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Register a new userExploring the Nature of the Brightest Hyper-luminous X-ray Source
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Authors
Sean Farrell
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The small subset of hyper-luminous X-ray sources with luminosities in excess of ~1E41 erg/s are hard to explain without the presence of an intermediate mass black hole, as significantly super-Eddington accretion and/or very small beaming angles are required. The recent discovery of HLX-1, the most luminous object in this class with a record breaking luminosity of ~1E42 erg/s in the galaxy ESO 243-49, therefore currently provides some of the strongest evidence for the existence of intermediate mass black holes. HLX-1 is almost an order of magnitude brighter than the other hyper-luminous sources, and appears to exhibit X-ray spectral and flux variability similar to Galactic stellar mass black hole X-ray binaries. In this paper we review the current state of knowledge on this intriguing source and outline the results of multi-wavelength studies from radio to ultra-violet wavelengths, including imaging and spectroscopy of the recently identified optical counterpart obtained with the Very Large Telescope. These results continue to support an intermediate mass black hole in excess of 500 Msun
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We report the discovery of an off-nuclear ultrasoft hyper-luminous X-ray source candidate 3XMM J141711.1+522541 in the inactive S0 galaxy SDSS J141711.07+522540.8 (z=0.41827, d_L=2.3 Gpc) in the Extended Groth Strip. It is located at a projected offset of ~1.0 (5.2 kpc) from the nucleus of the galaxy and was serendipitously detected in five XMM-Newton observations in 2000 July. Two observations have enough counts and can be fitted with a standard thermal disk with an apparent inner disk temperature kT_MCD ~ 0.13 keV and a 0.28-14.2 keV unabsorbed luminosity L_X ~ 4X10^{43} erg/s in the source rest frame. The source was still detected in three Chandra observations in 2002 August, with similarily ultrasoft but fainter spectra (kT_MCD ~ 0.17 keV, L_X ~ 0.5X10^{43} erg/s). It was not detected in later observations, including two by Chandra in 2005 October, one by XMM-Newton in 2014 January, and two by Chandra in 2014 September-October, implying a long-term flux variation factor of >14. Therefore the source could be a transient with an outburst in 2000-2002. It has a faint optical counterpart candidate, with apparent magnitudes of m_F606W=26.3 AB mag and m_F814W=25.5 AB mag in 2004 December (implying an absolute V-band magnitude of ~-15.9 AB mag). We discuss various explanations for the source and find that it is best explained as a massive black hole (BH) embedded in the nucleus of a possibly stripped satellite galaxy, with the X-ray outburst due to tidal disruption of a surrounding star by the BH. The BH mass is ~10^5 Msun, assuming the peak X-ray luminosity at around the Eddington limit.
In this paper we present the best quality XMM-Newton and Suzaku data from M82 X-1 so far. We analyze the spectra of this remarkable Ultra-Luminous X-ray Source in a self-consistent manner. We have disentangled emission from the host galaxy, responsible for the soft X-ray emission (E<2.5 keV), which is successfully described by a two-temperature thermal emission from a hot plasma in multi-phase state, plus a narrow Fe line emission at 6.7 keV. This allowed us to properly study the intrinsic continuum emission from M82 X-1. The continuum of the Suzaku spectrum is curved and the high quality data of the Suzaku spectrum allowed us to significantly detect a weakly broadened Fe K-alpha emission line. The Equivalent-Width is in the range 30-80 eV and it does not depend on the model applied for the continuum. Assuming that this line is coming from the ULX via disc fluorescence, the data indicates a disc truncation at a radius of 6-20 gravitational radii. This value is comparable to or even larger than the Innermost Stable Circular Orbit of a non-spinning (Schwarzschild) black hole. Future longer observations might test this scenario.
