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Pires A.M.,Leibniz Institute for Astrophysics Potsdam | Motch C.,University of Strasbourg | Turolla R.,University of Padua | Turolla R.,University College London | And 5 more authors.
Astronomy and Astrophysics | Year: 2012

While fewer in number than the dominant rotation-powered radio pulsar population, peculiar classes of isolated neutron stars (INSs)-which include magnetars, the ROSAT-discovered "Magnificent Seven" (M7), rotating radio transients (RRATs), and central compact objects in supernova remnants (CCOs)-represent a key element in understanding the neutron star phenomenology. We report the results of an observational campaign to study the properties of the source 2XMM J104608.7-594306, a newly discovered thermally emitting INS. The evolutionary state of the neutron star is investigated by means of deep dedicated observations obtained with the XMM-Newton Observatory, the ESO Very Large Telescope, as well as publicly available γ-ray data from the Fermi Space Telescope and the AGILE Mission. The observations confirm previous expectations and reveal a unique type of object. The source, which is likely within the Carina Nebula (N H = 2.6 × 10 21 cm -2), has a spectrum that is both thermal and soft, with kT ∞ = 135 eV. Non-thermal (magnetospheric) emission is not detected down to 1% (3σ, 0.1-12 keV) of the source luminosity. Significant deviations (absorption features) from a simple blackbody model are identified in the spectrum of the source around energies 0.6 keV and 1.35 keV. While the former deviation is likely related to a local oxygen overabundance in the Carina Nebula, the latter can only be accounted for by an additional spectral component, which is modelled as a Gaussian line in absorption with EW = 91 eV and σ = 0.14 keV (1σ). Furthermore, the optical counterpart is fainter than m V = 27 (2σ) and no γ-ray emission is significantly detected by either the Fermi or AGILE missions. Very interestingly, while these characteristics are remarkably similar to those of the M7 or the only RRAT so far detected in X-rays, which all have spin periods of a few seconds, we found intriguing evidence of very rapid rotation, P = 18.6 ms, at the 4σ confidence level. We interpret these new results in the light of the observed properties of the currently known neutron star population, in particular those of standard rotation-powered pulsars, recycled objects, and CCOs. We find that none of these scenarios can satisfactorily explain the collective properties of 2XMM J104608.7-594306, although it may be related to the still poorly known class of Galactic anti-magnetars. Future XMM-Newton data, granted for the next cycle of observations (AO11), will help us to improve our currentobservational interpretation of the source, enabling us to significantly constrain the rate of pulsar spin down. © 2012 ESO. Source

Johnston H.M.,University of Sydney | Broderick J.W.,University of Sydney | Broderick J.W.,University of Southampton | Cotter G.,University of Oxford | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present optical spectra and high-resolution multiwavelength radio observations of the compact steep-spectrum radio source MRC B1221-423 (z = 0.1706). MRC B1221-423 is a very young (∼105 yr), powerful radio source which is undergoing a tidal interaction with a companion galaxy. We find strong evidence of interaction between the active galactic nucleus (AGN) and its environment. The radio morphology is highly distorted, showing a dramatic interaction between the radio jet and the host galaxy, with the jet being turned almost back on itself. H i observations show strong absorption against the nucleus at an infall velocity of ∼250 km s-1 compared to the stellar velocity, as well as a second, broader component which may represent gas falling into the nucleus. Optical spectra show that star formation is taking place across the whole system. Broad optical emission lines in the nucleus show evidence of outflow. Our observations confirm that MRC B1221-423 is a young radio source in a gas-rich nuclear environment, and that there was a time delay of a few times 100 Myr between the onset of star formation and the triggering of the AGN. © 2010 The Authors. Journal compilation © 2010 RAS. Source

