A Radio Through X-ray Study of the Jet/Companion-Galaxy Interaction in 3C 321
Daniel A. Evans, Wen-Fai Fong, Martin J. Hardcastle, Ralph P. Kraft, Julia C. Lee, Diana M. Worrall, Mark Birkinshaw, Judith H. Croston, Tom W. B. Muxlow
We present a multiwavelength study of the nucleus, environment, jets, and hotspots of the nearby FRII radio galaxy 3C 321, using new and archival data from MERLIN, the VLA, Spitzer, HST, and Chandra. An initially collimated radio jet extends northwest from the nucleus of its host galaxy and produces a compact knot of radio emission adjacent (in projection) to a companion galaxy, after which it dramatically flares and bends, extending out in a diffuse structure 35 kpc northwest of the nucleus. We argue that the simplest explanation for the unusual morphology of the jet is that it is undergoing an interaction with the companion galaxy. Given that the northwest hotspot that lies >250 kpc from the core shows X-ray emission, which likely indicates in situ high-energy particle acceleration, we argue that the jet-companion interaction is not a steady-state situation. Instead, we suggest that the jet has been disrupted on a timescale less than the light travel time to the end of the lobe, $\sim 10^6$ years, and that the jet flow to this hotspot will only be disrupted for as long as the jet-companion interaction takes place. The host galaxy of 3C 321 and the companion galaxy are in the process of merging, and each hosts a luminous AGN. As this is an unusual situation, we investigate the hypothesis that the interacting jet has driven material on to the companion galaxy, triggering its AGN. Finally, we present detailed radio and X-ray observations of both hotspots, which show that there are multiple emission sites, with spatial offsets between the radio and X-ray emission.
We present numerical simulations of the interaction between a collimated, bipolar ``pulse'' ejected from a star and a continuous wind ejected from a stellar companion. We explore the characteristics of the predicted H$α$ intensity maps by varying selected input parameters. We find that the asymmetry (in size and strength) between the two lobes of the proto-planetary nebula OH 231.8+4.2 is reproduced in this scenario if the wind ejected by the companion star has a strong latitude dependence.
We discuss the formation of pulsars with massive companions in eccentric orbits. We demonstrate that the probability for a non-recycled radio pulsar to have a white dwarf as a companion is comparable to that of having an old neutron star as a companion. Special emphasis is given to PSR B1820-11 and PSR B2303+46. Based on population synthesis calculations we argue that PSR B1820-11 and PSR B2303+46 could very well be accompanied by white dwarfs with mass > 1.1Msun. For PSR B1820-11, however, we can not exclude the possibility that its companion is a main-sequence star with a mass between about …
We present low-resolution, near-IR JHK spectra of the weak z=2.39 radio galaxy 53W002 and its companion objects #18 and #19, obtained with OHS/CISCO on the Subaru Telescope. They cover rest-frame wavelengths of 3400-7200A, and many rest-optical emission lines are detected. Contributions to the broad-band flux from these emission lines are found to be very large, up to 40% in the H and K'-bands and 30% in the J-band.
