36 research outputs found
Examples of extreme intraday variability
No full textThe original publication can be found at www.springerlink.comLucyna Kedziora-Chudczer, David L. Jauncey, Mark A. Wieringa, Anastasios K. Tzioumis and Hayley E. Bignal
Radio intra-day variability: Answers and questions
No full textThe original publication can be found at www.springerlink.comIntra-day variability (IDV) of active galactic nuclei (AGN) has been detected from gamma-ray energies to radio wavelengths. At high energies, such variability appears to be intrinsic to the sources themselves. However, at radio wavelengths, brightness temperatures as high as1018 to 1021 K are encountered if the IDV is intrinsic to the source. We discuss here the accumulating evidence showing that, at radio wavelengths where the highest brightness temperatures are encountered, interstellar scintillation (ISS) is the principal mechanism causing IDV. While ISS reduces the implied brightness temperatures, they still remain uncomfortably high.David L. Jauncey, Lucyna Kedziora-Chudczer, James E.J. Lovell, Jean-Pierre Macquart, George D. Nicolson, Rick A. Perley, John E. Reynolds, Anastasios K. Tzioumis, Mark H. Wieringa and Hayley E. Bignal
Revisiting the relativistic ejection event in XTE J1550-564 during the 1998 outburst
No full textWe revisit the discovery outburst of the X-ray transient XTE J1550−564 during which relativistic jets were observed in 1998 September, and review the radio images obtained with the Australian Long Baseline Array, and light curves obtained with the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array. Based on Hi spectra, we constrain the source distance to between 3.3 and 4.9 kpc. The radio images, taken some 2 d apart, show the evolution of an ejection event. The apparent separation velocity of the two outermost ejecta is at least 1.3c and may be as large as 1.9c; when relativistic effects are taken into account, the inferred true velocity is ≥ 0.8c. The flux densities appear to peak simultaneously during the outburst, with a rather flat (although still optically thin) spectral index of −0.2
The Deep X-ray Radio Blazar Survey (DXRBS) - II. New identifications
No full textThe definitive version may be found at www.wiley.comHermine Landt, Paolo Padovani, Eric S. Perlman, Paolo Giommi, Hayley Bignall and Anastasios Tzioumi
On the masses and evolutionary status of the black hole binary GX 339-4: a twin system of XTE J1550-564?
No full textWe apply the K-correction to the black hole low-mass X-ray binary (LMXB) GX 339-4 which implies MX? 6 M? by only assuming that the companion is more massive than ?0.17 M?, the lower limit allowed by applying a ‘stripped-giant’ model. This evolutionary model successfully reproduces the observed properties of the system. We obtain a maximum mass for the companion of M2? 1.1 M? and an upper limit to the mass ratio of q(=M2/MX) ? 0.125. The high X-ray activity displayed by the source suggests a relatively large mass transfer rate which, according to the model, results in M2? 0.3 M? and MX? 7 M?. We have also applied this scenario to the black hole binary XTE J1550-564, which has a similar orbital period but the donor is detected spectroscopically. The model successfully reproduces the observed stellar parameter
Upper limits on central black hole masses of globular clusters from radio emission and a possible black hole detection in the Ursa Minor dwarf galaxy
No full textUvA-DARE (Digital Academic Repository) Link to publication Citation for published version (APA): QUENCHING OF THE RADIO JET DURING THE X-RAY HIGH STATE OF GX 339Ϫ4
No full textQuenching of the radio jet during the x-ray high state in GX 339-4 Fender, R.P.; Corbel, S.; Tzioumis, A.K.; Sood, R.; McIntyre, V.; Campbell-Wilson, D.; Durouchoux, P.; Harmon, B.A. Published in: Astrophysical Journal DOI: 10.1086/312128 Link to publication Citation for published version (APA): Fender, R. P., Corbel, S., Tzioumis, A. K., Sood, R., McIntyre, V., Campbell-Wilson, D., ... Harmon, B. A. (1999). Quenching of the radio jet during the x-ray high state in GX 339-4. Astrophysical Journal, 519, L165-L168. https://doi.org/10.1086/312128 General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 29 Jun 2019 L165 The Astrophysical Journal, 519:L165-L168, 1999 July 10 ᭧ 1999. The American Astronomical Society. All rights reserved. Printed in U.S.A. ABSTRACT We have observed the black hole candidate X-ray binary GX 339Ϫ4 at radio wavelengths before, during, and after the 1998 high/soft X-ray state transition. We find that the radio emission from the system is strongly correlated with the hard X-ray emission and is reduced by a factor of ≥25 during the high/soft state compared with the more usual low/hard state. At the points of state transition, we