arXiv subjects

A. De Luca

Publications and source records attributed to A. De Luca.

At least 55 records · Page 3Linked to original sources

arXiv2015

Multi-wavelength observations of 3FGL J2039.6-5618: a candidate redback millisecond pulsar

We present multi-wavelength observations of the unassociated gamma-ray source 3FGL J2039.6-5618 detected by the Fermi Large Area Telescope. The source gamma-ray properties suggest that it is a pulsar, most likely a millisecond pulsar, for which neither radio nor $γ$-ray pulsations have been detected yet. We observed 3FGL J2039.6-5618 with XMM-Newton and discovered several candidate X-ray counterparts within/close to the gamma-ray error box. The brightest of these X-ray sources is variable with a period of 0.2245$\pm$0.0081 d. Its X-ray spectrum can be described by a power law with photon index $Γ_X =1.36\pm0.09$, and hydrogen column density $N_{\rm H} < 4 \times 10^{20}$ cm$^{-2}$, which gives an unabsorbed 0.3--10 keV X-ray flux of $1.02 \times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$. Observations with the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND) discovered an optical counterpart to this X-ray source, with a time-average magnitude $g'\sim 19.5$. The counterpart features a flux modulation with a period of 0.22748$\pm$0.00043 d that coincides, within the errors, with that of the X-ray source, confirming the association based on the positional coincidence. We interpret the observed X-ray/optical periodicity as the orbital period of a close binary system where one of the two members is a neutron star. The light curve profile of the companion star, with two asymmetric peaks, suggests that the optical emission comes from two regions at different temperatures on its tidally-distorted surface. Based upon its X-ray and optical properties, we consider this source as the most likely X-ray counterpart to 3FGL J2039.6-5618, which we propose to be a new redback system.

astro-ph.HE↗

arXiv2015

Science with the EXTraS Project: Exploring the X-ray Transient and variable Sky

The EXTraS project (Exploring the X-ray Transient and variable Sky) will characterise the temporal behaviour of the largest ever sample of objects in the soft X-ray range (0.1-12 keV) with a complex, systematic and consistent analysis of all data collected by the European Photon Imaging Camera (EPIC) instrument onboard the ESA XMM-Newton X-ray observatory since its launch. We will search for, and characterize variability (both periodic and aperiodic) in hundreds of thousands of sources spanning more than nine orders of magnitude in time scale and six orders of magnitude in flux. We will also search for fast transients, missed by standard image analysis. Our analysis will be completed by multiwavelength characterization of new discoveries and phenomenological classification of variable sources. All results and products will be made available to the community in a public archive, serving as a reference for a broad range of astrophysical investigations.

astro-ph.HE↗

arXiv2015

An overview of the EXTraS project: Exploring the X-ray Transient and Variable Sky

The EXTraS project (Exploring the X-ray Transient and variable Sky) will harvest the hitherto unexplored temporal domain information buried in the serendipitous data collected by the European Photon Imaging Camera (EPIC) instrument onboard the ESA XMM-Newton X-ray observatory since its launch. This will include a search for fast transients, as well as a search and characterization of variability (both periodic and aperiodic) in hundreds of thousands of sources spanning more than nine orders of magnitude in time scale and six orders of magnitude in flux. X-ray results will be complemented by multiwavelength characterization of new discoveries. Phenomenological classification of variable sources will also be performed. All our results will be made available to the community. A didactic program in selected High Schools in Italy, Germany and the UK will also be implemented. The EXTraS project (2014-2016), funded within the EU/FP7 framework, is carried out by a collaboration including INAF (Italy), IUSS (Italy), CNR/IMATI (Italy), University of Leicester (UK), MPE (Germany) and ECAP (Germany).

astro-ph.HE↗

arXiv2015

Radio-quiet and radio-loud pulsars: similar in Gamma-rays but different in X-rays

We present new Chandra and XMM-Newton observations of a sample of eight radio-quiet Gamma-ray pulsars detected by the Fermi Large Area Telescope. For all eight pulsars we identify the X-ray counterpart, based on the X-ray source localization and the best position obtained from Gamma-ray pulsar timing. For PSR J2030+4415 we found evidence for an about 10 arcsec-long pulsar wind nebula. Our new results consolidate the work from Marelli et al. 2011 and confirm that, on average, the Gamma-ray--to--X-ray flux ratios (Fgamma/Fx) of radio-quiet pulsars are higher than for the radio-loud ones. Furthermore, while the Fgamma/Fx distribution features a single peak for the radio-quiet pulsars, the distribution is more dispersed for the radio-loud ones, possibly showing two peaks. We discuss possible implications of these different distributions based on current models for pulsar X-ray emission.