Observations of the core of the giant radio galaxy NGC315 made with VLBI interferometers are discussed in the context of a relativistic jet. The sidedness asymmetry suggests Doppler favoritism from a relativistic jet. The presence of moving features in the jet as well as jet counter--jet brightness ratios hint at an accelerating, relativistic jet. An increasing jet velocity is also supported by a comparison of the jet's observed properties with the predictions of an adiabatic expansion model. On the parsec scale, the jet is unpolarized at a wavelength of 6 cm to a very high degree in clear dis…
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 pro…
Markwardt and Oegelman (1995) used ROSAT to reveal a 12 by 45 arcmin structure in 1 keV X rays around the Vela pulsar, which they interpret as a jet emanating from the pulsar. We here present an alternative view of the nature of this feature, namely that it consists of material from very deep inside the exploding star, close to the mass cut between material that became part of the neutron star and ejected material. The initial radial velocity of the inner material was lower than the bulk of the ejecta, and formed a bubble of slow material that started expanding again due to heating by the youn…
We discuss the origin of superluminal radio jets in Black hole X-ray binaries with relativistic radio jets in our Galaxy popularly known as microquasars. We classify the relativistic superluminal jet according to the radio emission in black hole X-ray binaries (transient or persistent) rather than the mass of the companion. The black hole X-ray binaries with transient radio emission (mostly LMXBs) produce superluminal jets with $β_{app} >$ 1 when the accretion rate, $\dot{m}_{accr}$ is high and the bolometric luminosity L$_{bol}$ approaches the Eddington Luminosity, L$_{Edd}$. On the other han…
The jet formation is thought to be closely connected with the mass of central supermassive black hole in Active Galactic Nuclei. The radio luminosity commonly used in investigating this issue is merely an indirect measure of the energy transported through the jets from the central engine, and severely Doppler boosted in core-dominated radio quasars. In this work, we investigate the relationship between the jet power and black hole mass, by estimating the jet power using extrapolated extended 151 MHz flux density from the VLA 5 GHz extended radio emission, for a sample of 146 radio loud quasars…
A simple integral relation is obtained for the distribution functions of jet speeds and jet-counterjet flux asymmetries of classical double radio sources. Analytic expressions relating the mean jet speed and the mean jet flux asymmetry, and their variances are derived. The results are considered in the light of orientation-based unified schemes, and an analytical equation for the critical angle separating quasars and radio galaxies is derived. The mean jet speeds of classical double radio sources are estimated using the asymmetry of jet-counterjet flux densities taken from the 3CRR and B2 samp…
In order to investigate the genesis of powerful radio jet, we have mapped the central 10 pc region of the nearby radio galaxy NGC 6251 with a 0.2 pc resolution using Very Long Baseline Interferometer (VLBI) at two radio frequencies, 5 GHz and 15 GHz, we have found the sub-parsec-scale counterjet for the first time in this radio galaxy. This discovery allows us to investigate the jet acceleration based on the relativistic beaming model.
The observational evidence for jets and phenomena arising from rotation powered radio pulsars is reviewed, including many recent and exciting discoveries at X-ray wavelengths. The well studied jets of the Crab pulsar are summarised, including recent results from the HST. The evolutionary links between the known binary radio pulsars and jets sources in X-ray binaries are discussed.
We review the observational properties, from radio to X-rays, of the eight systems for which there is strong evidence for the formation of a radio jet in a X-ray binary system.
We report the discovery of a very unusual, highly asymmetric radio galaxy whose radio jet, the largest yet detected, emits strongly polarized synchrotron radiation and can be traced all the way from the galactic nucleus to the hot spot located ~440 kpc away. This jet emanates from an extremely massive black hole (>10^9 solar mass) and forms a strikingly compact radio lobe. No radio lobe is detected on the side of the counterjet, even though it is similar to the main jet in brightness up to a scale of tens of kiloparsecs. Thus, contrary to the nearly universal trend, the brightness asymmetry in…
