An 8.56 keV Absorption Line in the Hyperluminous X-Ray Source in NGC 4045: Ultrafast Outflow or Cyclotron Line?

Murray Brightman; Peter Kosec; Felix Fürst; Hannah Earnshaw; Marianne Heida; Matthew J Middleton; Daniel Stern; Dominic J Walton

doi:10.3847/1538-4357/ac5e37

An 8.56 keV Absorption Line in the Hyperluminous X-Ray Source in NGC 4045: Ultrafast Outflow or Cyclotron Line?

Murray Brightman, Peter Kosec, Felix Fürst, Hannah Earnshaw, Marianne Heida, Matthew J Middleton, Daniel Stern, Dominic J Walton

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Abstract

We report on the discovery of an absorption line at E=8.56−0.11+0.05 keV detected with a significance of >3.3σ in the NuSTAR and XMM-Newton spectra of a newly discovered hyperluminous X-ray source (L X > 1041 erg s−1) in the galaxy NGC 4045 at a distance of 32 Mpc. The source was first discovered serendipitously in a Swift/XRT observation of the galaxy, and Swift monitoring reveals a highly variable source changing by over an order of magnitude from maximum to minimum. The origin of the absorption line appears likely to be from highly ionized iron with a blueshift of 0.19c, indicating an ultrafast outflow. However, the large equivalent width of the line ( EW=−0.22−0.09+0.08 keV) paired with the lack of other absorption lines detected is difficult to reconcile with models. An alternative explanation is that the line is due to a cyclotron resonance scattering feature produced by the interaction of X-ray photons with the powerful magnetic field of a neutron star.

Original language	English
Article number	138
Number of pages	9
Journal	The Astrophysical Journal
Volume	929
Issue number	2
DOIs	https://doi.org/10.3847/1538-4357/ac5e37
Publication status	Published - 21 Apr 2022

Keywords

330
High-Energy Phenomena and Fundamental Physics

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10.3847/1538-4357/ac5e37Licence: CC BY

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© 2022. The Author(s). Published by the American Astronomical Society. This work is licenced under the terms of the Creative Commons license. https://creativecommons.org/licenses/by/4.0/
Final published version, 941 KBLicence: CC BY

Cite this

@article{c4a2fc84959f4ac0aec87d20316acc12,

title = "An 8.56 keV Absorption Line in the Hyperluminous X-Ray Source in NGC 4045: Ultrafast Outflow or Cyclotron Line?",

abstract = "We report on the discovery of an absorption line at E=8.56−0.11+0.05 keV detected with a significance of >3.3σ in the NuSTAR and XMM-Newton spectra of a newly discovered hyperluminous X-ray source (L X > 1041 erg s−1) in the galaxy NGC 4045 at a distance of 32 Mpc. The source was first discovered serendipitously in a Swift/XRT observation of the galaxy, and Swift monitoring reveals a highly variable source changing by over an order of magnitude from maximum to minimum. The origin of the absorption line appears likely to be from highly ionized iron with a blueshift of 0.19c, indicating an ultrafast outflow. However, the large equivalent width of the line ( EW=−0.22−0.09+0.08 keV) paired with the lack of other absorption lines detected is difficult to reconcile with models. An alternative explanation is that the line is due to a cyclotron resonance scattering feature produced by the interaction of X-ray photons with the powerful magnetic field of a neutron star.",

keywords = "330, High-Energy Phenomena and Fundamental Physics",

author = "Murray Brightman and Peter Kosec and Felix F{\"u}rst and Hannah Earnshaw and Marianne Heida and Middleton, {Matthew J} and Daniel Stern and Walton, {Dominic J}",

note = "{\textcopyright} 2022. The Author(s). Published by the American Astronomical Society. This work is licenced under the terms of the Creative Commons license. https://creativecommons.org/licenses/by/4.0/",

year = "2022",

month = apr,

day = "21",

doi = "10.3847/1538-4357/ac5e37",

language = "English",

volume = "929",

journal = "The Astrophysical Journal",

issn = "0004-637X",