Swift/XRT discovery of a dust scattering halo in V404 Cyg.
ATel #7736; A. P. Beardmore (U. Leicester), D. Altamirano (U. Southampton), E. Kuulkers (ESA/ESAC), S. E. Motta (U. Oxford), J. P. Osborne (U. Leicester), K. L. Page (U. Leicester), G. R. Sivakoff (U. Alberta) & S. A. Vaughan (U. Leicester)
on 30 Jun 2015; 16:07 UT
Credential Certification: Kim Page (firstname.lastname@example.org)
Subjects: Black Hole, Transient
Swift/XRT observations of the black hole X-ray binary V404 Cyg (GS
2023+33), which started on 2015-06-15, have continued approximately
2-3 times daily.
As previously reported (e.g. ATel #7647, #7665, #7694, #7727), the
X-ray emission from the source is highly variable, with 1D Windowed
Timing (WT) mode 0.3-10 keV count rates varying from 10 to >10,000 c/s
(pile-up corrected). Subsequent to the last reported observations,
another intense flaring episode was seen in the Swift/XRT observation
starting 2015-06-26 12:35 UT, in which the WT count rate peaked above
The following XRT observation, taken on 2015-06-26 23:46 UT,
revealed a 1D detector profile which had significantly extended
wings, approximately 1.6 arcminute in radius. Subsequent WT observations
show this extended emission dominates over the central source
point spread function, while increasing in size and fading with time. By
2015-06-28 16:05 UT, the emission had extended in size to fill the
WT mode 7.8-arcminute wide window. Re-analysis of an earlier
WT observation taken on 2015-06-21 also reveals a broader than expected
profile, suggesting a similar event.
Given these findings, a 1 ks Photon Counting (PC) mode observation was
taken at 2015-06-30 10:52 UT. The image reveals 4 concentric rings at
angular separations of 2.15, 3.86, 4.26 and 5.59 arcminute from the
central source, caused by dust scattering along the line of sight to
the source. The rings and diffuse structure could be associated with
differing flaring episodes from the central binary system, though
multiple dust clouds can also influence the ring structure.
Analysis is ongoing. Further Swift/XRT observations are planned in PC
mode to study evolution of the rings.
We thank the Swift team for continued observations of this fascinating
A 3 colour image from the PC observation.