In this paper, analytical arguments are presented that there exists a synchrotron X-ray jet on large scales in most radio-loud AGNs, based on the knowledge of the nature and physics of blazars. In blue blazars and blue-blazar-like radio galaxies, the large scale X-ray jet may get faint along the jet, while in most red blazars and red-blazar-like radio galaxies, the X-ray jet is bright on 10 kpc scales whether the jet is highly relativistic on large scales or not. In extreme red blazars in which the jet is still highly relativistic on large scales and the synchrotron peak of the inner jet lies …
We have observed the radio source NGC 3862 (3C264) simultaneously with the EVN and the MERLIN arrays, obtaining detailed images of its radio structure from parsec to sub-kiloparsec scales. 3C264 shows a one-sided jet, with evident variations in its morphological properties with distance. We have analyzed HST optical data of NGC 3862 finding a one-to-one correspondence between radio and optical features in the jet. The radio to optical spectral index is approximately constant along the jet. Synchrotron appears as the most plausible mechanism for the observed jet emission at radio and optical wa…
We present results for the first three low-power radio galaxies from the B2 bright sample to have been observed with Chandra. Two have kpc-scale radio jets, and in both Chandra resolves jet X-ray emission, and detects soft X-ray core emission and an X-ray emitting galaxy-scale atmosphere of luminosity a few 10^41 ergs s^-1. These are the first detections of X-ray jets in low-power radio galaxies more distant than Cen A and M 87. The cooling time of the galaxy-scale gas implies mass infall rates of order one solar mass per year. The gas pressure near the jets is comparable to the minimum pressu…
Almost every strong cooling core contains an active radio galaxy. Combined radio and X-ray images reveal the dramatic interaction which is taking place between the radio jet and the central cluster plasma. At least two important questions can in principle be answered by comparing the new data to theoretical models. The first is how the radio jet propagates, and disrupts, in the cooling core environment: why are these cluster-center radio sources unusual? The second is the effect the radio jet has on the cooling core: is it energetically important to the core? Thanks to the new data we are begi…
We report on large-scale, regular morphological patterns found in the radio jet of the nearby radio galaxy NGC 6251. Investigating morphological properties of this radio jet from the nucleus to a radial distance of $\sim$ 300 arcsec ($\approx$ 140 kpc) mapped at 1662 MHz and 4885 MHz by Perley, Bridle, & Willis, we find three chains, each of which consists of five radio knots. We also find that eight radio knots in the first two chains consist of three small sub-knots (the triple-knotty substructures). We discuss the observational properties of these regular morphological patterns.
Young cavities in the X-ray emitting hot gas in galaxy clusters are often filled with radio synchrotron emission and it is widely thought that the cavities are inflated by these cosmic rays. At a later stage of its evolution, when the cavity becomes buoyant, the converging flow of gas beneath the cavity results in a filament of thermal gas, a cavity jet, that moves radially outward at large subsonic velocities. As the cavity jet forms, the cosmic ray electrons may diffuse through the cavity walls, filling a large volume surrounding the cavity jet, as observed in M87/Virgo and elsewhere, someti…
We present the completed results of a high resolution radio imaging survey of all (~200) low-luminosity active galactic nuclei (LLAGNs) and AGNs in the Palomar Spectroscopic Sample. The high incidences of pc-scale radio nuclei, with T(brightness) >=10^7 K, and sub-parsec jets argue for accreting black holes in >=50% of all LINERs and low-luminosity Seyferts; there is no evidence against all LLAGNs being mini-AGNs. The radio luminosity function (RLF) of Palomar Sample LLAGNs and AGNs extends three orders of magnitude below, and is continuous with, that of `classical' AGNs. We find marginal evid…
We describe our program to search for and study the kilo-parsec scale radio jets in a sample of high-redshift (greater than 3.4), flat spectrum quasars using new and archival VLA data. Two of these radio jets have been imaged with Chandra, and have X-ray counterparts and are briefly discussed. These high-redshift sources are important targets for testing current X-ray jet emission models for kpc-scale jets and follow-up multi-wavelength observations will shed light on this problem.
