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  • 1
    Electronic Resource
    Electronic Resource
    A high-velocity black hole on a Galactic-halo orbit in the solar neighbourhood (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 413 (2001), S. 139-141 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Only a few of the dozen or so known stellar-mass black holes have been observed away from the plane of the Galaxy. Those few could have been ejected from the plane as a result of a ‘kick’ received during a supernova explosion, or they could be remnants of the population of massive ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35093060
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  • 2
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    Gemini optical observations of binary millisecond pulsars (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-16
    Description: Millisecond pulsars (MSPs) are rapidly spinning neutron stars, with spin periods P s 10 ms, which have been most likely spun up after a phase of matter accretion from a companion star. In this work, we present the results of the search for the companion stars of four binary MSPs, carried out with archival data from the Gemini South telescope. Based upon a very good positional coincidence with the pulsar radio coordinates, we likely identified the companion stars to three MSPs, namely PSR J0614–3329 ( g  = 21.95 ± 0.05), J1231–1411 ( g  = 25.40 ± 0.23), and J2017+0603 ( g  = 24.72 ± 0.28). For the last pulsar (PSR J0613–0200) the identification was hampered by the presence of a bright star ( g  = 16 ± 0.03) at ~2 arcsec from the pulsar radio coordinates and we could only set 3 upper limits of g  = 25.0, r  = 24.3, and i  = 24.2 on the magnitudes of its companion star. The candidate companion stars to PSR J0614–3329, J1231–1411, and J2017+0603 can be tentatively identified as He white dwarfs (WDs) on the basis of their optical colours and brightness and the comparison with stellar model tracks. From the comparison of our multiband photometry with stellar model tracks we also obtained possible ranges on the mass, temperature, and gravity of the candidate WD companions to these three MSPs. Optical spectroscopy observations are needed to confirm their possible classification as He WDs and accurately measure their stellar parameters.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 3
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    Observations of three young {gamma}-ray pulsars with the Gran Telescopio Canarias (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-29
    Description: We report the analysis of the first deep optical observations of three isolated -ray pulsars detected by the Fermi Gamma-ray Space Telescope : the radio-loud PSR J0248+6021 and PSR J0631+1036, and the radio-quiet PSR J0633+0632. The latter has also been detected in the X-rays. The pulsars are very similar in their spin-down age ( ~ 40–60 kyr), spin-down energy ( $\dot{E} \sim 10^{35}$  erg s –1 ), and dipolar surface magnetic field ( B  ~ 3–5  x  10 12  G). These pulsars are promising targets for multiwavelength observations, since they have been already detected in -rays and in radio or X-rays. None of them has been detected yet in the optical band. We observed the three pulsar fields in 2014 with the Spanish 10.4 m Gran Telescopio Canarias (GTC). We could not find any candidate optical counterpart to the three pulsars close to their most recent radio or Chandra positions down to 3 limits of g ' ~ 27.3, g ' ~ 27, g ' ~ 27.3 for PSR J0248+6021, J0631+1036, and J0633+0632, respectively. From the inferred optical upper limits and estimated distance and interstellar extinction, we derived limits on the pulsar optical luminosity. We also searched for the X-ray counterpart to PSR J0248+6021 with Chandra but we did not detect the pulsar down to a 3 flux limit of 5  x  10 –14  erg cm –2  s –1 (0.3–10 keV). For all these pulsars, we compared the optical flux upper limits with the extrapolations in the optical domain of the -ray spectra and compared their multiwavelength properties with those of other -ray pulsars of comparable age.
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  • 4
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    The X-ray outburst of the Galactic Centre magnetar SGR J1745-2900 during the first 1.5 year (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-05
    Description: In 2013 April a new magnetar, SGR 1745–2900, was discovered as it entered an outburst, at only 2.4 arcsec angular distance from the supermassive black hole at the centre of the Milky Way, Sagittarius A*. SGR 1745–2900 has a surface dipolar magnetic field of ~2 x 10 14  G, and it is the neutron star closest to a black hole ever observed. The new source was detected both in the radio and X-ray bands, with a peak X-ray luminosity L X ~ 5 x 10 35  erg s –1 . Here we report on the long-term Chandra (25 observations) and XMM–Newton (eight observations) X-ray monitoring campaign of SGR 1745–2900 from the onset of the outburst in 2013 April until 2014 September. This unprecedented data set allows us to refine the timing properties of the source, as well as to study the outburst spectral evolution as a function of time and rotational phase. Our timing analysis confirms the increase in the spin period derivative by a factor of ~2 around 2013 June, and reveals that a further increase occurred between 2013 October 30 and 2014 February 21. We find that the period derivative changed from 6.6 x 10 –12 to 3.3 x 10 –11  s s –1 in 1.5 yr. On the other hand, this magnetar shows a slow flux decay compared to other magnetars and a rather inefficient surface cooling. In particular, starquake-induced crustal cooling models alone have difficulty in explaining the high luminosity of the source for the first ~200 d of its outburst, and additional heating of the star surface from currents flowing in a twisted magnetic bundle is probably playing an important role in the outburst evolution.
