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  • 1
    Publication Date: 2015-08-21
    Description: The deepest XMM–Newton mosaic map of the central 1 $_{.}^{\circ}$ 5 of the Galaxy is presented, including a total of about 1.5 Ms of EPIC-pn cleaned exposures in the central 15 arcsec and about 200 ks outside. This compendium presents broad-band X-ray continuum maps, soft X-ray intensity maps, a decomposition into spectral components and a comparison of the X-ray maps with emission at other wavelengths. Newly discovered extended features, such as supernova remnants (SNRs), superbubbles and X-ray filaments are reported. We provide an atlas of extended features within ±1° of Sgr A * . We discover the presence of a coherent X-ray-emitting region peaking around G0.1–0.1 and surrounded by the ring of cold, mid-IR-emitting material known from previous work as the ‘Radio Arc Bubble’ and with the addition of the X-ray data now appears to be a candidate superbubble. Sgr A's bipolar lobes show sharp edges, suggesting that they could be the remnant, collimated by the circumnuclear disc, of an SN explosion that created the recently discovered magnetar, SGR J1745–2900. Soft X-ray features, most probably from SNRs, are observed to fill holes in the dust distribution, and to indicate a direct interaction between SN explosions and Galactic centre (GC) molecular clouds. We also discover warm plasma at high Galactic latitude, showing a sharp edge to its distribution that correlates with the location of known radio/mid-IR features such as the ‘GC Lobe’. These features might be associated with an inhomogeneous hot ‘atmosphere’ over the GC, perhaps fed by continuous or episodic outflows of mass and energy from the GC region.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 2
    Publication Date: 2016-07-15
    Description: We report on the identification of the new Galactic Centre (GC) transient Swift J174540.7–290015 as a likely low-mass X-ray binary located at only 16 arcsec from Sgr A * . This transient was detected on 2016 February 6, during the Swift GC monitoring, and it showed long-term spectral variations compatible with a hard- to soft-state transition. We observed the field with XMM–Newton on February 26 for 35 ks, detecting the source in the soft state, characterized by a low level of variability and a soft X-ray thermal spectrum with a high energy tail (detected by INTEGRAL up to ~50 keV), typical of either accreting neutron stars or black holes. We observed: (i) a high column density of neutral absorbing material, suggesting that Swift J174540.7–290015 is located near or beyond the GC and; (ii) a sub-Solar iron abundance, therefore we argue that iron is depleted into dust grains. The lack of detection of Fe K absorption lines, eclipses or dipping suggests that the accretion disc is observed at a low inclination angle. Radio (Very Large Array) observations did not detect any radio counterpart to Swift J174540.7–290015. No evidence for X-ray or radio periodicity is found. The location of the transient was observed also in the near-infrared (near-IR) with gamma-ray burst optical near-IR detector at MPG/European Southern Observatory La Silla 2.2 m telescope and VLT/ NaCo pre- and post-outburst. Within the Chandra error region, we find multiple objects that display no significant variations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
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  • 3
    Publication Date: 2016-07-09
    Description: We report on the results of a ~40-d multi-wavelength monitoring of the Be X-ray binary system IGR J05007–7047 (LXP 38.55). During that period the system was monitored in the X-rays using the Swift telescope and in the optical with multiple instruments. When the X-ray luminosity exceeded 10 36  erg s –1 we triggered an XMM–Newton ToO observation. Timing analysis of the photon events collected during the XMM–Newton observation reveals coherent X-ray pulsations with a period of 38.551(3) s (1), making it the 17th known high-mass X-ray binary pulsar in the LMC. During the outburst, the X-ray spectrum is fitted best with a model composed of an absorbed power law ( = 0.63) plus a high-temperature blackbody ( kT ~2 keV) component. By analysing ~12 yr of available OGLE optical data we derived a 30.776(5) d optical period, confirming the previously reported X-ray period of the system as its orbital period. During our X-ray monitoring the system showed limited optical variability while its IR flux varied in phase with the X-ray luminosity, which implies the presence of a disc-like component adding cooler light to the spectral energy distribution of the system.
