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Spallucci E.,University of Trieste | Ansoldi S.,International Center for Relativistic Astrophysics | Ansoldi S.,University of Udine
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

In this Letter we investigate the role of regular (curvature singularity-free) black holes in the framework of UV self-complete quantum gravity. The existence of a minimal length, shielding the trans-Planckian regime to any physical probe, is self-consistently included into the black hole probe itself. In this way we obtain to slightly shift the barrier below the Planck length, with the UV self-complete scenario self-consistently confirmed. © 2011 Elsevier B.V. Source

Della Valle M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Della Valle M.,International Center for Relativistic Astrophysics
Memorie della Societa Astronomica Italiana, Supplementi - Journal of the Italian Astronomical Society, Supplement | Year: 2010

I review the observational status of Supernovae originating from the explosion of massive stars. © SAIt 2010. Source

Van Putten M.H.P.M.,Korea Institute for Advanced Study | Della Valle M.,Istituto Nazionale di AstrofisicaOsservatorio Astronomico di Capodimonte | Della Valle M.,International Center for Relativistic Astrophysics | Levinson A.,Tel Aviv University
Astronomy and Astrophysics | Year: 2011

Context. Some core-collapse supernovae appear to be hyper-energetic, and a subset of these are aspherical and associated with long GRBs. Aims. We use observations of electromagnetic emission from core-collapse supernovae and GRBs to impose constraints on their free energy source as a prior to searches for their gravitational wave emission. Methods. We review these events based on a finite efficiency for the conversion of spin energy to magnetic winds powering supernovae. Results. We find that some of the hyper-energetic events cannot be powered by the spindown of rapidly rotating proto-neutron stars by virtue of their limited rotational energy. They can, instead, be produced by the spindown of black holes providing a distinct prospect for gravitational-wave emission of interest to LIGO, Virgo, and the LCGT. © 2011 ESO. Source

Hofmann F.,Max Planck Institute for Extraterrestrial Physics | Pietsch W.,Max Planck Institute for Extraterrestrial Physics | Henze M.,Max Planck Institute for Extraterrestrial Physics | Henze M.,European Space Agency | And 7 more authors.
Astronomy and Astrophysics | Year: 2013

Context. The central field of the Andromeda galaxy (M 31) was monitored from 2006 to 2012 using the Chandra HRC-I detector (about 0.1-10 keV energy range) with the main aim of detecting X-rays from optical novae. We present a systematic analysis of all X-ray sources found in the 41 nova monitoring observations, along with 23 M 31 central field HRC-I observations available from the Chandra data archive starting in December 1999. Aims. Based on these observations, we studied the X-ray long-term variability of the source population and especially of X-ray binaries in M 31. Methods. We created a catalogue of sources detected in the 64 available observations that adds up to a total exposure time of about 1 Ms. To study the variability, we developed a processing pipeline to derive long-term Chandra HRC-I light curves for each source over the 13 years of observations. We also searched for extended X-ray sources in the merged images. Results. We present a point-source catalogue containing 318 X-ray sources with detailed long-term variability information, 28 of which are published for the first time. The spatial and temporal resolution of the catalogue allows us to classify 115 X-ray binary candidates showing high X-ray variability or even outbursts, as well as 14 globular cluster X-ray binary candidates showing no significant variability. The analysis may suggest that outburst sources are less frequent in globular clusters than in the field of M 31. We detected seven supernova remnants, one of which is a new candidate, and also resolved the first X-rays from a known radio supernova remnant. In addition to 33 known optical nova/X-ray source correlations, we discovered one previously unknown super-soft X-ray outburst and several new nova candidates. Conclusions. The catalogue contains a large sample of detailed long-term X-ray light curves in the M 31 central field, which helps in understanding the X-ray population of our neighbouring spiral galaxy M 31. © 2013 ESO. Source

Henze M.,Max Planck Institute for Extraterrestrial Physics | Henze M.,European Space Astronomy Center | Pietsch W.,Max Planck Institute for Extraterrestrial Physics | Haberl F.,Max Planck Institute for Extraterrestrial Physics | And 9 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. Aims. We performed a dedicated monitoring of the M 31 central region, which aimed to detect SSS counterparts of CNe, with XMM-Newton and Chandra between Nov. and Mar. of the years 2009/10, 2010/11, and 2011/12. Methods. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and also their spectral properties in the case of XMM-Newton data. Additionally, we determined luminosity upper limits for all previously known X-ray emitting novae, which are not detected anymore, and for all CNe in our field of view with recent optical outbursts. Results. In total, we detected 24 novae in X-rays. Seven of these sources were known from previous observations, including the M 31 nova with the longest SSS phase, M31N 1996-08b, which was found to fade below our X-ray detection limit 13.8 yr after outburst. Of the new discoveries, several novae exhibit significant variability in their short-term X-ray light curves with one object showing a suspected period of about 1.3 h. We studied the SSS state of the most recent outburst of a recurrent nova, which had previously shown the shortest time ever observed between two outbursts (~5 yr). The total number of M 31 novae with X-ray counterpart was increased to 79, and we subjected this extended catalogue to detailed statistical studies. Four previously indicated correlations between optical and X-ray parameters could be confirmed and improved. Furthermore, we found indications that the multi-dimensional parameter space of nova properties might be dominated by a single physical parameter, and we provide interpretations and suggest implications. We studied various outliers from the established correlations and discuss evidence of a different X-ray behaviour of novae in the M 31 bulge and disk. Conclusions. Exploration of the multi-wavelength parameter space of optical and X-ray measurements is shown to be a powerful tool for examining properties of extragalactic nova populations. While there are hints that the different stellar populations of M 31 (bulge vs. disk) produce dissimilar nova outbursts, there is also growing evidence that the overall behaviour of an average nova might be understood in surprisingly simple terms. © ESO, 2014. Source

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