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  • 1
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    An extremely luminous X-ray outburst at the birth of a supernova (2008)
    Nature Publishing Group (NPG)
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    Publication Date: 2008-05-24
    Description: Massive stars end their short lives in spectacular explosions--supernovae--that synthesize new elements and drive galaxy evolution. Historically, supernovae were discovered mainly through their 'delayed' optical light (some days after the burst of neutrinos that marks the actual event), preventing observations in the first moments following the explosion. As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of the explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the 'break-out' of the supernova shock wave from the progenitor star, and show that the inferred rate of such events agrees with that of all core-collapse supernovae. We predict that future wide-field X-ray surveys will catch each year hundreds of supernovae in the act of exploding.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Soderberg, A M -- Berger, E -- Page, K L -- Schady, P -- Parrent, J -- Pooley, D -- Wang, X-Y -- Ofek, E O -- Cucchiara, A -- Rau, A -- Waxman, E -- Simon, J D -- Bock, D C-J -- Milne, P A -- Page, M J -- Barentine, J C -- Barthelmy, S D -- Beardmore, A P -- Bietenholz, M F -- Brown, P -- Burrows, A -- Burrows, D N -- Bryngelson, G -- Cenko, S B -- Chandra, P -- Cummings, J R -- Fox, D B -- Gal-Yam, A -- Gehrels, N -- Immler, S -- Kasliwal, M -- Kong, A K H -- Krimm, H A -- Kulkarni, S R -- Maccarone, T J -- Meszaros, P -- Nakar, E -- O'Brien, P T -- Overzier, R A -- de Pasquale, M -- Racusin, J -- Rea, N -- York, D G -- England -- Nature. 2008 May 22;453(7194):469-74. doi: 10.1038/nature06997.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, New Jersey 08544, USA. alicia@astro.princeton.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18497815" 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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  • 2
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    Two stellar-mass black holes in the globular cluster M22 (2012)
    Nature Publishing Group (NPG)
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    Publication Date: 2012-10-06
    Description: Hundreds of stellar-mass black holes probably form in a typical globular star cluster, with all but one predicted to be ejected through dynamical interactions. Some observational support for this idea is provided by the lack of X-ray-emitting binary stars comprising one black hole and one other star ('black-hole/X-ray binaries') in Milky Way globular clusters, even though many neutron-star/X-ray binaries are known. Although a few black holes have been seen in globular clusters around other galaxies, the masses of these cannot be determined, and some may be intermediate-mass black holes that form through exotic mechanisms. Here we report the presence of two flat-spectrum radio sources in the Milky Way globular cluster M22, and we argue that these objects are black holes of stellar mass (each approximately 10-20 times more massive than the Sun) that are accreting matter. We find a high ratio of radio-to-X-ray flux for these black holes, consistent with the larger predicted masses of black holes in globular clusters compared to those outside. The identification of two black holes in one cluster shows that ejection of black holes is not as efficient as predicted by most models, and we argue that M22 may contain a total population of approximately 5-100 black holes. The large core radius of M22 could arise from heating produced by the black holes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Strader, Jay -- Chomiuk, Laura -- Maccarone, Thomas J -- Miller-Jones, James C A -- Seth, Anil C -- England -- Nature. 2012 Oct 4;490(7418):71-3. doi: 10.1038/nature11490.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA. strader@pa.msu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23038466" 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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    Doppler shifts on the spin period of the intermediate polar FO Aqr with K2 (2016)
    Oxford University Press
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    Publication Date: 2016-07-31
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    A far-ultraviolet variable with an 18-minute period in the globular cluster NGC 1851 (2016)
    Oxford University Press
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    Publication Date: 2016-06-24
    Description: We present the detection of a variable star with an 18.05 min period in far-ultraviolet (FUV) images of the globular cluster NGC 1851 taken with the Hubble Space Telescope ( HST ). A candidate optical counterpart lies on the red horizontal branch or the asymptotic giant branch star of the cluster, but it is statistically possible that this is a chance superposition. This interpretation is supported by optical spectroscopy obtained with HST /Space Telescope Imaging Spectrograph (STIS): the spectrum contains none of the strong emission lines that would be expected if the object was a symbiotic star (i.e. a compact accretor fed by a giant donor). We therefore consider two other possibilities for the nature of FUV variable: (i) an intermediate polar (i.e. a compact binary containing an accreting magnetic white dwarf), or (ii) an AM CVn star (i.e. an interacting double-degenerate system). In the intermediate polar scenario, the object is expected to be an X-ray source. However, no X-rays are detected at its location in ~=65 ksec of Chandra imaging, which limits the X-ray luminosity to L X ≤ 10 32  erg s –1 . We therefore favour the AM CVn interpretation, but a FUV spectrum is needed to distinguish conclusively between the two possibilities. If the object is an AM CVn binary, it would be the first such system known in any globular cluster.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    SN 2013ab: a normal Type IIP supernova in NGC 5669 (2015)
    Oxford University Press
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    Publication Date: 2015-05-08
    Description: We present densely sampled ultraviolet/optical photometric and low-resolution optical spectroscopic observations of the Type IIP supernova 2013ab in the nearby (~24 Mpc) galaxy NGC 5669, from 2 to 190 d after explosion. Continuous photometric observations, with the cadence of typically a day to one week, were acquired with the 1–2 m class telescopes in the Las Cumbres Observatory Global Telescope network, ARIES telescopes in India and various other telescopes around the globe. The light curve and spectra suggest that the supernova (SN) is a normal Type IIP event with a plateau duration of ~80 d with mid-plateau absolute visual magnitude of –16.7, although with a steeper decline during the plateau (0.92 mag 100 d –1 in V band) relative to other archetypal SNe of similar brightness. The velocity profile of SN 2013ab shows striking resemblance with those of SNe 1999em and 2012aw. Following the Rabinak & Waxman prescription, the initial temperature evolution of the SN emission allows us to estimate the progenitor radius to be ~800 R , indicating that the SN originated from a red supergiant star. The distance to the SN host galaxy is estimated to be 24.3 Mpc from expanding photosphere method. From our observations, we estimate that 0.064 M of 56 Ni was synthesized in the explosion. General relativistic, radiation hydrodynamical modelling of the SN infers an explosion energy of 0.35  x 10 51  erg, a progenitor mass (at the time of explosion) of ~9 M and an initial radius of ~600 R .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Demonstrating the likely neutron star nature of five M31 globular cluster sources with Swift-NuSTAR spectroscopy (2016)
