GCN Circular 13284

P. D'Avanzo, A. Melandri (INAF-OAB), K. L. Page, P. A. Evans (U
Leicester), M. Perri (ASDC), S. T. Holland (NASA/GSFC) report on behalf of
the Swift team:

The Swift XRT and UVOT instruments observed the centre of the error circle
for the MAXI-detected GRB 120510A (Serita et al., GCN Circ. 13282
Not found
 
 
) from
21.4 to 33.0 ks after the trigger.

The XRT data comprise 2.0 ks of Photon Counting (PC) mode data. A faint
source is detected RA, Dec = 44.04666, +72.88692 which is equivalent to:

RA (J2000):        02h 56m 11.20s
Dec (J2000):        +72d 53' 12.9"

with an uncertainty of 4.8 arcsec (radius, 90% confidence). The observed
count rate is (3.3 +/- 1.3) x 10^-3 cts/s. This corresponds to an observed
0.3-10 keV flux of (1.4 +/- 0.5) x 10^-13 erg/cm2/s (assuming a typical
GRB spectrum with photon spectral index of 2). If we consider the Galactic
absorption in this direction (2.3 x 10^21 cm^-2; Kalberla et al. 2005)
this corresponds to an unabsorbed flux of (2.0 +/- 0.8) x 10^-12
erg/cm2/s. Given the limited statistics, it is not possible to determine
whether the source is fading. We note that the XRT position lies 15.6
arcsec from the ROSAT source 1RXS J025613.2+725300 (RA(J2000), Dec(J2000)=
02h 56m 13.2s, +72d 52' 59", with an error radius of 11 arcsec). We also
note that the XRT field of view covers only about 69% of the reported 16
arcmin radius error circle GRB 120510A (Serita et al., GCN Circ. 13282
Not found
 
 
).

The XRT coordinates correspond to the bright, catalogued ultraviolet
source HD 17785 with a magnitude of uvw2 = 11.85 +/- 0.02 mag.  There is
very weak evidence in the UVOT data that the source may have increased in
brightness by about 0.2 mag between 28 ks and 33 ks after the burst.