GCN Circular 4996

K. L. Page (U Leicester), S. D. Barthelmy (GSFC),
J. R. Cummings (NASA/ORAU), J. A. Kennea (PSU),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD) and
D. M. Palmer (LANL) report on behalf of the Swift Team:

At 04:36:54 UT, the Swift Burst Alert Telescope (BAT) triggered and
located emission from Markarian 421 (trigger=206476).  Swift did not
immediately slew to this source.  The BAT on-board calculated location
is RA,Dec 166.088, +38.212 {11h 04m 21s, +38d 12' 43"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  This is 1.3 arcmin from Mrk 421.  Because this
was a long image trigger (21 minute integration), there is no usable
lightcurve at this time. 

We note that Mrk 421 has been slowly rising in the BAT survey data
for the last 7 days.