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arXiv · 2203.11955

An 8.56 keV absorption line in the hyperluminous X-ray source in NGC 4045: ultra-fast 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 $E=8.56^{+0.05}_{-0.11}$ keV detected with a significance of $>3.3σ$ in the NuSTAR and XMM-Newton spectra of a newly discovered hyperluminous X-ray source (HLX, $L_{\rm X}>10^{41}$ ergs$^{-1}$) 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 by highly ionized iron with a blue shift of 0.19$c$, indicating an ultrafast outflow (UFO). However, the large equivalent width of the line (EW$=-0.22^{+0.08}_{-0.09}$ keV) paired with the lack of other absorption lines detected are difficult to reconcile with models. An alternative explanation is that the line is due to a cyclotron resonance scattering feature (CRSF), produced by the interaction of X-ray photons with the powerful magnetic field of a neutron star.

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Murray Brightman, Peter Kosec, Felix Fürst, Hannah Earnshaw, Marianne Heida, Matthew J Middleton, Daniel Stern, Dominic J Walton. 2022-03-22. An 8.56 keV absorption line in the hyperluminous X-ray source in NGC 4045: ultra-fast outflow or cyclotron line?. https://doi.org/10.3847/1538-4357%2Fac5e37

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