Lord of the Rings - Return of the King : The Dust Scattering Halo of V404 Cygni

During its 2015-June outburst, V404 Cyg experienced extreme X-ray
variability, as witnessed by the X-ray light curves from the
Swift-BAT/XRT and INTEGRAL JEM-X/IBIS instruments, culminating in a
final flaring episode which exceeded ~20 Crab on 2015-Jun-26.
Over the days that followed, the XRT detected a series of bright rings,
caused by X-rays scattered from the otherwise unobservable dust layers
in the ISM in the direction of the source. Simple geometrical modeling
of the angular evolution of the rings reveal they have the same temporal
origin, coincident with the brightest flare seen by INTEGRAL's JEM X-1.
Furthermore, the distribution of the dust along the line of sight to the
source can be estimated, with the densest scattering layers ranging in
distance from 1.19--2.13 kpc. Comparison of the inner rings' azimuthal X-ray evolution with archival
Spitzer mid-IR data suggests the second most distant ring follows the
general IR emission trend, which increases in brightness towards the
Galactic north side of the source.