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  • 1
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    An accurate geometric distance to the compact binary SS Cygni vindicates accretion disc theory (2013)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2013-05-25
    Description: Dwarf novae are white dwarfs accreting matter from a nearby red dwarf companion. Their regular outbursts are explained by a thermal-viscous instability in the accretion disc, described by the disc instability model that has since been successfully extended to other accreting systems. However, the prototypical dwarf nova, SS Cygni, presents a major challenge to our understanding of accretion disc theory. At the distance of 159 +/- 12 parsecs measured by the Hubble Space Telescope, it is too luminous to be undergoing the observed regular outbursts. Using very long baseline interferometric radio observations, we report an accurate, model-independent distance to SS Cygni that places the source substantially closer at 114 +/- 2 parsecs. This reconciles the source behavior with our understanding of accretion disc theory in accreting compact objects.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Miller-Jones, J C A -- Sivakoff, G R -- Knigge, C -- Kording, E G -- Templeton, M -- Waagen, E O -- New York, N.Y. -- Science. 2013 May 24;340(6135):950-2. doi: 10.1126/science.1237145.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉International Centre for Radio Astronomy Research, Curtin University, Perth, WA 6845, Australia. james.miller-jones@curtin.edu.au〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23704566" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10 (2011)
    Nature Publishing Group (NPG)
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    Publication Date: 2011-01-11
    Description: Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Reines, Amy E -- Sivakoff, Gregory R -- Johnson, Kelsey E -- Brogan, Crystal L -- England -- Nature. 2011 Feb 3;470(7332):66-8. doi: 10.1038/nature09724. Epub 2011 Jan 9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Astronomy, University of Virginia, 530 McCormick Road, Charlottesville, Virginia 22904, USA. areines@virginia.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21217688" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Rapid compact jet quenching in the Galactic black hole candidate X-ray binary MAXI J1535−571 (2020)
    Oxford University Press
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    Publication Date: 2020-09-01
    Description: We present results from six epochs of quasi-simultaneous radio, (sub-)millimetre, infrared, optical, and X-ray observations of the black hole X-ray binary MAXI J1535−571. These observations show that as the source transitioned through the hard–intermediate X-ray state towards the soft–intermediate X-ray state, the jet underwent dramatic and rapid changes. We observed the frequency of the jet spectral break, which corresponds to the most compact region in the jet where particle acceleration begins (higher frequencies indicate closer to the black hole), evolves from the infrared band into the radio band (decreasing by ≈3 orders of magnitude) in less than a day. During one observational epoch, we found evidence of the jet spectral break evolving in frequency through the radio band. Estimating the magnetic field and size of the particle acceleration region shows that the rapid fading of the high-energy jet emission was not consistent with radiative cooling; instead, the particle acceleration region seems to be moving away from the black hole on approximately dynamical time-scales. This result suggests that the compact jet quenching is not caused by local changes to the particle acceleration, rather we are observing the acceleration region of the jet travelling away from the black hole with the jet flow. Spectral analysis of the X-ray emission shows a gradual softening in the few days before the dramatic jet changes, followed by a more rapid softening ∼1–2 d after the onset of the jet quenching.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 4
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    Erratum: Disc-jet coupling in the Terzan 5 neutron star X-ray binary EXO 1745-248 (2016)
    Oxford University Press
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    Publication Date: 2016-07-22
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    The reproducible radio outbursts of SS Cygni (2016)
    Oxford University Press
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    Publication Date: 2016-06-24
