[vsnet-grb-info 8315] GRB 090823: Swift XRT possible detection of the X-ray afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9840
SUBJECT: GRB 090823: Swift XRT possible detection of the X-ray afterglow 
DATE:    09/08/25 19:20:00 GMT
FROM:    Dirk Grupe at PSU/Swift-XRT  <grupe at astro.psu.edu>

D. Grupe (PSU), E. Hoversten (PSU) and Jay Cummings (NASA/GSFC)
report on behalf of the Swift  team:

We have analysed the XRT and UVOT data of the IPN burst GRB090823
(Cummings et al. GCN Circ. 9835), beginning on 2009-08-24 at
22:17, 30 hours after the Suzaku WAM trigger. The data contain 4.7
ks in XRT  photon counting mode. We clearly detect a possible X-ray
afterglow within the 4' BAT error circle given by Cummings and Copete
et al. (GCN circs. 9838 and 9839, respectively) at
  RA-2000,Dec-2000=128.67676, +60.65169 which corresponds to

RA-2000 = 08h 34m 42.42s
Dec-2000 = +60d 39' 06.1"
with an uncertainty of 5.5"

During the 4.7 ks observation on 2009-08-24 the X-ray source had a
count rate of (5.7+/-1.1)e-3 counts s-1 in the XRT which converts
to an observed flux in the 0.3-10 keV band of (2.9+/-0.5)e-13
ergs s-1 cm-2 assuming a typical GRB afterglow spectrum.


The Swift/UVOT began settled observations of the field of GRB 090823
108380 s after the BAT trigger (Cummings, et al., GCN Circ. 9835).
No optical afterglow consistent with the XRT position
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are:

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

white        109194       115699         1464         >21.8
v               110009       116640         1680         >20.1
u               108380       114954         1597         >20.7

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.06 in the direction of the burst
(Schlegel et al. 1998).

Swift is planning to re-observe the field of GRB 090823 on
2009-08-27 for 10 ks in order to see if the X-ray source has faded.


This circular is an official product of the Swift team.