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Gereb K.,Eotvos Lorand University | Gereb K.,University of Groningen | Frey S.,FOMI Satellite Geodetic Observatory | Frey S.,MTA Research Group for Physical Geodesy and Geodynamics
Advances in Space Research | Year: 2011

The point source list of the Wilkinson Microwave Anisotropy Probe (WMAP) is a uniform, all-sky catalogue of bright sources with flux density measurements at high (up to 94 GHz) radio frequencies. We investigated the five-year WMAP list to compile a new catalogue of bright and compact extragalactic radio sources to be potentially studied with Very Long Baseline Interferometry at millimeter wavelengths (mm-VLBI) and Space VLBI (SVLBI). After comparing the WMAP data with the existing mm-VLBI catalogues, we sorted out the yet unexplored sources. Using the 41, 61 and 94 GHz WMAP flux densities, we calculated the spectral indices. By collecting optical identifications, lower-frequency radio flux densities and VLBI images from the literature, we created a list of objects which have not been investigated with VLBI at 86 GHz before. With total flux density at least 1 Jy and declination above -40°, we found 37 suitable new targets. It is a nearly 25% addition to the known mm-VLBI sources. Such objects are also potentially useful as phase-reference calibrators for the future Japanese SVLBI mission ASTRO-G at its highest observing frequency (43 GHz). The phase-referencing capability of ASTRO-G would allow long integrations and hence better sensitivity for observing faint target sources close to suitable phase calibrators in the sky. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. 18.

Rushton A.,European Southern Observatory | Miller-Jones J.C.A.,Curtin University Australia | Campana R.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Evangelista Y.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 10 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present evidence for the presence of a weak compact jet during a soft X-ray state of Cygnus X-1. Very-high-resolution radio observations were taken with the VLBA, EVN and MERLIN during a hard-to-soft spectral state change, showing the hard state jet to be suppressed by a factor of about 3-5 in radio flux and unresolved to direct imaging observations (i.e. ≲1 mas at 4cm). High time-resolution X-ray observations with the RXTE-PCA were also taken during the radio monitoring period, showing the source to make the transition from the hard state to a softer state (via an intermediate state), although the source may never have reached the canonical soft state. Using astrometric very long baseline interferometry (VLBI) analysis and removing proper motion, parallax and orbital motion signatures, the residual positions show a scatter of ∼0.2 mas (at 4cm) and ∼3 mas (at 13cm) along the position angle of the known jet axis; these residuals suggest that there is a weak unresolved outflow, with varying size or opacity, during intermediate and soft X-ray states. Furthermore, no evidence was found for extended knots or shocks forming within the jet during the state transition, suggesting that the change in outflow rate may not be sufficiently high to produce superluminal knots. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Cseh D.,University Paris Diderot | Corbel S.,University Paris Diderot | Kaaret P.,University of Iowa | Lang C.,University of Iowa | And 6 more authors.
Astrophysical Journal | Year: 2012

We present new radio, optical, and X-ray observations of three ultraluminous X-ray sources (ULXs) that are associated with large-scale nebulae. We report the discovery of a radio nebula associated with the ULX IC 342 X-1 using the Very Large Array (VLA). Complementary VLA observations of the nebula around Holmberg II X-1, and high-frequency Australia Telescope Compact Array and Very Large Telescope spectroscopic observations of NGC 5408 X-1 are also presented. We study the morphology, ionization processes, and the energetics of the optical/radio nebulae of IC 342 X-1, Holmberg II X-1, and NGC 5408 X-1. The energetics of the optical nebula of IC 342 X-1 is discussed in the framework of standard bubble theory. The total energy content of the optical nebula is 6 × 1052erg. The minimum energy needed to supply the associated radio nebula is 9.2 × 1050erg. In addition, we detected an unresolved radio source at the location of IC 342 X-1 at the VLA scales. However, our Very Long Baseline Interferometry (VLBI) observations using the European VLBI Network likely rule out the presence of any compact radio source at milliarcsecond (mas) scales. Using a simultaneous Swift X-ray Telescope measurement, we estimate an upper limit on the mass of the black hole in IC 342 X-1 using the "fundamental plane" of accreting black holes and obtain M BH ≤ (1.0 0.3) × 103 M. Arguing that the nebula of IC 342 X-1 is possibly inflated by a jet, we estimate accretion rates and efficiencies for the jet of IC 342 X-1 and compare with sources like S26, SS433, and IC 10 X-1. © 2012 The American Astronomical Society. All rights reserved.

Alexandroff R.,Princeton University | Overzier R.A.,University of Texas at Austin | Paragi Z.,Joint Institute for VLBI in Europe JIVE | Paragi Z.,MTA Research Group for Physical Geodesy and Geodynamics | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We have used the European very long baseline interferometry (VLBI) Network (EVN) to observe a sample of Lyman break analogues (LBAs), nearby (z < 0.3) galaxies with properties similar to the more distant Lyman break galaxies (LBGs). The study of LBGs may help define the feedback relationship between black holes (BHs) and their host galaxies. Previous Very Large Array (VLA) observations have shown that the kpc-scale radio emission from LBAs is dominated by starbursts. The main targets of this VLBI experiment were selected because they possessed emission-line properties between starbursts and Type 2 (obscured) active galactic nuclei (AGN). Eight targets (three star-forming LBAs, four composite LBAs and one Type 1 AGN) were observed at 5GHz, four of which (one star-forming LBA and three composite LBAs) were also observed at 1.7GHz. One star-forming LBA and one composite LBA were detected above 5σ at 1.7GHz (only), while the AGN was detected at 5GHz. In both LBAs, the radio luminosity (L R) exceeds that expected from supernovae (remnants) based on a comparison with Arp 220, Arp 229A and Mrk 273, by factors of. The composite LBA exhibits a compact core emitting around 10per cent of the VLA flux density. The high T b of 3.5 × 10 7K and excess core L R with respect to the L R/L X relation of radio-quiet AGN indicate that this LBA possesses an obscured AGN (M BH∼ 10 5 - 7M ⊙). In three other composite LBAs detected previously in the X-ray, no radio sources were detected, indicating either variability or the presence of an obscured AGN below our radio sensitivity. While weak AGN may coexist with the starbursts as shown in at least one of the LBAs, their contribution to the total radio flux is fairly minimal. Our results show that the detection of such weak AGN presents a challenge at radio, X-ray and optical emission-line wavelengths at z∼ 0.2, indicating the great difficulties that need to be overcome in order to study similar processes at high redshift when these types of galaxies were common. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Yang J.,Joint Institute for VLBI in Europe | Brocksopp C.,University College London | Corbel S.,University Paris Diderot | Paragi Z.,Joint Institute for VLBI in Europe | And 3 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010

The recently discovered Galactic X-ray transient XTE J1752-223 entered its first known outburst in 2010, emitting from the X-ray to the radio regimes. Its general X-ray properties were consistent with those of a black hole candidate in various spectral states, when ejection of jet components is expected. To verify this, we carried out very long baseline interferometry (VLBI) observations. The measurements were carried out with the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA) at four epochs in 2010 February. The images at the first three epochs show a moving jet component that is significantly decelerated by the last epoch, when a new jet component appears that is likely to be associated with the receding jet side. The overall picture is consistent with an initially mildly relativistic jet, interacting with the interstellar medium or with swept-up material along the jet. The brightening of the receding ejecta at the final epoch can be well explained by initial Doppler deboosting of the emission in the decelerating jet. © 2010 The Authors. Journal compilation © 2010 RAS.

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