
2015-06-18T13:30:43Z (9 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester),
J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester) and M. H. Siegel (PSU) report on behalf of
the Swift Team:

At 13:09:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located again V404 Cyg (trigger=644627) (GCNs 17929, 17944, and 17945). 
Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 306.014, +33.869, which is 
   RA(J2000)  =  20h 24m 03s
   Dec(J2000) = +33d 52' 09"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several slightly overlapping
peaks with a duration of about 15 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 13:10:06.9 UT, 46.5 seconds after
the BAT trigger. XRT found a bright X-ray source located at RA, Dec
306.0154, 33.8666 which is equivalent to:
   RA(J2000)  = +20h 24m 3.70s
   Dec(J2000) = +33d 51' 59.8"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
position is 8.1 arcseconds from a known X-ray source: 1SXPS
J202404.2+335155. This source is in the Swift XRT 1SXPS catalogue with
a mean 0.3-10 keV count-rate of 0.0183 +/- 0.0015 ct/sec; see
http://www.swift.ac.uk/1SXPS/1SXPSJ202404.2%2B335155 for details of
these previous observations. No event data are yet available to
determine the column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 1.26e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 56 seconds after the BAT trigger. V404 Cyg is detected with a
white magnitude of 15.0 +/- 0.2. No correction has been made for the large,
but uncertain extinction expected.
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