note brief periods of unusually optically thin radio emission that may correspond to discrete ejection events. We propose that in the low/hard state, black hole X-ray binaries produce a quasi-continuous outflow, that in the high/soft state, this outflow is suppressed, and that state transitions often result in one or more discrete ejection events. Future models for low/hard states, such as advection-dominated solutions, need to take into account the strong outflow of relativistic electrons from the system. We propose that the inferred Comptonizing corona and the base of the jetlike outflow are the same thing, based on the strong correlation between radio and hard X-ray emission in GX 339Ϫ4 and other X-ray binaries and on the similarity in inferred location and composition of these two components. QUENCHING OF THE RADIO JET DURING THE X-RAY HIGH STATE OF GX 339Ϫ
The nature of the X-ray transient MAXI J0556−332
No full textPhase-resolved spectroscopy of the newly discovered X-ray transient MAXIJ0556-332 has revealed the presence of narrow emission lines in the Bowen region that most likely arise on the surface of the mass donor star in this low-mass X-ray binary. A period search of the radial velocities of these lines provides two candidate orbital periods (16.43 ± 0.12 and 9.754 ± 0.048h), which differ from any potential X-ray periods reported. Assuming that MAXIJ0556-332 is a relatively high-inclination system that harbours a precessing accretion disc in order to explain its X-ray properties, it is only possible to obtain a consistent set of system parameters for the longer period. These assumptions imply a mass ratio of q≃ 0.45, a radial velocity semi-amplitude of the secondary of K 2≃ 190kms -1 and a compact object mass of the order of the canonical neutron star mass, making a black hole nature for MAXIJ0556-332 unlikely. We also report the presence of strong Niii emission lines in the spectrum, thereby inferring a high N/O abundance. Finally, we note that the strength of all emission lines shows a continuing decay over the ≃1 month of our observations
Circinus X-1: survivor of a highly asymmetric supernova
No full textWe have analyzed the kinematical parameters of Cir X-1 to constrain the nature of its companion star, the eccentricity of the binary and the pre-supernova parameter space. We argue that the companion is most likely to be a low-mass (< 2.0 M_sun) unevolved star and that the eccentricity of the orbit is 0.94 +/- 0.04. We have evaluated the dynamical effects of the supernova explosion and we find it must have been asymmetric. On average, we find that a kick of 740 km/s is needed to account for the recently measured radial velocity of +430 km/s (Johnston, Fender & Wu) for this extreme system. The corresponding minimum kick velocity is 500 km/s. This is the largest kick needed to explain the motion of any observed binary system. If Cir X-1 is associated with the supernova remnant G321.9-0.3 then we find a limiting minimum age of this remnant of 60000 yr. Furthermore, we predict that the companion star has lost 10% of its mass as a result of stripping and ablation from the impact of the supernova shell shortly after the explosion
A simple disc wind model for broad absorption line quasars
No full textApproximately 20 per cent of quasi-stellar objects (QSOs) exhibit broad, blue-shifted absorption lines in their ultraviolet spectra. Such features provide clear evidence for significant outflows from these systems, most likely in the form of accretion disc winds. These winds may represent the ‘quasar’ mode of feedback that is often invoked in galaxy formation/evolution models, and they are also key to unification scenarios for active galactic nuclei (AGN) and QSOs. To test these ideas, we construct a simple benchmark model of an equatorial, biconical accretion disc wind in a QSO and use a Monte Carlo ionization/radiative transfer code to calculate the ultraviolet spectra as a function of viewing angle. We find that for plausible outflow parameters, sightlines looking directly into the wind cone do produce broad, blue-shifted absorption features in the transitions typically seen in broad absorption line (BAL) QSOs. However, our benchmark model is intrinsically X-ray weak in order to prevent overionization of the outflow, and the wind does not yet produce collisionally excited line emission at the level observed in non-BAL QSOs. As a first step towards addressing these shortcomings, we discuss the sensitivity of our results to changes in the assumed X-ray luminosity and mass-loss rate, Ṁwind. In the context of our adopted geometry, Ṁwind ∼ Ṁacc is required in order to produce significant BAL features. The kinetic luminosity and momentum carried by such outflows would be sufficient to provide significant feedback
