1,289 research outputs found
Hadronic gamma-ray images of Sedov supernova remnants
A number of modern experiments in high-energy astrophysics produce images of
supernova remnants (SNRs) in the TeV and GeV gamma-rays. Either relativistic
electrons (due to the inverse-Compton scattering) or protons (due to the pion
decays) may be responsible for this emission. In particular, the broad-band
spectra of SNRs may be explained in both leptonic and hadronic scenarios.
Another kind of observational data, namely, images of SNRs, is an important
part of experimental information. We present a method to model gamma-ray images
of Sedov SNRs in uniform media and magnetic field due to hadronic emission.
These gamma-rays are assumed to appear as a consequence of meson decays
produced in inelastic collisions of accelerated protons with thermal protons
downstream of the shock - a model would be relevant for SNRs without firm
confirmations of the shock-cloud interaction, as e.g. SN1006. Distribution of
surface brightness of the shell-like SNR is synthesized numerically for a
number of configurations. An approximate analytical formula for azimuthal and
radial variation of hadronic gamma-ray brightness close to the shock is
derived. The properties of images as well as the main factors determining the
surface brightness distribution are determined. Some conclusions which would be
relevant to SN1006 are discussed.Comment: 11 pages, 7 figures, to be published in MNRA
Thermal X-ray composites as an effect of projection
A new possibility to explain the nature of thermal X-ray composites (TXCs),
i.e. a class of supernova remnants (SNRs) with a thermal X-ray centrally-filled
morphology within a radio shell, as a projection effect of the 2- or
3-dimensional shell-like SNR evolved in a nonuniform medium with scale-height
<10 pc is proposed. Both X-ray and radio morphologies, as well as the basic
theoretical features of this kind of SNR and the surrounding medium, are
considered. Theoretical properties of a shell-like SNR evolved at the edge of a
molecular cloud correspond to the observed properties of TXCs if the gradient
of the ambient density does not lie in the projection plane and the magnetic
field is nearly aligned with the line of sight. So, at least a part of objects
from the class may be interpreted within the framework of the considered
effect. The proposed model suggests that SNRs with barrel-like radio and
centrally-brightened thermal X-ray morphologies should exist. The model allows
us to consider TXCs as prospective sources of proton origin gamma-rays.Comment: 7 pages, 4 figures; added one figure, few subsections and references,
corrected typos; accepted for publication in A&
Observational constraints on the modeling of SN1006
Experimental spectra and images of the supernova remnant SN1006 have been
reported for radio, X-ray and TeV gamma-ray bands. Several comparisons between
models and observations have been discussed in the literature, showing that the
broad-band spectrum from the whole remnant as well as a sharpest radial profile
of the X-ray brightness can be both fitted by adopting a model of SN1006 which
strongly depends on the non-linear effects of the accelerated cosmic rays;
these models predict post-shock magnetic field (MF) strengths of the order of
150 micro G. Here we present a new way to compare models and observations, in
order to put constraints on the physical parameters and mechanisms governing
the remnant. In particular, we show that a simple model based on the classic
MHD and cosmic rays acceleration theories allows us to investigate the
spatially distributed characteristics of SN1006 and to put observational
constraints on the kinetics and MF. Our method includes modelling and
comparison of the azimuthal and radial profiles of the surface brightness in
radio, hard X-rays and TeV gamma-rays as well as the azimuthal variations of
the electron maximum energy. In addition, this simple model also provides good
fits to the radio-to-gamma-ray spectrum of SN1006. We find that our best-fit
model predicts an effective MF strength inside SN1006 of 32 micro G, in good
agreement with the `leptonic' model suggested by the HESS Collaboration (2010).
Finally, some difficulties in both the `classic' and the non-linear models are
discussed. A number of evidences about non-uniformity of MF around SN1006 are
noted.Comment: 15 pages, 13 figures, accepted for publication on MNRA
Some properties of synchrotron radio and inverse-Compton gamma-ray images of supernova remnants
The synchrotron radio maps of supernova remnants (SNRs) in uniform
interstellar medium and interstellar magnetic field (ISMF) are analyzed,
allowing different `sensitivity' of injection efficiency to the shock
obliquity. The very-high energy gamma-ray maps due to inverse Compton process
are also synthesized. The properties of images in these different wavelength
bands are compared, with particular emphasis on the location of the bright
limbs in bilateral SNRs. Recent H.E.S.S. observations of SN 1006 show that the
radio and IC gamma-ray limbs coincide, and we found that this may happen if: i)
injection is isotropic but the variation of the maximum energy of electrons is
rather quick to compensate for differences in magnetic field; ii) obliquity
dependence of injection (either quasi-parallel or quasi-perpendicular) and the
electron maximum energy is strong enough to dominate magnetic field variation.
In the latter case, the obliquity dependence of the injection and the maximum
energy should not be opposite. We argue that the position of the limbs alone
and even their coincidence in radio, X-rays and gamma-rays, as it is discovered
by H.E.S.S. in SN 1006, cannot be conclusive about the dependence of the
electron injection efficiency, the compression/amplification of ISMF and the
electron maximum energy on the obliquity angle.Comment: Accepted for publication in MNRA
Analytic Solutions for the Evolution of Radiative Supernova Remnants
We present the general analytic solution for the evolution of radiative
supernova remnants in a uniform interstellar medium, under thin-shell
approximation. This approximation is shown to be very accurate approach to this
task. For a given set of parameters, our solution closely matches the results
of numerical models, showing a transient in which the deceleration parameter
reaches a maximum value of 0.33, followed by a slow convergence to the
asymptotic value 2/7. Oort (1951) and McKee and Ostriker (1977) analytic
solutions are discussed, as special cases of the general solution we have
found.Comment: 5 pages, 1 figure, Astronomy and Astrophysics, accepte
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