The jet in 3C273 is a high-power quasar jet with radio, optical and X-ray emission whose size and brightness allow a detailed study of the emission processes acting in it. We present deep Chandra observations of this jet and analyse the spectral properties of the jet emission from radio through X-rays. We find that the X-ray spectra are significantly softer than the radio spectra in all regions of the bright part of the jet except for the first bright "knot A", ruling out a model in which the X-ray emission from the entire jet arises from beamed inverse-Compton scattering of cosmic microwave b…
We present results from a combined radio, optical, and X-ray study of the jet-associated emission features in NGC1052. We analyse the radio-optical morphology and find a good positional correlation between the radio jet and the optical emission cone. Two optical emission knots are directly associated with radio counterparts exhibiting a radio to X-ray broadband spectrum not compatible with synchrotron emission. We discuss the possibility that the thermal soft spectrum of the extended X-ray emission originates from jet driven shocks produced in the interaction between the jet-plasma and its sur…
We revisit a method to obtain upper limits on the jet matter content combining synchrotron self-absorption constraints and the large scale bubble energy. We use both X-ray observations, which give limits on the jet power from the energies and timescales of bubbles found in clusters of galaxies, and radio observations, which give limits on the magnetic field in the jets. Combining the two imposes constraints on the particle number density, and hence the jet content. Out of a sample of clusters which have clear radio bubbles, there are only two which have sufficient resolution in the radio image…
The relationships between supermassive black holes and the properties of their associated dark-matter halos imply that outflows from accreting black holes provide a feedback mechanism regulating galaxy formation. Accreting black holes with weak or undetectable radio jets (radio-quiet quasars) outnumber those with powerful jets (radio-loud quasars) by a factor ~10-100, so powerful-jet outflows are often neglected. However, whenever powerful jets are triggered, there is a dramatic (factor >100) step-function increase in the efficiency of feedback. We use a feedback model, together with the measu…
By summing a large number of ROSAT High Resolution Imager (HRI) observations of the variable radio galaxy 3C 390.3, we demonstrate that the X-ray emission associated with the northern radio lobe (reported by Prieto 1997) can be identified with hotspot B. None of the other hotspots have been detected. We present evidence that the anomalous X-ray emission is the consequence of a strong shock produced where the northern radio jet impinges onto an external galaxy.
We discuss optical (HST/WFPC2 F555W) and radio (15 GHz VLA) polarimetry observations of the M87 jet taken during 1994-1995. Many knot regions are very highly polarized ($\sim 40-50%$, approaching the theoretical maximum for optically thin synchrotron radiation), suggesting highly ordered magnetic fields. High degrees of polarization are also observed in interknot regions. While the optical and radio polarization maps share many similarities, we observe significant differences between the radio and optical polarized structures, particularly for bright knots in the inner jet, giving us important…
The different methods to derive the jet velocity and orientation on the parsec scale are presented. From these methods I will discuss the velocity distribution of parsec scale jets and the possible presence of acceleration or deceleration in the jet velocity. Moreover, evidences of jet velocity structures will be reported. Finally I will present new data on the superluminal giant radio source 1144+35 to discuss in detail the properties of pc scale jets.
We report sensitive VLA 3.6 cm radio observations toward the head of the Cone nebula in NGC 2264, made in 2006. The purpose of these observations was to study a non-thermal radio jet recently discovered, that appears to emanate from the head of the Cone nebula. The jet is highly polarized, with well-defined knots, and one-sided. The comparison of our images with 1995 archive data indicates no evidence of proper motions nor polarization changes. We find reliable flux density variations in only one knot, which we tentatively identify as the core of a quasar or radio galaxy. An extragalactic loca…
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 approx. 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 t…
IRAS 16547-4247 is the most luminous (6.2 x 10^4 Lsun) embedded young stellar object known to harbor a thermal radio jet. We report the discovery using VLT-ISAAC of a chain of H_2 2.12 um emission knots that trace a collimated flow extending over 1.5 pc. The alignment of the H_2 flow and the central location of the radio jet implies that these phenomena are intimately linked. We have also detected using TIMMI2 an isolated, unresolved 12 um infrared source towards the radio jet . Our findings affirm that IRAS 16547-4247 is excited by a single O-type star that is driving a collimated jet. We arg…
We have analyzed galaxy properties in the environment of a sample of 70 Ultra Steep Spectrum (USS) radio sources selected from the Sydney University Molonglo sky Survey and the NRAO VLA Sky Survey catalogues, using near-IR data complete down to Ks=20. We have quantified galaxy excess around USS targets using an Abell-type measurement N0.5 (Hill & Lilly 1991). We find that most of the USS fields studied are compatible with being Abell class 0 richness clusters. A statistical analysis of the distribution of companion galaxies around USS radio sources show a pronounced tendency for such objects t…
Using new deep VLA and HST observations of the large-scale jet in 3C273 matched to 0.3" resolution, we have detected excess near-ultraviolet emission (300 nm) above a synchrotron cutoff spectrum accounting for the emission from radio through optical (3.6 cm - 620 nm). This necessitates a two-component model for the emission. The radio-optical-X-ray spectral energy distributions suggest a common origin for the UV excess and the X-rays from the jet.
