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We present Chandra X-ray results for the jet, nucleus, and gaseous atmosphere ofNGC315, a nearby radio galaxy whose jet kinematics are known through deep radio map-ping. Diffuse X-ray synchrotron emission is detected from the jet out to 30 arcsec from thenucleus, through regions both of fast bulk flow and decelerat ion. The X-ray to radio flux ra-tio drops considerably where the flow decelerates, but the X-ray and radio emissions showsimilar transverse extents throughout, requiring distributed particle acceleration to maintainthe supply of X-ray-emitting electrons. A remarkable knotty filament within the jet is seen inboth the radio and X-ray, contributing roughly 10 per cent ofthe diffuse emission along itsextent at both wavelengths. No completely satisfactory explanation for the filament is found,though its oscillatory appearance, roughly aligned magnetic field, and requirements for par-ticle acceleration, suggest that it is a magnetic strand within a shear layer between fast innerand slower outer flow.Keywords: galaxies:active– galaxies:individual:NGC315– galaxies :jets –radiationmech-anisms: non-thermal – radio continuum: general – X-rays: galaxies

We present results on the physical states of three high-redshift powerful radio galaxies (3C 292 at z=0.7, 3C 184 at z=1, and 3C322 at z=1.7). They were obtained by combining radio measurements with X-ray measurements from XMM-Newton that separate spectrally and/or spatially radio-related and hot-gas X-ray emission. Originally observed as part of a programme to trace clusters of galaxies at high redshift, none of the sources is found to lie in a rich X-ray-emitting environment similar to those of some powerful radio galaxies at low redshift, although the estimated gas pressures are sufficient to confine the radio lobes. The weak gas emission is a particularly interesting result for 3C 184, where a gravitational arc is seen, suggesting the presence of a very massive cluster. Here Chandra data complement the XMM-Newton measurements in spatially separating X-ray extended emission from that associated with the nucleus and rather small radio source. 3C 292 is the source for which the X-ray-emitting gas is measured with the greatest accuracy, and its temperature of 2 keV and luminosity of 6.5E43 erg/s are both characteristic of a poor cluster. This source allows the most accurate measurement of inverse-Compton X-ray emission associated with the radio lobes. In all structures where the magnetic-field strength can be estimated through combining measurements of radio-synchrotron and inverse-Compton-X-ray emission, the field strengths are consistent with sources being in a state of minimum total energy., Comment: 5 pages, 7 figures. To appear in "X-ray and Radio Connections", eds. Sjouwerman, L.O. & Dyer, K.K. (see http://www.aoc.nrao.edu/events/xraydio/)

We present results from two {\em Chandra}/ACIS-I observations and one {\em XMM-Newton} observation of X-ray emission from the ISM and the inner radio lobes of the nearby radio galaxy Centaurus A. The ISM has an average radial surface brightness profile that is well described by a $\beta$-model profile with index $\beta$=0.40$\pm$0.04 and a temperature of $k_BT_{ISM}\sim$0.29 keV beyond 2 kpc from the nucleus. We find that diffuse X-ray emission is coincident with the outer half of the southwest radio lobe, and a bright X-ray enhancement is detected along the edge of the lobe. On the basis of energetic and lifetime arguments, we reject a nonthermal explanation for this emission. We model this emission as a thin, hot shell or cap of X-ray emitting plasma surrounding the radio lobe that was created by the supersonic inflation of the lobe. This plasma shell is both hotter than ($k_BT_{SH}\sim$2.9 keV) and greatly overpressurized relative to the ambient ISM indicating supersonic expansion. We estimate that the lobe is expanding into the ISM at approximately Mach 8.5 or 2400 km s$^{-1}$. We are not directly observing the bow shock, but rather the cooler, denser material that is accumulating ahead of the contact discontinuity. The thermal energy in the shell is a significant fraction of the thermal energy of the hot ISM, demonstrating the possibility that the hot ISM of early galaxies can be re-energized by outflows from nuclear activity. Interestingly, no similarly bright X-ray emission is detected in or along the edge of the NE lobe, implying that there are differences in the dynamics and evolution of the kpc-scale radio components.

One of ROSAT’s major achievements has been its ability to separate X‐ray emission components in many radio galaxies, where this was previously possible only for a very few well‐known sources, e.g.,M87 and Cen A. The dominant X‐ray emission mechanism in radio galaxies as a class was unclear, with correlations between the X‐ray and radio emissions used on one hand to argue for a nuclear origin for the X‐rays, and on the other hand for a thermal origin. Now, with ROSAT we find the presence of both resolved (thermal) and unresolved emission to be typical.Our results are illustrated with PSPC data from the first six radio galaxies in our study. Spectral and spatial measurements independently support the presence of multiple emission components. The resolved emission can be modeled as thermal radiation from gas of galaxy, group, or cluster dimension depending on object. The unresolved emission may be thermal or nonthermal. Evidence is presented to support a nonthermal origin for most of the unresolved emission:...

The ROSAT PSPC spectrum of NGC 6251 can be fitted with either a multiple‐component model obscured by the gas column within our Galaxy or by a single power‐law component obscured by this Galactic gas and an additional column N=1.3×1021 cm−2. We have used the VLA to search for the the HI line in absorption towards the radio core of NGC 6251 to set limits on the total X‐ray absorbing column. We find marginal evidence for a weak, broad, absorption feature associated with NGC 6251 which could provide the extra HI column suggested by the simpler X‐ray spectral fit.

The hypothesis that normal galaxies are on the average more luminous in the X-ray region than the Milky Way galaxy or M31 and therefore are possible candidates for the low-luminosity sources of the 2 to 60 keV extragalactic diffuse background is tested. Data from the A-2 detectors on the HEAO-1 spacecraft were examined for emission from positions coincident with 76 selected normal galaxies, and upper limits to the average galactic luminosity for various luminosity distributions resulting in the observed count rate distribution were determined. For uniform and exponential galactic luminosity distributions, limits of 2.7 x 10 to the 38th erg/sec and 3.4 x 10 to the 38th erg/sec, respectively, at the 90% confidence level were obtained. It is shown that the Hubble-constant-independent upper limit to galactic emissivity is less than 1% of the diffuse background emissivity, indicating that normal galaxies are not responsible for the diffuse X-ray background and have luminosities comparable to that of the Galaxy.

A sample of 25 QSOs was used to investigate the average spectrum between the soft X-ray energy band of the Einstein Observatory image proportional counter, and the higher energy band of the HEAO 1 A2 experiment. The spectrum is similar to thoe exhibited by Seyfert galaxies and narrow emission line galaxies above 2 keV. The spectrum is soft enough that if these objects are typical of the higher redshift, more radio-quiet QSOs, then it is possible to exclude QSOs as being the dominant origin of the diffuse X-ray background.

The HEAO A2 experiment data was systematically searched for unresolved galactic disc emission. Although there were suggestions of non-uniformities in the emission, the data were consistent with a disc of half-thickness 241 + 22 pc and surface emissivity (2-10 keV) at galactic radius R(kpc) of 2.2 10 to the minus 7th power exp(-R/3.5) erg/sq cm to the (-2)power/s (R 7.8 kpc). giving a luminosity of approximately 4.4 10 to the 37th power erg S to the (-1) power. If the model is extrapolated to radii less than 7.8 kpc, the unresolved disc emission is approximately 1.4 10 to the 38th power erg S to the (-1) power (2-10 keV) i.e., a few percent of the luminosity of the galaxy in resolved sources. the disc emission has a spectrum which is significantly softer than that of the high galactic latitude diffuse X-ray background and it is most probably of discrete source origin.