Villanueva de la Cañada, Spain
Villanueva de la Cañada, Spain
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Alexander K.D.,Harvard - Smithsonian Center for Astrophysics | Wieringa M.H.,CSIRO | Berger E.,Harvard - Smithsonian Center for Astrophysics | Saxton R.D.,XMM SOC | Komossa S.,Guizhou University for Nationalities
Astrophysical Journal | Year: 2017

We present radio observations of the tidal disruption event candidate (TDE) XMMSL1 J0740-85 spanning 592 to 875 days post X-ray discovery. We detect radio emission that fades from an initial peak flux density at 1.6 GHz of 1.19 ±0.06 mJy to 0.65 ±0.06 mJy, suggesting an association with the TDE. This makes XMMSL1 J0740-85 at d = 75 Mpc the nearest TDE with detected radio emission to date and only the fifth TDE with radio emission overall. The observed radio luminosity rules out a powerful relativistic jet like that seen in the relativistic TDE Swift J1644+57. Instead, we infer from an equipartition analysis that the radio emission most likely arises from a non-relativistic outflow similar to that seen in the nearby TDE ASASSN-14li, with a velocity of about 104 km s-1 and a kinetic energy of about 1048 erg, expanding into a medium with a density of about 102 cm-3. Alternatively, the radio emission could arise from a weak initially relativistic but decelerated jet with an energy of erg, or (for an extreme disruption geometry) from the unbound debris. The radio data for XMMSL1 J0740-85 continues to support the previous suggestion of a bimodal distribution of common non-relativistic isotropic outflows and rare relativistic jets in TDEs (in analogy with the relation between Type Ib/c supernovae and long-duration gamma-ray bursts). The radio data also provide a new measurement of the circumnuclear density on a sub-parsec scale around an extragalactic supermassive black hole. © 2017. The American Astronomical Society. All rights reserved.

Saxton R.D.,XMM SOC | Read A.M.,University of Leicester | Komossa S.,Guizhou University for Nationalities | Komossa S.,Max Planck Institute for Radio Astronomy | And 3 more authors.
Astronomy and Astrophysics | Year: 2017

Aims. We study X-ray bright tidal disruption events (TDE), close to the peak of their emission, with the intention of understanding the evolution of their light curves and spectra. Methods. Candidate TDE are identified by searching for soft X-ray flares from non-active galaxies in recent XMM-Newton slew data. Results. In April 2014, X-ray emission was detected from the galaxy XMMSL1 J074008.2-853927 (a.k.a. 2MASX 07400785-8539307), a factor 20 times higher than an upper limit from 20 years earlier. Both the X-ray and UV flux subsequently fell, by factors of 70 and 12 respectively. The bolometric luminosity peaked at Lbol ∼ 2 × 1044 ergs s-1 with a spectrum that may be modelled with thermal emission in the UV band, a power-law with Γ ∼ 2 dominating in the X-ray band above 2 keV and a soft X-ray excess with an effective temperature of ∼86 eV. Rapid variability locates the X-ray emission to within <73 Rg of the nuclear black hole. Radio emission of flux density ∼1 mJy, peaking at 1.5 GHz was detected 21 months after discovery. Optical spectra indicate that the galaxy, at a distance of 73 Mpc (z = 0.0173), underwent a starburst 2 Gyr ago and is now quiescent. We consider a tidal disruption event to be the most likely cause of the flare. If this proves to be correct then this is a very clean example of a disruption exhibiting both thermal and non-thermal radiation. © 2017 ESO.

Saxton R.,XMM SOC | Komossa S.,Guizhou University for Nationalities | Read A.,University of Leicester | Lira P.,University of Chile | And 2 more authors.
Proceedings of the International Astronomical Union | Year: 2016

XMM-Newton performs a survey of the sky in the 0.2-12 keV X-ray band while slewing between observation targets. The sensitivity in the soft X-ray band is comparable with that of the ROSAT all-sky survey, allowing bright transients to be identified in near real-time by a comparison of the flux in both surveys. Several of the soft X-ray flares are coincident with galaxy nuclei and five of these have been interpreted as candidate tidal disruption events (TDE). The first three discovered had a soft X-ray spectrum, consistent with the classical model of TDE, where radiation is released during the accretion phase by thermal processes. The remaining two have an additional hard, power-law component, which in only one case was accompanied by radio emission. Overall the flares decay with the classical index of t -5/3 but vary greatly in the early phase. © International Astronomical Union 2017.

