Intermittent jet activity in the radio galaxy 4C�29.30

The Astrophysical Journal, 2002

We present the first results from an X-ray and optical survey of a sample of radio jets in active galactic nuclei with Chandra and the Hubble Space Telescope (HST). We focus here on the first six sources observed in X-ray, in four of which a bright X-ray jet was detected for the first time. In three out of the four cases, optical emission from the jet is also detected in our HST images. We compare the X-ray morphology with the radio as derived from improved processing of archival Very Large Array data, and we construct spectral energy distributions (SEDs) for the most conspicuous emission knots. In most cases, the SEDs, together with the similarity of the X-ray and radio morphologies, favor an inverse Compton origin for the X-rays. The most likely origin of the seed photons is the cosmic microwave background, implying the jets are still relativistic on kiloparsec scales. However, in the first knot of the PKS 1136À135 jet, X-rays are likely produced via the synchrotron process. In all four cases, bulk Lorentz factors of a few are required. The radio maps of the two jets not detected by either Chandra or HST suggest that they are less beamed at large scales than the other four detected sources. Our results demonstrate that, at the sensitivity and resolution of Chandra, X-ray emission from extragalactic jets is common, yielding essential information on their physical properties.

The Astrophysical Journal, 2002

During the course of an investigation of the interaction of the radio galaxy M84 and its ambient cluster gas, we found excess X-ray emission aligned with the northern radio jet. The emission extends from the X-ray core of the host galaxy as a weak bridge and then brightens to a local peak coincident with the first detectable radio knot at ≈ 2.5 ′′ from the core. The second radio knot at 3.3 ′′ is brighter in both radio and X-rays. The X-ray jet terminates 3.9 ′′ from the core. Although all the evidence suggests that Doppler favoritism augments the emission of the northern jet, it is unlikely that the excess X-ray emission is produced by inverse Compton emission. We find many similarities between the M84 X-ray jet and recent jet detections from Chandra data of low luminosity radio galaxies. For most of these current detections synchrotron emission is the favored explanation for the observed X-rays.

The Astrophysical Journal, 2012

We report results from our deep Chandra X-ray observations of a nearby radio galaxy, 4C+29.30 (z = 0.0647). The Chandra image resolves structures on sub-arcsec to arcsec scales, revealing complex X-ray morphology and detecting the main radio features: the nucleus, a jet, hotspots, and lobes. The nucleus is absorbed (N H 3.95 +0.27 -0.33 × 10 23 cm -2 ) with an unabsorbed luminosity of L 2-10 keV (5.08 ± 0.52) × 10 43 erg s -1 characteristic of Type 2 active galactic nuclei. Regions of soft (<2 keV) X-ray emission that trace the hot interstellar medium (ISM) are correlated with radio structures along the main radio axis, indicating a strong relation between the two. The X-ray emission extends beyond the radio source and correlates with the morphology of optical-line-emitting regions. We measured the ISM temperature in several regions across the galaxy to be kT 0.5 keV, with slightly higher temperatures (of a few keV) in the center and in the vicinity of the radio hotspots. Assuming that these regions were heated by weak shocks driven by the expanding radio source, we estimated the corresponding Mach number of 1.6 in the southern regions. The thermal pressure of the X-ray-emitting gas in the outermost regions suggests that the hot ISM is slightly underpressured with respect to the cold optical-line-emitting gas and radio-emitting plasma, which both seem to be in a rough pressure equilibrium. We conclude that 4C+29.30 displays a complex view of interactions between the jet-driven radio outflow and host galaxy environment, signaling feedback processes closely associated with the central active nucleus.

Monthly Notices of the Royal Astronomical Society, 1998

We present radio observations of the radio galaxy PKS 2152-699 obtained with the Australia Telescope Compact Array (ATCA). The much higher resolution and s/n of the new radio maps reveals the presence of a bright radio component about 10 arcsec NE of the nucleus. This lies close to the highly ionized cloud previously studied in the optical and here shown in a broadband red snapshot image with the HST PC 2. It suggests that PKS 2152-699 may be a jet/cloud interaction similar to 3C277.3. This could cause the change in the position angle (of ∼ 20 •) of the radio emission from the inner to the outer regions. On the large scale, the source has Fanaroff & Riley type II morphology although the presence of the two hot-spots in the centres of the lobes is unusual. The northern lobe shows a particularly relaxed structure while the southern one has an edge-brightened, arc-like structure.

