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1.
There is currently a clear discrepancy in the proper motions measured on different angular scales in the approaching radio jets of the black hole X-ray binary GRS 1915+105. Lower velocities were measured with the Very Large Array (VLA) prior to 1996 than were subsequently found from higher resolution observations made with the Very Long Baseline Array and the Multi-Element Radio Linked Interferometer Network. We initiated an observing campaign to use all three arrays to attempt to track the motion of the jet knots from the 2006 February outburst of the source, giving us unprecedented simultaneous coverage of all angular scales, from milliarcsecond scales out to arcsecond scales. The derived proper motion, which was dominated by the VLA measurements, was found to be 17.0 mas d−1, demonstrating that there has been no significant permanent change in the properties of the jets since 1994. We find no conclusive evidence for deceleration of the jet knots, unless this occurs within 70 mas of the core. We discuss possible causes for the varying proper motions recorded in the literature.  相似文献   

2.
We present multifrequency radio continuum as well as H  i observations of the superwind galaxy NGC 1482, with both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). This galaxy has a remarkable hourglass-shaped optical emission-line outflow as well as bipolar soft X-ray bubbles on opposite sides of the galactic disc. The low-frequency, lower-resolution radio observations show a smooth structure. From the non-thermal emission, we estimate the available energy in supernovae, and examine whether this would be adequate to drive the observed superwind outflow. The high-frequency, high-resolution radio image of the central starburst region located at the base of the superwind bi-cone shows one prominent peak and more extended emission with substructure. This image has been compared with the infrared, optical red continuum, Hα, and soft and hard X-ray images from Chandra to understand the nature and relationship of the various features seen at different wavelengths. The peak of the infrared emission is the only feature that is coincident with the prominent radio peak, and possibly defines the centre of the galaxy.
The H  i observations with the GMRT show two blobs of emission on opposite sides of the central region. These are rotating about the centre of the galaxy and are located at ∼2.4 kpc from it. In addition, these observations also reveal a multicomponent H  i absorption profile against the central region of the radio source, with a total width of ∼250 km s−1. The extreme blue- and redshifted absorption components are at 1688 and 1942 km s−1, respectively, while the peak absorption is at 1836 km s−1. This is consistent with the heliocentric systemic velocity of  1850 ± 20 km s−1  , estimated from a variety of observations. We discuss possible implications of these results.  相似文献   

3.
We report multi-frequency and multi-epoch radio continuum observations with multi-spatial resolution for the low-luminosity active galactic nucleus (LLAGN) NGC 266. In the centimetre regime, we find diffuse components with Very Large Array (VLA) observations, and a variable compact core with a rising spectrum with Very Long Baseline Array (VLBA) observations. Although the spectral index of the rising spectrum is consistent with the prediction of the simple advection-dominated accretion flow (ADAF) model, the observed radio power is slightly high compared with that of the model prediction. A spectral break at centimetre-to-millimetre wavelengths is inferred from the upper limits of flux densities from Nobeyama Millimetre Array (NMA) and James Clerk Maxwell Telescope (JCMT) data at millimetre and submillimetre wavelengths, respectively. More complicated considerations are required for the theoretical model to interpret such observed radio properties.  相似文献   

4.
New data acquired on the active, cool binary CC Eri ranged across the spectrum from Chandra X-ray to broadband photometry and microwave observations using the VLA and ATCA. Also, high-dispersion spectropolarimetry using the AAT enabled Zeeman-Doppler imaging to be performed. Our interpretations infer strong localised concentrations of the stellar magnetic field, manifested by surface activity and related large coronal plasma structures. Comprehensive matching of the modelling parameters awaits more detailed investigation.This brief interim review includes consideration of the ATCA data. Microwave radio emission is usually low level (‘quiescent’), but occasionally flares of several mJy peak intensity are observed. We associate the emission, generally, with wave-like mechanisms, expanding through the outer atmosphere. Related characteristics of this emission are discussed.  相似文献   