astro-ph.HE↗

arXiv2015

The study of neutron star magnetospheres with LOFT

This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of magnetospheres of isolated neutron stars. For a summary, we refer to the paper.

astro-ph.HE↗

arXiv2014

The Large Observatory For x-ray Timing

The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final down-selection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supra-nuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m 2 effective area, 2-30 keV, 240 eV spectral resolution, 1 deg collimated field of view) and a WideField Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.

astro-ph.IM↗

arXiv2014

Anderson localization on the Bethe lattice: non-ergodicity of extended states

Statistical analysis of the eigenfunctions of the Anderson tight-binding model with on-site disorder on regular random graphs strongly suggests that the extended states are multifractal at any finite disorder. The spectrum of fractal dimensions $f(α)$ defined in Eq.(3), remains positive for $α$ noticeably far from 1 even when the disorder is several times weaker than the one which leads to the Anderson localization, i.e. the ergodicity can be reached only in the absence of disorder. The one-particle multifractality on the Bethe lattice signals on a possible inapplicability of the equipartition law to a generic many-body quantum system as long as it remains isolated.

cond-mat.stat-mech↗

arXiv2014

On the puzzling high-energy pulsations of the energetic radio-quiet $γ$-ray pulsar J1813$-$1246

We have analyzed the new deep {\it XMM-Newton} and {\it Chandra} observations of the energetic radio-quiet pulsar J1813$-$1246. The X-ray spectrum is non-thermal, very hard and absorbed. Based on spectral considerations, we propose that J1813 is located at a distance further than 2.5 kpc. J1813 is highly pulsed in the X-ray domain, with a light curve characterized by two sharp, asymmetrical peaks, separated by 0.5 in phase. We detected no significant X-ray spectral changes during the pulsar phase. We extended the available {\it Fermi} ephemeris to five years. We found two glitches. The $γ$-ray lightcurve is characterized by two peaks, separated by 0.5 in phase, with a bridge in between and no off-pulse emission. The spectrum shows clear evolution in phase, being softer at the peaks and hardenning towards the bridge. The X-ray peaks lag the $γ$-ray ones by 0.25 in phase. We found a hint of detection in the 30-500 keV band with {\it INTEGRAL} IBIS/ISGRI, that is consistent with the extrapolation of both the soft X-ray and $γ$-ray emission of J1813. The peculiar X and $γ$-ray phasing suggests a singular emission geometry. We discuss some possibilities within the current pulsar emission models. Finally, we develop an alternative geometrical model where the X-ray emission comes from polar cap pair cascades.

astro-ph.HE↗

arXiv2014

High-energy pulsations and phase-resolved spectroscopy of PSR J1741-2054

We report the results of a deep XMM-Newton observation of the radio-faint $γ$-ray pulsar J1741-2054 and its nebula together with the analysis of 5 years of Fermi LAT data. The X-ray spectrum of the pulsar is consistent with an absorbed power law plus a blackbody, originating at least partly from the neutron star cooling. The nebular emission is consistent with that of a synchrotron pulsar wind nebula, with hints of spatial spectral variation. We extended the available Fermi LAT ephemeris and folded the $γ$-ray and X-ray data. We detected X-ray pulsations from the neutron star: both the thermal and non-thermal components are about 35-40% pulsed, with phase-aligned maxima. A sinusoid fits the thermal folded profile well. A 10-bin phase-resolved analysis shows softening of the non-thermal spectrum during the on-pulse phases. The radio, X-ray and $γ$-ray light curves are single-peaked, not phase-aligned, with the X-ray peak trailing the $γ$-ray peak by over half a rotation. Spectral considerations suggest that the most probable pulsar distance is in the 0.3-1.0 kpc range.

astro-ph.HE↗

arXiv2013

X-ray observations and the search for Fermi-LAT gamma-ray pulsars

The Large Area Telescope (LAT) on Fermi has detected ~150 gamma-ray pulsars, about a third of which were discovered in blind searches of the $γ$-ray data. Because the angular resolution of the LAT is relatively poor and blind searches for pulsars (especially millisecond pulsars, MSPs) are very sensitive to an error in the position, one must typically scan large numbers of locations. Identifying plausible X-ray counterparts of a putative pulsar drastically reduces the number of trials, thus improving the sensitivity of pulsar blind searches with the LAT. I discuss our ongoing program of Swift, XMM-Newton, and Chandra observations of LAT unassociated sources in the context of our blind searches for gamma-ray pulsars.

