X-RAY RADIATION MECHANISMS AND BEAMING EFFECT OF HOT SPOTS AND KNOTS IN ACTIVE GALACTIC NUCLEAR JETS
- National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, Kunming, Yunnan 650011 (China)
The observed radio-optical-X-ray spectral energy distributions (SEDs) of 22 hot spots and 45 knots in the jets of 35 active galactic nuclei are complied from the literature and modeled with single-zone lepton models. It is found that the observed luminosities at 5 GHz (L{sub 5{sub GHz}}) and at 1 keV (L{sub 1{sub keV}}) are tightly correlated, and the two kinds of sources can be roughly separated with a division of L{sub 1{sub keV}} = L{sub 5{sub GHz}}. Our SED fits show that the mechanisms of the X-rays are diverse. While the X-ray emission of a small fraction of the sources is a simple extrapolation of the synchrotron radiation for the radio-to-optical emission, an inverse Compton (IC) scattering component is necessary to model the X-rays for most of the sources. Considering the sources at rest (the Doppler factor delta = 1), the synchrotron-self-Compton (SSC) scattering would dominate the IC process. This model can interpret the X-rays of some hot spots with a magnetic field strength (B {sup delta}{sup =1}{sub ssc}) being consistent with the equipartition magnetic field (B {sup delta}{sup =1}{sub eq}) in 1 order of magnitude, but an unreasonably low B {sup delta}{sup =1}{sub ssc} is required to model the X-rays for all knots. Measuring the deviation between B {sup delta}{sup =1}{sub ssc} and B {sup delta}{sup =1}{sub eq} with ratio R{sub B} {identical_to} B {sup delta}{sup =1}{sub eq}/B {sup delta}{sup =1}{sub ssc}, we find that R{sub B} is greater than 1 and it is tightly anti-correlated with ratio R{sub L} {identical_to} L{sub 1{sub keV}}/L{sub 5{sub GHz}} for both the knots and the hot spots. We propose that the deviation may be due to the neglect of the relativistic bulk motion for these sources. Considering this effect, the IC/cosmic microwave background (CMB) component would dominate the IC process. We show that the IC/CMB model well explains the X-ray emission for most sources under the equipartition condition. Although the derived beaming factor (delta) and co-moving equipartition magnetic field (B'{sub eq}) of some hot spots are comparable to the knots, the delta values of the hot spots tend to be smaller and their B'{sub eq} values tend to be larger than that of the knots, favoring the idea that the hot spots are jet termination and knots are a part of a well-collimated jet. Both B{sub eq}{sup '} and delta are tentatively correlated with R{sub L} . Corrected by the beaming effect, the L'{sub 5{sub GHz}}-L'{sub 1{sub keV}} relations for the two kinds of sources are even tighter than the observed ones. These facts suggest that, under the equipartition condition, the observational differences of the X-rays from the knots and hot spots may be mainly due to the differences on the Doppler boosting effect and the co-moving magnetic field of the two kinds of sources. Our IC scattering models predict a prominent GeV-TeV component in the SEDs for some sources, which are detectable with H.E.S.S. and Fermi/LAT.
- OSTI ID:
- 21394452
- Journal Information:
- Astrophysical Journal, Vol. 710, Issue 2; Other Information: DOI: 10.1088/0004-637X/710/2/1017; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
EMISSION
ENERGY SPECTRA
EXTRAPOLATION
GALAXY NUCLEI
GEV RANGE
GHZ RANGE 01-100
HOT SPOTS
LEPTONS
LUMINOSITY
MAGNETIC FIELDS
RELATIVISTIC RANGE
RELICT RADIATION
SCATTERING
SYNCHROTRON RADIATION
TEV RANGE
X-RAY GALAXIES
BREMSSTRAHLUNG
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ENERGY RANGE
FERMIONS
FREQUENCY RANGE
GALAXIES
GHZ RANGE
MATHEMATICAL SOLUTIONS
MICROWAVE RADIATION
NUMERICAL SOLUTION
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
SPECTRA