Smail I.,Durham University | Geach J.E.,University of Hertfordshire | Swinbank A.M.,Durham University | Tadaki K.,Japan National Astronomical Observatory | And 24 more authors.
Astrophysical Journal | Year: 2014

We analyze new SCUBA-2 submillimeter and archival SPIRE far-infrared imaging of a z = 1.62 cluster, Cl 0218.3-0510, which lies in the UKIRT Infrared Deep Sky Survey/Ultra-Deep Survey field of the SCUBA-2 Cosmology Legacy Survey. Combining these tracers of obscured star-formation activity with the extensive photometric and spectroscopic information available for this field, we identify 31 far-infrared/submillimeter-detected probable cluster members with bolometric luminosities ≳1012 L and show that by virtue of their dust content and activity, these represent some of the reddest and brightest galaxies in this structure. We exploit ALMA submillimeter continuum observations, which cover one of these sources, to confirm the identification of a SCUBA-2-detected ultraluminous star-forming galaxy in this structure. Integrating the total star-formation activity in the central region of the structure, we estimate that it is an order of magnitude higher (in a mass-normalized sense) than clusters at z 0.5-1. However, we also find that the most active cluster members do not reside in the densest regions of the structure, which instead host a population of passive and massive, red galaxies. We suggest that while the passive and active populations have comparable near-infrared luminosities at z = 1.6, MH -23, the subsequent stronger fading of the more active galaxies means that they will evolve into passive systems at the present day that are less luminous than the descendants of those galaxies that were already passive at z 1.6 (MH -20.5 and MH -21.5, respectively, at z 0). We conclude that the massive galaxy population in the dense cores of present-day clusters were already in place at z = 1.6 and that in Cl 0218.3-0510 we are seeing continuing infall of less extreme, but still ultraluminous, star-forming galaxies onto a pre-existing structure. © 2014. The American Astronomical Society. All rights reserved..

Read A.M.,University of Leicester | Rosen S.R.,University of Leicester | Saxton R.D.,XMM SOC | Ramirez J.,Leibniz Institute for Astrophysics Potsdam
Astronomy and Astrophysics | Year: 2011

Aims. We describe here a new full 2D parameterization of the PSFs of the three XMM-Newton EPIC telescopes as a function of instrument, energy, off-axis angle and azimuthal angle, covering the whole field-of-view (FoV) of the three EPIC detectors. It models the general PSF envelopes, the primary and secondary spokes, their radial dependencies, and the large-scale azimuthal variations. Methods. This PSF model has been constructed via the stacking and centering of a large number of bright, but not significantly piled-up point sources from the full FoV of each EPIC detector, and azimuthally filtering the resultant PSF envelopes to form the spoke structures and the gross azimuthal shapes observed. Results. This PSF model is available for use within the XMM-Newton science analysis system via the usage of current calibration files XRTi-XPSF-0011.CCF and later versions. Initial source-searching tests showed substantial reductions in the numbers of spurious sources being detected in the wings of bright point sources. Furthermore, we have uncovered a systematic error in the previous PSF system, affecting the entire mission to date, whereby returned source RA and Dec values are seen to vary sinusoidally about the true position (amplitude ≈≈0.8″″) with source azimuthal position. Conclusions. The new PSF system is now available and is seen as a major improvement with regard to the detection of spurious sources. The new PSF also largely removes the discovered astrometry error and is seen to improve the positional accuracy of EPIC. The modular nature of the PSF system allows for further refinements in the future. © 2011 ESO.

Saxton R.D.,XMM SOC | Read A.M.,University of Leicester | Esquej P.,University of Leicester | Komossa S.,TU Munich | And 8 more authors.
Astronomy and Astrophysics | Year: 2012

Aims. The study of tidal disruption flares from galactic nuclei has historically been hampered by a lack of high quality spectral observations taken around the peak of the outburst. Here we introduce the first results from a program designed to identify tidal disruption events at their peak by making near-real-time comparisons of the flux seen in XMM-Newton slew sources with that seen in ROSAT. Methods. Flaring extragalactic sources, which do not appear to be AGN, are monitored with Swift and XMM-Newton to track their temporal and spectral evolution. Timely optical observations are made to monitor the reaction of circumnuclear material to the X-ray flare. Results. SDSS J120136.02+300305.5 was detected in an XMM-Newton slew from June 2010 with a flux 56 times higher than an upper limit from ROSAT, corresponding to L X ∼ 3 × 10 44 erg s -1. It has the optical spectrum of a quiescent galaxy (z = 0.146). Overall the X-ray flux has evolved consistently with the canonical t -5/3 model, expected for returning stellar debris, fading by a factor ∼300 over 300 days. In detail the source is very variable and became invisible to Swift between 27 and 48 days after discovery, perhaps due to self-absorption. The X-ray spectrum is soft but is not the expected tail of optically thick thermal emission. It may be fit with a Bremsstrahlung or double-power-law model and is seen to soften with time and declining flux. Optical spectra taken 12 days and 11 months after discovery indicate a deficit of material in the broad line and coronal line regions of this galaxy, while a deep radio non-detection implies that a jet was not launched during this event. © 2012 ESO.

