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McKean J.P.,ASTRON | Berciano Alba A.,ASTRON | Volino F.,Argelander Institute For Astronomie | Tudose V.,ASTRON | And 9 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2011

The bright submillimetre (sub-mm) galaxy MM18423+5938 at redshift 3.9296 has been predicted from mid-infrared (MIR) and millimetre photometry to have an exceptionally large total IR luminosity. We present new radio imaging at 1.4 GHz with the Westerbork Synthesis Radio Telescope that is used to determine a radio-derived total IR luminosity for MM18423+5938 via the well-established radio-far-IR correlation. The flux density is found to be S 1.4GHz = 217 ± 37 μJy, which corresponds to a rest-frame luminosity density of L 1.4GHz = 2.32 ±0.40×10 25 μ -1 W Hz -1, where μ is the magnification from a probable gravitational lens. The radio-derived total IR luminosity and star formation rate are L 8-1000 μm = 5.6 +4.1 -2.4 × 10 13 μ -1 L⊙ and SFR = 9.4 +7.4 -4.9 × 10 3 μ -1M⊙ yr -1, respectively, which are ~9 times smaller than those previously reported. These differences are attributed to the IR spectral energy distribution of MM18423+5938 being poorly constrained by the limited number of reliable photometric data that are currently available, and from a previous misidentification of the object at 70 μm. Using the radio derived total IR luminosity as a constraint, the temperature of the cold dust component is found to be T d ~ 24 +7 -5 K for a dust emissivity of β = 1.5 ± 0.5. The radio-derived properties of this galaxy are still large given the low excitation temperature implied by the CO emission lines and the temperature of the cold dust. Therefore, we conclude that MM18423+5938 is probably gravitationally lensed. © 2011 The Authors Monthly Notices of the Royal Astronomical Society. © 2011 RAS. Source

Marti-Vidal I.,Max Planck Institute for Radio Astronomy | Tudose V.,Netherlands Institute for Radio Astronomy | Tudose V.,Astronomical Institute of the Romanian Academy | Tudose V.,Research Center for Atomic Physics and Astrophysics | And 14 more authors.
Astronomy and Astrophysics | Year: 2011

We report on the VLBI detection of supernova SN2011dh at 22 GHz using a subset of the EVN array. The observations took place 14 days after the discovery of the supernova, thus resulting in a VLBI image of the youngest radio-loud supernova ever. We provide revised coordinates for the supernova with milli-arcsecond precision, linked to the ICRF. The recovered flux density is a factor ~2 below the EVLA flux density reported by other authors at the same frequency and epoch of our observations. This discrepancy could be due to extended emission detected with the EVLA or to calibration problems in the VLBI and/or EVLA observations. © ESO, 2011. Source

Jones S.,University of Southampton | Mchardy I.,University of Southampton | Moss D.,University of Southampton | Seymour N.,University of Southampton | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present intensive quasi-simultaneous X-ray and radio monitoring of the narrow line Seyfert 1 galaxy NGC 4051, over a 16-month period in 2000-01. The X-ray observations were made with the Proportional Counter Array on the Rossi Timing X-ray Explorer (RXTE) and radio observations were made at 8.4 and 4.8 GHz with the Very Large Array (VLA). In the X-ray band NGC 4051 behaves very much like the analogue of a Galactic black hole binary (GBH) system in a 'soft state'. In such systems, there has so far been no firm evidence for an active, radio-emitting jet like those found in 'hard-state' GBHs. VLBI observations of NGC 4051 show three well-separated compact components almost in a line. This structure resembles the core and outer hot spots seen in powerful, jet-dominated, extragalactic radio sources and, although no jet is visible in NGC 4051, suggests that a weak jet may exist. However it has not previously been clear whether the nucleus is currently active in the radio band and whether there is any link between the radio and X-ray emission processes. Radio monitoring of the core of NGC 4051 is complicated by the presence of surrounding extended emission and by the changing array configurations of the VLA. Only in the A configuration is the core reasonably resolved. We have carefully removed the differing contaminations of the core by extended emission in the various arrays. The resulting lightcurve shows no sign of large amplitude variability (i.e. factor 50 per cent) over the 16-month period and is consistent with being constant. Within the 6 A configuration observations where we have greatest sensitivity we see marginal evidence for radio core variability of ∼25 per cent (∼0.12 mJy at 8.4 GHz) on a 2-week time-scale, correlated with X-ray variations. These percentage variations are similar to those of the Seyfert galaxy NGC 5548, which is 10 times brighter. Even if the radio variations in NGC 4051 are real, the percentage variability is much less than in the X-ray band. Within the B configuration observations, although sensitivity is somewhat reduced, there is no sign of correlated X-ray/radio variability. NGC 4051 is one decade lower in radio luminosity than the radio/X-ray/mass fundamental plane for jet-dominated hard-state black holes, although the scatter around the plane is of the same order. The lack of radio variability commonly seen in hard-state GBHs may be explained by orientation effects. Another possibility, consistent with the lack of radio variability, is that the radio emission arises from the X-ray corona although, in that case, the linear structure of the compact radio components is hard to explain. A combination of corona and jet may explain the observations. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

Miller-Jones J.C.A.,NRAO Headquarters | Sivakoff G.R.,University of Virginia | Altamirano D.,University of Amsterdam | Tudose V.,Netherlands Institute for Radio Astronomy | And 24 more authors.
Astrophysical Journal Letters | Year: 2010

The 2009 November outburst of the neutron star X-ray binary Aquila X-1 (Aql X-1) was observed with unprecedented radio coverage and simultaneous pointed X-ray observations, tracing the radio emission around the full X-ray hysteresis loop of the outburst for the first time. We use these data to discuss the disk-jet coupling, finding the radio emission to be consistent with being triggered at state transitions, both from the hard to the soft spectral state and vice versa. Our data appear to confirm previous suggestions of radio quenching in the soft state above a threshold X-ray luminosity of ∼10% of the Eddington luminosity. We also present the first detections of Aql X-1 with very long baseline interferometry, showing that any extended emission is relatively diffuse and consistent with steady jets rather than arising from discrete, compact knots. In all cases where multi-frequency data were available, the source radio spectrum is consistent with being flat or slightly inverted, suggesting that the internal shock mechanism that is believed to produce optically thin transient radio ejecta in black hole X-ray binaries is not active in Aql X-1. © 2010. The American Astronomical Society. All rights reserved.. Source

Russell D.M.,University of Amsterdam | Lewis F.,University of Cardiff | Lewis F.,Open University Milton Keynes | Lewis F.,University of South Wales | And 10 more authors.
Proceedings of the International Astronomical Union | Year: 2010

Most accretion-powered relativistic jet sources in our Galaxy are transient X-ray binaries (XBs). Efforts to coordinate multiwavelength observations of these objects have improved dramatically over the last decade. Now the challenge is to interpret broadband spectral energy distributions (SEDs) of XBs that are well sampled in both wavelength and time. Here we focus on the evolution of the jet in their broadband spectra. Some of the most densely sampled broadband SEDs of a neutron star transient (IGR J00291+5934) are used to constrain the optically thick-thin break in the jet spectrum. For the black hole transient XTE J1550-564, infrared - X-ray correlations, evolution of broadband spectra and timing signatures indicate that synchrotron emission from the jet likely dominates the X-ray power law at low luminosities (∼ (2 × 10 -4 - 2 × 10-3 ) LEdd ) during the hard state outburst decline. © International Astronomical Union 2011. Source

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