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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 × 1043 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 ~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. [ABSTRACT FROM AUTHOR]

The X-ray source 2XMM J123103.2+110648 was previously found to show pure thermal X-ray spectra and an ~3.8 h periodicity in three XMM-Newton X-ray observations in 2003- 2005, and the optical spectrum of the host galaxy suggested it as a type 2 active galactic nucleus candidate.We have obtained new X-ray observations of the source, with Swift and Chandra in 2013-2016, in order to shed new light on its nature based on its long-term evolution property. We found that the source could be in an X-ray outburst, with the X-ray flux decreasing by an order of magnitude in the Swift and Chandra observations, compared with the XMM-Newton observations 10 yr ago. There seemed to be significant spectral softening associated with the drop of X-ray flux (disc temperature kT ~ 0.16-0.2 keV in XMM-Newton observations versus kT ~ 0.09 ± 0.02 keV in the Chandra observation). Therefore, the Swift and Chandra followup observations support our previous suggestion that the source could be a tidal disruption event (TDE), though it seems to evolve slower than most of the other TDE candidates. The apparent long duration of this event could be due to the presence of a long super-Eddington accretion phase and/or slow circularization. [ABSTRACT FROM AUTHOR]

In this paper we present a comprehensive study of the mass of the intermediate mass black hole candidate HLX-1 in the galaxy ESO 243-49. We analyse the continuum X-ray spectra collected by Swift, XMM-Newton, and Chandra with the slim disc model, slimbh, and estimate the black hole mass for the full range of inclination (inc = 0°-85°) and spin (a* = 0-0:998). The relativistic slimbh model is particularly suited to study high luminosity disc spectra as it incorporates the e ects of advection, such as the shift of the inner disc edge towards smaller radii and the increasing height of the disc photosphere (including relativistic ray-tracing from its proper location rather than the mid-plane of the disc). We find for increasing values of inclination that a zero spin black hole has a mass range of 6300-50 900 M☉ and a maximally spinning black hole has a mass between 16 900-191 700 M☉. This is consistent with previous estimates and reinforces the idea that HLX-1 contains an intermediate mass black hole. [ABSTRACT FROM AUTHOR]

With an inferred bolometric luminosity exceeding 1042 erg s-1, HLX-1 in ESO 243-49 is the most luminous of ultraluminous X-ray sources and provides one of the strongest cases for the existence of intermediate-mass black holes. We obtain good fits to disk-dominated observations of the source with BHSPEC, a fully relativistic black hole accretion disk spectral model. Due to degeneracies in the model arising from the lack of independent constraints on inclination and black hole spin, there is a factor of 100 uncertainty in the best-fit black hole mass M. Nevertheless, spectral fitting of XMM-Newton observations provides robust lower and upper limits with 3000 M≲ ≲ M≲ ≲ 3 x 105 M⊙, at 90% confidence, placing HLX-l firmly in the intermediate-mass regime. The lower bound on M is entirely determined by matching the shape and peak energy of the thermal component in the spectrum. This bound is consistent with (but independent of) arguments based solely on the Eddington limit. Joint spectral modeling of the XMM-Newton data with more luminous Swift and Chandra observations increases the lower bound to 6000 M≲, but this tighter constraint is not independent of the Eddington limit. The upper bound on M≲ is sensitive to the maximum allowed inclination i, and is reduced to M ≲ l05 M≲ if we limit i ≲ 75°. [ABSTRACT FROM AUTHOR]