719 research outputs found
Modelling of blazar SEDs with the nonlinear SSC cooling process
Observations of blazar flaring states reveal remarkably different variability
time scales. Especially rapid flares with flux doubling time scales of the
order of minutes have been puzzling for quite some time. Many modeling attempts
use the well known linear relations for the cooling and emission processes in
the jet in a steady-state scenario, albeit the obvious strongly time-dependent
nature of flares. Due to the feedback of self-produced radiation with
additional scattering by relativistic electrons, the synchrotron-self Compton
(SSC) effect is inherently time-dependent. Although this feedback is usually
implemented in numerical treatments, only recently an analytical analysis of
the effects of this nonlinear behaviour has been performed. Here, we report our
results concerning the effect of the time-dependent SSC on the spectral energy
distribution (SED) of blazars. We calculated analytically the synchrotron and
the SSC component, giving remarkably different spectral features compared to
the standard linear approach. Adding an external photon field to the original
setting, we could implement quite easily the effect of an additional external
Compton (EC) cooling, since such strong external photon fields are observed in
flat spectrum radio quasars (FSRQ), a subclass of blazars. Calculating the
resulting flux due to the EC cooling, we were able to show that the resulting
inverse Compton component strongly depends on the free parameters, and that SSC
could potentially have a strong effect in FSRQs, contrary to what is usually
assumed.Comment: Contribution to the GAMMA2012 conference in Heidelberg, to be
published in the AIP Proceedings "High Energy Gamma-Ray Astronomy, eds. F.
Aharonian, W. Hofmann, F. Rieger
The Extended Jet In AP Librae As The Source Of The VHE -ray Emission
Most modeling attempts of blazars use a small emission zone located close to
the central black hole in order to explain the broad-band spectral energy
distribution. Here we present a case where additionally to the small region a
kpc-scale jet is required to successfully reproduce the spectrum and
especially the TeV emission, namely the low-frequeny peaked BL Lac object AP
Librae detected in the TeV domain by the H.E.S.S. experiment. Given that other
parts of the spectral energy distribution follow the characteristics implied by
the source classification, the inverse Compton component spans 10 orders of
magnitude, which cannot be reproduced by the one-zone model. Additionally,
observational constraints in both the synchrotron and inverse Compton
compoenent strongly constrain the parameters of a self-consistent model ruling
out the possibility of TeV photon production in the vicinity of the galactic
center. We discuss the possibility that the TeV radiation is emitted by highly
energetic particles in the extended, arcsec-scale jet, which has been detected
at radio and X-ray energies. The slope of the jet X-ray spectrum indicates an
inverse Compton origin, and an extrapolation to higher energies coincides with
a break feature in the -ray band. Modeling the jet emission with
inverse Compton scattering of the cosmic microwave background results in an
excellent fit of the radio, X-ray and TeV emission. Implications will be
discussed, such as properties of the jet, acceleration scenarios, and
observations to test the model. If confirmed, large scale jets are able to
efficiently accelerate particles and to keep relativistic speeds up to
distances of several 100kpc.Comment: 5 pages, 1 figure, to appear in the AIP Conference proceedings of the
"High Energy Gamma-Ray Astronomy (Gamma2016)", edited by F. Aharonian, W.
Hofmann, F. Riege
Attenuation of TeV -rays by the starlight photon field of the host galaxy
The absorption of TeV -ray photons produced in relativistic jets by
surrounding soft photon fields is a long-standing problem of jet physics. In
some cases the most likely emission site close to the central black hole is
ruled out because of the high opacity caused by strong optical and infrared
photon sources, such as the broad line region. Mostly neglected for jet
modeling is the absorption of -rays in the starlight photon field of
the host galaxy. Analyzing the absorption for arbitrary locations and
observation angles of the -ray emission site within the host galaxy we
find that the distance to the galaxy center, the observation angle, and the
distribution of starlight in the galaxy are crucial for the amount of
absorption. We derive the absorption value for a sample of TeV detected
blazars with a redshift . The absorption value of the -ray
emission located in the galaxy center may be as high as with an average
value of . This is important in order to determine the intrinsic blazar
parameters. We see no significant trends in our sample between the degree of
absorption and host properties, such as starlight emissivity, galactic size,
half-light radius, and redshift. While the uncertainty of the spectral
properties of the extragalactic background light exceeds the effect of
absorption by stellar light from the host galaxy in distant objects, the latter
is a dominant effect in nearby sources. It may also be revealed in a
differential comparison of sources with similar redshifts.Comment: 9 pages, 4 figures; accepted for publication in MNRA
On the evolution of the particle distribution and the cascade in a moving, expanding emission region in blazar jets
There is a large variety in the models explaining blazar flares. Here, we
study the flare profile induced by a moving and expanding blob with special
emphasize on the gamma-gamma pair production. We first develop a simple
semi-analytical model to study the evolution of the particle distribution in
the expanding blob and show the influence of the pair production. In a second
step, we produce a realistic simulation using the OneHaLe code based upon
parameters of PKS 1510-089. The semi-analytical model shows that the pair
production significantly influences the flare evolution, while the opening
angle and the expansion can prolong flares considerably. The simulation based
on PKS 1510-089 indicate that flares of a moving expanding blob result in
strongly wavelength dependant light curves including delayed, secondary flares.
A moving, expanding blob can cause significant flaring events with a large
variety in light curve profiles. High-cadence multiwavelength observations are
necessary to derive the details causing the flare. Extended observations beyond
the initial burst may provide important information on the opening angle and
the particle content due to delayed secondary flares in some energy bands.Comment: 15 pages, 11 figures, accepted for publication in A&
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