677 research outputs found
Modeling the Radio and X-ray Emission of SN 1993J and SN 2002ap
Modeling of radio and X-ray observations of supernovae interacting with their
circumstellar media are discussed, with special application to SN 1993J and SN
2002ap. We emphasize the importance of including all relevant physical
mechanisms, especially for the modeling of the radio light curves. The
different conclusions for the absorption mechanism (free-free or synchrotron
self-absorption), as well as departures from an CSM, as
inferred by some authors, are discussed in detail. We conclude that the
evidence for a variation in the mass loss rate with time is very weak. The
results regarding the efficiencies of magnetic field generation and
relativistic particle acceleration are summarized.Comment: 10 pages, 2 figures. Uses svmult.cls. To appear in proceedings of IAU
Colloquium 192 "Supernovae (10 years of SN 1993J)", April 2003, Valencia,
Spain, eds. J. M. Marcaide and K. W. Weile
Circumstellar interaction in supernovae in dense environments - an observational perspective
In a supernova explosion, the ejecta interacting with the surrounding
circumstellar medium (CSM) give rise to variety of radiation. Since CSM is
created from the mass lost from the progenitor star, it carries footprints of
the late time evolution of the star. This is one of the unique ways to get a
handle on the nature of the progenitor star system. Here, I will focus mainly
on the supernovae (SNe) exploding in dense environments, a.k.a. Type IIn SNe.
Radio and X-ray emission from this class of SNe have revealed important
modifications in their radiation properties, due to the presence of high
density CSM. Forward shock dominance of the X-ray emission, internal free-free
absorption of the radio emission, episodic or non-steady mass loss rate,
asymmetry in the explosion seem to be common properties of this class of SNe.Comment: Fixed minor typos. 31 pages, 9 figures, accepted for publication in
Space Science Reviews. Chapter in International Space Science Institute
(ISSI) Book on "Supernovae" to be published in Space Science Reviews by
Springe
Supernova Interaction with a Circumstellar Medium
The explosion of a core collapse supernova drives a powerful shock front into
the wind from the progenitor star. A layer of shocked circumstellar gas and
ejecta develops that is subject to hydrodynamic instabilities. The hot gas can
be observed directly by its X-ray emission, some of which is absorbed and
re-radiated at lower frequencies by the ejecta and the circumstellar gas.
Synchrotron radiation from relativistic electrons accelerated at the shock
fronts provides information on the mass loss density if free-free absorption
dominates at early times or the size of the emitting region if synchrotron
self-absorption dominates. Analysis of the interaction leads to information on
the density and structure of the ejecta and the circumstellar medium, and the
abundances in these media. The emphasis here is on the physical processes
related to the interaction.Comment: 22 pages, 7 figures, to appear as a Chapter in "Supernovae and
Gamma-Ray Bursts," edited by K. W. Weiler (Springer-Verlag
Self-consistent stability analysis of spherical shocks.
In this paper, we study self-similar solutions, and their linear stability as well, describing the flow within a spherical shell with finite thickness, expanding according to a power law of time, t q , where q>0. The shell propagates in a medium with initially uniform density and it is bounded by a strong shock wave at its outer border while the inner face is submitted to a time-dependent uniform pressure. For q=2/5, the well-known Sedov–Taylor solution is recovered. In addition, although both accelerated and decelerated shells can be unstable against dynamic perturbations, they exhibit highly different behaviors. Finally, the dispersion relation derived earlier by Vishniac (Vishniac, E.T. in Astrophys. J. 274:152, 1983) for an infinitely thin shell is obtained in the limit of an isothermal shock wave
Low frequency radio and X-ray properties of core-collapse supernovae
Radio and X-ray studies of young supernovae probe the interaction between the
supernova shock waves and the surrounding medium and give clues to the nature
and past of the progenitor star. Here we discuss the early emission from type
Ic SN 2002ap and argue that repeated Compton boosting of optical photons by hot
electrons presents the most natural explanation of the prompt X-ray emission.
We describe the radio spectrum of another type Ic SN 2003dh (GRB030329)
obtained with combined GMRT and VLA data. We report on the low frequency radio
monitoring of SN 1995N and our objectives of distinguishing between competing
models of X-ray emission from this SN and the nature of its progenitor by X-ray
spectroscopy. Radio studies on SN 2001gd, SN 2001ig and SN 2002hh are
mentioned.Comment: 5 pages, 4 figures. Uses svmult.cls. To appear in proceedings of IAU
Colloquium 192 "Supernovae (10 years of SN 1993J)", April 2003, Valencia,
Spain, eds. J. M. Marcaide and K. W. Weile
Numerical studies on the structure of the cosmic ray electron halo in starburst galaxies
The structure of the cosmic ray electron halo of a starburst galaxy depends
strongly on the nature of galactic wind and the configuration of the magnetic
field. We have investigated these dependencies by solving numerically the
propagation of electrons originating in starburst galaxies, most likely in
supernova remnants. The calculations are made for several models for the
galactic winds and for the configuration of the magnetic fields for comparison
with observations. Our simulation of a quasi-radio halo reproduces both the
extended structure of ~ 9 kpc and the subtle hollow structure near the polar
region of the radio halo that are observed in the starburst galaxy NGC 253.
