GCN Circular 3180

A. Parsons (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC),
  E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), S. 
Hunsberger (PSU),
  H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),  D. Palmer (LANL),
  T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama),
  J. Tueller (GSFC) D. Burrows, J. Kennea, J. Nousek (PSU), G. 
Chincarini,
  P. Romano (INAF-OAB)
  on behalf of the Swift team:

  At 15:58:48.40 UT Swift-BAT triggered on burst GRB 050406 (trigger 
113872).
The BAT-derived position is RA,Dec= 34.428, -50.178 (J2000). 
Significant emission
has been detected for at least 3 sec with possible low significance 
peaks over
an additional 30 sec.  The peak count rate was 800 cnts/sec. The source 
was
detected at 15 degrees off the bore-site and thus is in the fully-coded 
field-of-view.

Swift slewed promptly and the UVOT imaged the field at the end of the 
slew and did
not find a bright optical source in the 8 arcmin square binned field of 
view centered
on the BAT position.

The XRT also imaged the field promptly and did not find a bright X-ray 
source within
the field of view.  Based on previous experience, this lack of prompt 
x-ray afterglow
suggests either that this trigger is not a GRB, or that it is a very 
interesting and
unusual GRB.  The BAT rate trigger and image are significant enough to 
lean
toward an interpretation of an unusual GRB.