GCN Circular 5262

The Unusually Long-Lived Afterglow of GRB 060614

P. J. Brown (Penn State), S. T. Holland (NASA/GSFC & USRA),
V. Mangano (INAF-IASFPA), A. M. Parsons (NASA/GSFC),
& N. Gehrels (NASA/GSFC) report on behalf of the Swift Team:

     Swift/UVOT observations of the optical afterglow of
GRB 060614 (trigger=214805; Parsons et al. GCN 5252
Not found
 
 
) show
that the V-band light from the afterglow remains approximately
constant at V ~ 19.8 until at least 80,000 s after the
BAT trigger (the latest data presently available).  Similar
behaviour is seen in the B-, U-, and UVW1-bands.
There is weak evidence that the UVM2 and UVW2
fluxes decrease after approximately 10,000 s.  The UV-optical
colors are similar to GRB060218/SN2006aj, whose shock breakout
peaked at about 40,000 s in the UV and optical and then
began fading before being overtaken by the rising SN
(Campana et al. Nature, in press, astro-ph/0603279).
Though we do not see as prominent of a rise in the UVOT
data for GRB060614, other observers have noted rising and
fading in the R band (Schmidt, Peterson, & Lewis GCN 5258
Not found
 
 
;
French et al. GCN 5257
Not found
 
 
), and Malesani et al. (GCN 5261
Not found
 
 
) have
also noted the similarity to GRB060218.

     The BAT lightcurve of GRB 060614 (Barthelmy et al. GCN 5256
Not found
 
 
)
shows a hard, bright initial flare followed by softer,
extended prompt emission.  The T90 duration of the prompt
emission was 108 s.  The prompt fluence was the greatest
of all Swifts burst that have been located by the BAT.

     The X-ray light curve (Mangano et al. GCN 5254
Not found
 
 
) was
unusually bright and decayed rapidly with a strong hard to
soft evolution.  This was followed by an extended period
of near-constant emission, that shows evidence for small-scale
flares, out to approximately 70,000 s.  The hardness ratio of
the flat part of the light curve is nearly constant, and the
power law fit of the spectrum gives a standard afterglow
photon index of 1.8 with no absorption in excess the
Galactic N_H.

     In light of the peculiar characteristics observed by all
three Swift instruments and ground based observers,
we encourage further observations of this unusual afterglow.