Showing papers by "Zsolt Paragi published in 2005"

High-resolution radio imaging of the most distant radio quasar SDSS J0836+0054

Abstract: We observed SDSS J0836+0054, the most distant radio-loud quasar known at present ($z=5.774$) with the European Very Long Baseline Interferometry (VLBI) Network at the 5 GHz frequency on 2003 November 4. The source is compact at the milli-arcsecond (mas) angular scale with a flux density of 0.34 mJy. The observations with the Very Large Array (VLA) made on the consecutive day support a conclusion that the radio emission from SDSS J0836+0054 is essentially confined within the central 40 pc. Based on our phase-referenced VLBI observation, we obtained the astrometric position of the source accurate to ~2 mas.

High-resolution radio imaging of the most distant radio quasar SDSS J0836+0054

Abstract: We observed SDSS J0836+0054, the most distant radio-loud quasar known at present (z=5.774) with the European Very Long Baseline Interferometry (VLBI) Network at the 5 GHz frequency on 2003 November 4. The source is compact at the milli-arcsecond (mas) angular scale with a flux density of 0.34 mJy. The observations with the Very Large Array (VLA) made on the consecutive day support a conclusion that the radio emission from SDSS J0836+0054 is essentially confined within the central 40 pc. Based on our phase-referenced VLBI observation, we obtained the astrometric position of the source accurate to ~2 mas.

Structure in the radio counterpart to the 2004 Dec 27 giant flare from SGR 1806-20

Abstract: On Dec 27, 2004, the magnetar SGR 1806-20 underwent an enormous outburst resulting in the formation of an expanding, moving, and fading radio source. We report observations of this radio source with the Multi-Element Radio-Linked Interferometer Network (MERLIN) and the Very Long Baseline Array (VLBA). The observations confirm the elongation and expansion already reported based on observations at lower angular resolutions, but suggest that at early epochs the structure is not consistent with the very simplest models such as a smooth flux distribution. In particular there appears to be significant structure on small angular scales, with ~10% of the radio flux arising on angular scales <100 milliarcsec. This structure may correspond to localised sites of particle acceleration during the early phases of expansion and interaction with the ambient medium.

e-VLBI observations of SN2001em - an off-axis GRB candidate

Abstract: Studying transient phenomena with the Very Long Baseline Interferometry (VLBI) technique faces severe difficulties because the turnaround time of the experiments from the observations to the scientific result is rather long. The e-VLBI technique has made it possible to transfer the data from a number of European VLBI Network (EVN) telescopes to the central data processor at JIVE through optical fibres, and correlate them in real time. The main goal of this paper is to introduce this rapidly developing new technique, by presenting observational results from a recent experiment. We observed SN2001em, a Type Ib/c supernova with an e-VLBI array and the Multi-Element Radio Linked Interferometer Network (MERLIN) in the UK. The source is marginally detected in our observations. We cannot make definite conclusions whether it is resolved at 1.6 GHz or not. Our data show that SN2001em either started fading in the last couple of months, or its radio spectrum is inverted at low frequencies,indicating free-free or synchrotron self-absorption. This is quite unusual, but not unprecedented in radio SNe.

Detecting sub-mJy sources with the EVN

Abstract: Some microquasars are permanently bright radio sources while others are faint but produce powerful radio outbursts. Most of the X-ray binaries (XRB) however are very faint or undetected in the radio regime. The European VLBI Network (EVN) recently introduced the Mark5 recording system which allows data rates of up to 1 Gbit s -1 . This increases the sensitivity of the array significantly. We briefly describe recent developments in the EVN in terms of reliability of the network and also data quality. We demonstrate the power of the EVN in detecting sub-mJy radio sources with modest integration times (order of hours). This high sensitivity capability will permit the study of variable Galactic sources at milli-arcsecond resolution. An estimate is given for the lowest detectable mass of hypothetical intermediate-mass black holes (IMBH) in nearby galaxies, provided these are located in radio-jet systems analogous to microquasars and active galactic nuclei.

e-VLBI observations of SN2001em - an off-axis GRB candidate .

Abstract: Studying transient phenomena with the Very Long Baseline Interferometry (VLBI) technique faces severe difficulties because the turnaround time of the experiments from the observations to the scientific result is rather long. The e-VLBI technique has made it possible to transfer the data from a number of European VLBI Network (EVN) telescopes to the central data processor at JIVE through optical fibres, and correlate them in real time. The main goal of this paper is to introduce this rapidly developing new technique, by presenting observational results from a recent experiment. We observed SN2001em, a Type Ib/c supernova with an e-VLBI array and the Multi-Element Radio Linked Interferometer Network (MERLIN) in the UK. The source is marginally detected in our observations. We cannot make definite conclusions whether it is resolved at 1.6 GHz or not. Our data show that SN2001em either started fading in the last couple of months, or its radio spectrum is inverted at low frequencies, indicating free-free or synchrotron self-absorption. This is quite unusual, but not unprecedented in radio SNe.