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First Detection of Mid-infrared Variability from an Ultraluminous X-Ray Source Holmberg II X-1

Lau, R. M. and Heida, M. and Kasliwal, M. M. and Walton, D. J. (2017) First Detection of Mid-infrared Variability from an Ultraluminous X-Ray Source Holmberg II X-1. Astrophysical Journal Letters, 838 (2). Art. No. L17. ISSN 2041-8205. doi:10.3847/2041-8213/aa6746.

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We present mid-infrared (IR) light curves of the Ultraluminous X-ray Source (ULX) Holmberg II X-1 from observations taken between 2014 January 13 and 2017 January 5 with the Spitzer Space Telescope at 3.6 and 4.5 μm in the Spitzer Infrared Intensive Transients Survey. The mid-IR light curves, which reveal the first detection of mid-IR variability from a ULX, is determined to arise primarily from dust emission rather than from a jet or an accretion disk outflow. We derived the evolution of the dust temperature (T_d ~ 600-800 K), IR luminosity (L_(IR) ~ 3 x 10^4 L_⊙), mass (M_d ~ 1-3 x 10^(-6) M_⊙), and equilibrium temperature radius (R_(eq) ~ 10-20 au). A comparison of X-1 with a sample of spectroscopically identified massive stars in the Large Magellanic Cloud on a mid-IR color–magnitude diagram suggests that the mass donor in X-1 is a supergiant (sg) B[e]-star. The sgB[e]-interpretation is consistent with the derived dust properties and the presence of the [Fe ii] (λ =1.644 µm) emission line revealed from previous near-IR studies of X-1. We attribute the mid-IR variability of X-1 to the increased heating of dust located in a circumbinary torus. It is unclear what physical processes are responsible for the increased dust heating; however, it does not appear to be associated with the X-ray flux from the ULX, given the constant X-ray luminosities provided by serendipitous, near-contemporaneous X-ray observations around the first mid-IR variability event in 2014. Our results highlight the importance of mid-IR observations of luminous X-ray sources traditionally studied at X-ray and radio wavelengths.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Heida, M.0000-0002-1082-7496
Kasliwal, M. M.0000-0002-5619-4938
Walton, D. J.0000-0001-5819-3552
Additional Information:© 2017. The American Astronomical Society. Received 2017 January 1; revised 2017 March 8; accepted 2017 March 9; published 2017 March 30. R.L. would like to thank Kaew Tinyanont, Bob Gehrz, and the anonymous referee for the valuable comments and insight. R.L. would also like to thank Michael Ressler and the rest of the SPIRITS team. This work made use of observations from the Spitzer Space Telescope operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA (PIDS 10136, 11063, & 13053). This work was partially carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Group:Infrared Processing and Analysis Center (IPAC), Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
Subject Keywords:black hole physics; circumstellar matter; infrared: ISM; ISM: individual objects (Holmberg II X-1)
Issue or Number:2
Record Number:CaltechAUTHORS:20170331-092410654
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Official Citation:R. M. Lau et al 2017 ApJL 838 L17
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75568
Deposited By: George Porter
Deposited On:31 Mar 2017 16:47
Last Modified:15 Nov 2021 16:34

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