1,037 research outputs found
The X-ray spectrum of 3C 273
An X-ray spectral measurement of the quasar 3C 273 with the HEAO-A2 experiment in June/July 1978 is reported. The best power law fit to the photon flux over the range 2-60 keV gives a slope of 1.41 + or - 0.02. However, structure is observed, indicating a slope of 1.52 between 2 keV and 9 keV and a slight flattening between 9 keV and 30 keV. Observations with the same experiment in December 1977 and OSO-8 in June 1976 allows confirmation of 40% intensity variability on the time scale of months, although within limits provided by the poorer statistical quality of the additional data no spectral change is discerned. Absorption from the source is found to be low, with the 1978 data yielding a 90% confidence upper limit to the hydrogen column density of 4.5 x 10 to the 21st power atoms/sq cm
Variable X-ray spectra of BL Lac objects: HEAO-1 observations of PKS 0548-322 and 2A 1219+305
X-ray spectra for the BL Lac objects PKS 0548-322 and 2A 1219+305 measured with the HEAO-1 A2 detectors during pointing maneuvers on September 30, 1978 and May 31, 1978 respectively are presented. Both fit single power law components with low energy absorption. For 2A 1219+305, a thermal bremsstrahlung form gives an unacceptable fit. From a comparison with other statistically poorer observations taken at 6 month intervals while the satellite was in its normal scanning mode, it is found that the sources exhibit spectral variability. A summary of measurements of the 5 BL Lac objects detected with the A2 experiment is presented and it is concluded that X-ray spectral changes in this class of source are common. Their general X-ray spectral characteristics distinguish BL Lac objects from other classes of X-ray emitting active galactic nuclei. Analysis of their total spectra indicates that most of the energy is emitted in the 5 to 100 eV band
Multifrequency Study of The Radio Galaxy NGC326
We present the results of a multi-frequency study of the inversion symmetric
radio galaxy NGC326 based on Very Large Array observations at 1.4, 1.6, 4.8,
8.5 and 14.9 GHz. The morphological, spectral and polarization properties of
this peculiar object are studied at different levels of spatial resolutions.
The interpretation of the data will be discussed in forthcoming papers.Comment: 15 pages, 15 ps figures, accepted by A&
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Simultaneous X-ray and Radio Monitoring of the Unusual Binary LSI+61 303: Measurements of the Lightcurve and High-Energy Spectrum
The binary system, LSI+61 303, is unusual both because of the dramatic,
periodic, radio outbursts, and because of its possible association with the 100
MeV gamma-ray source, 2CG135+01. We have performed simultaneous radio and Rossi
X-ray Timing Explorer X-ray observations at eleven intervals over the 26.5 day
orbit, and in addition searched for variability on timescales ranging from
milliseconds to hours. We confirm the modulation of the X-ray emission on
orbital timescales originally reported by Taylor et al. (1996), and in addition
we find a significant offset between the peak of the X-ray and radio flux. We
argue that based on these results, the most likely X-ray emission mechanism is
inverse Compton scattering of stellar photons off of electrons accelerated at
the shock boundary between the relativistic wind of a young pulsar and the Be
star wind. In these observations we also detected 2 -- 150 keV flux from the
nearby low-redshift quasar QSO~0241+622. Comparing these measurements to
previous hard X-ray and gamma-ray observations of the region containing both
LSI+61 303 and QSO~0241+622, it is clear that emission from the QSO dominates.Comment: 23 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
A Chandra Study of the Lobe/ISM Interactions Around the Inner Radio Lobes of Centaurus A: Constraints on the Temperature Structure and Transport Processes
We present results from deeper {\em Chandra} observations of the southwest
radio lobe of Centaurus A, first described by Kraft et al. (2003). We find that
the sharp X-ray surface brightness discontinuity extends around 75% of
the periphery of the radio lobe, and detect significant temperature jumps in
the brightest regions of this discontinuity nearest to the nucleus. This
demonstrates that this discontinuity is indeed a strong shock which is the
result of an overpressure which has built up in the entire lobe over time.