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    Electronic ISSN: 1365-2966
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  • 4
    Publication Date: 2013-06-09
    Description: We present a detailed study of Australia Telescope Compact Array observations of a newly discovered Large Magellanic Cloud supernova remnant (SNR), SNR J0533–7202. This object follows a horseshoe morphology, with a size of 37 pc  x 28 pc (1 pc uncertainty in each direction). It exhibits a radio spectrum with the intrinsic synchrotron spectral index of α = –0.47 ± 0.06 between 73 and 6 cm. We report detections of regions showing moderately high fractional polarization at 6 cm, with a peak value of 36 ± 6 per cent and a mean fractional polarization of 12 ± 7 per cent. We also estimate an average rotation measure across the remnant of –591 rad m –2 . The current lack of deep X-ray observation precludes any conclusion about high-energy emission from the remnant. The association with an old stellar population favours a thermonuclear supernova origin of the remnant.
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    Electronic ISSN: 1365-2966
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  • 5
    Publication Date: 2014-09-19
    Description: We identify a new candidate for a Be/X-ray binary in the XMM–Newton slew survey and archival Swift observations that is located in the transition region of the Wing of the Small Magellanic Cloud and the Magellanic Bridge. We investigated and classified this source with follow-up XMM–Newton and optical observations. We model the X-ray spectra and search for periodicities and variability in the X-ray observations and the Optical Gravitational Lensing Experiment I -band light curve. The optical counterpart has been classified spectroscopically, with data obtained at the South African Astronomical Observatory 1.9 m telescope, and photometrically, with data obtained using the Gamma-ray Burst Optical Near-ir Detector at the MPG 2.2 m telescope. The X-ray spectrum is typical of a high-mass X-ray binary with an accreting neutron star. We detect X-ray pulsations, which reveal a neutron-star spin period of P s  = (264.516 ± 0.014) s. The source likely shows a persistent X-ray luminosity of a few 10 35 erg s –1 and in addition type-I outbursts that indicate an orbital period of ~146 d. A periodicity of 0.867 d, found in the optical light curve, can be explained by non-radial pulsations of the Be star. We identify the optical counterpart and classify it as a B1-2II-IVe star. This confirms SXP 265 as a new Be/X-ray binary pulsar originating in the tidal structure between the Magellanic Clouds.
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  • 6
    Publication Date: 2015-01-09
    Description: On MJD 56590-1 (2013 Oct 25–26), observations of the Magellanic Clouds by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) observatory discovered a previously unreported bright, flaring X-ray source. This source was initially given the identification IGR J00569-7226. Subsequent multiwavelength observations identified the system as new Be/X-ray binary system in the Small Magellanic Cloud (SMC). Follow-up X-ray observations by Swift and XMM–Newton revealed an X-ray pulse period of 5.05 s and that the system underwent regular occultation/eclipse behaviour every 17 d. This is the first reported eclipsing Be/X-ray binary system in the SMC, and only the second such system known to date. Furthermore, the nature of the occultation makes it possible to use the neutron star to ‘X-ray’ the circumstellar disc, thereby, for the first time, revealing direct observational evidence for its size and clumpy structure. Swift timing measurements allowed for the binary solution to be calculated from the Doppler-shifted X-ray pulsations. This solution suggests this is a low-eccentricity binary relative to others measured in the SMC. Finally, it is interesting to note that the mass determined from this dynamical method for the Be star (~13.0 M ) is significantly different from that inferred from the spectroscopic classification of B0.2Ve (~16.0 M ) – an effect that has been noted for some other high mass X-ray binary systems.
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  • 7
    Publication Date: 2014-08-02
    Description: We present new optical spectroscopy of 20 candidate counterparts of 17 X-ray sources in the direction of the M31 disc. By comparing the X-ray catalogue from the XMM–Newton survey of M31 with star catalogues from the Local Group Galaxy Survey, we chose counterpart candidates based on optical colour and X-ray hardness. We have discovered 17 counterpart candidates with spectra containing stellar features. Eight of these are early-type stars of O or B type in M31, with hard X-ray spectra, making them good high-mass X-ray binary (HMXB) candidates. Three of these eight exhibit emission lines, which we consider to be the strongest HMXB candidates. In addition, our spectra reveal two likely Galactic cataclysmic variables, one foreground M star, two probable low-mass X-ray binaries related to M31 globular clusters, one emission-line region with an embedded Wolf–Rayet star and one newly discovered supernova remnant. Finally, two of the sources have stellar spectra with no features indicative of association with an X-ray source.
