Multiwavelength follow-up observations of the tidal disruption event candidate 2XMMi J184725.1-631724


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.

accretion, accretion discs, black hole physics, galaxies: individual: 2XMMi J184725.1-631724, X-rays: galaxies, X-RAY SOURCES, SUPERMASSIVE BLACK-HOLES, PHOTON IMAGING CAMERA, STAR-FORMATION RATE, XMM-NEWTON, PARAMETER-ESTIMATION, CALIBRATION, CHANDRA, FLARE, LUMINOSITY, Astronomy & Astrophysics
Lin, D., Strader, J., Carrasco, E., Godet, O., Grupe, D., Webb, N., Barret, D., Irwin, J. (2017): Multiwavelength Follow-up Observations of the Tidal Disruption Event Candidate 2XMMi J184725.1-631724. Monthly Notices of the Royal Astronomical Society, 474 (3). DOI: 10.1093/mnras/stx2940