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

Dage, Kristen C. and Brumback, McKinley and Neilsen, Joey and Hu, Chin-Ping and Altamirano, Diego and Bahramian, Arash and Charles, Philip A. and Clarkson, William I. and Haggard, Daryl and Hickox, Ryan C. and Kennea, Jamie (2022) Monitoring observations of SMC X-1’s excursions (MOOSE)–I. Programme description and initial high state spectral results. Monthly Notices of the Royal Astronomical Society, 514 (4). pp. 5457-5464. ISSN 0035-8711. doi:10.1093/mnras/stac1674.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemSwift/BAT light curves
Dage, Kristen C.0000-0002-8532-4025
Brumback, McKinley0000-0002-4024-6967
Neilsen, Joey0000-0002-8247-786X
Hu, Chin-Ping0000-0001-8551-2002
Altamirano, Diego0000-0002-3422-0074
Bahramian, Arash0000-0003-2506-6041
Clarkson, William I.0000-0002-2577-8885
Haggard, Daryl0000-0001-6803-2138
Hickox, Ryan C.0000-0003-1468-9526
Kennea, Jamie0000-0002-6745-4790
Alternate Title:Monitoring Observations of SMC X-1's Excursions (MOOSE) I: Program Description and Initial High-State Spectral Results
Additional Information:© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2022 June 13. Received 2022 June 11; in original form 2022 April 7. The authors thank the anonymous referee for helpful feedback. KCD and DH acknowledge funding from the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canada Research Chairs (CRC) programme. KCD acknowledges fellowship funding from the McGill Space Institute. DA acknowledges support from the Royal Society. The authors thank Elizabeth Ferrara and the NICER team for their efforts with the observation scheduling. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and NASA’s Astrophysics Data System Bibliographic Services, as well as the software packes NUMPY (van der Walt, Colbert & Varoquaux 2011) and MATPLOTLIB (Hunter 2007). DATA AVAILABILITY. The NICER and XMM–Newton observations are publicly available on HEASARC, and the Swift/BAT (Krimm et al. 2013) light curves can be downloaded from
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Canada Research Chairs ProgramUNSPECIFIED
McGill Space InstituteUNSPECIFIED
Subject Keywords:accretion, accretion discs, pulsars: individual: SMC X-1, X-rays: binaries1
Issue or Number:4
Record Number:CaltechAUTHORS:20220801-490192000
Persistent URL:
Official Citation:Kristen C Dage, McKinley Brumback, Joey Neilsen, Chin-Ping Hu, Diego Altamirano, Arash Bahramian, Philip A Charles, William I Clarkson, Daryl Haggard, Ryan C Hickox, Jamie Kennea, Monitoring observations of SMC X-1’s excursions (MOOSE)–I. Programme description and initial high state spectral results, Monthly Notices of the Royal Astronomical Society, Volume 514, Issue 4, August 2022, Pages 5457–5464,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116001
Deposited By: George Porter
Deposited On:01 Aug 2022 23:15
Last Modified:01 Aug 2022 23:15

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