77 research outputs found
Radio-to-TeV γ -ray emission from PSRB1259-63
We discuss theimplications of therecent X-ray and TeV γ-ray observations of thePSRB1259-63 system (a young rotation powered pulsar orbiting a Be star) for thetheoretical models of interaction of pulsar and stellar winds. We show that previously considered models have problems to account for the observed behaviour of thesystem. We develop amodel in which thebroad band emission from thebinary system is produced in result of collisions of GeV-TeV energy protons accelerated by thepulsar wind and interacting with thestellar disk. In this model thehigh energy γ-rays are produced in thedecays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton emission produced by low-energy (≤100MeV) electrons from thedecays of secondary charged π ± mesons. This model can explain not only theobserved energy spectra, but also thecorrelations between TeV, X-ray and radio emission component
Hour time-scale QPOs in the X-ray and radio emission of LS I +61303
LS I +61303 is an X-ray binary with a radio outburst every ~27
days. Previous studies of the stellar system revealed radio microflares
superimposed on the large radio outburst. We present here new radio
observations of LS I +61303 at 2.2 GHz with the Westerbork Synthesis
Radio Telescope (WSRT). Using various timing analysis methods we find
significant Quasi-Periodic Oscillations (QPOs) of 55 minutes stable over the
duration of 4 days. We also use archival data obtained from the Suzaku
satellite at X-ray wavelengths. We report here for the first time significant
X-ray QPOs of about 2 hours present over the time span of 21 hours. We compare
our results with the previously reported QPO observations and we conclude that
the QPOs seem to be associated with the radio outburst, independent of the
amplitude of the outburst. Finally, the different QPO time-scales are discussed
in the context of magnetic reconnection
A compact pulsar wind nebula model of the γ-ray-loud binary LS I +61○303
We study a model of LS I +61°303 in which its radio to TeV emission is due to interaction of a relativistic wind from a young pulsar with the wind from its companion Be star. The detailed structure of the stellar wind plays a critical role in explaining the properties of the system. We assume the fast polar wind is clumpy, which is typical for radiatively driven winds. The clumpiness and some plasma instabilities cause the two winds to mix. The relativistic electrons from the pulsar wind are retained in the moving clumps by inhomogeneities of the magnetic field, which explains the X-ray variability observed on time-scales much shorter than the orbital period. We calculate detailed inhomogeneous spectral models reproducing the average broad-band spectrum from radio to TeV. Given the uncertainties on the magnetic field within the wind and the form of the distribution of relativistic electrons, the X-ray spectrum could be dominated by either Compton or synchrotron emission. The recent Fermi observations constrain the high-energy cut-off in the electron distribution to be at the Lorentz factor of 2 × 104 or ∼108 in the former and latter model, respectively. We provide formulae comparing the losses of the relativistic electrons due to Compton, synchrotron and Coulomb processes versus the distance from the Be star. We calculate the optical depth of the wind to free-free absorption, showing that it will suppress most of the radio emission within the orbit, including the pulsed signal of the rotating neutron star. We point out the importance of Compton and Coulomb heating of the stellar wind within and around the γ-ray emitting region. Then, we find the most likely mechanism explaining the orbital modulation at TeV energies is anisotropy of emission, with relativistic electrons accelerated along the surface of equal ram pressure of the two winds. Pair absorption of the TeV emission suppresses one of the two maxima expected in an orbi
On the nature of the energy-dependent morphology of the composite multi-TeV gamma-ray source HESS J1702-420
HESS J1702-420 is a multi-TeV gamma-ray source with an unusual
energy-dependent morphology. The recent H.E.S.S. observations suggest that the
emission is well described by a combination of point-like HESS J1702-420A
(dominating at highest energies, 30 TeV ) and diffuse (
0.3) HESS J1702-420B (dominating below 5TeV) sources with
very hard () and soft ( ~2.6) power-law spectra,
respectively. Here we propose a model which postulates that the proton
accelerator is located at the position of HESS J1702-420A and is embedded into
a dense molecular cloud that coincides with HESS J1702-420B. In the proposed
model, the VHE radiation of HESS J1702-420 is explained by the pion-decay
emission from the continuously injected relativistic protons propagating
through a dense cloud. The energy-dependent morphology is defined by the
diffusive nature of the low-energy protons propagation, transiting sharply to
(quasi) ballistic propagation at higher energies. Adopting strong energy
dependence of the diffusion coefficient, with , we argue that HESS J1702-420 as the system of two gamma-ray sources is the
result of the propagation effect. Protons injected by a single accelerator at
the rate can reasonably reproduce the morphology and fluxes
of two gamma-ray components.Comment: accepted to Ap
Hadronic model for radio-to-TeV gamma-ray emission from PSR B1259-63
We discuss the implications of the recent X-ray and TeV gamma-ray
observations of the PSR B1259-63 system (a young rotation powered pulsar
orbiting a Be star) for the theoretical models of interaction of pulsar and
stellar winds. We show that previously considered models in which the pulsar
wind is purely electron loaded have problems to account for the observed
behaviour of the system in the TeV and X-ray bands. We develop a model in which
the broad band (radio, X-ray and high energy gamma-ray) emission from the
binary system is produced in result of collisions of GeV-TeV energy protons
accelerated by the pulsar wind and interacting with the stellar disk. In this
model the high energy gamma-rays are produced in the decays of secondary
neutral pions, while radio and X-ray emission are synchrotron and inverse
Compton emission produced by low-energy (< 100 MeV) electrons from the decays
of secondary charged pi mesons. This model can explain not only the observed
energy spectra, but also the correlations between TeV, X-ray and radio emission
components.Comment: Proceeding of "The multi messenger approach to high energy gamma ray
sources", Barcelona, June 200
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