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GCN Circular 30548

GRB 210730A: Swift detection of a burst near M82
2021-07-30T05:23:03Z (3 years ago)
David Palmer at LANL <>
E. Sonbas (Adiyaman Univ.), S. D. Barthelmy (GSFC),
A. D'Ai (INAF-IASFPA), D. M. Palmer (LANL), T. Sakamoto (AGU),
B. Sbarufatti (PSU) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 04:57:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210730A (trigger=1062150).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 149.592, +69.705 which is 
   RA(J2000) = 09h 58m 22s
   Dec(J2000) = +69d 42' 19"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Although the BAT lightcurve is not immediately
available due to telemetry limitations, the trigger information indicates
a very bright peak (68 sigma in rates) of at least 1 second duration. 

The XRT began observing the field at 04:58:50.8 UT, 81.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 149.59149, 69.69227 which
is equivalent to:
   RA(J2000)  = 09h 58m 21.96s
   Dec(J2000) = +69d 41' 32.2"
with an uncertainty of 8.2 arcseconds (radius, 90% containment). This
location is 45 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

The initial flux in the 2.5 s image was 6.73e-10 erg cm^-2 s^-1 (0.2-10

UVOT took a finding chart exposure of 113 seconds with the White filter
starting 90 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image processing
FAILED because of no aspect solution. Data from the list of sources generated
on-board are not available at this time. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.096. 

We note that this location is close to the nearby galaxy M82, although
well outside the main disk.  For this reason, the initial GCN Notice
misreported it as a Galactic transient. 

Burst Advocate for this burst is E. Sonbas (edasonbas 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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