Radio Objects Research Articles

XMM-Newtonobservations of four high mass X-ray binaries and IGR J17348−2045

We present the results of the XMM-Newton observations of five hard X-ray emitters: IGR J08262-3736, IGR J17354-3255, IGR J16328-4726, SAX J1818.6-1703, and IGR J17348-2045. The first source is a confirmed supergiant high mass X-ray binary, the following two are candidates supergiant fast X-ray transients, SAX J1818.6-1703 is a confirmed supergiant fast X-ray transient and IGR J17348-2045 is one of the still unidentified objects discovered with INTEGRAL. The XMM-Newton observations permitted the first detailed soft X-ray spectral and timing study of IGR J08262-3736 and provided further support in favor of the association of IGR J17354-3255 and IGR J16328-4726 with the supergiant fast X-ray transients. SAX J1818.6-1703 was not detected by XMM-Newton, thus supporting the idea that this source reaches its lowest X-ray luminosity (~10^32 erg/s) around apastron. For IGR J17348-2045 we identified for the first time the soft X-ray counterpart and proposed the association with a close-by radio object, suggestive of an extragalactic origin.

Development of ephemeris support in observations of distant radio sources and solar system objects at RATAN-600 radio telescope

New elements of the algorithmic and software bases of the ephemeris support for the RATAN-600 radio telescope observations of distant radio sources and objects of the Solar system are briefly described.

RECOILING SUPERMASSIVE BLACK HOLES IN SPIN-FLIP RADIO GALAXIES

Numerical relativity simulations predict that coalescence of supermassive black hole (SMBH) binaries not only leads to a spin flip but also to a recoiling of the merger remnant SMBHs. In the literature, X-shaped radio sources are popularly suggested to be candidates for SMBH mergers with spin flip of jet-ejecting SMBHs. Here we investigate the spectral and spatial observational signatures of the recoiling SMBHs in radio sources undergoing black hole spin flip. Our results show that SMBHs in most spin-flip radio sources have mass ratio $q\ga 0.3$ with a minimum possible value $q_{\rm min} \simeq 0.05$. For major mergers, the remnant SMBHs can get a kick velocity as high as $2100 km s^{-1}$ in the direction within an angle $\la 40^\circ$ relative to the spin axes of remnant SMBHs, implying that recoiling quasars are biased to be with high Doppler-shifted broad emission lines while recoiling radio galaxies are biased to large apparent spatial off-center displacements. We also calculate the distribution functions of line-of-sight velocity and apparent spatial off-center for spin-flip radio sources with different apparent jet reorientation angles. Our results show that the larger the apparent jet reorientation angle is, the larger the Doppler-shifting recoiling velocity and apparent spatial off-center displacement will be. We investigate the effects of recoiling velocity on the dust torus in spin-flip radio sources and suggest that recoiling of SMBHs would lead to "dust poor" AGNs. Finally, we collect a sample of 19 X-shaped radio objects and for each object give the probability of detecting the predicted signatures of recoiling SMBH.

Methanol as a Sensitive Probe for Spatial and Temporal Variations of the Proton-to-Electron Mass Ratio

The 6.7 and 12.2 GHz masers, corresponding to the 5(1) → 6(0)A+ and 2(0) → 3(-1)E transitions in methanol (CH3OH), respectively, are among the brightest radio objects in the sky. We present calculations for the sensitivity of these and other transitions in the ground state of methanol to a variation of the proton-to-electron mass ratio. We show that the sensitivity is greatly enhanced due to a cancellation of energies associated with the hindered internal rotation and the overall rotation of the molecule. We find sensitivities of K(μ) = -42 and K(μ) = -33, for the 5(1) → 6(0)A+ and 2(0) → 3(-1)E transitions, respectively. The sensitivities of other transitions in the different isotopologues of methanol range from -88 to 330. This makes methanol a sensitive probe for spatial and temporal variations of the proton-to-electron mass ratio.

