GCN Circular 25702

S. D. Barthelmy (GSFC), F. E. Marshall (NASA/GSFC),
B. Sbarufatti (PSU) and A. Tohuvavohu (Toronto) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 07:02:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located MAXI J1807+132 (trigger=924641).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 272.070, +13.258 which is 
   RA(J2000)  =  18h 08m 17s
   Dec(J2000) = +13d 15' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several overlapping peaks
with a total duration of about 30 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 07:04:04.1 UT, 94.7 seconds after
the BAT trigger. XRT found a bright X-ray source located
at RA, Dec 272.0331, 13.2514 which is equivalent to:
   RA(J2000)  = 18h 08m 7.94s
   Dec(J2000) = +13d 15' 05.0"
with an uncertainty of 5.5 arcseconds (radius, 90% containment). This
location is 131 arcseconds from the BAT onboard position, within the
BAT error circle, and 5.5 arcseconds from the known position of MAXI J1807+132 
(Kennea et al., ATel #10215). No event data are yet available to 
determine the column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 1.11e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 105 seconds after the BAT trigger. There is a bright source in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	18:08:07.54 = 272.03143
  DEC(J2000) = +13:15:05.7  =  13.25159
with a 90%-confidence error radius of about 0.61 arc sec. This position is 5.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.17 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.15.