GCN Circular 11516

N.P.M. Kuin (MSSL/UCL) and J.M. Gelbord (PSU) report on behalf of
the Swift/UVOT team:

As reported earlier (Gelbord et al., GCN Circ. 11473
Not found
 
 
; Kuin et al.,
GCN Circ. 11482
Not found
 
 
), Swift/UVOT observations of GRB 101219B detected an
optical afterglow in all its bands with initial magnitudes of about
18 mag. The optical afterglow has been unusually slow to decay, and
is around 23 mag at present in the u and uv bands. The UVOT has
obtained a good light curve in all bands up to about 300ks, with
continuing detections through 1000ks in u, uvw1, uvm2, and uvw2 (v
and b measurements after 300ks are significantly affected by the PSF
wings of a B = 15.5 mag star located 7 arcsec to the SW). The light
curve still appears to be decaying and there is some indication that
this decay may not be smooth.

GRB 101219B is further interesting because the UVOT light curve
exhibits an early decay to about 600 seconds after the trigger time
T, after which a second brightness rise to a maximum around T+850s
occurs. A corresponding break is found in the X-ray light curve, in
that the decay observed by XRT flattens approximately at T+700s.

The only constraint on the redshift of this burst is an upper limit
around 1.5 implied by the detection in uvw2, as there have not been
any spectroscopic observations announced to date. However, if this
burst is bright because it is close, then we might detect a supernova
bump in the coming days.

We consider this an interesting burst and would like to bring this
to the attention of the community as an opportunity for further
observations.