astro-ph.HE↗

arXiv2013

The ASTRI Mini-Array Science Case

ASTRI is a Flagship Project financed by the Italian Ministry of Education, University and Research, and led by INAF, the Italian National Institute of Astrophysics. Within this framework, INAF is currently developing an end-to-end prototype of a Small Size Telescope in a dual-mirror configuration (SST-2M) for the Cherenkov Telescope Array (CTA), scheduled to start data acquisition in 2014. Although the ASTRI SST-2M prototype is mainly a technological demonstrator, it will perform scientific observations of the Crab Nebula, Mrk 421 and Mrk 501 at E>1 TeV. A remarkable improvement in terms of performance could come from the operation, in 2016, of a SST-2M mini-array, composed of a few SST-2M telescopes to be placed at final CTA Southern Site. The SST mini-array will be able to study in great detail relatively bright sources (a few x 10E-12 erg/cm2/s at 10 TeV) with angular resolution of a few arcmin and energy resolution of about 10-15%. Thanks to the stereo approach, it will be possible to verify the wide field of view (FoV) performance through the detections of very high-energy showers with core located at a distance up to 500 m, to compare the mini-array performance with the Monte Carlo expectations by means of deep observations of selected targets, and to perform the first CTA science at the beginning of the mini-array operations. Prominent sources such as extreme blazars, nearby well-known BL Lac objects and radio-galaxies, galactic pulsar wind nebulae, supernovae remnants, micro-quasars, and the Galactic Center can be observed in a previously unexplored energy range, in order to investigate the electron acceleration and cooling, relativistic and non relativistic shocks, the search for cosmic-ray (CR) Pevatrons, the study of the CR propagation, and the impact of the extragalactic background light on the spectra of the sources.

astro-ph.HE↗

arXiv2013

The dual-mirror Small Size Telescope for the Cherenkov Telescope Array

In this paper, the development of the dual mirror Small Size Telescopes (SST) for the Cherenkov Telescope Array (CTA) is reviewed. Up to 70 SST, with a primary mirror diameter of 4 m, will be produced and installed at the CTA southern site. These will allow investigation of the gamma-ray sky at the highest energies accessible to CTA, in the range from about 1 TeV to 300 TeV. The telescope presented in this contribution is characterized by two major innovations: the use of a dual mirror Schwarzschild-Couder configuration and of an innovative camera using as sensors either multi-anode photomultipliers (MAPM) or silicon photomultipliers (SiPM). The reduced plate-scale of the telescope, achieved with the dual-mirror optics, allows the camera to be compact (40 cm in diameter), and low-cost. The camera, which has about 2000 pixels of size 6x6 mm^2, covers a field of view of 10°. The dual mirror telescopes and their cameras are being developed by three consortia, ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana, Italy/INAF), GATE (Gamma-ray Telescope Elements, France/Paris Observ.) and CHEC (Compact High Energy Camera, universities in UK, US and Japan) which are merging their efforts in order to finalize an end-to-end design that will be constructed for CTA. A number of prototype structures and cameras are being developed in order to investigate various alternative designs. In this contribution, these designs are presented, along with the technological solutions under study.

astro-ph.IM↗

arXiv2013

Expected performance of the ASTRI-SST-2M telescope prototype

ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) is an Italian flagship project pursued by INAF (Istituto Nazionale di Astrofisica) strictly linked to the development of the Cherenkov Telescope Array, CTA. Primary goal of the ASTRI program is the design and production of an end-to-end prototype of a Small Size Telescope for the CTA sub-array devoted to the highest gamma-ray energy region. The prototype, named ASTRI SST-2M, will be tested on field in Italy during 2014. This telescope will be the first Cherenkov telescope adopting the double reflection layout in a Schwarzschild-Couder configuration with a tessellated primary mirror and a monolithic secondary mirror. The collected light will be focused on a compact and light-weight camera based on silicon photo-multipliers covering a 9.6 deg full field of view. Detailed Monte Carlo simulations have been performed to estimate the performance of the planned telescope. The results regarding its energy threshold, sensitivity and angular resolution are shown and discussed.

