arXiv subjects

Andrea Tramacere

Publications and source records attributed to Andrea Tramacere.

22 records · Page 2Linked to original sources

arXiv2013

The high-energy spectrum of 3C 273

The high energy spectral shape of 3C 273 is usually understood in terms of Inverse-Compton emission in a relativistic leptonic jet. This model predicts variability patterns and delays which could be tested if simultaneous observations are available from the infrared to the GeV range. The instruments IBIS, SPI, JEM-X on board INTEGRAL, PCA on board RXTE and LAT on board Fermi have enough sensitivity to follow the spectral variability from the keV to the GeV and to compare them with model predictions. We are presenting preliminary results on the high energy spectrum of 3C 273 and its variability and compare these results to predictions. We found that a single component is not able to adequately fit the multiwavelength spectrum (5 keV - 10 GeV) when the statistics in Fermi data is sufficient to constraint γ-ray emission. This suggests that the X-rays emission is not originated in the jet. A possible explanation could be that X-rays are dominated by a Seyfert-like thermal inverse Compton.

astro-ph.HE↗

arXiv2007

A MST algorithm for source detection in gamma-ray images

We developed a source detection algorithm based on the Minimal Spanning Tree (MST), that is a graph-theoretical method useful for finding clusters in a given set of points. This algorithm is applied to gamma-ray bidimensional images where the points correspond to the arrival direction of photons, and the possible sources are associated with the regions where they clusterize. Some filters to select these clusters and to reduce the spurious detections are introduced. An empirical study of the statistical properties of MST on random fields is carried in order to derive some criteria to estimate the best filter values. We introduce also two parameters useful to verify the goodness of candidate sources. To show how the MST algorithm works in the practice, we present an application to an EGRET observation of the Virgo field, at high galactic latitude and with a low and rather uniform background, in which several sources are detected.

astro-ph↗

arXiv2007

Spectral modelling of the high energy emission of the magnetar 4U 0142+614

We present an empirical spectral modelling of the high energy emission of the anomalous X-ray pulsar 4U 0142+614, based on simultaneous Swift and INTEGRAL observations from X to gamma-ray energies. We adopted models contained in the XSPEC analysis package, as well as models based on recent theoretical studies, and restricted ourselves to those combinations of up to three components which produce a good fit while requiring the lowest number of free parameters. Only three models were found to fit satisfactorily the 0.5-250keV spectrum of 4U 0142+614: i) a ~0.4keV blackbody and two power-laws, ii) a resonant cyclotron scattering model plus a power-law and iii) two log-parabolic functions. We found that only the latter two models do not over-predict the infrared/optical emission observed simultaneously from this AXP, and only the log-parabolic functions can naturally account for the upper limits set by COMPTEL in the gamma-ray range. A possible interpretation of the two log-parabolae in terms of inverse Compton scattering of soft X-ray photons by very energetic particles is discussed.

astro-ph↗

arXiv2003

A numerical code to study the variability of Blazar emission

We present a numerical code, written in C, which can be used to simulate or to analyze the emission of Blazars over the entire electromagnetic spectrum. Our code can reproduce the following features: synchrotron emission, inverse Compton emission (Thomson Klein-Nishina regime) external Compton emission, accretion disk variability using a Cellular Automata algorithm, temporal evolution of the emitting plasma energy distribution, flaring phenomena, light curves in the rest and in the observer frame (taking account for time crossing effects). In this paper we will show mainly the accretion disk simulation, and the implications in the External Compton scenario.

astro-ph↗