Application of the MST clustering to the high energy gamma-ray sky. III - New detections of gamma-ray emission from blazars

We present the results of a photon cluster search in the gamma-ray sky observed by the Fermi Large Area Telescope, using the new Pass 8 dataset, at energies higher than 10 GeV. By means of the Minimum Spanning Tree (MST) algorithm, we found 25 clusters associated with catalogued blazars not previously known as gamma-ray emitters. The properties of these sources are discussed.Comment: 10 pages, 3 figures. Accepted for publication in Astrophysics & Space Scienc

Application of the MST clustering to the high energy gamma-ray sky. I - New possible detection of high-energy gamma-ray emission associated with BL Lac objects

In this paper we show an application of the Minimum Spanning Tree (MST) clustering method to the high-energy gamma-ray sky observed at energies higher than 10 GeV in 6.3 years by the Fermi-Large Area Telescope. We report the detection of 19 new high-energy gamma-ray clusters with good selection parameters whose centroid coordinates were found matching the positions of known BL Lac objects in the 5th Edition of the Roma-BZCAT catalogue. A brief summary of the properties of these sources is presented.Comment: 11 pages, 7 figures. Accepted for publication in Astrophysics & Space Scienc

A new flaring high energy gamma-ray source

We report the detection of a new gamma-ray source in the Fermi-LAT sky using a source detection tool based on the Minimal Spanning Tree algorithm. The source, not reported in previous LAT catalogues but very recently observed in the X-rays and optical bands, is characterized by an increasing gamma-ray activity in 2012 June-September, reaching a weekly peak flux of (3.3+-0.6)*10^-7 photons cm^-2 s^-1. A search for a possible counterpart provides indication that it can be associated with the radio source NVSS J141828+354250 whose optical SDSS colours are typical of a blazar.Comment: 4 pages, 3 figures. Accepted for publication in Astronomy & Astrophysic

The optical to gamma-ray emission of the Crab pulsar: a multicomponent model

We present a multicomponent model to explain the features of the pulsed emission and spectrum of the Crab Pulsar, on the basis of X and gamma-ray observations obtained with BeppoSAX, INTEGRAL and CGRO. This model explains the evolution of the pulse shape and of the phase-resolved spectra, ranging from the optical/UV to the GeV energy band, on the assumption that the observed emission is due to more components. The first component, C_O, is assumed to have the pulsed double-peaked profile observed at the optical frequencies, while the second component, C_X, is dominant in the interpeak and second peak phase regions. The spectra of these components are modelled with log-parabolic laws and their spectral energy distributions have peak energies at 12.2 and 178 keV, respectively. To explain the properties of the pulsed emission in the MeV-GeV band, we introduce two more components, C_Ogamma and C_Xgamma, with phase distributions similar to those of C_O and C_X and log-parabolic spectra with the same curvature but peak energies at about 300 MeV and 2 GeV. This multicomponent model is able to reproduce both the broadband phase-resolved spectral behaviour and the changes of the pulse shape with energy. We also propose some possible physical interpretations in which C_O and C_X are emitted by secondary pairs via a synchrotron mechanism while C_Ogamma and C_Xgamma can originate either from Compton scattered or primary curvature photons.Comment: 14 pages, 16 figures; accepted by Astronomy and Astrophysic

Review of Cosmic Ray experiments with underground detectors

The most important underground detectors addressing Cosmic Ray physics are described, with a special emphasis on the description of the used technology.Comment: Invited talk at 6th International Conference on advanced Technology and Particle Physics, Villa Olmo, Como, Italy, October 5-9, 1998, To be published in Nucl. Phys. B, Proc. Supp

Further Constraints on Thermal Quiescent X-ray Emission from SAX J1808.4-3658

We observed SAX J1808.4-3658 (1808), the first accreting millisecond pulsar, in deep quiescence with XMM-Newton and (near-simultaneously) Gemini-South. The X-ray spectrum of 1808 is similar to that observed in quiescence in 2001 and 2006, describable by an absorbed power-law with photon index 1.74+-0.11 and unabsorbed X-ray luminosity L_X=7.9+-0.7*10^{31} ergs/s, for N_H=1.3*10^{21} cm^{-2}. Fitting all the quiescent XMM-Newton X-ray spectra with a power-law, we constrain any thermally emitting neutron star with a hydrogen atmosphere to have a temperature less than 30 eV and L_{NS}(0.01-10 keV)<6.2*10^{30} ergs/s. A thermal plasma model also gives an acceptable fit to the continuum. Adding a neutron star component to the plasma model produces less stringent constraints on the neutron star; a temperature of 36^{+4}_{-8} eV and L_{NS}(0.01-10 keV)=1.3^{+0.6}_{-0.8}*10^{31} ergs/s. In the framework of the current theory of neutron star heating and cooling, the constraints on the thermal luminosity of 1808 and 1H 1905+000 require strongly enhanced cooling in the cores of these neutron stars. We compile data from the literature on the mass transfer rates and quiescent thermal flux of the largest possible sample of transient neutron star LMXBs. We identify a thermal component in the quiescent spectrum of the accreting millisecond pulsar IGR J00291+5934, which is consistent with the standard cooling model. The contrast between the cooling rates of IGR J00291+5934 and 1808 suggests that 1808 may have a significantly larger mass. This can be interpreted as arising from differences in the binary evolution history or initial neutron star mass in these otherwise similar systems.Comment: ApJ in press, 7 pages, 2 color figure