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Lord of the Rings – Return of the King: Swift-XRT observations of dust scattering rings around V404 Cygni

Lord of the Rings – Return of the King: Swift-XRT observations of dust scattering rings around V404 Cygni
Lord of the Rings – Return of the King: Swift-XRT observations of dust scattering rings around V404 Cygni
On 2015 June 15, the black hole X-ray binary V404 Cygni went into outburst, exhibiting extreme X-ray variability which culminated in a final flare on June 26. Over the following days, the Swift-X-ray Telescope detected a series of bright rings, comprising five main components that expanded and faded with time, caused by X-rays scattered from the otherwise unobservable dust layers in the interstellar medium in the direction of the source. Simple geometrical modelling of the rings’ angular evolution reveals that they have a common temporal origin, coincident with the final, brightest flare seen by INTEGRAL's JEM X-1, which reached a 3–10 keV flux of ~25 Crab. The high quality of the data allows the dust properties and density distribution along the line of sight to the source to be estimated. Using the Rayleigh–Gans approximation for the dust scattering cross-section and a power-law distribution of grain sizes a, ∝ a-q, the average dust emission is well modelled by q = 3.90+0.09-0.08 and maximum grain size of a+ = 0.147+0.024-0.004 μm, though significant variations in q are seen between the rings. The recovered dust density distribution shows five peaks associated with the dense sheets responsible for the rings at distances ranging from 1.19 to 2.13 kpc, with thicknesses of ~40 – 80 pc and a maximum density occurring at the location of the nearest sheet. We find a dust column density of Ndust ~ (2.0–2.5) × 1011 cm-2, consistent with the optical extinction to the source. Comparison of the inner rings’ azimuthal X-ray evolution with archival Wide-field Infrared Survey Explorer (WISE) mid-IR data suggests that the second most distant ring follows the general IR emission trend, which increases in brightness towards the Galactic north side of the source.
0035-8711
1847-1863
Beardmore, A.P.
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Willingale, R.
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Kuulkers, E.
bbe4b980-0d14-46c7-92a4-7bc8149a1947
Altamirano, D.
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Motta, S.E.
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Osborne, J.P.
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Page, K.L.
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Sivakoff, G.R.
d3dd17f7-f61d-4139-acb4-e97e13c7d3b8
Beardmore, A.P.
d72591c2-c08f-42b6-9f46-645aacb4e3e0
Willingale, R.
e6a311ac-0ea8-4119-a2f2-404de7de2b05
Kuulkers, E.
bbe4b980-0d14-46c7-92a4-7bc8149a1947
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Motta, S.E.
b6813310-4162-4bb5-985e-c6daaa33f2e1
Osborne, J.P.
edc077a5-96df-4189-a3da-5bf63507101a
Page, K.L.
2f98a3ec-a907-45b8-b26f-547fb1446e11
Sivakoff, G.R.
d3dd17f7-f61d-4139-acb4-e97e13c7d3b8

Beardmore, A.P., Willingale, R., Kuulkers, E., Altamirano, D., Motta, S.E., Osborne, J.P., Page, K.L. and Sivakoff, G.R. (2016) Lord of the Rings – Return of the King: Swift-XRT observations of dust scattering rings around V404 Cygni. Monthly Notices of the Royal Astronomical Society, 462 (2), 1847-1863. (doi:10.1093/mnras/stw1753).

Record type: Article

Abstract

On 2015 June 15, the black hole X-ray binary V404 Cygni went into outburst, exhibiting extreme X-ray variability which culminated in a final flare on June 26. Over the following days, the Swift-X-ray Telescope detected a series of bright rings, comprising five main components that expanded and faded with time, caused by X-rays scattered from the otherwise unobservable dust layers in the interstellar medium in the direction of the source. Simple geometrical modelling of the rings’ angular evolution reveals that they have a common temporal origin, coincident with the final, brightest flare seen by INTEGRAL's JEM X-1, which reached a 3–10 keV flux of ~25 Crab. The high quality of the data allows the dust properties and density distribution along the line of sight to the source to be estimated. Using the Rayleigh–Gans approximation for the dust scattering cross-section and a power-law distribution of grain sizes a, ∝ a-q, the average dust emission is well modelled by q = 3.90+0.09-0.08 and maximum grain size of a+ = 0.147+0.024-0.004 μm, though significant variations in q are seen between the rings. The recovered dust density distribution shows five peaks associated with the dense sheets responsible for the rings at distances ranging from 1.19 to 2.13 kpc, with thicknesses of ~40 – 80 pc and a maximum density occurring at the location of the nearest sheet. We find a dust column density of Ndust ~ (2.0–2.5) × 1011 cm-2, consistent with the optical extinction to the source. Comparison of the inner rings’ azimuthal X-ray evolution with archival Wide-field Infrared Survey Explorer (WISE) mid-IR data suggests that the second most distant ring follows the general IR emission trend, which increases in brightness towards the Galactic north side of the source.

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Accepted/In Press date: 15 July 2016
e-pub ahead of print date: 22 July 2016
Published date: 21 October 2016
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 401429
URI: https://eprints.soton.ac.uk/id/eprint/401429
ISSN: 0035-8711
PURE UUID: e1206a37-8ac7-46e1-86d7-0c0880b41dbd
ORCID for D. Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 12 Oct 2016 08:15
Last modified: 10 Jul 2018 00:29

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Contributors

Author: A.P. Beardmore
Author: R. Willingale
Author: E. Kuulkers
Author: D. Altamirano ORCID iD
Author: S.E. Motta
Author: J.P. Osborne
Author: K.L. Page
Author: G.R. Sivakoff

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