2,599 research outputs found
Testing the homogeneous synchrotron self Compton model for gamma ray production in Mrk 421
Based on the detected variability time scales of X-ray and TeV gamma-ray
emission, and the observed multiwavelength photon spectrum, of Mrk 421 we place
constraints on the allowed parameter space (magnetic field and Doppler factor
of the emission region) for the homogeneous synchrotron self-Compton model. The
spectra calculated for the allowed parameters are marginally consistent with
the available spectral information above TeV reported by the Whipple
Observatory in the case of a 1 day flare time scale. However, for the recently
reported very short duration flares varying on a time scale of 15 min, the
calculated spectra are significantly steeper, suggesting that the homogeneous
synchrotron self Compton model has problems in describing the relatively flat
observed spectra extending above a few TeV. We determine the maximum ratio of
TeV gamma-ray luminosity to X-ray luminosity during flaring which is allowed by
the homogeneous synchrotron self-Compton model for the case of no significant
photon-photon absorption in the source.Comment: 5 pages, 2 figures, LaTeX uses mn.sty, submitted to MNRA
Gamma rays from interactions of stars with AGN jets
We have developed a model for gamma ray emission in jets of active galactic
nuclei in which particle acceleration takes place at a shock in the
relativistic jet plasma due to a massive star in the central region of the host
galaxy moving through the jet. The gamma rays are produced in a pair-Compton
cascade in the radiation field of the star initiated by accelerated electrons.
Our model may account for the observed GeV to TeV gamma ray spectrum and
variability of Markarian 421 and other blazars detected by the EGRET instrument
on the Compton Gamma Ray Observatory.Comment: 5 pages, 3 figures, latex (uses mn.sty), submitted to MNRA
The physical parameters of Markarian 501 during flaring activity
We determine the physical parameters (magnetic field and Doppler factor) of
the homogeneous synchrotron self-Compton model allowed by the observed X-ray to
gamma-ray spectra and variability of Markarian~501 during the 15-16 April 1997
flaring activity. We find that magnetic fields between 0.07 G and 0.6 G and
Doppler factors between 12 and 36 could fit (depending on observed variability
time scale) these observations. We take account of photon-photon pair
production interactions of gamma-ray photons occurring both inside the emission
region and during propagation to Earth and find these to be extremely important
in correctly determining the allowed model parameters. Previous estimates of
the allowed parameter space have neglected this effect. Future multi-wavelength
campaigns during strong flaring activity, including observations from optical
to TeV gamma-rays, should enable the physical parameters to be further
constrained.Comment: 18 pages, 5 figures, minor changes, additional reference, accepted
for publication in MNRA
Optical depths for gamma-rays in the radiation field of a star heated by external X-ray source in LMXBs: Application to Her X-1 and Sco X-1
The surface of a low mass star inside a compact low mass X-ray binary system
(LMXB) can be heated by the external X-ray source which may appear due to the
accretion process onto a companion compact object (a neutron star or a black
hole). As a result, the surface temperature of the star can become
significantly higher than it is in the normal state resulting from
thermonuclear burning. We wonder whether high energy electrons and gamma-rays,
injected within the binary system, can efficiently interact with this enhanced
radiation field. To decide this, we calculate the optical depths for the
gamma-ray photons in the radiation field of such irradiated star as a function
of the phase of the binary system. Based on these calculations, we conclude
that compact low mass X-ray binary systems may also become sources of high
energy gamma-rays since conditions for interaction of electrons and gamma-rays
are quite similar to these ones observed within the high mass TeV gamma-ray
binaries such as LS 5039 and LSI 303 +61. However, due to differences in the
soft radiation field, the expected gamma-ray light curves can significantly
differ between low mass and high mass X-ray binaries. As an example, we apply
such calculations to two well known LMXBs: Her X-1 and Sco X-1. It is concluded
that electrons accelerated to high energies inside these binaries should find
enough soft photon target from the companion star for efficient gamma-ray
production.Comment: 10 pages, 8 figures, accepted to A&
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