GCN Circular 9342

N. P. M. Kuin (MSSL/UCL) and  E.A. Hoversten (PSU)  report on
behalf of the Swift UVOT team.

The Swift UltraViolet/Optical Telescope (UVOT) began observations of
the short hard burst GRB 090510 (Swift BAT trigger number 351588;
Hoversten et al. GCN Circ. 9331
Not found
 
 
) on May 10, 2009, at 00:24:24 UT,
80 seconds after the BAT trigger with a settling exposure in the
UVOT v filter.

A new optical source was found by the UVOT (Marshall and Hoversten,
GCN Circ. 9332
Not found
 
 
) for which we have a refined position (based on
matching the UVOT field sources to the USNO-B1 catalogue) of
RA, DEC =  333.55208, -26.58311, which is equivalent to:
RA = 22:14:12.5, DEC = -26:34:59.2, with an uncertainty of 1.5"
(90% confidence). The refined UVOT position is offset 1.6" from
the refined XRT position (Goad et al., GCN Circ. 9339
Not found
 
 
) and is
consistent with the revised NOT position (Malesani, GCN Circ. 9340
Not found
 
 
)
to within 0.2".	

GRB 090510 is detected in all UVOT filters, except perhaps in b,
which implies that the redshift is less than about 1.5. The
emission is seen to rise to a peak around 600s after the trigger.
The initial magnitude observed in the UVOT filters are given below:

Filter  Tstart(s)  Tstop(s)  Exposure(s)  Magnitude

wh       97        247          147.4     19.63 +/- 0.17
wh      588        608           19.5     18.76 +/- 0.22
wh     1167       1526           58.3     19.16 +/- 0.20
v        80       1410           97.3     18.46 +/- 0.33
b       564       1502           97.2    >19.62 (2.2 sigma)
u       712       1477          323.6     19.05 +/- 0.17
uvw1    687       1452           75.9     18.61 +/- 0.27
uvm2    662       1434           93.7s    18.10 +/- 0.22
uvw2    614       1552          115.4s    18.31 +/- 0.18

The values quoted above are on the UVOT Photometric System
(Poole et al, 2008, MNRAS 383,627). They are not corrected for the
expected galactic reddening of E(B-V) = 0.020 in the direction of
the burst (Schlegel et al. 1998).