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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.

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.

Valle M.D.,National institute for astrophysics | Valle M.D.,International Center for Relativistic Astrophysics
International Journal of Modern Physics D | Year: 2011

In this paper I shall shortly review the observational status of the Supernova and Gamma-ray Bursts connection including the most recent observations: the discovery of a new case of association at z = 0.53 (SN 2008 hw/GRB 081007) and the case of SN 2008D associated with the XRF 080109, a borderline object which may link GRBs with "standard" core-collapse events. © 2011 World Scientific Publishing Company.

Mankuzhiyil N.,National Institute of Nuclear Physics, Italy | Mankuzhiyil N.,University of Udine | Mankuzhiyil N.,University of Turin | Ansoldi S.,National Institute of Nuclear Physics, Italy | And 7 more authors.
Astrophysical Journal | Year: 2012

We study the variation of the broadband spectral energy distribution (SED) of the BLLac object Mrk501 as a function of source activity, from quiescent to flaring. Through χ2-minimization we model eight simultaneous SED data sets with a one-zone synchrotron self-Compton (SSC) model, and examine how model parameters vary with source activity. The emerging variability pattern of Mrk501 is complex, with the Compton component arising from γ-e scatterings that sometimes are (mostly) Thomson and sometimes (mostly) extreme Klein-Nishina. This can be seen from the variation of the Compton to synchrotron peak distance according to source state. The underlying electron spectra are faint/soft in quiescent states and bright/hard in flaring states. A comparison with Mrk421 suggests that the typical values of the SSC parameters are different in the two sources: however, in both jets the energy density is particle-dominated in all states. © 2012. The American Astronomical Society. All rights reserved..

Mankuzhiyil N.,University of Udine | Ansoldi S.,International Center for Relativistic Astrophysics | Ansoldi S.,University of Udine | Persic M.,National institute for astrophysics | Tavecchio F.,National institute for astrophysics
Astrophysical Journal | Year: 2011

For the high-frequency-peaked BL Lac object Mrk 421, we study the variation of the spectral energy distribution (SED) as a function of source activity, from quiescent to active. We use a fully automatized χ2- minimization procedure, instead of the "eyeball" procedure more commonly used in the literature, to model nine SED data sets with a one-zone synchrotron self-Compton (SSC) model and examine how the model parameters vary with source activity. The latter issue can finally be addressed now, because simultaneous broadband SEDs (spanning from optical to very high energy photon) have finally become available. Our results suggest that in Mrk 421 the magnetic field (B) decreases with source activity, whereas the electron spectrum's break energy (γbr) and the Doppler factor (δ) increase - the other SSC parameters turn out to be uncorrelated with source activity. In the SSC framework, these results are interpreted in a picture where the synchrotron power and peak frequency remain constant with varying source activity, through a combination of decreasing magnetic field and increasing number density of γ ≤ γbr electrons: since this leads to an increased electron-photon scattering efficiency, the resulting Compton power increases, and so does the total (= synchrotron plus Compton) emission. © 2011. The American Astronomical Society. All rights reserved..

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.

Montani G.,ENEA | Montani G.,University of Rome La Sapienza | Montani G.,International Center for Relativistic Astrophysics | Benini R.,University of Rome La Sapienza | Benini R.,International Center for Relativistic Astrophysics
General Relativity and Gravitation | Year: 2011

We present a discussion of two-dimensional magneto-hydrodynamics (MHD) configurations, concerning the equilibria of accretion disks of a strongly magnetized astrophysical object. We set up a viscoresistive scenario which generalizes previous two-dimensional analyses by reconciling the ideal MHD coupling of the vertical and the radial equilibria within the disk with the standard mechanism of the angular momentum transport, relying on dissipative properties of the plasma configuration. The linear features of the considered model are analytically developed and the non-linear configuration problem is addressed, by fixing the entire disk profile at the same order of approximation. Indeed, the azimuthal and electron force balance equations are no longer automatically satisfied when poloidal currents and matter fluxes are included in the problem. These additional components of the equilibrium configuration induce a different morphology of the magnetic flux surface, with respect to the ideal and simply rotating disk. © 2010 Springer Science+Business Media, LLC.

Della Valle M.,Instituto Nazionale Of Astrofisica | 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.

Van Putten M.H.P.M.,Korea Institute for Advanced Study | Della Valle M.,Instituto Nazionale Of Astrofisicaosservatorio Astronomico Of 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.

Van Putten M.H.P.M.,Sejong University | Lee G.M.,Sejong University | Valle M.D.,Instituto Nazionale Of Astrofisica | Valle M.D.,International Center for Relativistic Astrophysics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

The Burst and Transient Source Experiment classifies cosmological gamma-ray bursts (GRBs) into short (less than 2 s) and long (over 2 s) events, commonly attributed to mergers of compact objects and, respectively, peculiar core-collapse supernovae. This standard classification has recently been challenged by the Swift discovery of short GRBs showing extended emission (SGRBEE) and nearby long GRBs without an accompanying supernovae (LGRBN). Both show an initial hard pulse, characteristic of SGRBs, followed by a long duration soft tail. We here consider the spectral peak energy (Ep, i)-radiated energy (Eiso) correlation and the redshift distributions to probe the astronomical and physical origin of these different classes of GRBs. We consider Swift events of 15 SGRBs, 7 SGRBEEs, 3 LGRBNs and 230 LGRBs detected by Swift. The spectral-energy properties of the initial pulse of both SGRBEE and LGRBNs are found to coincide with those of SGRBs. A Monte Carlo simulation shows that the redshift distributions of SGRBs, SGRBEE and LGRBNs fall outside the distribution of LGRBs at 4.75σ, 4.67σ and 4.31σ, respectively. A distinct origin of SGRBEEs with respect to LGRBs is also supported by the elliptical host galaxies of the SGRBEE events 050509B and 050724. This combined evidence supports the hypothesis that SGRBEE and LGRBNs originate in mergers as SGRBs. Moreover, long/soft tail of SGRB and LGRBNs satisfy the same Ep,i-Eiso Amati correlation holding for normal LGRBs. This fact points to rapidly rotating black holes as a common long-lived inner engine produced by different astronomical progenitors (mergers and supernovae). © 2014 The Authors.

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