CaltechAUTHORS
Published November 2019 | Version Submitted + Published
Journal Article Open

MAXI J1820+070 with NuSTAR I. An increase in variability frequency but a stable reflection spectrum: coronal properties and implications for the inner disc in black hole binaries

Creators

  • 1. ROR icon University of Cambridge
  • 2. ROR icon Research Institute in Astrophysics and Planetology
  • 3. ROR icon French National Centre for Scientific Research
  • 4. ROR icon European Space Astronomy Centre
  • 5. ROR icon University of Southampton
  • 6. ROR icon California Institute of Technology
  • 7. ROR icon University of Erlangen-Nuremberg
  • 8. ROR icon University of Maryland, College Park
  • 9. ROR icon University of Michigan–Ann Arbor
  • 10. ROR icon University of Alberta
  • 11. ROR icon University of California, Berkeley

Abstract

MAXI J1820+070 (optical counterpart ASASSN-18ey) is a black hole candidate discovered through its recent very bright outburst. The low extinction column and long duration at high flux allow detailed measurements of the accretion process to be made. In this work, we compare the evolution of X-ray spectral and timing properties through the initial hard state of the outburst. We show that the inner accretion disc, as measured by relativistic reflection, remains steady throughout this period of the outburst. Nevertheless, subtle spectral variability is observed, which is well explained by a change in coronal geometry. However, characteristic features of the temporal variability – low-frequency roll-over and quasi-periodic oscillation frequency – increase drastically in frequency, as the outburst proceeds. This suggests that the variability time-scales are governed by coronal conditions rather than solely by the inner disc radius. We also find a strong correlation between X-ray luminosity and coronal temperature. This can be explained by electron pair production with a changing effective radius and a non-thermal electron fraction of ∼20 per cent.

Additional Information

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2019 September 20. Received 2019 September 19; in original form 2019 May 31. Published: 27 September 2019. We thank Fiona Harrison for approval of these DDT observations and Karl Forster for their prompt scheduling. DJKB acknowledges financial support from the Science and Technology Facilities Council (STFC). ACF acknowledges support from the ERC Advanced Grant FEEDBACK 340442. AWS is supported by an NSERC Discovery Grant and a Discovery Accelerator Supplement. This work has used data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This research has used the NuSTARDAS jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).

Attached Files

Published - stz2681.pdf

Submitted - 1909.04688.pdf

Files

1909.04688.pdf

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Additional details

Identifiers

Eprint ID
98683
Resolver ID
CaltechAUTHORS:20190917-134739032

Related works

Describes
https://arxiv.org/abs/1909.04688 (URL)

Funding

Science and Technology Facilities Council (STFC)
European Research Council (ERC)
340442
Natural Sciences and Engineering Research Council of Canada (NSERC)
NASA/JPL/Caltech

Dates

Created
2019-09-17
Created from EPrint's datestamp field
Updated
2021-11-16
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
NuSTAR , Space Radiation Laboratory