[vsnet-grb-info 18111] Swift detection of a dust-scattered halo around GRB 160623A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19559
SUBJECT: Swift detection of a dust-scattered halo around GRB 160623A
DATE:    16/06/23 23:43:24 GMT
FROM:    Giacomo Vianello at SLAC  <giacomov at slac.stanford.edu>

A. Tiengo (IUSS Pavia), G. Vianello (Stanford), P. Esposito (API/UVA),
R. Salvaterra (INAF/IASF Milano)

report on behalf of a larger collaboration:

GRB 160623A was detected by Fermi/LAT on 2016 June 23 (Vianello et al.
GCN Circ. 19553) and its X-ray afterglow was identified by Swift/XRT
(Maselli et al. GCN Circ. 19558).

The XRT observation started on 2016 June 23 at 16:11:43 UT (40.3 ks
after the Fermi trigger) and lasted until 17:37:24, collecting data in
PC mode for a net exposure time of approximately 1.9 ks.

This burst was exceptionally bright and located at low Galactic
latitude (b=-2.6). The total Galactic extinction towards the GRB is Av
= 4.1 according to Schlafly & Finkbeiner 2011, ApJ 737, 103, or 4.8
according to Schlegel et al. 1998, ApJ 500, 525.

A bright X-ray halo with radius of approximately 3.5 arcmin  is
clearly visible around the GRB. This halo is possibly composed by
multiple rings produced by dust clouds in our Galaxy that scatter the
GRB X-ray emission.

The observation is too short to detect confidently the expansion of
the halo. From the size of the halo and the time of the GRB, we derive
a distance of about 800 pc for the closest dust structure responsible
for the scattering.