A MERLIN pilot study of faint variable VLA FIRST radio sources

We present the results of a pilot study in which we obtained Multi-Element Radio Linked Interferometer Network (MERLIN) L-band snapshot images of the 20 strongest radio sources from a sample of 123 radio objects that exhibit significant flux density variations at 1.4 GHz on a seven year base-line. The sample was created using FIRST VLA B-array data from 1995 and 2002 on a strip around zero declination near the south Galactic cap. The primary purpose is to assess the presence of radio jets and provide direct evidence between long-term variability and jet structures, as several models suggest. The radio structure of all the sources in this subsample appears very compact and our high resolution MERLIN observations reveal for the first time the presence of small milli-arcsecond (mas) jets and/or jet-like extensions in 17 of the 20 variable sources (literature data show core-jet structures or hints of extended structure in the other three objects which are point sources in our MERLIN observations). In the future we will use the radio results from the complete study, in combination with their optical Sloan Digital Sky Survey (SDSS) data, in order to investigate trends and possible differences or similarities between the quasars and galaxies that host these radio sources, and so examine existing unification schemes or open up new aspects in AGN unification.

A survey of low-luminosity compact sources and its implication for the evolution of radio-loud active galactic nuclei - I. Radio data

We present a new sample of Compact Steep Spectrum (CSS) sources with radio luminosity below 10^26 W/Hz at 1.4 GHz called the low luminosity compact (LLC) objects. The sources have been selected from FIRST survey and observed with MERLIN at L-band and C-band. The main criterion used for selection was luminosity of the objects and approximately one third of the CSS sources from the new sample have a value of radio luminosity comparable to FRIs. About 80% of the sources have been resolved and about 30% of them have weak extended emission and disturbed structures when compared with the observations of higher luminosity CSS sources. We studied correlation between radio power and linear size, and redshift with a larger sample that included also published samples of compact objects and large scale FRIIs and FRIs. The low luminosity compact objects occupy the space in radio power versus linear size diagram below the main evolutionary path of radio objects. We suggest that many of them might be short-lived objects, and their radio emission may be disrupted several times before becoming FRIIs. We conclude that there exists a large population of short-lived low luminosity compact objects unexplored so far and part of them can be precursors of large scale FRIs.

EVIDENCE FOR INFRARED-FAINT RADIO SOURCES ASz> 1 RADIO-LOUD ACTIVE GALACTIC NUCLEI

Infrared-Faint Radio Sources (IFRSs) are a class of radio objects found in the Australia Telescope Large Area Survey (ATLAS) which have no observable mid-infrared counterpart in the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. The extended Chandra Deep Field South now has even deeper Spitzer imaging (3.6 to 70 micron) from a number of Legacy surveys. We report the detections of two IFRS sources in IRAC images. The non-detection of two other IFRSs allows us to constrain the source type. Detailed modeling of the SED of these objects shows that they are consistent with high redshift (z > 1) AGN.

Everolimus-eluting bioabsorbable stent – Abbot Vascular programme

Overview of the stent. (B) Magnified image of the stent. (C) Stent struts imaged by optical coherence tomography have a “black box” appearance. The stent strut thickness is 150 μm. (D and E) Multi-slice computed tomography delineates easily the contours of the stented vessel as the stent structures are not radio-opaque. The radio-opaque markers embedded at the stent extremities (white arrows) appear much larger than they really are because of a “blooming effect” due to partial volume averaging typical of highly radio opaque objects imaged by MSCT4.

PRONGS: Powerful Radio Objects Nested in Galaxies with Star Formation

AbstractWe have identified a new class of object that we term PRONGS (powerful radio objects nested in galaxies with star formation). These are powerful radio sources whose optical properties are that of spiral/star-forming galaxies, unlike classic powerful radio sources which are typically hosted by elliptical galaxies in the local Universe. Here we present a first look at these enigmatic sources.

