[vsnet-grb-info 7656] GRB090423 - Swift/UVOT upper limits.

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9210
SUBJECT: GRB090423 - Swift/UVOT upper limits.
DATE:    09/04/23 17:06:23 GMT
FROM:    Massimiliano de Pasquale at MSSL-UCL  <mdp at mssl.ucl.ac.uk>

  M. De Pasquale (MSSL/UCL) and H. Krimm (GSFC/GWU) report on
behalf of the Swift UVOT team:

The Swift/UVOT took the first settled exposure of GRB 090423 starting 
77 s after the BAT trigger (Krimm, et al., 2009, GCN Circ. 9198) in the 
white filter. We do not find any new source, at the enhanced position of 
the XRT afterglow (Evans, et al. 2009, GCN Circ. 9205) nor at the
position of the K band candidate found by UKIRT (Tanvir,
et al. 2009, GCN Circ. 9206). No source is detected even when all
the images of all filters are summed. The 3-sigma upper limits for
detecting a source in the white and u band first exposures, and
subsequent co-added images in all filters are:

Filter           T_start   T_stop   Exp(s)      Mag
----------------------------------------------------------
white               77      227     147         >20.7
u                   290     540     246         >20.0

v                  619      6162    413         >19.6
b                  545      5497    413         >20.2
u                  290      5342    462         >20.4
uvw1               668      6503    344         >20.1
uvm2               644      6367    413         >20.1
uvw2               594      5958    412         >20.5
white               77      5752    560         >21.3
---------------------------------------------------------

The quoted upper limits have not been corrected for the expected
modest Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.03 mag (Schlegel, et al., 1998, ApJS, 500,
525).  All photometry is on the UVOT photometry system described in
Poole et al. (2008, MNRAS, 383, 627).