    Description: We present the results of our intensive radio observing campaign of the dwarf nova SS Cyg during its 2010 April outburst. We argue that the observed radio emission was produced by synchrotron emission from a transient radio jet. Comparing the radio light curves from previous and subsequent outbursts of this system (including high-resolution observations from outbursts in 2011 and 2012) shows that the typical long and short outbursts of this system exhibit reproducible radio outbursts that do not vary significantly between outbursts, which is consistent with the similarity of the observed optical, ultraviolet and X-ray light curves. Contemporaneous optical and X-ray observations show that the radio emission appears to have been triggered at the same time as the initial X-ray flare, which occurs as disc material first reaches the boundary layer. This raises the possibility that the boundary region may be involved in jet production in accreting white dwarf systems. Our high spatial resolution monitoring shows that the compact jet remained active throughout the outburst with no radio quenching.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Lord of the Rings - Return of the King: Swift-XRT observations of dust scattering rings around V404 Cygni (2016)
    Oxford University Press
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    Publication Date: 2016-08-26
    Description: On 2015 June 15, the black hole X-ray binary V404 Cygni went into outburst, exhibiting extreme X-ray variability which culminated in a final flare on June 26. Over the following days, the Swift -X-ray Telescope detected a series of bright rings, comprising five main components that expanded and faded with time, caused by X-rays scattered from the otherwise unobservable dust layers in the interstellar medium in the direction of the source. Simple geometrical modelling of the rings’ angular evolution reveals that they have a common temporal origin, coincident with the final, brightest flare seen by INTEGRAL 's JEM X-1, which reached a 3–10 keV flux of ~25 Crab. The high quality of the data allows the dust properties and density distribution along the line of sight to the source to be estimated. Using the Rayleigh–Gans approximation for the dust scattering cross-section and a power-law distribution of grain sizes a , a – q , the average dust emission is well modelled by $q = 3.90^{+0.09}_{-0.08}$ and maximum grain size of $a_+ = 0.147^{+0.024}_{-0.004} {\rm \ \mu m}$ , though significant variations in q are seen between the rings. The recovered dust density distribution shows five peaks associated with the dense sheets responsible for the rings at distances ranging from 1.19 to 2.13 kpc, with thicknesses of ~40–80 pc and a maximum density occurring at the location of the nearest sheet. We find a dust column density of N dust (2.0–2.5)  x  10 11 cm –2 , consistent with the optical extinction to the source. Comparison of the inner rings’ azimuthal X-ray evolution with archival Wide-field Infrared Survey Explorer mid-IR data suggests that the second most distant ring follows the general IR emission trend, which increases in brightness towards the Galactic north side of the source.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Radio monitoring of the hard state jets in the 2011 outburst of MAXI J1836-194 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-30
    Description: MAXI J1836–194 is a Galactic black hole candidate X-ray binary that was discovered in 2011 when it went into outburst. In this paper, we present the full radio monitoring of this system during its ‘failed’ outburst, in which the source did not complete a full set of state changes, only transitioning as far as the hard intermediate state. Observations with the Karl G. Jansky Very Large Array (VLA) and Australia Telescope Compact Array (ATCA) show that the jet properties changed significantly during the outburst. The VLA observations detected linearly polarized emission at a level of ~1 per cent early in the outburst, increasing to ~3 per cent as the outburst peaked. High-resolution images with the Very Long Baseline Array (VLBA) show an ~15 mas jet along the position angle –21 ± 2°, in agreement with the electric vector position angle found from our polarization results (–21 ± 4°), implying that the magnetic field is perpendicular to the jet. Astrometric observations suggest that the system required an asymmetric natal kick to explain its observed space velocity. Comparing quasi-simultaneous X-ray monitoring with the 5 GHz VLA observations from the 2011 outburst shows an unusually steep hard-state radio/X-ray correlation of $L_{\rm R} \propto L_{\rm X}^{1.8\pm 0.2}$ , where L R and L X denote the radio and X-ray luminosities, respectively. With ATCA and Swift monitoring of the source during a period of re-brightening in 2012, we show that the system lay on the same steep correlation. Due to the low inclination of this system, we then investigate the possibility that the observed correlation may have been steepened by variable Doppler boosting.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate (2015)
    Oxford University Press
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    Publication Date: 2015-09-16