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  • 8
    Publication Date: 2014-03-01
    Description: We present a detailed radio, X-ray and optical study of a newly discovered Large Magellanic Cloud (LMC) supernova remnant (SNR) which we denote as MCSNR J0508–6902. Observations from the Australia Telescope Compact Array (ATCA) and the XMM–Newton X-ray observatory are complemented by deep Hα images and Anglo-Australian Telescope AAOmega spectroscopic data to study the SNR shell and its shock ionization. Archival data at other wavelengths are also examined. The remnant follows a filled-in shell-type morphology in the radio continuum and has a size of ~74 pc 57 pc at the LMC distance. The X-ray emission exhibits a faint soft shell morphology with Fe-rich gas in its interior – indicative of a Type Ia origin. The remnant appears to be mostly dissipated at higher radio-continuum frequencies leaving only the south-eastern limb fully detectable while in the optical it is the western side of the SNR shell that is clearly detected. The best-fitting temperature to the shell X-ray emission ( $kT = 0.41^{+0.05}_{-0.06}$  keV) is consistent with other large LMC SNRs. We determined an O/Fe ratio of 〈21 and an Fe mass of 0.5–1.8 M in the interior of the remnant, both of which are consistent with the Type Ia scenario. We find an equipartition magnetic field for the remnant of ~28 μG, a value typical of older SNRs and consistent with other analyses which also infer an older remnant.
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  • 9
    Publication Date: 2016-01-02
    Description: During a search for coherent signals in the X-ray archival data of XMM–Newton , we discovered a modulation at 1.2 s in 3XMM J004301.4+413017 (3X J0043), a source lying in the direction of an external arm of M 31. This short period indicates a neutron star (NS). Between 2000 and 2013, the position of 3X J0043 was imaged by public XMM–Newton observations 35 times. The analysis of these data allowed us to detect an orbital modulation at 1.27 d and study the long-term properties of the source. The emission of the pulsar was rather hard (most spectra are described by a power law with  〈 1) and, assuming the distance to M 31, the 0.3–10 keV luminosity was variable, from ~3  x  10 37 to 2  x  10 38 erg s –1 . The analysis of optical data shows that, while 3X J0043 is likely associated to a globular cluster in M 31, a counterpart with V 22 outside the cluster cannot be excluded. Considering our findings, there are two main viable scenarios for 3X J0043: a peculiar low-mass X-ray binary, similar to 4U 1822–37 or 4U 1626–67, or an intermediate-mass X-ray binary resembling Her X–1. Regardless of the exact nature of the system, 3X J0043 is the first accreting NS in M 31 in which the spin period has been detected.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
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  • 10
    Publication Date: 2016-12-16
    Description: NGC 7793 P13 is a variable (luminosity range ~100) ultraluminous X-ray source proposed to host a stellar-mass black hole of less than 15 M in a binary system with orbital period of 64 d and a 18–23 M B9Ia companion. Within the EXTraS (Exploring the X-ray Transient and variable Sky) project, we discovered pulsations at a period of ~0.42 s in two XMM–Newton observations of NGC 7793 P13, during which the source was detected at L X ~ 2.1 x 10 39 and 5 x 10 39 erg s –1 (0.3–10 keV band). These findings unambiguously demonstrate that the compact object in NGC 7793 P13 is a neutron star accreting at super-Eddington rates. While standard accretion models face difficulties accounting for the pulsar X-ray luminosity, the presence of a multipolar magnetic field with B ~ few x 10 13  G close to the base of the accretion column appears to be in agreement with the properties of the system.
    Print ISSN: 1745-3925
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