GCN Circular 3415

D. N. Burrows, D. Grupe (PSU), C. Kouvelioutou, S. Patel (MSFC), N. Gehrels
(GSFC), P. Meszaros (PSU), B. Zhang (UNLV), and R. Wijers (U. Amsterdam)
report:

We have observed the field of the short burst GRB 050509b (Hurkett et al. 2005,
GCN 3381
Not found
 
 
) with the Chandra ACIS instrument.  The 50 ks observation was centered
at the Swift XRT afterglow position reported by Kennea et al. (2005; GCN 3383
Not found
 
 
).
Within the ACIS S3 detector 20 point sources are found by XIMAGE in our
preliminary analysis.  Two of these sources fall within the revised 8 arcsecond 
radius error circle reported by Rol et al. (2005; GCN 3395
Not found
 
 
).  The coordinates 
and count rates of these sources are:

#5:  12 36 14.0 +28 59 02.5  2.46E-04+/-8.6E-05

#8:  12 36 13.9 +28 59 07.9  1.94E-04+/-7.8E-05 

Source #5 is 2.0 arcseconds from the revised XRT position and is tentatively
identified as the X-ray afterglow.  However, the source intensity is too low for
us to to verify whether this source is fading during our observation.  

Assuming a Crab-like spectrum absorbed by galactic NH (1.5E20), 
this count rate corresponds to a flux of 1.6E-15 cgs (0.2-10 keV). 
Combined with the Swift XRT flux measurement at early times, we estimate a
power-law decay index of approximately -1.0 over the 200 ks interval between 
the two observations.  Confirmation of this afterglow candidate will require
additional Chandra observations to see whether any of these sources are fading.