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  • 5
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    Gemini optical observations of binary millisecond pulsars (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-27
    Description: Millisecond pulsars (MSPs) are rapidly spinning neutron stars, with spin periods P s 10 ms, which have been most likely spun up after a phase of matter accretion from a companion star. In this work, we present the results of the search for the companion stars of four binary MSPs, carried out with archival data from the Gemini South telescope. Based upon a very good positional coincidence with the pulsar radio coordinates, we likely identified the companion stars to three MSPs, namely PSR J0614–3329 ( g  = 21.95 ± 0.05), J1231–1411 ( g  = 25.40 ± 0.23), and J2017+0603 ( g  = 24.72 ± 0.28). For the last pulsar (PSR J0613–0200) the identification was hampered by the presence of a bright star ( g  = 16 ± 0.03) at ~2 arcsec from the pulsar radio coordinates and we could only set 3 upper limits of g  = 25.0, r  = 24.3, and i  = 24.2 on the magnitudes of its companion star. The candidate companion stars to PSR J0614–3329, J1231–1411, and J2017+0603 can be tentatively identified as He white dwarfs (WDs) on the basis of their optical colours and brightness and the comparison with stellar model tracks. From the comparison of our multiband photometry with stellar model tracks we also obtained possible ranges on the mass, temperature, and gravity of the candidate WD companions to these three MSPs. Optical spectroscopy observations are needed to confirm their possible classification as He WDs and accurately measure their stellar parameters.
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    Topics: Physics
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  • 6
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    On the PSR B1133+16 optical counterpart (2013)
    Oxford University Press
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    Publication Date: 2013-10-08
    Description: The aim of this work is to confirm the optical identification of PSR B1133+16, whose candidate optical counterpart was detected in Very Large Telescope (VLT) images obtained back in 2003. We used new deep optical images of the PSR B1133+16 field obtained with both the 10.4 m Gran Telescopio Canarias (GTC) and the VLT in the g ' and B bands, respectively, to confirm the detection of its candidate optical counterpart and its coincidence with the most recent pulsar's radio coordinates. We did not detect any object at the position of the pulsar candidate counterpart ( B  ~ 28), measured in our 2003 VLT images. However, we tentatively detected an object of comparable brightness in both the 2012 GTC and VLT images, whose position is offset by ~ 3.03 arcsec from that of the pulsar's candidate counterpart in the 2003 VLT images and lies along the pulsar's proper motion direction. Accounting for the time span of ~9 yr between the 2012 quasi-contemporary GTC and VLT images and the 2003 VLT one, this offset is consistent with the yearly displacement of the pulsar due to its proper motion. Therefore, both the flux of the object detected in the 2012 GTC and VLT images and its position, consistent with the proper motion-corrected pulsar radio coordinates, suggest that we have detected the candidate pulsar counterpart that has moved away from its 2003 discovery position.
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  • 7
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    HST optical polarimetry of the Vela pulsar and nebula (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-02
    Description: Polarization measurements of pulsars offer a unique insight into the geometry of the emission regions in the neutron star magnetosphere. Therefore, they provide observational constraints on the different models proposed for the pulsar emission mechanisms. Optical polarization data of the Vela pulsar was obtained from the Hubble Space Telescope ( HST ) archive. The data, obtained in two filters ( F 606 W , central wavelength = 590.70 nm and F 550 M , central wavelength = 558.15 nm), consist of a series of observations of the pulsar taken with the HST /Advanced Camera for Surveys and cover a time span of 5 d. These data have been used to carry out the first high spatial resolution and multi-epoch study of the polarization of the pulsar. We produced polarization vector maps of the region surrounding the pulsar and measured the degree of linear polarization (P.D.) and the position angle (P.A.) of the pulsar's integrated pulse beam. We obtained P.D. = 8.1 ± 0.7 per cent and P.A. = 146 $_{.}^{\circ}$ 3 ± 2 $_{.}^{\circ}$ 4, averaged over the time span covered by these observations. These results not only confirm those originally obtained by Wagner & Seifert and Mignani et al., both using the Very Large Telescope, but are of greater precision. Furthermore, we confirm that the P.A. of the pulsar polarization vector is aligned with the direction of the pulsar proper motion. The pulsar wind nebula is undetected in polarized light as is the case in unpolarized light, down to a flux limit of 26.8 mag arcsec –2 .
