GCN Circular 7703

J. S. Bloom (UC Berkeley), W. Li (UC Berkeley), A. J. Levan (U. 
Warwick), D. A. Perley (UCB),  N. R. Tanvir (U. Leicester), N. R. Butler 
(UCB),  H-W. Chen (U. Chicago), R. Chornock (UCB), J. X. Prochaska 
(UCO/Lick), C. D. Bailyn (Yale), A. Bunker (U. Exeter), R. Chornock 
(UCB), B. Cobb (Yale), P. B. Hall (York U.), A. V. Filippenko (UCB), N. 
Gehrels (NASA/GSFC), K. Glazebrook (Swinburne), J. Granot (U. 
Hertfordshire), K. C. Hurley (UCB), D. Kocevski (UCB), B. Metzger (UCB), 
M. Modjaz (UCB), A. Miller (UCB), W. Lee (I. de Astronomia), S. Lopez 
(U. Chile), J. Norris (NASA/Ames), P. E. Nugent (LBNL), M. Pettini (U. 
Cambridge), D. Poznanski (UCB), A. L. Piro (UCB), E. Quataert (UCB), E. 
Ramirez-Ruiz (UCSC), J. Shiode (UCB), and T. Sakamoto (GSFC/UMBC) report:

Under Director's Discretionary Proposal (#11551), we acquired 
observations of GRB 080503 (Mao et al., GCN 7665
Not found
 
 
) with the Hubble Space 
Telescope (HST+WFPC2), starting at 15:08 and lasting until 20:45 (UT 
2008-05-08), approximately 5.2 days after the GRB.  The total 
integration time was 2x1200s + 2x1100s (2 orbits) in F606W, 3x700s (1 
orbit) in F814W, and 3x700s (1 orbit) in F450W. The data were collected 
in a small dither pattern around the WFALL position to mitigate against 
CTE losses.

We clearly detect a point source at a location consistent with the 
optical transient (Perley et al., GCN 7678
Not found
 
 
) in F606W, and marginally 
detect a source at this position in 450W.  The transient is not detected 
in F814W.  We report the following preliminary magnitudes:

F450W_AB = 26.95 +/- 0.27
F606W_AB = 26.86 +/- 0.15
F814W_AB > 26.6

The nearby source s1 (see Perley et al., GCN 7667
Not found
 
 
) is also detected, and 
appears visibly extended, though this extension does not reach s2.  Two 
other faint, extended sources ("s3" and "s4") are detected about 1 
arcsecond to the northwest and southeast of the transient, respectively. 
  There is no obviously extended source detected at the position of s2.

The source is significantly fainter than observed in our Gemini 
measurements, which may suggest a break (as expected from an off-axis 
jet) or an exponential decline (as expected from an LP mini-supernova). 
  However, LP mini-SN models also predict a red late-time color, which 
is not observed.  We note also the detection of an X-ray afterglow in 
late-time Chandra observations (Butler et al., GCN in prep.)

An additional epoch of HST imaging will be obtained starting 15:05 
12-May-2008 UT.

An preliminary image with less-than-optimal cosmic ray reduction is 
posted to:
http://lyra.berkeley.edu/~dperley/080503/080503_hst660w_ep1.png

We are grateful to all the people STSCI that made such a rapid ToO possible.