GCN Circular 9730

GRB 090728: Swift/UVOT Upper Limits

P.A. Curran (MSSL-UCL), V. Mangano (INAF-IASFPA), report on behalf of
the Swift/UVOT team:


The Swift/UVOT began settled observations of the field of GRB 090728
117s after the BAT trigger (Mangano et al., GCN 9725
Not found
 
 
). No optical
afterglow consistent with the refined XRT position (Osborne et al., GCN
9729
Not found
 
 
)  or the optical counterpart (Melandri et al. , GCN 9726
Not found
 
 
) is
detected in the UVOT exposures.  This is consistent with the R-band
non-detection of Melandri et al.


Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the initial finding chart (FC)
and subsequent exposures are:

Filter   T_start(s)    T_stop(s)    Exp(s)    Mag

v       422             6883           479        > 20.70
b       372             6643           491        > 21.45
u       117             366            150        > 20.00 (FC)
u       117             6437           842        > 21.34
uw1     472             6233           452        > 21.05
um2     447             6026           452        > 20.75
uw2     398             6849           490        > 20.89

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.07 in the direction of the burst
(Schlegel et al. 1998).