ACHANDRAX-RAY OBSERVATION OF L1251B

I report the results of a 60 ks X-ray observation of the L1251 dark cloud in Cepheus, which was acquired with the ACIS-I camera on board the Chandra X-Ray Observatory. Forty-three compact X-ray sources were detected. The field of view was centered on the position of IRAS 22376+7455, an embedded Class 0/I protostar that is closely associated with the bright CO emission core, L1251B-Core E. A very intense impulsive X-ray flare was observed from a location within the formal error ellipse of the IRAS source and in close proximity (within 1'') to a thermal continuum radio source, VLA 3. Given their small spatial offsets, the radio, far-infrared, and X-ray objects appear to be identical and consequently the likely origin and driving source of high-velocity gas flows that are observed in L1251B.

Diffuse radio emission from clusters in the MareNostrum Universe simulation

Large-scale diffuse radio emission is observed in some clusters of galaxies. There is ample of evidence that the emission has its origin in synchrotron losses of relativistic electrons that have been accelerated in cluster mergers. In a cosmological simulation, we estimate the radio emission of structure formation shocks as follows: introducing a novel approach to identify strong shock fronts in an smoothed particle hydrodynamics (SPH) simulation, we determine the Mach number as well as the downstream density and temperature in the MareNostrum Universe simulation which has 2 × 10243 particles in a 500 h−1Mpc box. Then, we estimate the radio emission using the formalism derived in Hoeft & Brüggen to produce artificial radio maps of massive clusters and to derive a luminosity function of diffuse radio sources. Several of our clusters show radio objects with similar morphology to observed large-scale radio relics, whereas about half of the clusters show only very little radio emission. In agreement with observational findings, the maximum diffuse radio emission of our clusters depends strongly on their X-ray temperature. We find that the so-called accretion shocks cause only very little radio emission. We conclude that a moderate efficiency of shock acceleration, namely ξe= 0.005, and moderate magnetic fields in the region of the relics, namely 0.07–0.8 μG are sufficient to reproduce the number density and luminosity of radio relics.

The AGN nature of three INTEGRAL sources: IGR J18249–3243, IGR J19443+2117, and IGR J22292+6647

Context. The third INTEGRAL/IBIS survey has revealed several new hard X-ray sources, which are still unidentified or unclassified. To identify these sources, we need to find their counterparts at other wavelengths and then study their nature. Aims. The aim of this work is to employ the capability of the X-ray telescope (XRT) onboard Swift to localise the sources with a positional accuracy of few arcseconds, thus allowing the search for optical/UV, infrared, and radio counterparts to be more efficient and reliable. A second objective is to provide spectral information over a broad range of frequencies. Methods. We analysed all XRT observations available for three unidentified INTEGRAL sources, IGR J18249–3243, IGR J19443+2117, and IGR J22292+6647, localised their soft X-ray counterparts, and searched for associations with objects in the radio band. We also combined X-/gamma-ray data, as well as all the available radio, infrared, and optical/UV information, in order to provide a broad-band spectral characterisation of each source and investigate its nature. Results. In all three cases, XRT observations provided a firm localisation of the X-ray counterpart and information on its optical/UV, infrared, and radio associations. All three sources are found to be bright and repeatedly observed radio objects, although poorly studied. The X-/gamma-ray spectrum of each source is described well by power laws with the photon indices typical of AGN; however, only IGR J19443+2117 may have absorption in excess of the Galactic value, while IGR J22292+6647 is certainly variable at X-ray energies. IGR J18249–3243 has a complex radio morphology and a steep radio spectrum, while the other two sources show flatter radio spectra and a more compact morphology. Overall, their radio, optical/UV, and infrared characteristics, as well as their X-/gamma-ray properties, point to an AGN classification for all three objects.