5.
We present 23-GHz MERLIN observations of the high-luminosity radio galaxy PKS 1117+146. The radio image obtained from these data shows, for the first time, a central weak component (designated C) that we identify as the core of the radio galaxy, and two outer components (designated N and S) which are the hotspots of the extended lobes observed at lower frequencies. Extended emission in components C and S is an indication of a possible jet connecting the core to the strongest component. The overall optical and radio properties of PKS 1117+146 are consistent with the source being classified as a compact symmetric object (CSO). We discuss this hypothesis, which would make PKS 1117+146 the largest CSO known so far.  相似文献   

6.
We comment on the main radio emitting properties of the proposed high mass X-ray binary LS 5039. Our study is based on multi-epoch observations with the VLA radio interferometer, at 2.0, 3.6, 6.0 and 20 cm wavelengths, as well as on the first data obtained by the GBI-NASA Monitoring Program at 3.6 and 13.3 cm wavelengths. The source appears to be compact (θ≤0′′.1) and moderately variable, with a non-thermal radio spectrum suggestive of synchrotron radiation.  相似文献   

7.
We present 85-GHz observations of the archetypal double-hotspot radio source 3C 20 made with the BIMA millimetre array. The resolution of BIMA allows us to separate the two components of the eastern hotspot. By comparing the BIMA observations with existing VLA data, we show that the spectra of the two hotspot components are very similar, despite the clear differences in their radio structure and their wide separation. We discuss the implications for models of double hotspot formation. Weak emission from the lobes of 3C 20 is detected at 85 GHz, at a level consistent with the predictions of standard spectral ageing models.  相似文献   

8.
We present new continuum VLA observations of the nearby Sy 1.5 galaxy NGC 5033, made at 4.9 and 8.4 GHz on 2003 April 8. Combined with VLA archival observations at 1.4- and 4.9-GHz made on 1993 August 7, 1999 August 29 and 1999 October 31, we sample the galaxy radio emission at scales ranging from the nuclear regions (≲100 pc) to the outer regions of the disc (∼40 kpc). The high-resolution VLA images show a core–jet structure for the Sy 1.5 nucleus. While the core has a moderately steep non-thermal radio spectrum ( S ν∝να; α4.91.5≈−0.4), the inner kpc region shows a steeper spectrum (α8.41.5≈−0.9). This latter spectrum is typical of galaxies where energy losses are high, indicating that the escape rate of cosmic ray electrons in NGC 5033 is low. The nucleus contributes little to the total 1.4-GHz radio power of NGC 5033 and, based on the radio to far-infrared (FIR) relation, it appears that the radio and FIR emission from NGC 5033 are dominated by a starburst that during the last 10 Myr produced stars at a rate of 2.8 M⊙ yr−1 yielding a supernova (type Ib/c and II) rate of 0.045 yr−1. This supernova rate corresponds to about 1 SN event every 22 yr. Finally, from our deep 8.4-GHz VLA-D image, we suggest the existence of a radio spur in NGC 5033, which could have been due to a hot superbubble formed as a consequence of sequential supernova explosions occurring during the lifetime of a giant molecular cloud.  相似文献   

9.
The few known γ-ray binary systems are all associated with variable radio and X-ray emission. The TeV source HESS J0632+057, apparently associated with the Be star MWC 148, is plausibly a new member of this class. Following the identification of a variable X-ray counterpart to the TeV source we conducted Giant Metrewave Radio Telescope (GMRT) and Very Large Array (VLA) observations in 2008 June–September to search for the radio counterpart of this object. A point-like radio source at the position of the star is detected in both 1280-MHz GMRT and 5-GHz VLA observations, with an average spectral index, α, of ∼0.6. In the VLA data there is significant flux variability on ∼month time-scales around the mean flux density of ≈0.3 mJy. These radio properties (and the overall spectral energy distribution) are consistent with an interpretation of HESS J0632+057 as a lower power analogue of the established γ-ray binary systems.  相似文献   

