[vsnet-grb-info 6325] Trigger 316063: Swift detection of a transient

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7945
SUBJECT: Trigger 316063: Swift detection of a transient
DATE:    08/07/05 21:56:09 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

P. A. Ward (MSSL-UCL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), P. J. Brown (PSU),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
N. P. M. Kuin (MSSL), C. B. Markwardt (CRESST/GSFC/UMD),
K. M. McLean (GSFC/UMD), C. Pagani (PSU), K. L. Page (U Leicester),
D. M. Palmer (LANL), D. Perez (U Leicester), P. Romano (INAF-IASFPA),
T. Sakamoto (NASA/UMBC), R. L. C. Starling (U Leicester) and
G. Tagliaferri (INAF-OAB) report on behalf of the Swift Team:

At 21:14:13 UT, the Swift Burst Alert Telescope (BAT) triggered and
located trigger 316063.  Swift slewed immediately to the location. 
The BAT on-board calculated location is RA, Dec 130.246, -45.098 which is 
   RA(J2000) = 08h 40m 59s
   Dec(J2000) = -45d 05' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As this was an image trigger, the BAT light
curve is unremarkable. 

The XRT began observing the field at 21:16:23.4 UT, 130.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, X-ray source located at RA, Dec 130.20005, -45.06074 which is
equivalent to:
   RA(J2000)  = 08h 40m 48.01s
   Dec(J2000) = -45d 03' 38.7"
with an estimated uncertainty of 6 arcseconds (radius, 90% containment). 
This location is 177 arcseconds from the BAT onboard position, within the
BAT error circle. Since this is 8 arcseconds from the catalogued position
of IGR J08408-4503, further than our nominal 6" error radius, we cannot
rule out a) that this is the IGR source, or b) that it is a GRB. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
9.32e+21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.61e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of nominal 400 seconds with the V  
filter  starting 134 seconds after the BAT trigger. Due to the  
brightness of LM Vel, a bright optical source also seen in Digitized
Sky Survey, we  cannot determine any variability or  the presence of
any nearby  unknown sources near the XRT position. 

Burst Advocate for this burst is P. A. Ward (paw AT mssl.ucl.ac.uk). 
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.)