A UNIFIED CATALOG OF RADIO OBJECTS DETECTED BY NVSS, FIRST, WENSS, GB6, AND SDSS

We construct a catalog of radio sources detected by the Green Bank 6 cm survey GB6, Faint Images of the Radio Sky at Twenty cm (FIRST) and NRAO VLA Sky Survey (NVSS) (20 cm), and Westerbork Northern Sky Survey (WENSS) (92 cm) radio surveys, and the Sloan Digital Sky Survey (SDSS) optical survey. The 2.7 million entries in the publicly-available master catalog are comprised of the closest three FIRST to NVSS matches (within 30'') and vice versa, and unmatched sources from each survey. Entries are supplemented by data from the other radio and optical surveys, where available. All objects with even a small probability of physical association are included, such that catalog users can easily implement their own selection criteria for data analysis. We perform data analysis in the ~ 3000 deg2 region of sky where the surveys overlap, which contains 140,000 NVSS-FIRST sources, of which 64,000 are detected by WENSS and 12,000 by GB6. About one third of each sample is detected by the SDSS. An automated classification method based on 20 cm fluxes defines three radio morphology classes: complex, resolved, and compact. Radio color-magnitude-morphology diagrams for these classes show structure suggestive of strong underlying physical correlations. Complex and resolved sources tend to have a steep spectral slope (α ~ –0.8) that is nearly constant from 6 to 92 cm, while the compact class (unresolved on ~5'' scale by FIRST) contains a significant number of flat-spectrum (α ~ 0) sources. In the optically-detected sample, quasars dominate the flat-spectrum compact sources while steep-spectrum and resolved objects contain substantial numbers of both quasars and galaxies. Differential radio counts of quasars and galaxies are similar at bright flux levels (>100 mJy at 20 cm), while at fainter levels the quasar counts are significantly reduced below galaxy counts. The optically-undetected sample is strongly biased toward steep-spectrum sources. In samples of quasars and galaxies with SDSS spectra (2885 and 1288 respectively), we find that radio properties such as spectral slope, morphology, and radio loudness are correlated with optical color and luminosity.

Continuum Observations at 3 and 12 mm of the High‐Mass Protostellar Jet IRAS 16547−4247

Continuum data at 25 and 88 GHz toward the luminous young stellar object IRAS 16547-4247 (G343.126-0.062) have been obtained with the Australia Telescope Compact Array. The triple emission source identified previously at lower frequencies has been detected at 25 GHz. For frequencies between 1.4 and 25 GHz, the flux density of the central continuum source is well fitted with a power-law dependence that is consistent with thermal emission from a jet. The two outer lobes are radio Herbig-Haro objects exhibiting thermal and nonthermal synchrotron emission. At 88 GHz, one unresolved emission source was detected, centered on the radio jet. At this frequency the emission does not arise from the jet but from the dusty molecular envelope within which the jet is embedded.

Infrared and radio features of galaxies with UV excess

This is a statistical study of galaxies with a UV excess. A sample of 702 Kazarian galaxies (KG) is used. The KGs are identified with objects from the MAPS, IRAS FSC, IRAS PSC, and NVSS catalogs. The O and E magnitudes are known for more than 92% of the KGs. It is shown that the KG sample is complete up to 16m.0 in the blue and to 16m.5 in the red. More than 36% of the KGs are identified with infrared (IR) sources at wavelengths of 12, 25, 60, and 100 m. Calculations of the far IR (FIR) luminosities show that 4% of the KGs are strong FIR emitters (LFIR ≥ 1011 L⊙). More than 32% of the KGs have been identified as radio sources at a frequency of 1.4 GHz. A determination of the radio luminosities shows that the sample of KGs with known radial velocities include one powerful, LR ≥ 1025 W/Hz, radio object (Kaz 273) which is a BL Lac object. A close correlation (r=0.93) is bound between the FIR and radio luminosities for galaxies with a UV excess. An examination of the relationship between the FIR and radio luminosities for galaxies in different spectral classes shows that the correlation coefficient is higher (r=0.99) and the slope of the fit curve is larger (a=1.18) for Seyfert galaxies. Calculations of the logarithm of the ratio of the FIR and radio fluxes indicate that the sample includes 4 KGs with a radio excess, while there are none with an IR excess.