astro-ph.IM↗

arXiv2013

Towards the ASTRI mini-array

The Cherenkov Telescope Array (CTA) will consist of an array of three types of telescopes covering a wide energy range, from tens of GeV up to more than 100 TeV. The high energy section (> 3 TeV) will be covered by the Small Size Telescopes (SST). ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) is a flagship project of the Italian Ministry of Research and Education led by INAF, aiming at the design and construction of a prototype of the Dual Mirror SST. In a second phase the ASTRI project foresees the installation of the first elements of the SST array at the CTA southern site, a mini-array of 5-7 telescopes. The optimization of the layout of this mini-array embedded in the SST array of the CTA Observatory has been the object of an intense simulation effort. In this work we present the expected mini-array performance in terms of energy threshold, angular and energy resolution and sensitivity.

astro-ph.IM↗

arXiv2013

Quench Dynamics in Randomly Generated Extended Quantum Models

We analyze the thermalization properties and the validity of the Eigenstate Thermalization Hypothesis in a generic class of quantum Hamiltonians where the quench parameter explicitly breaks a Z_2 symmetry. Natural realizations of such systems are given by random matrices expressed in a block form where the terms responsible for the quench dynamics are the off-diagonal blocks. Our analysis examines both dense and sparse random matrix realizations of the Hamiltonians and the observables. Sparse random matrices may be associated with local quantum Hamiltonians and they show a different spread of the observables on the energy eigenstates with respect to the dense ones. In particular, the numerical data seems to support the existence of rare states, i.e. states where the observables take expectation values which are different compared to the typical ones sampled by the micro-canonical distribution. In the case of sparse random matrices we also extract the finite size behavior of two different time scales associated with the thermalization process.

cond-mat.stat-mech↗

arXiv2013

The ASTRI Project: a mini-array of dual-mirror small Cherenkov telescopes for CTA

ASTRI is a flagship project of the Italian Ministry of Education, University and Research, which aims to develop an end-to-end prototype of the CTA small-size telescope. The proposed design is characterized by a dual-mirror Schwarzschild-Couder configuration and a camera based on Silicon photo-multipliers, two challenging but innovative technological solutions which will be adopted for the first time on a Cherenkov telescope. Here we describe the current status of the project, the expected performance and the possibility to realize a mini-array composed by a few small-size telescopes, which shall be placed at the final CTA Southern Site.

astro-ph.IM↗

arXiv2012

PSR J0357+3205: a fast moving pulsar with a very unusual X-ray trail

The middle-aged PSR J0357+3205 is a nearby, radio-quiet, bright gamma-ray pulsar discovered by the Fermi mission. Our previous Chandra observation revealed a huge, very peculiar structure of diffuse X-ray emission, originating at the pulsar position and extending for > 9' on the plane of the sky. To better understand the nature of such a nebula, we have studied the proper motion of the parent pulsar. We performed relative astrometry on Chandra images of the field spanning a time baseline of 2.2 yr, unveiling a significant angular displacement of the pulsar counterpart, corresponding to a proper motion of 0.165"+/-0.030" yr^(-1). At a distance of ~500 pc, the space velocity of the pulsar would be of ~390 km s^(-1) assuming no inclination with respect to the plane of the sky. The direction of the pulsar proper motion is perfectly aligned with the main axis of the X-ray nebula, pointing to a physical, yet elusive link between the nebula and the pulsar space velocity. No optical emission in the H_alpha line is seen in a deep image collected at the Gemini telescope, which implies that the interstellar medium into which the pulsar is moving is fully ionized.

astro-ph.HE↗

arXiv2012

The magnetar candidate AX J1818.8-1559

In October 2007 a hard X-ray burst was detected by the INTEGRAL satellite from a direction consistent with the position of AX J1818.8-1559, an X-ray source at low Galactic latitude discovered with the ASCA satellite in 1996-1999. The short duration (0.8 s) and soft spectrum (power law photon index of 3.0+/-0.2) of the burst in the 20-100 keV range are typical of Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars. We report on the results of an observation of AX J1818.8-1559 obtained with the Suzaku satellite in October 2011. The source spectrum, a power law with photon index 1.5, and flux 2x10^{-12} erg cm^-2 s^-1 (2-10 keV), do not show significant variations with respect to the values derived from archival data of various satellites (ROSAT, XMM-Newton, Chandra, Swift) obtained from 1993 to 2011. We discuss possible interpretations for AX J1818.8-1559 and, based on its association with the INTEGRAL burst, we propose it as a new member of the small class of magnetar candidates.

astro-ph.HE↗