The nature of the first unidentified VHE gamma-ray source with significant angular offset from the Galactic plane of 3.5 degrees, HESS J1507-622, is explored. Fermi-LAT data in the high-energy (HE, 100 MeV < E < 100 GeV) gamma-ray range collected over 34 month are used to describe the spectral energy distribution (SED) of the source. HESS J1507-622 is detected in the Fermi energy range and its spectrum is best described by a power law in energy with Gamma=1.7 +/- 0.1 stat +/- 0.2_sys and integral flux between (0.3-300) GeV of F = (2.0 +/-0.5_stat +/- 1.0_sys) x 10^-9 cm^-2 s^-1. With the available data it is not possible to discriminate between a hadronic and a leptonic scenario for HESS J1507-622. The location and compactness of the source indicate a considerable physical offset from the Galactic plane for this object. In case of a multiple-kpc distance, this challenges a pulsar wind nebula (PWN) origin for HESS J1507-622 since the time of travel for a pulsar born in the Galactic disk to reach such a location would exceed the inverse Compton (IC) cooling time of electrons that are energetic enough to produce VHE gamma-rays. However, an origin of this gamma-ray source connected to a pulsar that was born off the Galactic plane in the explosion of a hypervelocity star cannot be excluded. The nature of HESS J1507-622 is still unknown to date, and a PWN scenario cannot be ruled out in general. On the contrary HESS J1507-622 could be the first discovered representative of a population of spatially extended VHE gamma-ray emitters with HE gamma-ray counterpart that are located at considerable offsets from the Galactic plane. Future surveys in the VHE gamma-ray range are necessary to probe the presence or absence of such a source population.(abridged)
We report on the results of X-ray observations of 4XMM J111816.0-324910, a transient ultra-luminous X-ray source located in the galaxy NGC 3621. This system is characterised by a transient nature and marked variability with characteristic time-scale of ~3500 s, differently from other ULXs, which in the vast majority show limited intra-observation variability. Such a behaviour is very reminiscent of the so-called heartbeats sometimes observed in the Galactic black hole binary GRS 1915+105, where the variability time-scale is ~10-1000 s. We study the spectral and timing properties of this object and find that overall, once the differences in the variability time-scales are taken into account, they match quite closely those of both GRS 1915+105, and of a number of objects showing heartbeats in their light-curves, including a confirmed neutron star and a super-massive black hole powering an active galactic nucleus. We investigate the nature of the compact object in 4XMM J111816.0-324910 by searching for typical neutron star signatures and by attempting a mass estimate based on different methods and assumptions. Based on the current available data, we are not able to unambiguously determine the nature of the accreting compact object responsible for the observed phenomenology.
To reconcile the observed unusual high luminosity of NuSTAR X-ray pulsations from M82X-2 with the most extreme violation of the Eddington limit, and in view that the persistent X-ray radiation from M82X-2 almost precludes the possibility of common pulsars, we tackle the problem by the implications of {em microscopic theory of black hole} (MTBH). The preceding developments of MTBH are proved to be quite fruitful for the physics of ultra-high energy (UHE) cosmic-rays. Namely, replacing a central singularity by the infrastructures inside event horizon, subject to certain rules, MTBH explains the origin of ZeV-neutrinos which are of vital interest for the source of UHE-particles. The M82X-2 is assumed to be a spinning intermediate mass black hole resided in final stage of growth. As a corollary, the thermal blackbody X-ray emission arisen due to the rotational kinetic energy of black hole escapes from event horizon through the vista to outside world that detected as ultraluminous X-ray pulsations. The M82X-2 indeed releases $sim 99.6%$ of its pulsed radiative energy predominantly in the X-ray bandpass $0.3-30$ keV. We derive a pulse profile and give a quantitative account of energetics and orbital parameters of the semi-detached X-ray binary containing a primary accretor M82X-2 of inferred mass $Msimeq 138.5-226,M_{odot}$ and secondary massive, $M_{2}> 48.3- 64.9,M_{odot}$, O/B-type donor star with radius of $R> 22.1- 25.7,R_{odot}$, respectively. We compute the torque added to M82X-2 per unit mass of accreted matter which yields the measured spin-up rate.
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