We present the results from an X-ray and optical survey of a sample of 17 radio jets in AGN performed with Chandra and HST. The sample was selected from the radio and is unbiased toward detection at shorter wavelengths, but preferentially it includes beamed sources. We find that X-ray emission is common on kpc-scales, with over half radio jets exhibiting at least one X-ray knot on the Chandra images. The distributions of the radio-to-X-ray and radio-to-optical spectral indices for the detected jets are similar to the limits for the non-detections,suggesting all bright radio jets have X-ray cou…
Astrophysical jets seem to occur in nearly all types of accreting objects: from supermassive black holes to young stellar objects. Based on X-ray binaries, a unified scenario describing the disc/jet coupling has evolved and extended to many accreting objects. The only major exceptions are thought to be cataclysmic variables: Dwarf novae, weakly accreting white dwarfs, show similar outburst behaviour as X-ray binaries but no jet has yet been detected. Here we present radio observations of a dwarf nova in outburst showing variable flat-spectrum radio emission that is best explained as synchrotro…
We present simultaneous, sub-arcsecond (<=50pc) resolution 5 GHz, 8.4 GHz, and 15 GHz VLA observations of a well-defined sample of sixteen low-luminosity active galactic nuclei (LLAGNs). The radio emission in most of these nuclei does not show the rising spectrum (0.2 <= s <= 1.3, L_nu propto nu^{s}) expected from thermal electrons in an advection dominated accretion flow (ADAF) with or without weak to moderately-strong outflows. Rather, the flat radio spectra are indicative of either synchrotron self-absorbed emission from jets, convection-dominated accretion flows (CDAFs) with L >= 10^{-5} L…
We present an analysis of the energetics and particle content of the lobes of 24 radio galaxies at the cores of cooling clusters. The radio lobes in these systems have created visible cavities in the surrounding hot, X-ray-emitting gas, which allow direct measurement of the mechanical jet power of radio sources over six decades of radio luminosity, independently of the radio properties themselves. Using these measurements, we examine the ratio between radio power and total jet power (the radiative efficiency). We find that jet (cavity) power increases with radio synchrotron power approximately…
During the course of an investigation on the interaction of the radio galaxy 3C129 and its ambient cluster gas, we found excess X-ray emission aligned with the northern radio jet. The emission extends from the weak X-ray core of the host galaxy approximately 2.5" to the first resolved radio knot. On a smaller scale, we have also detected a weak radio extension in the same position angle with the VLBA. 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 fin…
We have analyzed the position angle (PA) differences between radio jets and dust distributions in the centers of Fanaroff & Riley Type 1 (FRI) radio galaxies. We model the observed PA differences to infer the three-dimensional relative orientation of jet and dust. Our main conclusion is that there is a dichotomy in dust-jet-galaxy orientation both in projection and in three-dimensional space. The orientation dichotomy can explain the contradictory results obtained in previous studies. We briefly mention scenarios that might explain the dichotomy.