The Astrophysical Journal, 2009

Extended X-ray structures are common in Active Galactic Nuclei (AGNs). Here we present the first case of a Compact Steep Spectrum (CSS) radio galaxy, 3C 305, in which the X-ray radiation appears to be associated with the optical emission line region, dominated by the [O III]5007. On the basis of a morphological study, performed using the comparison between the X-rays, the optical and the radio band, we argue that the high energy emission has a thermal nature and it is not directly linked to the radio jet and hotspots of this source. Finally, we discuss the origin of the extended X-ray structure connected with the optical emission line region following two different interpretations: as due to the interaction between matter outflows and shock-heated environment gas, or as due to gas photoionized by nuclear emission.

2010

A key issue of the star formation process is its independence from the environmental conditions. In particular, it is not clear whether star formation in the outer Galaxy occurs in the same way as in the inner Galaxy. We present preliminary results of the analysis of a ∼ 440Ks ACIS-Chandra observation of NGC1893, a young cluster (∼ 3−4Myrs), far away from the Galactic Center with the aim to study star formation in the outer region of the Galaxy and investigate the coronal properties of the cluster stars. We detect more than 1000 X-ray sources, most of which are likely cluster members. We present also a preliminary analysis of X-ray variability of the cluster stars.

The Astrophysical Journal, 2011

In this paper we consider the possibility that the structure of the largest radio galaxy J1420-0545 is formed by a restarted rather than a primary jet activity. This hypothesis is motivated by the unusual morphological properties of the source, suggesting almost ballistic propagation of powerful jets in a particularly low-density environment. New radio observations of J1420-0545 confirm its morphology consisting of only two narrow lobes; no trace of any outer low-density cavity due to the previous jet activity is therefore detected. Different model fits performed using the newly accessed radio data imply relatively young age of the source, its exceptionally high expansion velocity, large jet kinetic power, and confirm particularly low-density environment. We find that it is possible to choose a realistic set of the model parameters for which the hypothetical outer lobes of J1420-0545 are old enough so that their expected radio surface brightness is substantially below the rms noise level of the available radio maps. On the other hand, the extremely low density of the gas surrounding the J1420-0545 lobes is consistent with the mean density of the baryonic matter in the Universe. This suggests that the source may be instead located in a real void of the galaxy and matter distribution. In both cases the giant radio lobes of J1420-0545 are expected to modify substantially the surrounding matter by driving strong shocks and heating the gas located at the outskirts of the filamentary galactic distribution. Finally, we also find that the energetic requirements for the source are severe in terms of the total jet power and the total energy deposited by the outflows far away from the central engine.

Eprint Arxiv Astro Ph 0512393, 2005

Context. The "central engine" of AGN is thought to be powered by accretion on a central nucleus believed to be a super-massive black hole. The localization and exact mechanism of the energy release in AGN are still not well understood. Aims. We present observational evidence for the link between variability of the radio emission of the compact jet, optical and X-ray continua emission and ejections of new jet components in the radio galaxy 3C 390.3. Methods. The time delays between the light curves of the individual jet components and the light curve of the optical continuum are estimated by using minimization methods and the discret correlation function. Results. We find that the variations of the optical continuum are correlated with radio emission from a stationary feature in the jet. This correlation indicates that the source of variable non-thermal continuum radiation is located in the innermost part of the relativistic jet. Conclusions. We suggest that the continuum emission from the jet and counterjet ionizes material in a subrelativistic outflow surrounding the jet, which results in a formation of two conical regions with broad emission lines (in addition to the conventional broad line region around the central nucleus) at a distance > ∼ 0.4 parsecs from the central engine. Implications for modeling of the broad-line regions are discussed.

Monthly Notices of the Royal Astronomical Society, 2010

Context. The "central engine" of AGN is thought to be powered by accretion on a central nucleus believed to be a super-massive black hole. The localization and exact mechanism of the energy release in AGN are still not well understood. Aims. We present observational evidence for the link between variability of the radio emission of the compact jet, optical and X-ray continua emission and ejections of new jet components in the radio galaxy 3C 390.3. Methods. The time delays between the light curves of the individual jet components and the light curve of the optical continuum are estimated by using minimization methods and the discret correlation function. Results. We find that the variations of the optical continuum are correlated with radio emission from a stationary feature in the jet. This correlation indicates that the source of variable non-thermal continuum radiation is located in the innermost part of the relativistic jet. Conclusions. We suggest that the continuum emission from the jet and counterjet ionizes material in a subrelativistic outflow surrounding the jet, which results in a formation of two conical regions with broad emission lines (in addition to the conventional broad line region around the central nucleus) at a distance > ∼ 0.4 parsecs from the central engine. Implications for modeling of the broad-line regions are discussed.

ESO Astrophysics Symposia, 2008