[vsnet-grb-info 18131] GRB 160625A - two different events?

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19579
SUBJECT: GRB 160625A - two different events?
DATE:    16/06/26 00:01:31 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann at tls-tautenburg.de>

D. A. Kann (TLS Tautenburg) speculates:

Swift just triggered on GRB 160625A (Swift Trigger 701503, Maselli et al.,
GCN #19577). They reported several rather small peaks followed by very
strong emission ca. three minutes later.

This burst is seen to be extremely powerful in INTEGRAL SPI ACS and CALET
GBM. It seems to have begun with a short spike at about the same time as
the Swift BAT trigger (Fermi GBM trigger 488587220).

Three minutes later, Fermi LAT sent out a flight position at:

RA = 308.267
Dec. = +6.900

with an error of 0.5 degrees.

This position differs very strongly from the Swift BAT position. (Dec. of
-65!)

Additionally, Swift BAT has recently slewed to the BAT position and found
a faint X-ray afterglow (Burrows et al., GCN 19578), which is in contrast
to the very bright one one would expect from the extreme burst seen by
INTEGRAL and CALET.

I suggest that these are two different events, with the bright GRB seen
through side of the Swift spacecraft.

The Fermi LAT position is affected by a relatively low amount of
extinction (E_(B-V)=0.1), in contrast to the Swift position (E_(B-V)=1.3).

I strongly urge observations of the LAT position by Swift to determine an
XRT position, and by optical observatories as well. Judging from the
INTEGRAL SPI ACS light curve, this GRB is of similar intensity to GRB
160623A.