1,120 research outputs found
Witnessing the gradual slow-down of powerful extragalactic jets: The X-ray -- optical -- radio connection
A puzzling feature of the {\it Chandra}--detected quasar jets is that their
X-ray emission decreases faster along the jet than their radio emission,
resulting to an outward increasing radio to X-ray ratio. In some sources this
behavior is so extreme that the radio emission peak is located clearly
downstream of that of the X-rays. This is a rather unanticipated behavior given
that the inverse
Compton nature of the X-rays and the synchrotron radio emission are
attributed to roughly the same electrons of the jet's non-thermal electron
distribution. In this note we show that this morphological behavior can result
from the gradual deceleration of a relativistic flow and that the offsets in
peak emission at different wavelengths carry the imprint of this deceleration.
This notion is consistent with another recent finding, namely that the jets
feeding the terminal hot spots of powerful radio galaxies and quasars are still
relativistic with Lorentz factors . The picture of the
kinematics of powerful jets emerging from these considerations is that they
remain relativistic as they gradually decelerate from Kpc scales to the hot
spots, where, in a final collision with the intergalactic medium, they
slow-down rapidly to the subrelativistic velocities of the hot spot advance
speed.Comment: Submitted in ApJ Letters on Jan. 14, 200
Rapid TeV variability in Blazars as result of Jet-Star Interaction
We propose a new model for the description of ultra-short flares from TeV
blazars by compact magnetized condensations (blobs), produced when red giant
stars cross the jet close to the central black hole. Our study includes a
simple dynamical model for the evolution of the envelope lost by the star in
the jet, and its high energy nonthermal emission through different leptonic and
hadronic radiation mechanisms. We show that the fragmented envelope of the star
can be accelerated to Lorentz factors up to 100 and radiate effectively the
available energy in gamma-rays predominantly through proton synchrotron
radiation or external inverse Compton scattering of electrons. The model can
readily explain the minute-scale TeV flares on top of longer (typical
time-scales of days) gamma-ray variability as observed from the blazar PKS
2155-304. In the framework of the proposed scenario, the key parameters of the
source are robustly constrained. In the case of proton synchrotron origin of
the emission a mass of the central black hole of , a total jet power of and a Doppler factor, of the gamma-ray emitting blobs, of
are required. Whilst for the external inverse Compton model,
parameters of
, and the are required.Comment: 25 pages, 11 figures, Submitted to Ap
Time dependent spectral modeling of Markarian 421 during a violent outburst in 2010
We present the results of extensive modeling of the spectral energy
distributions (SEDs) of the closest blazar (z=0.031) Markarian 421 (Mrk 421)
during a giant outburst in February 2010. The source underwent rapid flux
variations in both X-rays and very high energy (VHE) gamma-rays as it evolved
from a low-flux state on 2010 February 13-15 to a high-flux state on 2010
February 17. During this period, the source exhibited significant spectral
hardening from X-rays to VHE gamma-rays while exhibiting a "harder when
brighter" behavior in these energy bands. We reproduce the broadband SED using
a time-dependent multi-zone leptonic jet model with radiation feedback. We find
that an injection of the leptonic particle population with a single power-law
energy distribution at shock fronts followed by energy losses in an
inhomogeneous emission region is suitable for explaining the evolution of Mrk
421 from low- to high-flux state in February 2010. The spectral states are
successfully reproduced by a combination of a few key physical parameters, such
as the maximum minimum cutoffs and power-law slope of the electron
injection energies, magnetic field strength, and bulk Lorentz factor of the
emission region. The simulated light curves and spectral evolution of Mrk 421
during this period imply an almost linear correlation between X-ray flux at
1-10 keV energies and VHE gamma-ray flux above 200 GeV, as has been previously
exhibited by this source. Through this study, a general trend that has emerged
for the role of physical parameters is that, as the flare evolves from a low-
to a high-flux state, higher bulk kinetic energy is injected into the system
with a harder particle population and a lower magnetic field strength.Comment: 13 pages, 5 figures, accepted for publication in MNRA
The connection between the radio jet and the gamma-ray emission in the radio galaxy 3C 120
We present the analysis of the radio jet evolution of the radio galaxy 3C 120
during a period of prolonged gamma-ray activity detected by the Fermi satellite
between December 2012 and October 2014. We find a clear connection between the
gamma-ray and radio emission, such that every period of gamma-ray activity is
accompanied by the flaring of the mm-VLBI core and subsequent ejection of a new
superluminal component. However, not all ejections of components are associated
with gamma-ray events detectable by Fermi. Clear gamma-ray detections are
obtained only when components are moving in a direction closer to our line of
sight.This suggests that the observed gamma-ray emission depends not only on
the interaction of moving components with the mm-VLBI core, but also on their
orientation with respect to the observer. Timing of the gamma-ray detections
and ejection of superluminal components locate the gamma-ray production to
within almost 0.13 pc from the mm-VLBI core, which was previously estimated to
lie about 0.24 pc from the central black hole. This corresponds to about twice
the estimated extension of the broad line region, limiting the external photon
field and therefore suggesting synchrotron self Compton as the most probable
mechanism for the production of the gamma-ray emission. Alternatively, the
interaction of components with the jet sheath can provide the necessary photon
field to produced the observed gamma-rays by Compton scattering.Comment: Already accepted for publication in The Astrophysical Journa
Chandra Discovery of 10 New X-Ray Jets Associated With FR II Radio Core-Selected AGNs in the MOJAVE Sample
The Chandra X-ray observatory has proven to be a vital tool for studying
high-energy emission processes in jets associated with Active Galactic Nuclei
(AGN).We have compiled a sample of 27 AGN selected from the radio flux-limited
MOJAVE (Monitoring of Jets in AGN with VLBA Experiments) sample of highly
relativistically beamed jets to look for correlations between X-ray and radio
emission on kiloparsec scales. The sample consists of all MOJAVE quasars which
have over 100 mJy of extended radio emission at 1.4 GHz and a radio structure
of at least 3" in size. Previous Chandra observations have revealed X-ray jets
in 11 of 14 members of the sample, and we have carried out new observations of
the remaining 13 sources. Of the latter, 10 have Xray jets, bringing the
overall detection rate to ~ 78%. Our selection criteria, which is based on
highly compact, relativistically beamed jet emission and large extended radio
flux, thus provides an effective method of discovering new X-ray jets
associated with AGN. The detected X-ray jet morphologies are generally well
correlated with the radio emission, except for those displaying sharp bends in
the radio band. The X-ray emission mechanism for these powerful FR II
(Fanaroff-Riley type II) jets can be interpreted as inverse Compton scattering
off of cosmic microwave background (IC/CMB) photons by the electrons in the
relativistic jets. We derive viewing angles for the jets, assuming a
non-bending, non-decelerating model, by using superluminal parsec scale speeds
along with parameters derived from the inverse Compton X-ray model. We use
these angles to calculate best fit Doppler and bulk Lorentz factors for the
jets, as well as their possible ranges, which leads to extreme values for the
bulk Lorentz factor in some cases. When both the non-bending and
non-decelerating assumptions are relaxed [abridged]Comment: 38 Pages, 4 Figures, 5 Tables, accepted for publication in Ap
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