[vsnet-grb-info 4376] GRB 070227: Swift/UVOT Upper Limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6160
SUBJECT: GRB 070227: Swift/UVOT Upper Limits
DATE:    07/02/28 23:52:35 GMT
FROM:    Shashi Pandey at MSSL  <sbp2 at mssl.ucl.ac.uk>

S. B. Pandey (UCL-MSSL) and C. Pagani (PSU) report on behalf of
the Swift/UVOT Team:

The Swift/UVOT started observing the field of GRB 070227 (trigger 262347)
56680 s after the BAT trigger (Pagani et al., GCN Circ. 6156). UVOT
observations started late because the BAT observation did not result
in an automated response, but was found during the ground analysis.

The 3-sigma upper limits for detecting a source inside the XRT error 
circle (Pagani, Grupe & Burrows, GCN Circ. 6157) in the co-added
exposures are:

Filter     T_start   T_stop   Exp(s)  Mag (3-sigma upper limit)
---------------------------------------------------------------
     V       56680     57586    885    20.90
     B       63392     64113    702    21.58
     U       62480     63386    885    21.31
   UVW1      61573     62473    886    21.17
   UVM2      57592     58329    726    21.34
   UVW2      55773     56673    886    21.04
---------------------------------------------------------------

Caution should be taken due to the presence of a nearby bright star. The 
XRT error circle lies lies within the wings of the PSF of the bright star 
in all the UVOT frames. This complicates the photometry, so these limits 
could possibly be underestimated.

The values quoted above are not corrected for the expected Galactic
extinction E_{B-V} = 0.34 mag towards the direction of the burst
(Schlegel et al. 1998).