We present five epochs of simultaneous radio (VLA) and X-ray (Chandra) observations of SS 433, to study the relation between the radio and X-ray emission in the arcsecond-scale jets of the source. We detected X-ray emission from the extended jets in only one of the five epochs of observation, indicating that the X-ray reheating mechanism is transient. The reheating does not correlate with the total flux in the core or in the extended radio jets. However, the radio emission in the X-ray reheating regions is enhanced when X-ray emission is present. Deep images of the jets in linear polarization …
An empirical relation between `canonical' X-ray states in black hole X-ray binaries and radio emission is presented. In the Low/Hard state a quasi-continuous radio-emitting jet is produced. In the the High/Soft state the jet is not observed. In the Very High state and at major state transitions, which may correspond physically to rapid and/or significant changes in the inner accretion disc radius, discrete ejection events, which manifest themselves as radio flares, are observed. These relations appear to hold for both transient and persistent systems. Furthermore it is argued that the extremel…
We report Australia Telescope Compact Array (ATCA) radio-continuum and ROSAT PSPC X-ray observations of the region surrounding the peculiar galaxy pair ESO 295-IG022, lying at the centre of the poor cluster Abell S0102. We identify a radio galaxy coincident with the galaxy pair, with bipolar, bent radio jets appearing centred on the southern galaxy, and extending both to the south, for about 95 arcseconds (approximately 100 kpc at the distance of ESO 295-IG022), and to the north, for approximately 80 arcseconds, encompassing the northern galaxy. We discuss also the idea of an additional single…
We have studied the accretion disk during the radio plateau state and the following superluminal relativistic radio jets and have provided a tight correlation between accretion disk and superluminal jet parameters. We find that accretion rate during the plateaux is very high and suggest that the accretion disk during the radio plateaux is always associated with radiation-driven wind. The internal shock forms in the previously generated slowly moving wind (during plateau) with $β$ $\le$ 0.01 as the fast moving discrete jet (usually at the end of plateau) with $β$ $\sim$ 1 catches up and interac…
We examine the properties of central dust in nearby quiescent and active early-type galaxies. The active galaxies are low-power radio galaxies with Fanaroff & Riley Type I or I/II radio jets. We focus on the comparison of the dust distributions in the active and quiescent galaxy samples and the relation between the radio jet and dust orientations. Our main observational conclusions are: (a) radio galaxies contain a higher fraction of regular dust 'ellipses' compared to quiescent galaxies which contain more often irregular dust distributions; (b) the morphology, size and orientation of dust ell…
A mechanism of ultra-high energy (UHE) cosmic ray acceleration in extragalactic radio sources at the interface between the relativistic jet and the ambient medium is discussed as a supplement to the shock acceleration in `hot spots'. Particles accelerated at the jet side boundary are expected to dominate at highest energies. The spectrum formation near the cut-off energy is modeled using the Monte Carlo particle simulations.
We describe very accurate imaging of radio spectral index for the inner jets in three FR I radio galaxies. Where the jets first brighten, there is a remarkably small dispersion around a spectral index of 0.62. This is also the region where bright X-ray emission is detected. Further from the nucleus, the spectral index flattens slightly to 0.50 - 0.55 and X-ray emission, although still detectable, is fainter relative to the radio. The brightest X-ray emission from the jets is therefore not associated with the flattest radio spectra, but rather with some particle-acceleration process whose chara…
We study the jet and counterjet of the powerful classical double FRII radio galaxy Cygnus A as seen in the 5, 8 and 15-GHz radio bands using the highest spatial resolution and signal-to-noise archival data available. We demonstrate that the trace of the radio knots that delineate the jet and counterjet deviates from a straight line and that the inner parts can be satisfactorily fitted with the precession model of Hjellming & Johnston. The parameter values of the precession model fits are all plausible although the jet speed is rather low (< 0.5 c) but, on investigation, found to be consistent …
The recent detection of resolved radio emission from AG Dra by MERLIN reported by Ogley et al. is discussed in the context of the wind environment and the physical parameters and geometry of this symbiotic binary system. In particular, it is shown that the two radio components are closely aligned with the binary axis, and their separation suggests their origin in jets ejected from AG Dra during the recent 1995--98 series of oubtbursts.
