A luminous X-ray flare from the nucleus of the dormant bulgeless spiral galaxy NGC 247
- Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)
- Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States)
- Center for Astrophysics, Tsinghua University, Beijing 100084 (China)
- Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara 252-5258 (Japan)
- Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
- Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, F-67000 Strasbourg (France)
NGC 247 is a nearby late-type bulgeless spiral galaxy that contains an inactive nucleus. We report a serendipitous discovery of an X-ray flare from the galaxy center with a luminosity of up to 2×10{sup 39} erg s{sup −1} in the 0.3–10 keV band with XMM-Newton. A Chandra observation confirms that the new X-ray source is spatially coincident with the galaxy nucleus. The XMM-Newton data revealed a hard power-law spectrum with a spectral break near 3–4 keV, no pulsations on timescales longer than 150 ms, and a flat power spectrum consistent with Poisson noise from 1 mHz to nearly 10 Hz. Follow-up observations with Swift detected a second flux peak followed by a luminosity drop by a factor of almost 20. The spectral and temporal behaviors of the nuclear source are consistent with the scenario that the flare was due to an outburst of a low-mass X-ray binary that contains a stellar-mass black hole emitting near its Eddington limit at the peak. However, it cannot be ruled out that the sudden brightening in the nucleus was due to accretion onto a possible low-mass nuclear black hole, fed by a tidally disrupted star or a gas cloud; the Monitor of All-sky X-ray Image observations limit the peak luminosity of the flare to less than ∼10{sup 43} erg s{sup −1}, suggesting that it is either a low-mass black hole or an inefficient tidal disruption event.
- OSTI ID:
- 22882926
- Journal Information:
- Astrophysical Journal, Vol. 807, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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