2,535 research outputs found
Status of Identification of VHE gamma-ray sources
With the recent advances made by Cherenkov telescopes such as H.E.S.S., the
field of very high-energy (VHE) gamma-ray astronomy has recently entered a new
era in which for the first time populations of Galactic sources such as e.g.
Pulsar wind nebulae (PWNe) or Supernova remnants (SNRs) can be studied.
However, while some of the new sources can be associated by positional
coincidence as well as by consistent multi-wavelength data to a known
counterpart at other wavelengths, most of the sources remain not finally
identified. In the following, the population of Galactic H.E.S.S. sources will
be used to demonstrate the status of the identifications, to classify them into
categories according to this status and to point out outstanding problems.Comment: To appear in Astrophysics and Space Science (Proceedings of "The
multimessenger approach to unidentified gamma-ray sources
Recent Topics on Very High Energy Gamma-ray Astronomy
With the advent of imaging atmospheric Cherenkov telescopes in late 1980's,
ground-based observation of TeV gamma-rays came into reality after struggling
trials by pioneers for twenty years, and the number of gamma-ray sources
detected at TeV energies has increased to be over seventy now. In this review,
recent findings from ground-based very-high-energy gamma-ray observations are
summarized (as of 2008 March), and up-to-date problems in this research field
are presented.Comment: 6 pages, 4 figures, Proceedings of the International Workshop on
Advances in Cosmic Ray Science, March 17-19, 2008, Waseda University, Tokyo,
Japan; to be published in Journal of the Physical Society of Japan
(supplement
Proton synchrotron radiation of large-scale jets in active galactic nuclei
I propose a new mechanism for explanation of nonthernal X-ray emission of
large-scale AGN jets. Namely, I assume that this radiation has synchrotron
origin emitted by extremely high energy protons, and discuss implications of
this model for several prominent hot spots and knots resolved by Chandra in
Pictor A, 3C 120, PKS 0637-752, 3C 273.Comment: 17 pages, 8 figures, submitted to MNRA
TeV Gamma Rays from BL Lac Objects due to Synchrotron Radiation of Extremely High Energy Protons
One of remarkable features of the gamma ray blazar Markarian 501 is the
reported shape of the TeV spectrum, which during strong flares of the source
remains essentially stable despite dramatic variations of the absolute
gamma-ray flux. I argue that this (to a large extent unexpected) behavior of
the source could be explained assuming that the TeV gamma-ray emission is a
result of synchrotron radiation of extremely high energy protons in highly
magnetized compact regions of the jet.Comment: 33 pages, 10 figures, slighly revised version to be published in New
Astronom
Gamma Rays from Molecular Clouds
I discuss the spectral features of pi-0 decay gamma-radiation from
clouds/targets located in proximity of relatively young proton accelerators,
and speculate that such ``accelerator+target'' systems in our Galaxy can be
responsible for a subset of unidentified EGRET sources. Also, I argue that the
recent observations of high energy gamma-rays from the Orion complex contain
evidence that the level of the ``sea'' of galactic cosmic rays may differ
significantly from the flux and the spectrum of local (directly detected)
particles.Comment: The paper is based on presentations at 2 meetings of the workshop on
"The Astrophysics of Galactic Cosmic Rays" hosted by the International Space
Science Institute, Bern, October 1999 and May 2000; to be published in Space
Science Review
Constraining the Cosmic Background Light with four BL Lac TeV spectra
The intrinsic BL Lac spectra above few hundreds GeV can be very different
from the observed ones due to the absorption effects by the diffuse
Extragalactic Background Light (EBL), at present poorly known. With the recent
results, there are now 4 sources with good spectral information: Mkn 421
(z=0.031), Mkn 501 (z=0.034), 1ES 1426+428 (z=0.129) and 1ES 1959+650
(z=0.047). Making simple assumptions on the shape of the intrinsic spectra
(according to the present blazar knowledge), we have considered the effects of
different EBL spectral energy distributions (SED) for the first time on all 4
objects together, deriving constraints for the EBL fluxes. These resulted
significantly lower than many direct estimates.Comment: 4 pages, 8 figures; to appear in the proceedings of the 2nd Veritas
Symposium: "TeV Astrophysics of extragalactic sources". April 2003, Chicag
- …