Inskip K.J.,Max Planck Institute for Astronomy | Inskip K.J.,University of Sheffield | Tadhunter C.N.,University of Sheffield | Morganti R.,Netherlands Foundation for Research in Astronomy | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present the results of a program of K- and KS-band imaging of a sample of 2 Jy radio galaxies with redshifts 0.03 ≲ z ≲ 0.5, for which the host galaxy morphologies and structural parameters (effective radius, Sérsic index and unresolved nuclear point source contribution) have been determined using galfit. Two-thirds of our sample are best modelled as being hosted by massive elliptical galaxies with Sérsic indices of n = 4-6, with the remainder being better suited either by a mixture of morphological components (usually a bulge plus a small, less luminous, disc component) or by more discy galaxy models with n = 1-2. Our measured galaxy sizes are generally in very good agreement with other imaging programs, both space- and ground-based. We also determine a slightly higher average nuclear point source contribution than similar Hubble Space Telescope based programs. This is due to our inability to separate the active galactic nuclei emission from compact circum-nuclear stellar emission, but does not bias our modelling of the remainder of the host galaxies and our results remain robust. We also observe that roughly half of the objects in our sample are either undergoing major or minor merger activity or are clearly morphologically disturbed. © 2010 The Authors. Journal compilation © 2010 RAS. Source

Struve C.,Netherlands Foundation for Research in Astronomy | Struve C.,University of Groningen | Conway J.E.,Onsala Space Observatory
Astronomy and Astrophysics | Year: 2010

We present Very Long Baseline Array (VLBA) H i absorption observations of the core region of the powerful radio galaxy Cygnus A. These data show both broad (FWHM = 231 ± 21 km s-1) and narrow (FWHM < 30 km s-1) velocity width absorption components. The broad velocity absorption shows high opacity on the counter-jet, low opacity against the core and no absorption on the jet side. We argue that these results are most naturally explained by a circumnuclear H i absorbing disk orientated roughly perpendicular to the jet axis. We estimate that the H i absorbing gas lies at a radius of ∼80 pc has a scale height of about 20 pc, density n > 10 4 cm-3 and total column density in the range 10 23-1024 cm-2. Models in which the H i absorption is primarily from an atomic or a molecular gas phase can both fit our data. Modelling taking into account the effective beam shows that the broad H i absorbing gas component does not cover the radio core in Cygnus A and therefore does not contribute to the gas column that blocks our view of the hidden quasar nucleus. If however Cygnus A were observed from a different direction, disk gas on ∼ 100 pc radius scales would contribute significantly to the nuclear column density, implying that in some radio galaxies gas on these scales may contribute to the obscuration of the central engine. We argue that the circumnuclear torus in Cygnus A contains too little mass to power the AGN over > 107 yr but that material in the outer H i absorbing gas disk can provide a reservoir to fuel the AGN and replenish torus clouds. The second narrow H i absorption component is significantly redshifted (by 186 km s -1) with respect to the systemic velocity and probably traces infalling gas which will ultimately fuel the source. This component could arise either within a tidal tail structure associated with a recent (minor) merger or be associated with an observed infalling giant molecular cloud. © ESO, 2010. Source

Quillen A.C.,University of Rochester | Neumayer N.,European Southern Observatory | Oosterloo T.,Netherlands Foundation for Research in Astronomy | Oosterloo T.,University of Groningen | And 2 more authors.
Publications of the Astronomical Society of Australia | Year: 2010

We compile position and inclination angles for tilted ring fits to the warped dusty and gaseous disk of CenA, spanning a radius of 1.8 to 6500pc, from recent observations. For radii exterior to 1kpc, tilted-ring orientations lie on an arc, on a plot of polar-inclination versus position-angle, suggesting that precession following a merger can account for the ring morphology. Three kinks in the ring orientations are seen on the polar plot, the one at radius of about 1.3kpc we suspect corresponds to the location where self-gravity in the disk affects the ring precession rate. Another at a radius of about 600pc may be associated with a gap in the gas distribution. A third kink is seen at a radius of 100pc. A constant inclination tilted disk precessing about the jet axis may describe the disk between 100 and 20pc but not interior to this. A model with disk orientation matching the molecular circumnuclear disk at 100pc that decays at smaller radii to an inner flat disk perpendicular to the jet may account for disk orientations within 100pc. Neither model would account for the cusps or changes in disk orientation at 100 or 600pc. © Astronomical Society of Australia 2010. Source

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