105 research outputs found
On Spectral and Temporal Variability in Blazars and Gamma Ray Bursts
A simple model for variability in relativistic plasma outflows is studied, in
which nonthermal electrons are continuously and uniformly injected in the
comoving frame over a time interval dt. The evolution of the electron
distribution is assumed to be dominated by synchrotron losses, and the energy-
and time-dependence of the synchrotron and synchrotron self-Compton (SSC)
fluxes are calculated for a power-law electron injection function with index s
= 2. The mean time of a flare or pulse measured at photon energy E with respect
to the onset of the injection event varies as E^{-1/2} and E^{-1/4} for
synchrotron and SSC processes, respectively, until the time approaches the
limiting intrinsic mean time (1+z)dt/(2 D), where z is the redshift and D is
the Doppler factor. This dependence is in accord with recent analyses of blazar
and GRB emissions, and suggests a method to discriminate between external
Compton and SSC models of high-energy gamma radiation from blazars and GRBs.
The qualititative behavior of the X-ray spectral index/flux relation observed
from BL Lac objects can be explained with this model. This demonstrates that
synchrotron losses are primarily responsible for the X-ray variability behavior
and strengthens a new test for beaming from correlated hard X-ray/TeV
observations.Comment: 10 pages, 2 figures, accepted for publication in Astrophysical
Journal Letters; uses aaspp4.sty, epsf.st
The ASCA X-ray spectrum of the powerful radio galaxy 3C109
We report the results from an ASCA X-ray observation of the powerful Broad
Line Radio Galaxy, 3C109. The ASCA spectra confirm our earlier ROSAT detection
of intrinsic X-ray absorption associated with the source. The absorbing
material obscures a central engine of quasar-like luminosity. The luminosity is
variable, having dropped by a factor of two since the ROSAT observations 4
years before. The ASCA data also provide evidence for a broad iron emission
line from the source, with an intrinsic FWHM of ~ 120,000 km/s. Interpreting
the line as fluorescent emission from the inner parts of an accretion disk, we
can constrain the inclination of the disk to be degree, and the inner
radius of the disk to be Schwarzschild radii. Our results support
unified schemes for active galaxies, and demonstrate a remarkable similarity
between the X-ray properties of this powerful radio source, and those of lower
luminosity, Seyfert 1 galaxies.Comment: MNRAS in press. 7 pages, 5 figures in MNRAS LaTex styl
ASCA Observations of Blazars and Multiband Analysis
We present data for 18 blazars observed with ASCA, half of which were also
observed contemporaneously with EGRET as parts of multi-wavelength campaigns.
The observations show a clear difference in the spectra between three
subclasses of blazars, namely the High-energy peaked BL Lac objects (HBLs),
Low-energy peaked BL Lac objects (LBLs), and quasar-hosted blazars (QHBs). We
find that the radiation process responsible for the HE peak for HBLs can be
explained solely by Synchrotron-Self-Compton (SSC) emission, with the Doppler
factor consistent with the VLBI and/or gamma-ray variability data. For many
QHBs, on the other hand, the gamma-rays cannot be solely due to the SSC
mechanism unless the Doppler factor is significantly in excess of that inferred
from VLBI data. We consider an alternative scenario consistent with the
measured values of the Doppler factor, where the SSC component is still present
in QHBs and it dominates in the X-ray band, but it is below the observed
gamma-ray spectrum. With an assumption that the peak of the SSC emission is on
the extrapolation of the X-ray spectrum, and adopting the Doppler factor of 10,
we infer the magnetic field to be 0.1 - 1 Gauss, and Lorentz factors of
electrons radiating at the peak of the nu F(nu) spectrum of 10^3 for QHBs; this
is much lower than 10^5 for HBLs. This difference is most likely due to the
large photon density expected in QHBs.Comment: 24 pages, 4 figures, AAS Latex macro v4.0, to appear in The
Astrophysical Journa
研究速報 : A METHOD OF PATTERN RECOGNITION BY REGION COUNTER : FREE FROM SIZE, DEFORMATION AND ROTATION OF THE PATTERN
A simplified interpolation and conversion method of contour surface model to mesh surface model
研究速報 : A METHOD OF PATTERN RECOGNITION BY REGION COUNTER : FREE FROM SIZE, DEFORMATION AND ROTATION OF THE PATTERN
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