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GCN Circular 30656

Swift Trigger 1069242 is Cyg X-1
2021-08-18T16:55:58Z (3 years ago)
Kim Page at U.of Leicester <>
A. P. Beardmore (U Leicester), J.D. Gropp (PSU),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
M. H. Siegel (PSU) and A. Tohuvavohu (U Toronto) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 16:17:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located Cyg X-1 (trigger=1069242).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 299.819, +35.277 which is 
   RA(J2000) = 19h 59m 16s
   Dec(J2000) = +35d 16' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). This onboard position is 12 arcminutes from the 
known position of Cyg X-1, likely due to higher than typical attitude 
uncertainty from the star trackers. 
As is typical for an image trigger the prompt  BAT lightcurve shows no
evidence of structure, and the significance of the source in the BAT image
is consistent with the typical brightness of Cyg X-1. 

The XRT began observing the field at 16:19:20.2 UT, 139.8 seconds after
the BAT trigger. XRT found a bright X-ray source  in the field-of-view 26
arcseconds from the position of Cyg X-1, but  given the star trackers 
had lost lock is likely consistent with this source. 

There are no UVOT data available at this time.
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