We report preliminary results from the first targets observed as part of a program to image the X-ray jets in a complete sample of radio selected jets. We have acquired Australian Telescope Compact Array and Very Large Array data with resolution 1", matching the Chandra resolution. PKS 1202-262 and PKS 0208-512 show dramatic coincidence with the initial radio jet, with the X-ray emission dropping off at the large angle radio bends, similar to the structure of PKS 0637-752.
We have studied the effects of the interaction between the radio jet and the ambient gas in the powerful radio galaxy PKS2250-41 (z=0.31). Our results show that the gas has been accelerated, compressed, heated and collisionally ionized by the shock. This study helps us to understand the processes which determine the observed properties of many high redshift radio galaxies.
We argue that the narrow line regions of Seyfert galaxies are powered by the transport of energy and momentum by the radio-emitting jets and consequently that the ratio of the radio power to jet energy flux is much smaller than is usually assumed for radio galaxies. This can be partially attributed to the smaller ages ($\sim 10^6 yrs$) of Seyferts compared to radio galaxies but one also requires that either the magnetic energy density is more than an order of magnitude below the equipartition value, or more likely, that the internal energy densities of Seyfert jets are dominated by thermal pla…
We investigate the association between the accretion disk during radio plateau state and the following superluminal relativistic radio jets with peak intensity varies from 200 mJy to 1000 mJy observed over a period of five years and present the evidences of direct accretion disc-jet connection in microquasar GRS 1915+105. We have analysed RXTE PCA/HEXTE X-ray data and have found that the accretion rate, $\dot{m}_{accr}$, as inferred from the X-ray flux, is very high during the radio plateaux. We suggest that the accretion disk during the radio plateaux always associated with radiation-driven w…
We present HST observations of previously undetected optical jets in the low-luminosity radio galaxies B2 0755+37 and B2 1553+24. We show that there is accurate spatial coincidence between optical and radio emission, implying that the former is likely to be synchrotron radiation. The physical properties of the jets are similar to those known previously: their radio-optical spectral indices are ~0.7 and in B2 0755+37, the spectrum steepens between optical and X-ray wavelengths. Our results support the hypothesis that optical emission is detectable from jets orientated within ~20 degrees of the …
Deep, narrow-band Halpha observations taken with the TAURUS Tunable Filter (TTF) on the 4.2m WHT telescope are presented for two nearby radio galaxies with strong jet-cloud interactions. Although the brightest emission line components are closely aligned with the radio jets --- providing nearby examples of the ``alignment effect'' most commonly observed in high redshift (z > 0.5) radio galaxies --- lower surface brightness emission line structures are detected at large distances (10's of kpc) from the radio jet axis. These latter structures cannot be reconciled with anisotropic illumination of…
The recent discovery of an X-ray jet in the z=4.3 quasar GB 1508+5714 by Yuan et al. (astro-ph/0309318) and Siemiginowska et al. (astro-ph/0310241) prompted a search for its radio counterpart. Here, we report the successful discovery of faint radio emission from the jet at 1.4 GHz using archival VLA data. The X-ray emission is best interpreted as inverse Compton (IC) emission off the CMB as discussed by the previous investigators. In this scenario, its high X-ray to radio monochromatic luminosity ratio, compared to previously detected IC/CMB X-ray jets at lower redshift, is a natural consequen…
We report on deep radio images and optical spectroscopy of two BL Lac objects that have very close compact companions. The two targets, 1ES 0502+675 and 1ES 1440+122, were selected from the HST imaging survey of 110 BL Lacs as candidates for possible gravitational lensing. The new observations clearly demonstrate that the companion objects are not secondary images of the active nuclei but, in spite of the relatively low chance projection probability, foreground Galactic stars. Gravitational lensing appears to be unimportant to the BL Lac phenomenon. We discuss the radio properties of the BL La…