10.
We report multi-wavelength observations towards IRAS 16547–4247, a luminous infrared source with a bolometric luminosity of 6.2 × 104 L ⊙. Dust continuum observations at 1.2-mm indicate that this object is associated with a dust cloud with a size of about 0.4 pc in diameter and a mass of about 1.3 × 103 M ⊙. Radio continuum observations show the presence of a triple radio source consisting of a compact central object and two outer lobes, separated by about 0.3 pc, symmetrically located from the central source. Molecular hydrogen line observations show a chain of knots that trace a collimated flow extending over 1.5 pc. We suggest that IRAS 16547–4247 corresponds to a dense massive core which hosts near its central region a high-mass star in an early stage of evolution. This massive YSO is undergoing the ejection of a collimated stellar wind which drives the H2 flow. The radio emission from the lobes arises in shocks resulting from the interaction of the collimated wind with the surrounding medium. We conclude that the thermal jets found in the formation of low-mass stars are also produced in high-mass stars.  相似文献   

11.
In this paper we discuss a set of three consecutive VLBI observations of the binary system UX Arietis. The most interesting result is the variation with time of the source structure. The usual interpretation in terms of gyrosynchrotron emission from relativistic electrons trapped in a magnetic loop and undergoing collisional and radiative losses is not able, alone, to explain the observed variations. By using optical, radio and X-ray information we have produced a model of two giant loops anchored on a rotating star. As the star rotates, the loops change their relative position and orientation with respect to the line of sight, causing the observed variation of the source structure. The qualitative agreement found is consistent with our hypothesis and makes these observations a sort of a pilot experiment for a new way of using VLBI to observe radio-stars. In order to quantitatively test our model of evolving electrons confined in loops anchored on a rotating star, we plan in the near future a set of several phase-reference VLBI observations fully covering the 6.4 day rotational period.  相似文献   

12.
We present neutral hydrogen absorption observations of the luminous infrared merger NGC 6240 using MERLIN with a resolution of 0.2 arcsec. Broad absorption (a few hundred km s−1) has been found against two compact radio sources within the central kpc providing dynamical information about the neutral gas components in front of these sources. A narrow absorption component is also detected superimposed upon this broad absorption and additionally against some of the extended L -band continuum. From these results we deduce that the broad component is a result of absorption by a highly disturbed disc-like structure of neutral gas aligned along the position angle of the two compact radio sources, similar to the model previously proposed by Tacconi et al. at the end of the last century based on spectral CO emission data. The narrow component is likely to arise from absorption by less disturbed neutral gas at much larger scales within the system.
Continuum observations presented here at 1.4 and 5 GHz support the view that NGC 6240 contains a double nucleus resulting from a galactic merger event and show these as two compact radio sources separated by 1.52 arcsec. We have also applied luminosity and morphological considerations to the continuum results to determine the most feasible source of radio emission for this luminous merger galaxy. We conclude that the most likely source of the radio flux found in NGC 6240 is a combination of starburst emission from radio luminous supernova remnants, similar to those found in Arp 220, and emission from a weak AGN probably triggered by a merger event.  相似文献   

13.
The radio source 18P87, previously thought to be a point source, has been serendipitously found to be resolved into a core‐jet geometry in VLA maps. H I absorption of continuum emission (in data from the Canadian Galactic Plane Survey) appears in gas with radial velocities >+2 km/s but not in brightly emitting gas at lower radial velocity. Examination of further archival observations at radio, infrared and optical wavelengths suggests that the “obvious” interpretation as a radio galaxy requires a rather unusual object of this kind and a highly unusual local line of sight. We argue that 18P87 may be a Galactic object, a local astrophysical jet. If this is correct it could have arisen from outbursts of a microquasar (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
We present subarcsec angular resolution observations of the neutral gas in the nearby starburst galaxy NGC 520. The central kpc region of NGC 520 contains an area of significantly enhanced star formation. The radio continuum structure of this region resolves into ∼10 continuum components. By comparing the flux densities of the brightest of these components at 1.4 GHz with published 15-GHz data we infer that these components detected at 1.4 and 1.6 GHz are related to the starburst and are most likely to be collections of several supernova remnants within the beam. None of these components is consistent with emission from an active galactic nuclei. Both neutral hydrogen (H  i ) and hydroxyl (OH) absorption lines are observed against the continuum emission, along with a weak OH maser feature probably related to the star formation activity in this galaxy. Strong H  i absorption  ( N H∼ 1022 atoms cm−2)  traces a velocity gradient of 0.5 km s−1 pc−1 across the central kpc of NGC 520. The H  i absorption velocity structure is consistent with the velocity gradients observed in both the OH absorption and in CO emission observations. The neutral gas velocity structure observed within the central kpc of NGC 520 is attributed to a kpc-scale ring or disc. It is also noted that the velocity gradients observed for these neutral gas components appear to differ with the velocity gradients observed from optical ionized emission lines. This apparent disagreement is discussed and attributed to the extinction of the optical emission from the actual centre of this source hence implying that optical ionized emission lines are only detected from regions with significantly different radii to those sampled by the observations presented here.  相似文献   