    Description: We report the detection of steady radio emission from the known X-ray source X9 in the globular cluster 47 Tuc. With a double-peaked C  iv emission line in its ultraviolet spectrum providing a clear signature of accretion, this source had been previously classified as a cataclysmic variable. In deep ATCA (Australia Telescope Compact Array) imaging from 2010 and 2013, we identified a steady radio source at both 5.5 and 9.0 GHz, with a radio spectral index (defined as S α ) of α = –0.4 ± 0.4. Our measured flux density of 42 ± 4 μJy beam –1 at 5.5 GHz implies a radio luminosity ( L ) of 5.8  x  10 27  erg s –1 , significantly higher than any previous radio detection of an accreting white dwarf. Transitional millisecond pulsars, which have the highest radio-to-X-ray flux ratios among accreting neutron stars (still a factor of a few below accreting black holes at the same L X ), show distinctly different patterns of X-ray and radio variability than X9. When combined with archival X-ray measurements, our radio detection places 47 Tuc X9 very close to the radio/X-ray correlation for accreting black holes, and we explore the possibility that this source is instead a quiescent stellar-mass black hole X-ray binary. The nature of the donor star is uncertain; although the luminosity of the optical counterpart is consistent with a low-mass main-sequence donor star, the mass transfer rate required to produce the high quiescent X-ray luminosity of 10 33  erg s –1 suggests the system may instead be ultracompact, with an orbital period of order 25 min. This is the fourth quiescent black hole candidate discovered to date in a Galactic globular cluster, and the only one with a confirmed accretion signature from its optical/ultraviolet spectrum.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-27
    Description: We report the detection of steady radio emission from the known X-ray source X9 in the globular cluster 47 Tuc. With a double-peaked C  iv emission line in its ultraviolet spectrum providing a clear signature of accretion, this source had been previously classified as a cataclysmic variable. In deep ATCA (Australia Telescope Compact Array) imaging from 2010 and 2013, we identified a steady radio source at both 5.5 and 9.0 GHz, with a radio spectral index (defined as S α ) of α = –0.4 ± 0.4. Our measured flux density of 42 ± 4 μJy beam –1 at 5.5 GHz implies a radio luminosity ( L ) of 5.8  x  10 27  erg s –1 , significantly higher than any previous radio detection of an accreting white dwarf. Transitional millisecond pulsars, which have the highest radio-to-X-ray flux ratios among accreting neutron stars (still a factor of a few below accreting black holes at the same L X ), show distinctly different patterns of X-ray and radio variability than X9. When combined with archival X-ray measurements, our radio detection places 47 Tuc X9 very close to the radio/X-ray correlation for accreting black holes, and we explore the possibility that this source is instead a quiescent stellar-mass black hole X-ray binary. The nature of the donor star is uncertain; although the luminosity of the optical counterpart is consistent with a low-mass main-sequence donor star, the mass transfer rate required to produce the high quiescent X-ray luminosity of 10 33  erg s –1 suggests the system may instead be ultracompact, with an orbital period of order 25 min. This is the fourth quiescent black hole candidate discovered to date in a Galactic globular cluster, and the only one with a confirmed accretion signature from its optical/ultraviolet spectrum.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    A Chandra look at the X-ray faint millisecond pulsars in the globular cluster NGC 6752 (2014)
    Oxford University Press
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    Publication Date: 2014-05-04
    Description: We combine new and archival Chandra observations of the globular cluster NGC 6752 to create a deeper X-ray source list, and study the faint radio millisecond pulsars (MSPs) of this cluster. We detect four of the five MSPs in NGC 6752, and present evidence for emission from the fifth. The X-rays from these MSPs are consistent with thermal emission from the neutron star surfaces, with significantly higher fitted blackbody temperatures than other globular cluster MSPs (though we cannot rule out contamination by non-thermal emission or other X-ray sources). NGC 6752 E is one of the lowest- L X MSPs known, with L X (0.3–8 keV) = $1.0^{+0.9}_{-0.5}\times 10^{30}$ erg s –1 . We check for optical counterparts of the three isolated MSPs in the core using new Hubble Space Telescope Advanced Camera for Surveys images, finding no plausible counterparts, which is consistent with their lack of binary companions. We compile measurements of L X and spin-down power for radio MSPs from the literature, including errors where feasible. We find no evidence that isolated MSPs have lower L X than MSPs in binary systems, omitting binary MSPs showing emission from intrabinary wind shocks. We find weak evidence for an inverse correlation between the estimated temperature of the MSP X-rays and the known MSP spin period, consistent with the predicted shrinking of the MSP polar cap size with increasing spin period.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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