1,006 research outputs found
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
Connection between inner jet kinematics and broadband flux variability in the BL Lac object S5 0716+714
We present a high-frequency very long baseline interferometry (VLBI)
kinematical study of the BL Lac object S5 0716+714 over the time period of
September 2008 to October 2010. The aim of the study is to investigate the
relation of the jet kinematics to the observed broadband flux variability. We
find significant non-radial motions in the jet outflow of the source. In the
radial direction, the highest measured apparent speed is \sim37 c, which is
exceptionally high, especially for a BL Lac object. Patterns in the jet flow
reveal a roughly stationary feature \sim0.15 mas downstream of the core. The
long-term fits to the component trajectories reveal acceleration in the sub-mas
region of the jet. The measured brightness temperature, T_{B}, follows a
continuous trend of decline with distance, T_B \propto
r_{jet}^{-(2.36\pm0.41)}, which suggests a gradient in Doppler factor along the
jet axis. Our analysis suggest that a moving disturbance (or a shock wave) from
the base of the jet produces the high-energy (optical to \gamma-ray) variations
upstream of the 7 mm core, and then later causes an outburst in the core.
Repetitive optical/\gamma-ray flares and the curved trajectories of the
associated components suggest that the shock front propagates along a bent
trajectory or helical path. Sharper \gamma-ray flares could be related to the
passage of moving disturbances through the stationary feature. Our analysis
suggests that the \gamma-ray and radio emission regions have different Doppler
factors.Comment: 12 pages, 8 figures, accepted for publication in A&
Multiwavelength Variations of 3C 454.3 during the November 2010 to January 2011 Outburst
We present multiwavelength data of the blazar 3C 454.3 obtained during an
extremely bright outburst from November 2010 through January 2011. These
include flux density measurements with the Herschel Space Observatory at five
submillimeter-wave and far-infrared bands, the Fermi Large Area Telescope at
gamma-ray energies, Swift at X-ray, ultraviolet (UV), and optical frequencies,
and the Submillimeter Array at 1.3 mm. From this dataset, we form a series of
52 spectral energy distributions (SEDs) spanning nearly two months that are
unprecedented in time coverage and breadth of frequency. Discrete correlation
anlaysis of the millimeter, far-infrared, and gamma-ray light curves show that
the variations were essentially simultaneous, indicative of co-spatiality of
the emission, at these wavebands. In contrast, differences in short-term
fluctuations at various wavelengths imply the presence of inhomegeneities in
physical conditions across the source. We locate the site of the outburst in
the parsec-scale core, whose flux density as measured on 7 mm Very Long
Baseline Array images increased by 70 percent during the first five weeks of
the outburst. Based on these considerations and guided by the SEDs, we propose
a model in which turbulent plasma crosses a conical standing shock in the
parsec-scale region of the jet. Here, the high-energy emission in the model is
produced by inverse Compton scattering of seed photons supplied by either
nonthermal radiation from a Mach disk, thermal emission from hot dust, or (for
X-rays) synchrotron radiation from plasma that crosses the standing shock. For
the two dates on which we fitted the model SED to the data, the model
corresponds very well to the observations at all bands except at X-ray
energies, where the spectrum is flatter than observed.Comment: Accepted for publication in Astrophysical Journal. 82 pages, 13
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