First detection of mid-infrared variability from an ultraluminous X-ray source Holmberg II X-1
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
- Division of Physics, Mathematics and Astronomy, Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)
- Institute of Astronomy, Madingley Road, CB3 0HA Cambridge (United Kingdom)
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{sub d}∼600--800 K), IR luminosity (L{sub IR}∼3×10{sup 4} L{sub ⊙}), mass (M{sub d}∼1--3×10{sup −6} M{sub ⊙}), and equilibrium temperature radius (R{sub 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.
- OSTI ID:
- 22869170
- Journal Information:
- Astrophysical Journal Letters, Vol. 838, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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