[vsnet-grb-info 7630] GRB 090422: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9185
SUBJECT: GRB 090422: Swift detection of a burst
DATE:    09/04/22 03:51:57 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

T. N. Ukwatta (GSFC/GWU), S. D. Barthelmy (GSFC),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), D. M. Palmer (LANL),
M. Perri (ASDC), G. Stratta (ASDC) and L. Vetere (PSU) report on
behalf of the Swift Team:

At 03:35:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090422 (trigger=349931).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 294.756, +40.384 which is 
   RA(J2000) = 19h 39m 01s
   Dec(J2000) = +40d 23' 03"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two spikes
with a total duration of about 10 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 03:36:20.6 UT, 64.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 294.74931,
40.38530 which is equivalent to:
   RA(J2000)  = 19h 38m 59.83s
   Dec(J2000) = +40d 23' 07.1"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 18 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 gives a column density consistent with the Galactic value of
1.65e+21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 5.51e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 74 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 coverage of the XRT error circle by the 8'x8' region for the list of
sources generated on-board is uncertain because the large number of sources
filled the available telemetry. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.20. 

Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). 
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/too.html.)