The interplay between radio galaxies and cluster environment

Abstract By combining the REFLEX and NORAS cluster data sets with the NVSS radio catalogue, we obtain a sample of 145, z < 0.3, X-ray-selected clusters brighter than 3 × 10−12 erg s−1 cm−2 that show a central radio emission above 3 mJy. For virial masses Mvir≲ 1014.5 M⊙, 11 clusters out of 12 (corresponding to 92 per cent of the systems) are inhabited by a central radio source. This fraction decreases with higher masses as ∝M−0.4vir. If this decrease is a selection effect, it suggests that the majority of X-ray-selected clusters host in their centre a radio source brighter than ∼1020 W Hz−1 sr−1. A division of the sample into clusters harbouring either point-like or an extended radio-loud active galactic nucleus (AGN) reveals that the steepening of the LX–T relation for low-temperature clusters is strongly associated with the presence of central radio objects with extended jets and/or lobe structures. In the latter case, LX∝T4 while for point-like sources one recovers an approximately self-similar relation LX∝T2.3. Monte Carlo simulations show that the steepening of the LX–T relation is not caused by clusters being underluminous in the X-ray band, but rather by overheating, most likely caused by the interplay between the extended radio structures and the intracluster medium. In the case of low-mass systems, we also find a tight correlation between radio luminosity and cluster temperature. The effects of the central radio source on the thermal state of a cluster become less important with increasing cluster mass. The presence of radio sources with extended structures (61, corresponding to ∼42 per cent of the sample) is enhanced in X-ray luminous clusters with respect to ‘field’ radio-loud AGN. Furthermore, we find that the luminosity distribution of the cluster radio population differs from that of all radio sources, as there is a deficit of low-luminosity (LR≲ 1022 W Hz−1 sr−1) objects, while the number of high-luminosity ones is boosted. The net effect on the radio luminosity function of radio galaxies associated with cluster centres is of a flattening at all luminosities LR≲ 1024 W Hz−1 sr−1.

15 years of very long baseline interferometry observations of two compact radio sources in Messier 82

We present the results of a second epoch of 18-cm global very long baseline interferometry (VLBI) observations, taken on 2001 February 23, of the central kiloparsec of the nearby starburst galaxy Messier 82. These observations further investigate the structural and flux evolution of the most compact radio sources in the central region of M82. The two most compact radio objects in M82 have been investigated (41.95+575 and 43.31+592). Using this recent epoch of data in comparison with our previous global VLBI observations and two earlier epochs of European VLBI network observations, we measure expansion velocities in the range of 1500–2000 km s−1 for 41.95+575 and 9000–11 000 km s−1 for 43.31+592 using various independent methods. In each case, the measured remnant expansion velocities are significantly larger than the canonical expansion velocity (500 km s−1) of supernova remnants (SNRs) within M82 predicted from theoretical models. In this paper, we discuss the implications of these measured expansion velocities with respect to the high-density environment that the SNRs are expected to reside in within the centre of the M82 starburst.

The 2dF galaxy redshift survey: clustering properties of radio galaxies

The clustering properties of local, S_{1.4 GHz} > 1 mJy, radio sources are investigated for a sample of 820 objects drawn from the joint use of the FIRST and 2dF Galaxy Redshift surveys. To this aim, we present 271 new bj < 19.45 spectroscopic counterparts of FIRST radio sources to be added to those already introduced in Magliocchetti et al. (2002). The two-point correlation function for the local radio population is found to be entirely consistent with estimates obtained for the whole sample of 2dFGRS galaxies. We estimate the parameters of the real-space correlation function xi(r)=(r/r_0)^{-\gamma}, r_0=6.7^{+0.9}_{-1.1} Mpc and \gamma=1.6\pm 0.1, where h=0.7 is assumed. Different results are instead obtained if we only consider sources that present signatures of AGN activity in their spectra. These objects are shown to be very strongly correlated, with r_0=10.9^{+1.0}_{-1.2} Mpc and \gamma=2\pm 0.1, a steeper slope than has been claimed in other recent works. No difference is found in the clustering properties of radio-AGNs of different radio luminosity. These results show that AGN-fuelled sources reside in dark matter halos more massive than \sim 10^{13.4} M_{\sun}},higher the corresponding figure for radio-quiet QSOs. This value can be converted into a minimum black hole mass associated with radio-loud, AGN-fuelled objects of M_{BH}^{min}\sim 10^9 M_{\sun}. The above results then suggest -at least for relatively faint radio objects -the existence of a threshold black hole mass associated with the onset of significant radio activity such as that of radio-loud AGNs; however, once the activity is triggered, there appears to be no evidence for a connection between black hole mass and level of radio output. (abridged)