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  • 8
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    Optical polarimetry of the inner Crab nebula and pulsar (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-14
    Description: Time-resolved polarization measurements of pulsars offer a unique insight into the geometry of their emission regions. Such measurements provide observational constraints on the different models proposed for the pulsar emission mechanisms. Optical polarization data of the Crab nebula were obtained from the Hubble Space Telescope ( HST ) archive. The data set consists of a series of observations of the nebula taken with the HST /Advanced Camera for Surveys (ACS). We produced polarization vector maps of the inner nebula and measured, for the first time, the degree of linear polarization (P.D.) and the position angle (P.A.) of the pulsar's integrated pulse beam, and of its nearby synchrotron knot. This yielded P.D. = 5.2 ± 0.3 per cent and P.A. = 105 $^{\circ}_{.}$ 1 ± 1 $^{\circ}_{.}$ 6 for the pulsar, and P.D. = 59.0 ± 1.9 per cent and P.A. = 124 $^{\circ}_{.}$ 7 ± 1 $^{\circ}_{.}$ 0 for the synchrotron knot. This is the first high-spatial resolution multi-epoch study of the polarization of the inner nebula and pulsar. None of the main features in the nebula shows evidence of significant polarization evolution in the period covered by these observations. The results for the pulsar are consistent with those obtained by Slowikowska et al. using the high-time resolution photo-polarimeter – Optical Pulsar Timing Analyzer (OPTIMA), once the constant component (DC) component has been subtracted. Our results clearly prove that the knot is the main source of the DC component.
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  • 9
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    Evidence for vacuum birefringence from the first optical-polarimetry measurement of the isolated neutron star RX J1856.5-3754 (2016)
    Oxford University Press
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    Publication Date: 2016-12-01
    Description: The ‘Magnificent Seven’ (M7) are a group of radio-quiet isolated neutron stars discovered in the soft X-rays through their purely thermal surface emission. Owing to the large inferred magnetic fields ( B 10 13  G), radiation from these sources is expected to be substantially polarized, independently of the mechanism actually responsible for the thermal emission. A large observed polarization degree (PD) is, however, expected only if quantum-electrodynamic (QED) polarization effects are present in the magnetized vacuum around the star. The detection of a strong linearly polarized signal would therefore provide the first observational evidence of QED effects in the strong-field regime. While polarization measurements in the soft X-rays are not feasible yet, optical polarization measurements are within reach also for quite faint targets, like the M7 which have optical counterparts with magnitudes 26–28. Here, we report on the measurement of optical linear polarization for the prototype, and brightest member, of the class, RX J1856.5–3754 ( V  ~ 25.5), the first ever for one of the M7, obtained with the Very Large Telescope. We measured a PD = 16.43 ± 5.26 per cent and a polarization position angle PA = 145 $_{.}^{\circ}$ 39 ± 9 $_{.}^{\circ}$ 44, computed east of the North Celestial Meridian. The PD that we derive is large enough to support the presence of vacuum birefringence, as predicted by QED.
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  • 10
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    Binary pulsars studies with multiwavelength sky surveys - I. Companion star identification (2014)
    Oxford University Press
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    Publication Date: 2014-08-01
    Description: The identification of the stellar companions to binary pulsars is key to studying the evolution of the binary system and how this is influenced by the interactions between the two stars. For only a fraction of the known binary pulsars, the stellar companions have been identified. Here, we used 11 source catalogues available from multiwavelength (ultraviolet, optical, infrared) imaging sky surveys to search for the stellar companions of a sample of 144 field binary pulsars (i.e. not in globular clusters) selected from the Australia Telescope National Facility data base (version 1.48) and from the public list of -ray pulsars detected by Fermi . We found positional associations in at least one source catalogue for 22 pulsars, of which 10 are detected in -rays by Fermi , including 15 millisecond pulsars. For six pulsars in our compilation, we confirm their identifications. For another seven pulsars that had yet not been identified, we examine potential identifications. In particular, we identified a likely companion star candidate to PSR J2317+1439, whereas for both PSR B1953+29 and PSR J1935+1726 the companion star identification is more uncertain. Follow-up observations of these three pulsars are needed to settle the proposed identifications. For the remaining nine pulsars that had been already identified, we provide additional spectral information in at least one of the surveys’ spectral bands, which we will use to better constrain the stars’ spectral energy distributions.
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