2,076 research outputs found
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
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
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
Synchrotron and Inverse Compton Constraints on Lorentz Violations for Electrons
We present a method for constraining Lorentz violation in the electron
sector, based on observations of the photons emitted by high-energy
astrophysical sources. The most important Lorentz-violating operators at the
relevant energies are parameterized by a tensor c^{nu mu) with nine independent
components. If c is nonvanishing, then there may be either a maximum electron
velocity less than the speed of light or a maximum energy for subluminal
electrons; both these quantities will generally depend on the direction of an
electron's motion. From synchrotron radiation, we may infer a lower bound on
the maximum velocity, and from inverse Compton emission, a lower bound on the
maximum subluminal energy. With observational data for both these types of
emission from multiple celestial sources, we may then place bounds on all nine
of the coefficients that make up c. The most stringent bound, on a certain
combination of the coefficients, is at the 6 x 10^(-20) level, and bounds on
the coefficients individually range from the 7 x 10^(-15) level to the 2 x
10^(-17) level. For most of the coefficients, these are the most precise bounds
available, and with newly available data, we can already improve over previous
bounds obtained by the same methods.Comment: 28 page
A Note on TeV Cerenkov Events as Bose-Einstein Gamma Condensations
The idea that the TeV air showers, thought to be produced by >10 TeV gamma
rays from Mrk 501, can be mimicked by coherent bunches of sub-TeV photons is
reexamined, focusing on fundamental considerations. In particular, it is shown
that the minimum spot size of the beam of pulsed TeV photons arriving at Earth
is on the order of a few kilometers, unless a lens with certain characteristics
is placed between the TeV laser and Earth. The viability of the laser
production mechanism proposed by Harwit et al. (2000) is also reassessed.Comment: 4 page
Searching for galactic cosmic ray pevatrons with multi-TeV gamma rays and neutrinos
The recent HESS detections of supernova remnant shells in TeV gamma-rays
confirm the theoretical predictions that supernova remnants can operate as
powerful cosmic ray accelerators. If these objects are responsible for the bulk
of galactic cosmic rays, then they should accelerate protons and nuclei to
10^15 eV and beyond, i.e. act as cosmic PeVatrons. The model of diffusive shock
acceleration allows, under certain conditions, acceleration of particles to
such high energies and their gradual injection into the interstellar medium,
mainly during the Sedov phase of the remnant evolution. The most energetic
particles are released first, while particles of lower energies are more
effectively confined in the shell, and are released at later epochs. Thus the
spectrum of nonthermal paticles inside the shell extends to PeV energies only
during a relatively short period of the evolution of the remnant. For this
reason one may expect spectra of secondary gamma-rays and neutrinos extending
to energies beyond 10 TeV only from T \lesssim 1000 yr old supernova remnants.
On the other hand, if by a chance a massive gas cloud appears in the \lesssim
100 pc vicinity of the supernova remnant, ``delayed'' multi-TeV signals of
gamma-rays and neutrinos arise when the most energetic partices emerged from
the supernova shell reach the cloud. The detection of such delayed emission of
multi-TeV gamma-rays and neutrinos allows indirect identification of the
supernova remnant as a particle PeVatron.Comment: ApJ Letters, in press. Reference to recent MILAGRO results adde
Ultrahigh energy gamma rays: Carriers of cosmological information
Observational data being the basis of contemporary cosmological models are not numerous: Hubble law of redshift for galaxies, element abundances, and observation of cosmic microwave background radiation (MBR). The significance of MBR discovery predicted in the Big-Band model is particularly stressed. Radio astronomical measurements give an information on MBR only near the Earth. Experimental confirmation of evolution of MBR, i.e., its probing in remote epochs, might obviously present a direct verification of the hypothesis of hot expanding Universe. The carriers of similar cosmological information should be particles which, firstly, effectively interact with MBR, and secondly, make it possible to identify unambiguously the epoch of interaction. A possibility to verify a number of cosmological hypotheses by searching the cutoffs in spectra of ultrahigh energy gamma-rays (UHEGR) from extragalactic sources is discussed
- …