Additionally, we demonstrate that if the mean free path for ions to transfer
energy and momentum to the electrons behind the shock is as large as the
Spitzer value, the electron and proton temperatures will not have equilibrated
along the SW boundary of the radio lobe where the shock is strongest. Thus the
proton temperature of the shocked gas could be considerably larger than the
observed electron temperature, and the total energy of the outburst
correspondingly larger as well. We investigate this using a simple
one-dimensional shock model for a two-fluid (proton/electron) plasma. We find
that for the thermodynamic parameters of the Cen A shock the electron
temperature rises rapidly from 0.29 keV (the temperature of the ambient
ISM) to 3.5 keV at which point heating from the protons is balanced by
adiabatic losses. The proton and electron temperatures do not equilibrate in a
timescale less than the age of the lobe. We note that the measured electron
temperature of similar features in other nearby powerful radio galaxies in poor
environments may considerably underestimate the strength and velocity of the
shock.Comment: 29 pages, 9 figures, 2 tables - accepted for publication in the
Astrophysical Journa
Variability and Proper Motion of X-ray Knots in the Jet of Centaurus A
Accepted to ApJ, 14 pages, 8 figures, 2 tablesWe report results from Chandra observations analyzed for evidence of variability and proper motion in the X-ray jet of Centaurus A. Using data spanning 15 yr, collective proper motion of 11.3 ± 3.3 mas yr -1 , or 0.68 ± 0.20c, is detected for the fainter X-ray knots and other substructure present within the jet. The three brightest knots (AX1A, AX1C, and BX2) are found to be stationary to an upper limit of . Brightness variations up to 27% are detected for several X-ray knots in the jet. For the fading knots, BX2 and AX1C, the changes in spectral slope expected to accompany synchrotron cooling are not found, ruling it out and placing upper limits of ≃80 μG for each of their magnetic field strengths. Adiabatic expansion can account for the observed decreases in brightness. Constraints on models for the origin of the knots are established. Jet plasma overrunning an obstacle is favored as the generator of stationary knots, while moving knots are likely produced either by internal differences in jet speed or the late stages of jet interaction with nebular or cloud material.Peer reviewe
An X-ray study of magnetic field strengths and particle content in FRII radio sources
We present a Chandra and XMM-Newton study of X-ray emission from the lobes of
33 classical double radio galaxies and quasars. We report new detections of
lobe-related X-ray emission in 11 sources. Together with previous detections we
find that X-ray emission is detected from at least one radio lobe in ~75
percent of the sample. For all of the lobe detections, we find that the
measured X-ray flux can be attributed to inverse-Compton scattering of the
cosmic microwave background radiation, with magnetic field strengths in the
lobes between (0.3 - 1.3) B_eq, where the value B_eq corresponds to
equipartition between the electrons and magnetic field assuming a filling
factor of unity. There is a strong peak in the magnetic field strength
distribution at B ~ 0.7 B_eq. We find that > 70 percent of the radio lobes are
either at equipartition or electron dominated by a small factor. The
distribution of measured magnetic field strengths differs for narrow-line and
broad-line objects, in the sense that broad-line radio galaxies and quasars
appear to be further from equipartition; however, this is likely to be due to a
combination of projection effects and worse systematic uncertainty in the X-ray
analysis for those objects. Our results suggest that the lobes of classical
double radio sources do not contain an energetically dominant proton
population, because this would require the magnetic field energy density to be
similar to the electron energy density rather than the overall energy density
in relativistic particles.Comment: 44 pages, 4 figures. Accepted for publication in Ap
A Chandra Survey of Quasar Jets: First Results
We present results from Chandra X-ray imaging and spectroscopy of a
flux-limited sample of flat spectrum radio-emitting quasars with jet-like
extended structure. Twelve of twenty quasar jets are detected in 5 ks ACIS-S
exposures. The quasars without X-ray jets are not significantly different from
those in the sample with detected jets except that the extended radio emission
is generally fainter. New radio maps are combined with the X-ray images in
order to elucidate the relation between radio and X-ray emission in spatially
resolved structures. We find a variety of morphologies, including long straight
jets and bends up to 90 degrees. All X-ray jets are one-sided although the
radio images used for source selection often show lobes opposite the X-ray
jets. The FR II X-ray jets can all be interpreted as inverse Compton scattering
of cosmic microwave background photons by electrons in large-scale relativistic
jets although deeper observations are required to test this interpretation in
detail. Applying this interpretation to the jets as a population, we find that
the jets would be aligned to within 30 degrees of the line of sight generally,
assuming that the bulk Lorentz factor of the jets is 10.Comment: 25 pages with 5 pages of color figures; accepted for publication in
the Astrophysical Journal Supplements; higher resolution jpeg images are
available at http://space.mit.edu/home/jonathan/jets
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