413 research outputs found
Collective Evidence for Inverse Compton Emission from External Photons in High-Power Blazars
We present the first collective evidence that Fermi-detected jets of high
kinetic power (L_kin) are dominated by inverse Compton emission from
upscattered external photons. Using a sample with a broad range in orientation
angle, including radio galaxies and blazars, we find that very high power
sources (L_kin > 10^45.5 erg s^{-1}) show a significant increase in the ratio
of inverse Compton to synchrotron power (Compton dominance) with decreasing
orientation angle, as measured by the radio core dominance and confirmed by the
distribution of superluminal speeds. This increase is consistent with beaming
expectations for external Compton (EC) emission, but not for synchrotron self
Compton (SSC) emission. For the lowest power jets (L_kin < 10^43.5 erg s^{-1}),
no trend between Compton and radio core dominance is found, consistent with
SSC. Importantly, the EC trend is not seen for moderately high power flat
spectrum radio quasars with strong external photon fields. Coupled with the
evidence that jet power is linked to the jet speed (Kharb et al. 2010), this
finding suggests that external photon fields become the dominant source of seed
photons in the jet comoving frame only for the faster and therefore more
powerful jets.Comment: Accepted for Publication in ApJ Letters, 5 pages, 4 figure
External Compton emission from relativistic jets in Galactic black hole candidates and ultraluminous X-ray sources
Galactic binary systems that contain a black hole candidate emit hard X-rays
in their low luminosity mode. We show that this emission can be understood as
due to the Compton scattering of photons from the companion star and/or the
accretion disk by relativistic electrons in a jet. The same electrons are also
responsible for the radio emission. Two sources -- XTE J1118+480 and Cygnus X-1
-- are modelled as representatives of black holes with low and high luminosity
companion stars respectively. We further show that the ultraluminous compact
X-ray sources observed in nearby galaxies have the properties expected of
stellar mass black holes with high luminosity companions in which the jet is
oriented close to our line of sight.Comment: Submitted to A&A letters, Oct 16, 200
Chandra Observations of the Radio Galaxy 3C 445 and the Hotspot X-ray Emission Mechanism
We present new {\it Chandra} observations of the radio galaxy 3C 445,
centered on its southern radio hotspot. Our observations detect X-ray emission
displaced upstream and to the west of the radio-optical hotspot. Attempting to
reproduce both the observed spectral energy distribution (SED) and the
displacement, excludes all one zone models. Modeling of the radio-optical
hotspot spectrum suggests that the electron distribution has a low energy
cutoff or break approximately at the proton rest mass energy. The X-rays could
be due to external Compton scattering of the cosmic microwave background
(EC/CMB) coming from the fast (Lorentz factor ) part of a
decelerating flow, but this requires a small angle between the jet velocity and
the observer's line of sight (). Alternatively, the
X-ray emission can be synchrotron from a separate population of electrons. This
last interpretation does not require the X-ray emission to be beamed.Comment: 9 pages, 5 figures, ApJ, in pres
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