15.
We present radio images of NRAO 530 on scales ranging from pc to kpc. The observations include the EVN at 5 GHz, the VLBA at 1.6, 8.6 and 15 GHz, the MERLIN at 1.6 and 5 GHz, and the VLA at 5, 8.4, 15, 22, and 43 GHz. The VLBI images show a core-jet structure with an oscillating trajectory on a scale of about 30 mas north of the strongest compact component (core). Superluminal motions are detected in five of the jet compo-nents with apparent velocities in the range of 13.6 to 25.2c. A new component is detected at 15 GHz with the VLBA observations, which appears to be associated with the outburst in 2002. Significant polarized emission is detected around the core with the VLBA observationsat 15 GHz. Rapid variations of the polarization intensity and angle are found between the epochs in 2002 and 2004. On the kpc-scale, a distant component (labelled as WL) located 11 arcsec west (PA=-86°) of the core is detected beyond the core-jet structure which ex-tended to several hundreds of mas in the north-west direction (-50°). A significant emission between the core-jet structure and the WL is revealed. A clump of diffuse emission (labelled EL, 12 arcsec long) at PA 70° to the core, is also detected in the VLA observations, suggest-ing the presence of double lobes in the source. The core component shows a flat spectrum,while the distant components WL and EL have steep spectra. The steep spectra of the distantcomponents and the detection of the arched emission suggest that the distant components are lobes or hot-spots powered by the core of NRAO 530. The morphologies from pc-to kpc- scales and the bending of jets are investigated. The observed radio morphology from pc to kcp appears to favor the model in which precession or wobbling of the nuclear disk drives the helical motion of the radio plasma and produces the S-shaped structure on kpc scale.  相似文献   

16.
We have made a deep search for radio emission from all the northern hemisphere supersoft X-ray sources using the Very Large Array (VLA) and multi-element radio-linked interferometer network (MERLIN) telescopes, at 5 and 8.4 GHz. Three previously undetected sources, T Pyx, V1974 Cygni and RX J0019.8+2156, were imaged in quiescence using the VLA in order to search for any persistent emission. No radio emission was detected in any of the VLA fields down to a typical 1 σ rms noise of 20 μJy beam−1, however, 17 new point sources were detected in the fields with 5-GHz fluxes between 100 and 1500 μJy, giving an average 100-μJy source density of ∼200 deg−2, comparable to what was found in the MERLIN Hubble Deep Field survey. The persistent source AG Draconis was observed by MERLIN to provide a confirmation of previous VLA observations and to investigate the source at a higher resolution. The core is resolved at the milliarcsec scale into two components that have a combined flux of ∼1 mJy. It is possible that we are detecting nebulosity, which is becoming resolved out by the higher MERLIN resolution. We have investigated possible causes of radio emission from a wind environment, both directly from the secondary star, and also consequently, of the high X-ray luminosity from the white dwarf. There is an order of magnitude discrepancy between observed and modelled values that can be explained by the uncertainty in fundamental quantities within these systems.  相似文献   

