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Phase-resolved spectroscopy of a quasi-periodic oscillation in the black hole X-ray binary GRS 1915+105 with NICER and NuSTAR

Phase-resolved spectroscopy of a quasi-periodic oscillation in the black hole X-ray binary GRS 1915+105 with NICER and NuSTAR
Phase-resolved spectroscopy of a quasi-periodic oscillation in the black hole X-ray binary GRS 1915+105 with NICER and NuSTAR
Quasi-periodic oscillations (QPOs) are often present in the X-ray flux from accreting stellar mass black holes (BHs). If they are due to relativistic (Lense-Thirring) precession of an inner accretion flow which is misaligned with the disc, the iron emission line caused by irradiation of the disc by the inner flow will rock systematically between red and blue shifted during each QPO cycle. Here we conduct phase-resolved spectroscopy of a ∼ 2.2 Hz type-C QPO from the BH X-ray binary GRS 1915+105, observed simultaneously with NICER and NuSTAR. We apply a tomographic model in order to constrain the QPO phase-dependent illumination profile of the disc. We detect the predicted QPO phase-dependent shifts of the iron line centroid energy, with our best fit featuring an asymmetric illumination profile (> 2𝜎 confidence). The observed line energy shifts can alternatively be explained by the spiral density waves of the accretion-ejection instability model. However we additionally measure a significant (> 3𝜎) modulation in reflection fraction, strongly favouring a geometric QPO origin. We infer that the disc is misaligned with previously observed jet ejections, which is consistent with the model of a truncated disc with an inner precessing hot flow. However our inferred disc inner radius is small (𝑟in ∼ 1.4 𝐺𝑀/𝑐 2 ). For this disc inner radius, Lense-Thirring precession cannot reproduce the observed QPO frequency. In fact, this disc inner radius is incompatible with the predictions of all well-studied QPO models in the literature.
Nathan, Edward
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Ingram, Adam
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Homan, Jeroen
67eb2764-46f0-455b-b1f0-f4824c129e87
Huppenkothen, Daniela
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Uttley, Phil
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van der Klis, Michiel
673255ce-dd17-4da0-910c-e3cb78460636
Motta, Sara E.
2c9cd6cb-e027-46b7-92ce-2ace8a0154ff
Altamirano, Diego
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Middleton, Matthew
f91b89d9-fd2e-42ec-aa99-1249f08a52ad
Nathan, Edward
88bb10e8-8d0b-4083-a106-d557e4315db3
Ingram, Adam
01a02529-ad9f-4936-af5d-c200f88d4e53
Homan, Jeroen
67eb2764-46f0-455b-b1f0-f4824c129e87
Huppenkothen, Daniela
f03b1596-7c31-4b18-a869-13660a7b60c2
Uttley, Phil
51db40c3-a4df-4f1f-a3de-75493dcac042
van der Klis, Michiel
673255ce-dd17-4da0-910c-e3cb78460636
Motta, Sara E.
2c9cd6cb-e027-46b7-92ce-2ace8a0154ff
Altamirano, Diego
d5ccdb09-0b71-4303-9538-05b467be075b
Middleton, Matthew
f91b89d9-fd2e-42ec-aa99-1249f08a52ad

[Unknown type: UNSPECIFIED]

Record type: UNSPECIFIED

Abstract

Quasi-periodic oscillations (QPOs) are often present in the X-ray flux from accreting stellar mass black holes (BHs). If they are due to relativistic (Lense-Thirring) precession of an inner accretion flow which is misaligned with the disc, the iron emission line caused by irradiation of the disc by the inner flow will rock systematically between red and blue shifted during each QPO cycle. Here we conduct phase-resolved spectroscopy of a ∼ 2.2 Hz type-C QPO from the BH X-ray binary GRS 1915+105, observed simultaneously with NICER and NuSTAR. We apply a tomographic model in order to constrain the QPO phase-dependent illumination profile of the disc. We detect the predicted QPO phase-dependent shifts of the iron line centroid energy, with our best fit featuring an asymmetric illumination profile (> 2𝜎 confidence). The observed line energy shifts can alternatively be explained by the spiral density waves of the accretion-ejection instability model. However we additionally measure a significant (> 3𝜎) modulation in reflection fraction, strongly favouring a geometric QPO origin. We infer that the disc is misaligned with previously observed jet ejections, which is consistent with the model of a truncated disc with an inner precessing hot flow. However our inferred disc inner radius is small (𝑟in ∼ 1.4 𝐺𝑀/𝑐 2 ). For this disc inner radius, Lense-Thirring precession cannot reproduce the observed QPO frequency. In fact, this disc inner radius is incompatible with the predictions of all well-studied QPO models in the literature.

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2201.01765 - Accepted Manuscript
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Accepted/In Press date: 20 October 2021
Additional Information: arXiv:2201.01765

Identifiers

Local EPrints ID: 457820
URI: http://eprints.soton.ac.uk/id/eprint/457820
PURE UUID: 69635533-d3d9-4420-b2a9-377b4cbda7b3
ORCID for Diego Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 20 Jun 2022 16:34
Last modified: 21 Jun 2022 01:42

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Contributors

Author: Edward Nathan
Author: Adam Ingram
Author: Jeroen Homan
Author: Daniela Huppenkothen
Author: Phil Uttley
Author: Michiel van der Klis
Author: Sara E. Motta

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