423 research outputs found
On proton synchrotron blazar models: the case of quasar 3C 279
In the present work we propose an innovative estimation method for the
minimum Doppler factor and energy content of the gamma-ray emitting region of
quasar 3C 279, using a standard proton synchrotron blazar model and the
principles of automatic photon quenching. The latter becomes relevant for high
enough magnetic fields and results in spontaneous annihilation of gamma-rays.
The absorbed energy is then redistributed into electron-positron pairs and soft
radiation. We show that as quenching sets an upper value for the source
rest-frame gamma-ray luminosity, one has, by neccessity, to resort to Doppler
factors that lie above a certain value in order to explain the TeV
observations. The existence of this lower limit for the Doppler factor has also
implications on the energetics of the emitting region. In this aspect, the
proposed method can be regarded as an extension of the widely used one for
estimating the equipartition magnetic field using radio observations. In our
case, the leptonic synchrotron component is replaced by the proton synchrotron
emission and the radio by the VHE gamma-ray observations. We show specifically
that one can model the TeV observations by using parameter values that minimize
both the energy density and the jet power at the cost of high-values of the
Doppler factor. On the other hand, the modelling can also be done by using the
minimum possible Doppler factor; this, however, leads to a particle dominated
region and high jet power for a wide range of magnetic field values. Despite
the fact that we have focused on the case of 3C 279, our analysis can be of
relevance to all TeV blazars favoring hadronic modelling that have, moreover,
simultaneous X-ray observations.Comment: 12 pages, 11 figures, 1 Table, accepted for publication in MNRA
Identification of two new HMXBs in the LMC: a 2013 s pulsar and a probable SFXT
We report on the X-ray and optical properties of two high-mass X-ray binary
systems located in the Large Magellanic Cloud (LMC). Based on the obtained
optical spectra, we classify the massive companion as a supergiant star in both
systems. Timing analysis of the X-ray events collected by XMM-Newton revealed
the presence of coherent pulsations (spin period 2013 s) for XMMU
J053108.3-690923 and fast flaring behaviour for XMMU J053320.8-684122. The
X-ray spectra of both systems can be modelled sufficiently well by an absorbed
power-law, yielding hard spectra and high intrinsic absorption from the
environment of the systems. Due to their combined X-ray and optical properties
we classify both systems as SgXRBs: the 19 confirmed X-ray pulsar
and a probable supergiant fast X-ray transient in the LMC, the second such
candidate outside our Galaxy.Comment: 12 pages, 10 figures, accepted for publication in MNRA
Afterglow emission in the context of an ‘one-zone’ radiation-acceleration model
In the present work we focus on the interplay between stochastic acceleration of charged particles and radiation processes in a region of turbulent magnetized plasma, setting the framework for an ‘one-zone’ radiation-acceleration model for Gamma-Ray Burst (GRB) afterglows. Specifically, we assume that the particle distribution is isotropic in space and treat in detail the particle propagation in the momentum-space. The electron distibution is modified by the acceleration, synchrotron and Synchrotron Self-Compton (SSC) radiation and escape processes. The magnetic field as well as the particle injection rate are functions of time as measured in the comoving frame of the blast wave. In order to study the dynamical evolution of this system, we numerically solve the time-dependent Fokker-Planck equation for the electron distribution and present the obtained particle and photon spectra of an indicative example
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