17.
The excellent spatial resolution of the Chandra observatory offers the unprecedented possibility to measure proper motions at X-ray wavelength with relatively high accuracy using as reference the background of extragalactic or remote galactic X-ray sources. We took advantage of this capability to constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and lacking an optical counterpart. In this paper, we present results from a preliminary analysis from which we derive 2σ upper limits of 76 mas/yr and 138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022 respectively. We use these values together with those of other ROSAT discovered INSs to constrain the origin, distance and evolutionary status of this particular group of objects. We find that the tangential velocities of radio quiet ROSAT neutron stars are probably consistent with those of ‘normal’ pulsars. Their distribution on the sky and, for those having accurate proper motion vectors, their possible birth places, all point to a local population, probably created in the part of the Gould Belt nearest to the earth.   相似文献   

18.
The complex 10-component gravitational lens system B1933+503 has been monitored with the Very Large Array (VLA) during the period 1998 February–June with a view to measuring the time delay between the four compact components and hence to determine the Hubble parameter H 0. Here we present the results of an 'A' configuration 8.4-GHz monitoring campaign that consists of 37 epochs with an average spacing of 2.8 d. The data have yielded light curves for the four flat-spectrum radio components (components 1, 3, 4 and 6). We observe only small flux density changes in the four flat-spectrum components that we do not believe are predominantly intrinsic to the source. Therefore the variations do not allow us to determine the independent time delays in this system. However, the data do allow us to accurately determine the flux density ratios between the four flat-spectrum components. These will prove important as modelling constraints and could prove crucial in future monitoring observations should these data show only a monotonic increase or decrease in the flux densities of the flat-spectrum components.  相似文献   

19.
We present near-infrared adaptive optics, Very Large Array (VLA) radio and Hubble Space Telescope ( HST ) optical imaging of the nearby Seyfert galaxy NGC 2992. Spiral structure and an extension to the west are traced down to the core region at the limiting resolution of our near-infrared images. A faint, diffuse loop of near-infrared and radio emission is also observed to the north, embedded within the prominent 2-arcsec radio loop previously observed to the north-west. Near-infrared colour maps and CO narrow-band imaging are then used to identify which regions may not be purely reddened stellar populations. Our new data provide evidence that the VLA radio-loop morphology in the shape of a figure of 8 represents two components superimposed: (1) outflow bubbles out of the plane of the disc, coincident with the extended emission-line region (EELR); (2) star formation along the spiral arm within the galaxy disc and through the dust lane. The near-infrared continuum emission associated with the outflowing radio bubbles suggests that the radio loops are driven by the active nucleus.  相似文献   

20.
We present the results of a 22-cm radio survey carried out with the Australia Telescope Compact Array (ATCA) covering the A3558 complex, a chain formed by the merging ACO clusters A3556–A3558–A3562 and the two groups SC 1327−312 and SC 1323−313, located in the central region of the Shapley Concentration. The purpose of our survey is to study the effects of cluster mergers on the statistical properties of radio galaxies and to investigate the connection between mergers and the presence of radio haloes and relic sources.
We found that the radio source counts in the A3558 complex are consistent with the background source counts. The much higher optical density compared with the background is not reflected as a higher density of radio sources. Furthermore, we found that no correlation exists between the local density and the radio source power, and that steep-spectrum radio galaxies are not segregated in denser optical regions.
The radio luminosity function for elliptical and S0 galaxies is significantly lower than for cluster early-type galaxies and for those not selected to be in clusters at radio powers log  P 1.4≳22.5, implying that the probability of a galaxy becoming a radio source above this power limit is lower in the Shapley Concentration compared with any other environment. Possible explanations will be presented.
The detection of a head–tail source in the centre of A3562, coupled with careful inspection of the 20-cm NRAO VLA Sky Survey (NVSS) and of 36-cm MOST observations, allowed us to spot two extended sources in the region between A3562 and SC 1329−313, i.e. a candidate radio halo at the centre of A3562 and low brightness extended emission around a 14.96-mag Shapley galaxy. The relation between these two extended galaxies and the ongoing group merger in this region of the Shapley Concentration are discussed.  相似文献   

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