[vsnet-grb-info 5503] Refined Swift UVOT Analysis of SN 2008D (Transient in NGC 2770)

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7168
SUBJECT: Refined Swift UVOT Analysis of SN 2008D (Transient in NGC 2770)
DATE:    08/01/11 20:46:38 GMT
FROM:    Stefan Immler at NASA/GSFC  <immler at milkyway.gsfc.nasa.gov>

S. Immler (NASA/UMCP/GSFC), A. Cucchiara (PSU),  D. Fox (PSU),
A.M. Soderberg (Princeton U), E. Berger (Princeton U), K. Page (Leicester
U), P. O'Brian (Leicester U), D. Burrows (PSU), and N. Gehrels (GSFC),
report on behalf of the Swift team:

An optical counterpart to the X-ray transient in NGC 2770, now SN 2008D
(Atel 1353, 1355, GCN 7159-7167, CBET 1202), was marginally detected
with the Swift Ultraviolet/Optical Telescope (UVOT) in observations
starting 2008-01-09 13:32:53 UT. The following UVOT magnitudes were
measured: b = 20.5±0.3 (412 s exposure time) and u = 20.2±0.4 (412 s).
Upper limits were established for the other UVOT filters, v > 19.9 (412 s,
3-sigma), uvw1 > 20.4, uvm2 > 20.3, and uvw2 > 20.8.

The following UVOT magnitudes were measured for observations
starting 2008-01-11 02:37:28 UT:  v = 18.5±0.2 (216 s exposure time),
b = 18.9±0.1 (353 s), u = 18.6±0.1 (664 s), uvw1 = 19.8±0.2 (1707),
uvm2 > 19.8 (3-sigma UL, 571 s), uvm2 = 20.1±0.3 (864 s), and uvm2 >
20.4 (864 s).

We note that no optical/ultraviolet source was detected at the location of
the transient during routine observations of SN 2007uy on 2008-01-06
00:31:23 UT, down to the following 3-sigma upper limits: v > 20.2 (808 s
exposure time), b > 21.1 (808 s), u > 20.7 (808 s), uvw1 > 20.8 (1619 s),
uvm2 > 20.7 (2187 s), uvw2 > 21.2 (3234 s).

These magnitudes are on the UVOT photometric system (see Poole et al.,
2007, MNRAS, 383, 627) which in the optical is close to the Johnson UBV
system. They have not been corrected for Galactic extinction of E(B-V) =
0.023 mag (Schlegel et al. 1998, ApJ 500, 525). The UVOT photometry
and colors are similar to the early UVOT phase of SN 2006aj/GRB060218
(e.g., Campana et al. 2006, Nature 442, 1008) and consistent with an
emerging supernova, although other possibilities cannot be ruled out.