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تسجيل مستخدم جديدEvolution of tidal disruption candidates discovered by XMM-Newton
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It has been demonstrated that active galactic nuclei are powered by gas accretion onto supermassive black holes located at their centres. The paradigm that the nuclei of inactive galaxies are also occupied by black holes was predicted long ago by theory. In the last decade, this conjecture was confirmed by the discovery of giant-amplitude, non-recurrent X-ray flares from such inactive galaxies and explained in terms of outburst radiation from stars tidally disrupted by a dormant supermassive black hole at the nuclei of those galaxies. Due to the scarcity of detected tidal disruption events, the confirmation and follow-up of each new candidate is needed to strengthen the theory through observational data, as well as to shed new light on the characteristics of this type of events. Two tidal disruption candidates have been detected with XMM-Newton during slew observations. Optical and X-ray follow-up, post-outburst observations were performed on these highly variable objects in order to further study their classification and temporal evolution. We show that the detected low-state X-ray emission for these two candidates has properties such that it must still be related to the flare. The X-ray luminosity of the objects decreases according to theoretical predictions for tidal disruption events. At present, optical spectra of the sources do not present any evident signature of the disruption event. In addition, the tidal disruption rate as derived from the XMM-Newton slew survey has been computed and agrees with previous studies.
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We present results of follow-up optical spectroscopic observations of seven rare, extreme coronal line emitting galaxies reported by Wang et al. (2012) with Multi-Mirror Telescope (MMT). Large variations in coronal lines are found in four objects, ma
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XMM-Newtons large field of view and excellent sensitivity have resulted in hundreds of thousands of serendipitous X-ray detections. Whilst their spectra have been widely exploited, their variable nature has been little studied. Part of this is due to
the way XMM-Newton currently operates, where observations generally have a 12 month proprietary period. It is often too late to follow-up a serendipitous transient a year after detection. New robust software could be introduced into the pipeline to automatically identify bright transients that are not the target of the observation. Statistically, hundreds of tidal disruption events (TDEs) have been detected serendipitously by XMM-Newton. With prior consent from the PI of the observation, an automatic alert to a new transient could be set up, allowing it to be followed-up within weeks, ideal for TDEs that are bright for about a year. Over the next decade, hundreds more TDEs should be detected. Following-up the brightest in quasi-real time would allow constraints to be made on the black hole mass, spin and accretion regime and identify intermediate-mass black holes that are expected to be hidden in faint, low-mass galaxies. This article discusses the advantages that such changes would have on the follow-up of transients and TDEs.
We present follow-up observations of an optical transient (OT) discovered by ROTSE on Jan. 21, 2009. Photometric monitoring was carried out with ROTSE-IIIb in the optical and Swift in the UV up to +70 days after discovery. The light curve showed a fa
st rise time of ~10 days followed by a steep decline over the next 60 days, which was much faster than that implied by 56Ni - 56Co radioactive decay. The SDSS DR10 database contains a faint, red object at the position of the OT, which appears slightly extended. This and other lines of evidence suggest that the OT is of extragalactic origin, and this faint object is likely the host galaxy. A sequence of optical spectra obtained with the 9.2-m Hobby-Eberly Telescope (HET) between +8 and +45 days after discovery revealed a hot, blue continuum with no visible spectral features. A few weak features that appeared after +30 days probably originated from the underlying host. Fitting synthetic templates to the observed spectrum of the host galaxy revealed a redshift of z = 0.19. At this redshift the peak magnitude of the OT is close to -22.5, similar to the brightest super-luminous supernovae; however, the lack of identifiable spectral features makes the massive stellar death hypothesis less likely. A more plausible explanation appears to be the tidal disruption of a sun-like star by the central super-massive black hole. We argue that this transient likely belongs to a class of super-Eddington tidal disruption events.
We have calculated the coherence and detectable lifetimes of synthetic near-Earth object (NEO) families created by catastrophic disruption of a progenitor as it suffers a very close Earth approach. The closest or slowest approaches yield the most vio
lent `s-class disruption events. We found that the average slope of the absolute magnitude (H) distribution, $N(H)propto10^{(0.55pm0.04),H}$, for the fragments in the s-class families is steeper than the slope of the NEO population citep{mainzer2011} in the same size range. The families remain coherent as statistically significant clusters of orbits within the NEO population for an average of $bartau_c = (14.7pm0.6)times10^3$ years after disruption. The s-class families are detectable with the techniques developed by citet{fu2005} and citet{Schunova2012} for an average duration ($bartau_{det}$) ranging from about 2,000 to about 12,000 years for progenitors in the absolute magnitude ($H_p$) range from 20 to 13 corresponding to diameters in the range from about 0.5 to 10$km$ respectively. The short detectability lifetime explains why zero NEO families have been discovered to-date. Nonetheless, every tidal disruption event of a progenitor with D$>0.5km$ is capable of producing several million fragments in the $1meter$ to $10meter$ diameter range that can contribute to temporary local density enhancements of small NEOs in Earths vicinity. We expect that there are about 1,200 objects in the steady state NEO population in this size range due to tidal disruption assuming that one $1km$ diameter NEO tidally disrupts at Earth every 2,500 years. These objects may be suitable targets for asteroid retrieval missions due to their Earth-like orbits with corresponding low $v_{infty}$. The fragments from the tidal disruptions at Earth have $sim5times$ the collision probability with Earth compared to the background NEO population.
We constrain the recent star formation histories of the host galaxies of eight optical/UV-detected tidal disruption events (TDEs). Six hosts had quick starbursts of <200 Myr duration that ended 10 to 1000 Myr ago, indicating that TDEs arise at differ
ent times in their hosts post-starburst evolution. If the disrupted star formed in the burst or before, the post-burst age constrains its mass, generally excluding O, most B, and highly massive A stars. If the starburst arose from a galaxy merger, the time since the starburst began limits the coalescence timescale and thus the merger mass ratio to more equal than 12:1 in most hosts. This uncommon ratio, if also that of the central supermassive black hole (SMBH) binary, disfavors the scenario in which the TDE rate is boosted by the binary but is insensitive to its mass ratio. The stellar mass fraction created in the burst is 0.5-10% for most hosts, not enough to explain the observed 30-200x boost in TDE rates, suggesting that the hosts core stellar concentration is more important. TDE hosts have stellar masses 10^9.4 - 10^10.3 Msun, consistent with the SDSS volume-corrected, quiescent Balmer-strong comparison sample and implying SMBH masses of 10^5.5 - 10^7.5 Msun. Subtracting the host absorption line spectrum, we uncover emission lines; at least five hosts have ionization sources inconsistent with star formation that instead may be related to circumnuclear gas, merger shocks, or post-AGB stars.
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