    Oxford University Press
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    Publication Date: 2016-04-07
    Description: We present the results of a joint Swift -NuSTAR spectroscopy campaign on M31. We focus on the five brightest globular cluster X-ray sources in our fields. Two of these had previously been argued to be black hole candidates on the basis of apparent hard-state spectra at luminosities above those for which neutron stars are in hard states. We show that these two sources are likely to be Z-sources (i.e. low magnetic field neutron stars accreting near their Eddington limits), or perhaps bright atoll sources (low magnetic field neutron stars which are just a bit fainter than this level) on the basis of simultaneous Swift and NuSTAR spectra which cover a broader range of energies. These new observations reveal spectral curvature above 6–8 keV that would be hard to detect without the broader energy coverage the NuSTAR data provide relative to Chandra and XMM–Newton . We show that the other three sources are also likely to be bright neutron star X-ray binaries, rather than black hole X-ray binaries. We discuss why it should already have been realized that it was unlikely that these objects were black holes on the basis of their being persistent sources, and we re-examine past work which suggested that tidal capture products would be persistently bright X-ray emitters. We discuss how this problem is likely due to neglecting disc winds in older work that predict which systems will be persistent and which will be transient.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Accretion-induced variability links young stellar objects, white dwarfs, and black holes (2015)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2015-10-11
    Description: The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    Discovery of a high state AM CVn binary in the Galactic Bulge Survey (2016)
    Oxford University Press
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    Publication Date: 2016-08-10
    Description: We report on the discovery of a hydrogen-deficient compact binary (CXOGBS J175107.6-294037) belonging to the AM CVn class in the Galactic Bulge Survey. Deep archival X-ray observations constrain the X-ray positional uncertainty of the source to 0.57 arcsec, and allow us to uniquely identify the optical and UV counterpart. Optical spectroscopic observations reveal the presence of broad, shallow He i absorption lines while no sign of hydrogen is present, consistent with a high state system. We present the optical light curve from Optical Gravitational Lensing Experiment monitoring, spanning 15 yr. It shows no evidence for outbursts; variability is present at the 0.2 mag level on time-scales ranging from hours to weeks. A modulation on a time-scale of years is also observed. A Lomb–Scargle analysis of the optical light curves shows two significant periodicities at 22.90 and 23.22 min. Although the physical interpretation is uncertain, such time-scales are in line with expectations for the orbital and superhump periods. We estimate the distance to the source to be between 0.5 and 1.1 kpc. Spectroscopic follow-up observations are required to establish the orbital period, and to determine whether this source can serve as a verification binary for the eLISA gravitational wave mission.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Discovery of a long-lived, high-amplitude dusty infrared transient (2016)
    Oxford University Press
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    Publication Date: 2016-06-17
    Description: We report the detection of an infrared-selected transient which has lasted at least five years, first identified by a large mid-infrared and optical outburst from a faint X-ray source detected with the Chandra X-ray Observatory . In this paper we rule out several scenarios for the cause of this outburst, including a classical nova, a luminous red nova, AGN flaring, a stellar merger, and intermediate luminosity optical transients, and interpret this transient as the result of a young stellar object (YSO) of at least solar mass accreting material from the remains of the dusty envelope from which it formed, in isolation from either a dense complex of cold gas or massive star formation. This object does not fit neatly into other existing categories of large outbursts of YSOs (FU Orionis types) which may be a result of the object's mass, age, and environment. It is also possible that this object is a new type of transient unrelated to YSOs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Calcium-rich gap transients: tidal detonations of white dwarfs? (2015)
    Oxford University Press
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    Publication Date: 2015-05-22
    Description: We hypothesize that at least some of the recently discovered class of calcium-rich gap transients are tidal detonation events of white dwarfs (WDs) by black holes (BHs) or possibly neutron stars. We show that the properties of the calcium-rich gap transients agree well with the predictions of the tidal detonation model. Under the predictions of this model, we use a follow-up X-ray observation of one of these transients, SN 2012hn, to place weak upper limits on the detonator mass of this system that include all intermediate-mass BHs (IMBHs). As these transients are preferentially in the stellar haloes of galaxies, we discuss the possibility that these transients are tidal detonations of WDs caused by random flyby encounters with IMBHs in dwarf galaxies or globular clusters. This possibility has been already suggested in the literature but without connection to the calcium-rich gap transients. In order for the random flyby cross-section to be high enough, these events would have to be occurring inside these dense stellar associations. However, there is a lack of evidence for IMBHs in these systems, and recent observations have ruled out all but the very faintest dwarf galaxies and globular clusters for a few of these transients. Another possibility is that these are tidal detonations caused by three-body interactions, where a WD is perturbed towards the detonator in isolated multiple star systems. We highlight a number of ways this could occur, even in lower mass systems with stellar-mass BHs or neutron stars. Finally, we outline several new observational tests of this scenario, which are feasible with current instrumentation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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