On the Observed Rapid Motions in Extragalactic Radio Sources

Using interferometric methods, radio astronomers have shown that very rapid motions involving radio jets are detectable in a variety of active centers: the nuclei of low-redshift radio galaxies, QSOs and BL Lac objects, and active binary systems containing a black hole or a neutron star in our own Galaxy. By comparing the positions of about 80 extragalactic sources of this type with the position of the galaxies in the de Vaucouleurs catalog and the updated QSO catalog of Veron-Cetty and Veron, it is shown that about 50% of them lie within 1° of a low-redshift spiral galaxy, and about 15% lie so close to galaxies (Δθ ≤ 10') that the associations are highly significant. Thus, the sources are probably physically associated with these galaxies. All the galaxies are classified as spiral. In addition, many of the sources have other QSOs lying very close to them. These results suggest that the motions observed in these radio sources, as well as in the nuclei of radio galaxies and in Galactic microquasars, and perhaps in many more QSOs and other objects, are all similar and are mildly relativistic, and they do not require us to invoke large Lorentz factors. Some of the problems associated with this picture are discussed.

The Ultraviolet Continuum Emission of FR I and FR II Radio Galaxies and a Proposal for a Unified AGN Model for FR I sources

This paper is the second in a series of two on the UV continuum emission (in the range from 1400 to 3700 A) of radio galaxies that were extracted from the Hubble Space Telescope (HST) Archives. The sample consists of 31 3C and Parkes radio galaxies that have redshifts below 0.2 (the majority have redshifts of ~0.03) and radio powers of ~1025–1027 W Hz-1 (using H0 = 50 km-1 s-1 Mpc and q0 = 0.0). Paper I describes the sample selection and the properties of individual sources; this paper deals with the analysis. We find that only about half the radio galaxies display any UV flux at wavelengths shorter than 2300 A. More specifically, those galaxies that are dominated by a nuclear UV component are either BL Lac objects or radio galaxies with broad emission lines. We detect a nuclear and an extended UV component only among half the radio galaxies with narrow emission lines. Although we do not find a correlation of the UV luminosity with emission-line luminosity or radio power, there does appear to be a dependence on radio morphology. While (narrow line) FR II sources do not show a nuclear UV component, FR I's do, however, only if they also have an optical jet (this is the case for seven of 21 FR I's). These results are broadly consistent with orientation-dependent unification models. In radio galaxies in which the torus does not obscure our view of the engine, the observed UV radiation appears to be point source–like. This is the case for broad-line radio galaxies and BL Lac objects. In other radio galaxies that are oriented at an angle to us, the torus presumably blocks the nuclear UV component. The narrow-line FR I galaxies with optical jets can then be interpreted as objects at a critical angle at which some, but not all, nuclear UV emission is blocked. The UVλ luminosities (with λ ranging from 1400 to 3700 A) and the UVλ-V colors of radio galaxies show a larger scatter than those of radio-quiet elliptical galaxies. At wavelengths shorter than 2300 A, some radio galaxies have on average bluer colors, but beyond 3000 A, their colors are on average slightly redder. This picture is also consistent with unification models—the galaxies with bluer colors are either BL Lac objects or broad-line radio galaxies. All other radio galaxies (including the jetted FR I's) have somewhat redder colors than radio-quiet elliptical galaxies. We suspect that this is primarily due to reddening by dust, which we know is present in some of the radio galaxies in the sample. At longer wavelengths (>3000 A), all radio galaxies (14 of 14) show an extended component. The morphology of the extended emission is in most, but not all, cases comparable to the morphology at optical wavelengths, implying that this is likely to be starlight. However, the polarization images of two of seven radio galaxies indicate that scattered light from the active galactic nucleus may also contribute toward the UV luminosity.