Monitoring observations of SMC X-1’s excursions (MOOSE)–I. Programme description and initial high state spectral results

Author:

Dage Kristen C12ORCID,Brumback McKinley3,Neilsen Joey4,Hu Chin-Ping5ORCID,Altamirano Diego6,Bahramian Arash7ORCID,Charles Philip A6,Clarkson William I8,Haggard Daryl12,Hickox Ryan C9,Kennea Jamie10

Affiliation:

1. Department of Physics, McGill University , 3600 University Street, Montréal QC H3A 2T8, Canada

2. McGill Space Institute, McGill University , 3550 University Street, Montréal QC H3A 2A7, Canada

3. Cahill Center for Astronomy and Astrophysics, California Institute of Technology , 1216 E California Blvd, Pasadena, CA 91125, USA

4. Department of Physics, Villanova University , Villanova, PA 19085, USA

5. Department of Physics, National Changhua University of Education , Changhua 50007, Taiwan

6. Physics & Astronomy, University of Southampton , Southampton, Hampshire SO17 1BJ, UK

7. International Centre for Radio Astronomy Research, Curtin University , GPO Box U1987, Perth, WA 6845, Australia

8. Department of Natural Sciences, University of Michigan-Dearborn , 4901 Evergreen Road, Dearborn, MI, 48128, USA

9. Department of Physics & Astronomy , Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755, USA

10. Department of Astronomy and Astrophysics, The Pennsylvania State University , University Park, PA 16802, USA

Abstract

ABSTRACT SMC X-1 has exhibited three superorbital period excursions since the onset of X-ray monitoring beginning with the Rossi X-ray Timing Explorer's launch in 1995. TheNeutron star Interior Composition Explorer has recently probed a fourth observed excursion beginning in 2021 with our programme monitoring observations of SMC X-1’s excursions (moose). These sensitive new moose data probe different superorbital periods and phases within them. Spectral fits to the high-state continuum during 2021 April to 2022 January show that the intrinsic spectral shapes are characterized by a soft (kT ∼ 0.19 keV) disc component and a hard (Γ ∼ 0.7) power-law tail. When the 2021–2022 NICER observations, taken during an excursion, are compared to 2016 XMM–Newton observations (outside of an excursion), we find little evidence for intrinsic spectral variability across the high states, but find evidence for a >3σ change in the absorption, although we caution that there may be calibration differences between the two instruments. Thus, over different lengths of superorbital periods, we see little evidence for intrinsic spectral changes in the high state. Upcoming studies of the pulse profiles may shed light on the mechanism behind the excursions.

Funder

Natural Sciences and Engineering Research Council of Canada

Canada Research Chairs

McGill Space Institute

Royal Society

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

Cited by 3 articles. 订阅此论文施引文献 订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献

1. Rubin Observatory LSST Transients and Variable Stars Roadmap;Publications of the Astronomical Society of the Pacific;2023-10-01

2. Constraining the Evolution of the Unstable Accretion Disk in SMC X-1 with NICER;The Astrophysical Journal;2023-08-01

3. Monitoring observations of SMC X-1’s excursions (MOOSE)  – II. A new excursion accompanies spin-up acceleration;Monthly Notices of the Royal Astronomical Society;2023-02-06

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