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An Optical and Infrared Time-domain Study of the Supergiant Fast X-Ray Transient Candidate IC 10 X-2

Kwan, Stephanie and Lau, Ryan M. and Jencson, Jacob and Kasliwal, Mansi M. and Boyer, Martha L. and Ofek, Eran and Masci, Frank and Laher, Russ (2018) An Optical and Infrared Time-domain Study of the Supergiant Fast X-Ray Transient Candidate IC 10 X-2. Astrophysical Journal, 856 (1). Art. No. 38. ISSN 1538-4357. doi:10.3847/1538-4357/aaaf73.

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We present an optical and infrared (IR) study of IC 10 X-2, a high-mass X-ray binary in the galaxy IC 10. Previous optical and X-ray studies suggest that X-2 is a Supergiant Fast X-ray Transient: a large-amplitude (factor of ~100), short-duration (hours to weeks) X-ray outburst on 2010 May 21. We analyze R- and g-band light curves of X-2 from the intermediate Palomar Transient Factory taken between 2013 July 15 and 2017 February 14 that show high-amplitude (≳ 1 mag), short-duration (≾ 8 days) flares and dips (≳ 0.5 mag). Near-IR spectroscopy of X-2 from Palomar/TripleSpec show He i, Paschen-γ, and Paschen-β emission lines with similar shapes and amplitudes as those of luminous blue variables (LBVs) and LBV candidates (LBVc). Mid-IR colors and magnitudes from Spitzer/Infrared Array Camera photometry of X-2 resemble those of known LBV/LBVcs. We suggest that the stellar companion in X-2 is an LBV/LBVc and discuss possible origins of the optical flares. Dips in the optical light curve are indicative of eclipses from optically thick clumps formed in the winds of the stellar counterpart. Given the constraints on the flare duration (0.02–0.8 days) and the time between flares (15.1 ± 7.8 days), we estimate the clump volume filling factor in the stellar winds, f_V , to be $.01 < {f_V < 0.71, which overlaps with values measured from massive star winds. In X-2, we interpret the origin of the optical flares as the accretion of clumps formed in the winds of an LBV/LBVc onto the compact object.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kwan, Stephanie0000-0002-5308-7707
Jencson, Jacob0000-0001-5754-4007
Kasliwal, Mansi M.0000-0002-5619-4938
Boyer, Martha L.0000-0003-4850-9589
Ofek, Eran0000-0002-6786-8774
Masci, Frank0000-0002-8532-9395
Laher, Russ0000-0003-2451-5482
Additional Information:© 2018. The American Astronomical Society. Received 2017 September 25; revised 2018 January 26; accepted 2018 January 29; published 2018 March 22. This project received funding from the California Institute of Technology Student-Faculty Program's Summer Undergraduate Research Fellowship (SURF) and the Flintridge Foundation. S.K. would like to thank M. Kasliwal, R. Lau, and J. Jencson for their mentorship. R.L. thanks M. Heida for a valuable discussion on SFXTs. We thank the Spitzer InfraRed Intensive Transient Survey team and Palomar Observatory for their scientific support. Palomar Observatory is owned and operated by the California Institute of Technology, and administered by Caltech Optical Observatories. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has made use of the SVO Filter Profile Service ( supported from the Spanish MINECO through grant AyA2014-55216. The Intermediate Palomar Transient Factory project is a scientific collaboration among the California Institute of Technology, Los Alamos National Laboratory, the University of Wisconsin Milwaukee, the Oskar Klein Center, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe. Facilities: Hale - Palomar Observatory's 5.1m Hale Telescope, Spitzer IRAC - . Software: SAO DS9, CurveFit.
Group:Infrared Processing and Analysis Center (IPAC), Astronomy Department
Funding AgencyGrant Number
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Flintridge FoundationUNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)AyA2014-55216
Subject Keywords:accretion, accretion disks; stars: mass-loss; supergiants; X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20180328-133306261
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Official Citation:Stephanie Kwan et al 2018 ApJ 856 38
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85475
Deposited By: George Porter
Deposited On:28 Mar 2018 21:43
Last Modified:15 Nov 2021 20:29

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