Browsing by Author "Grupe, Dirk"

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    A likely decade-long sustained tidal disruption event
    (Nature Portfolio, 2017-02-02) Lin, Dacheng; Guillochon, James; Komossa, S.; Ramirez-Ruiz, Enrico; Irwin, Jimmy A.; Maksym, W. Peter; Grupe, Dirk; Godet, Olivier; Webb, Natalie A.; Barret, Didier; Zauderer, B. Ashley; Duc, Pierre-Alain; Carrasco, Eleazar R.; Gwyn, Stephen D. J.; University System Of New Hampshire; University of New Hampshire; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; University of California System; University of California Santa Cruz; University of Alabama Tuscaloosa; Seoul National University (SNU); Morehead State University; Centre National de la Recherche Scientifique (CNRS); Universite de Toulouse; Universite Toulouse III - Paul Sabatier; New York University; CEA; UDICE-French Research Universities; Universite Paris Cite; Universite Paris Saclay; National Research Council Canada
    Multiwavelength flares from tidal disruption and accretion of stars can be used to find and study otherwise dormant massive black holes in galactic nuclei(1). Previous well-monitored candidate flares were short-lived, with most emission confined to within similar to 1 year(2-5). Here we report the discovery of a well-observed super-long (> 11 years) luminous X-ray flare from the nuclear region of a dwarf starburst galaxy. After an apparently fast rise within similar to 4 months a decade ago, the X-ray luminosity, though showing a weak trend of decay, has been persistently high at around the Eddington limit (when the radiation pressure balances the gravitational force). The X-ray spectra are soft - steeply declining towards higher energies and can be described with Comptonized emission from an optically thick low-temperature corona, a super-Eddington accretion signature often observed in accreting stellar-mass black holes(6). Dramatic spectral softening was also caught in one recent observation, implying either a temporary transition from the super-Eddington accretion state to the standard thermal state, or the presence of a transient highly blueshifted (similar to 0.36c) warm absorber. All these properties in concert suggest a tidal disruption event with an unusually long super-Eddington accretion phase that has never before been observed.
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    Multiwavelength follow-up observations of the tidal disruption event candidate 2XMMi J184725.1-631724
    (Oxford University Press, 2017-11-16) Lin, Dacheng; Strader, Jay; Carrasco, Eleazar R.; Godet, Olivier; Grupe, Dirk; Webb, Natalie A.; Barret, Didier; Irwin, Jimmy A.; University System Of New Hampshire; University of New Hampshire; Michigan State University; Centre National de la Recherche Scientifique (CNRS); Universite de Toulouse; Universite Toulouse III - Paul Sabatier; Morehead State University; University of Alabama Tuscaloosa; Seoul National University (SNU)
    The ultrasoft X-ray flare 2XMMi J184725.1-631724 was serendipitously detected in two XMM-Newton observations in 2006 and 2007, with a peak luminosity of 6 x 10(43) erg s(-1). It was suggested to be a tidal disruption event (TDE) because its position is consistent with the centre of an inactive galaxy. It is the only known X-ray TDE candidate whose X-ray spectra showed evidence of a weak steep power-law component besides a dominant supersoft thermal disc. We have carried out multiwavelength follow-up observations of the event. Multiple X-ray monitorings show that the X-ray luminosity has decayed significantly after 2011. Especially, in our deep Chandra observation in 2013, we detected a very faint counterpart that supports the nuclear origin of 2XMMi J184725.1-631724 but had an X-ray flux a factor of similar to 1000 lower than in the peak of the event. Compared with follow-up ultraviolet (UV) observations, we found that there might be some enhanced UV emission associated with the TDE in the first XMM-Newton observation. We also obtained a high-quality UV-optical spectrum with the Southern Astrophysical Research (SOAR) Telescope and put a very tight constraint on the persistent nuclear activity, with a persistent X-ray luminosity expected to be lower than the peak of the flare by a factor of > 2700. Therefore, our multiwavelength follow-up observations strongly support the TDE explanation of the event.
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    AN ULTRASOFT X-RAY FLARE FROM 3XMM J152130.7+074916: A TIDAL DISRUPTION EVENT CANDIDATE
    (IOP Publishing, 2015-09-20) Lin, Dacheng; Maksym, Peter W.; Irwin, Jimmy A.; Komossa, S.; Webb, Natalie A.; Godet, Olivier; Barret, Didier; Grupe, Dirk; Gwyn, Stephen D. J.; University System Of New Hampshire; University of New Hampshire; University of Alabama Tuscaloosa; Max Planck Society; Universite de Toulouse; Universite Toulouse III - Paul Sabatier; Centre National de la Recherche Scientifique (CNRS); Morehead State University; National Research Council Canada
    We report on the discovery of an ultrasoft X-ray transient source, 3XMM J152130.7+074916. It was serendipitously detected in an XMM-Newton observation on 2000 August 23, and its location is consistent with the center of the galaxy SDSS J152130.72+074916.5 (z = 0.17901 and d(L) = 866 Mpc). The high-quality X-ray spectrum can be fitted with a thermal disk with an apparent inner disk temperature of 0.17 keV and a rest-frame 0.24-11.8 keV unabsorbed luminosity of similar to 5 x 10(43) erg s(-1), subject to a fast-moving warm absorber. Short-term variability was also clearly observed, with the spectrum being softer at lower flux. The source was covered but not detected in a Chandra observation on 2000 April 3, a Swift observation on 2005 September 10, and a second XMM-Newton observation on 2014 January 19, implying a large variability (>260) of the X-ray flux. The optical spectrum of the candidate host galaxy, taken similar to 11 years after the XMM-Newton detection, shows no sign of nuclear activity. This, combined with its transient and ultrasoft properties, leads us to explain the source as tidal disruption of a star by the supermassive black hole in the galactic center. We attribute the fast-moving warm absorber detected in the first XMM-Newton observation to the super-Eddington outflow associated with the event and the short-term variability to a disk instability that caused fast change of the inner disk radius at a constant mass accretion rate.