[vsnet-grb-info 3912] GRB 061019: dust-scattered X-ray halo detected in Swift/XRT

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5737
SUBJECT: GRB 061019: dust-scattered X-ray halo detected in Swift/XRT        
DATE:    06/10/19 21:29:32 GMT
FROM:    Pat Romano at OAB-Swift  <patrizia.romano at brera.inaf.it>

P. Romano, C. Guidorzi (Univ Bicocca & INAF-OAB), A. Moretti (INAF-OAB),
K. L. Page, (U. Leicester) on behalf of the Swift-XRT team

Analysis of the Swift XRT observation of GRB 061019 in Photon Counting
(PC) mode has revealed in the first three orbits a diffuse X-ray halo
centered around the afterglow location.
The halo has the form of a complete ring which increases in radius through
the observation and reached the distance of >=100 arcsec during the first
~17ks after the trigger (T0).
We can exclude it is due to instrumental effects.
During the observation, which started ~2800 seconds after the burst
trigger time, the observed halo follows the expected behaviour
of a "light-echo" as X-rays are scattered by dust in our Galaxy.

GRB 061019 is in the direction (Galactic) l = 181.74, b = 4.26 degrees, in
which the density of the interstellar medium is quite high as testified by
both the neutral Hydrogen column density nH=4.8E21 cm-2 and the optical
extinction E(B-V)=1.144 (A_B=4.939).