63 research outputs found
Interpretation of the Radio/X-ray knots of kilo parsec scale AGN jets within the internal shock model framework
Brightest Fermi-LAT Flares of PKS 1222+216: Implications on Emission and Acceleration Processes
We present a high time resolution study of the two brightest -ray
outbursts from a blazar PKS 1222+216 observed by the \textit{Fermi} Large Area
Telescope (LAT) in 2010. The -ray light-curves obtained in four
different energy bands: 0.1--3, 0.1--0.3, 0.3--1 and 1--3 GeV, with time bin of
6 hr, show asymmetric profiles with a similar rise time in all the bands but a
rapid decline during the April flare and a gradual one during the June. The
light-curves during the April flare show days long plateau in 0.1--0.3
GeV emission, erratic variations in 0.3--1 GeV emission, and a daily recurring
feature in 1--3 GeV emission until the rapid rise and decline within a day. The
June flare shows a monotonic rise until the peak, followed by a gradual decline
powered mainly by the multi-peak 0.1--0.3 GeV emission. The peak fluxes during
both the flares are similar except in the 1--3 GeV band in April which is twice
the corresponding flux during the June flare. Hardness ratios during the April
flare indicate spectral hardening in the rising phase followed by softening
during the decay. We attribute this behavior to the development of a shock
associated with an increase in acceleration efficiency followed by its decay
leading to spectral softening. The June flare suggests hardening during the
rise followed by a complicated energy dependent behavior during the decay.
Observed features during the June flare favor multiple emission regions while
the overall flaring episode can be related to jet dynamics.Comment: 17 pages, 9 figures, 4 tables, accepted for publication in Ap
High Energy Emission Processes in OJ 287 during 2009 Flare
The broadband spectrum of a BL Lac object, OJ 287, from radio to
-rays obtained during a major -ray flare detected by
\emph{Fermi} in 2009 are studied to understand the high energy emission
mechanism during this episode. Using a simple one-zone leptonic model,
incorporating synchrotron and inverse Compton emission processes, we show that
the explanation of high energy emission from X-rays to -rays, by
considering a single emission mechanism, namely, synchrotron self-Compton (SSC)
or external Compton (EC) requires unlikely physical conditions. However, a
combination of both SSC and EC mechanisms can reproduce the observed high
energy spectrum satisfactorily. Using these emission mechanisms we extract the
physical parameters governing the source and its environment. Our study
suggests that the emission region of OJ 287 is surrounded by a warm infrared
(IR) emitting region of . Assuming this region as a spherical
cloud illuminated by an accretion disk, we obtain the location of the emission
region to be . This supports the claim that the -ray
emission from OJ 287 during the 2009 flare arises from a location far away from
the central engine as deduced from millimeter-gamma ray correlation study and
very long baseline array images.Comment: 22 pages, 7 figures, 1 table, accepted for publication in MNRA
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