These findings suggest the existence of strong galactic wind in NGC 253.Comment: 4 pages, 6 figures, to appear in Proceeding of the conference "The
multi messenger approach to high energy gamma ray sources", Barcelona, July
200
The X-ray nebula around the Seyfert 2 galaxy NGC4388
We report on X-ray emission from the Seyfert 2 galaxy NGC4388 observed with
the Chandra X-ray Observatory. A hard X-ray peak is found at the position of
the active nucleus suggested by optical and radio observations. Extended soft
X-ray emission correlates well with the ionization cone found in optical line
emission. A large soft X-ray extension is found up to 16 kpc to the north of
the galaxy. Photoionized gas with low ionization parameters (xi<3) appears to
be the likely explanation of this emission. The same ionized gas clouds could
be responsible for the optical [OIII] emission. Fe K line emission from cold
material is found to be extended by a few kpc.Comment: 12 pages, one colour figure included, MNRAS in pres
Guiding the Way to Gamma-Ray Sources: X-ray Studies of Supernova Remnants
Supernova remnants have long been suggested as a class of potential
counterparts to unidentified gamma-ray sources. The mechanisms by which such
gamma-rays can arise may include emission from a pulsar associated with a
remnant, or a variety of processes associated with energetic particles
accelerated by the SNR shock. Imaging and spectral observations in the X-ray
band can be used to identify properties of the remnants that lead to gamma-ray
emission, including the presence of pulsar-driven nebulae, nonthermal X-ray
emission from the SNR shells, and the interaction of SNRs with dense
surrounding material.Comment: 16 pages, 11 figures, To appear in the proceedings of the workshop:
"The Nature of the Unidentified Galactic Gamma-Ray Sources" held at INAOE,
Mexico, October 2000, (A.Carraminana, O. Reiner and D. Thompson, eds.
Non-stationary Rayleigh-Taylor instability in supernovae ejecta
The Rayleigh-Taylor instability plays an important role in the dynamics of
several astronomical objects, in particular, in supernovae (SN) evolution. In
this paper we develop an analytical approach to study the stability analysis of
spherical expansion of the SN ejecta by using a special transformation in the
co-moving coordinate frame. We first study a non-stationary spherical expansion
of a gas shell under the pressure of a central source. Then we analyze its
stability with respect to a no radial, non spherically symmetric perturbation
of the of the shell. We consider the case where the polytropic constant of the
SN shell is and we examine the evolution of a arbitrary shell
perturbation. The dispersion relation is derived. The growth rate of the
perturbation is found and its temporal and spatial evolution is discussed. The
stability domain depends on the ejecta shell thickness, its acceleration, and
the perturbation wavelength.Comment: 16 page
Dynamic Evolution Model of Isothermal Voids and Shocks
We explore self-similar hydrodynamic evolution of central voids embedded in
an isothermal gas of spherical symmetry under the self-gravity. More
specifically, we study voids expanding at constant radial speeds in an
isothermal gas and construct all types of possible void solutions without or
with shocks in surrounding envelopes. We examine properties of void boundaries
and outer envelopes. Voids without shocks are all bounded by overdense shells
and either inflows or outflows in the outer envelope may occur. These
solutions, referred to as type void solutions, are further
divided into subtypes and
according to their characteristic behaviours across the sonic critical line
(SCL). Void solutions with shocks in envelopes are referred to as type
voids and can have both dense and quasi-smooth edges.
Asymptotically, outflows, breezes, inflows, accretions and static outer
envelopes may all surround such type voids. Both cases of
constant and varying temperatures across isothermal shock fronts are analyzed;
they are referred to as types and
void shock solutions. We apply the `phase net matching procedure' to construct
various self-similar void solutions. We also present analysis on void
generation mechanisms and describe several astrophysical applications. By
including self-gravity, gas pressure and shocks, our isothermal self-similar
void (ISSV) model is adaptable to various astrophysical systems such as
planetary nebulae, hot bubbles and superbubbles in the interstellar medium as
well as supernova remnants.Comment: 24 pages, 13 figuers, accepted by ApS
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