Agis-Gonzalez B.,CSIC - National Institute of Aerospace Technology | Miniutti G.,CSIC - National Institute of Aerospace Technology | Kara E.,Institute of Astronomy | Fabian A.C.,Institute of Astronomy | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We report results from multi-epoch X-ray observations of the Seyfert 1.5 galaxyESO362-G18 performed between 2005 November and 2010 June. ESO 362-G18 generally exhibits the typical X-ray spectrum of type 1 active galactic nuclei. A disc-reflection component accounts for broad residuals in the iron K band and above 10 keV, as well as for a significant soft excess. From our best-fitting reflection model, we measure a black hole spin a ≥ 0.92 at the 99.99 per cent confidence level. ESO 362-G18 is also (typically) mildly absorbed by a column of neutral gas. The absorber is variable and one observation, performed ~2 months after a typical mildly absorbed one, is heavily absorbed by a cold column density of ~3-4 × 1023 cm-2, nearly two orders of magnitude higher than that during any other observation. UV variability between the heavily absorbed observation and the others suggests that the absorber can be identified with a dusty, clumpy torus. The absorption variability time-scale enables us to locate the X-ray-emitting region within the innermost ~50 gravitational radii. Such result holds not only for the X-ray continuum, but also for the soft excess. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Miniutti G.,CSIC - National Institute of Aerospace Technology | Saxton R.D.,XMM SOC | Rodriguez-Pascual P.M.,XMM SOC | Read A.M.,University of Leicester | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

A bright, soft X-ray source was detected on 2010 July 14 during an XMM-Newton slew at a position consistent with the galaxy GSN 069 (z = 0.018). Previous ROSAT observations failed to detect the source and imply that GSN 069 is now ≥240 times brighter than it was in 1994 in the soft X-ray band. Optical spectra (from 2001 to 2003) are dominated by unresolved emission lines with no broad components, classifying GSN 069 as a Seyfert 2 galaxy. We report here results from a ~1 yr monitoring with Swift and XMM-Newton, as well as from new optical spectroscopy. GSN 069 is an unabsorbed, ultrasoft source in X-rays, with no flux detected above ~1 keV. The soft X-rays exhibit significant variability down to time-scales of hundreds of seconds. The UV-to-X-ray spectrum of GSN 069 is consistent with a pure accretion disc model which implies an Eddington ratio λ ≃ 0.5 and a black hole mass of ≃ 1.2 × 106Mȯ. A new optical spectrum, obtained ~3.5 months after the XMM-Newton slew detection, is consistent with earlier spectra and lacks any broad-line component. The lack of cold X-ray absorption and the short time-scale variability in the soft X-rays rule out a standard Seyfert 2 interpretation of the source. The present Eddington ratio of GSN 069 exceeds the critical value below which no emitting broad-line region (BLR) forms, according to popular models, so that GSN 069 can be classified as a bona-fide high Eddington-ratio true Seyfert 2 galaxy. We discuss our results within the framework of two possible scenarios for the BLR in AGN, namely the two-phase model (cold BLR clouds in pressure equilibrium with a hotter medium), and models in which the BLR is part of an outflow, or disc-wind. Finally, we point out that GSN 069 may be a member of a population of super-soft active galactic nuclei (AGN) whose spectral energy distribution is completely dominated by accretion disc emission, as it is the case in some black hole X-ray binary transients during their outburst evolution. The disc emission for a typical AGN with black hole mass of 107-108Mȯ does not enters the soft X-ray band, so that GSN 069-like objects with larger black hole mass (i.e. the bulk of the AGN population) are missed by current X-ray surveys, or misclassified as Compton-thick candidates. If the analogy between black hole X-ray binary transients and AGN holds, the lifetime of these super-soft states inAGNmay be longer than 104 years, implying that the actual population of super-soft AGN may not be negligible, possibly contaminating the estimated fraction of heavily obscured AGN from current X-ray surveys.

Warwick R.S.,University of Leicester | Saxton R.D.,XMM SOC | Read A.M.,University of Leicester
Astronomy and Astrophysics | Year: 2012

Context. The on-going XMM-Newton Slew Survey (XSS) provides coverage of a significant fraction of the sky in a broad X-ray bandpass. Although shallow by contemporary standards, in the "classical" 2-10 keV band of X-ray astronomy, the XSS provides significantly better sensitivity than any currently available all-sky survey. Aims. We investigate the source content of the XSS, focussing on detections in the hard 2-10 keV band down to a very low threshold (≤4 counts net of background). At the faint end, the survey reaches a flux sensitivity of roughly 3 × 10-12 erg cm-2 s -1 (2-10 keV). Methods. Our starting point was a sample of 487 sources detected in the XSS (up to and including release XMMSL1d2) at high galactic latitude in the hard band. Through cross-correlation with published source catalogues from surveys spanning the electromagnetic spectrum from radio through to gamma-rays, we find that 45% of the sources have likely identifications with normal/active galaxies. A further 18% are associated with other classes of X-ray object (nearby coronally active stars, accreting binaries, clusters of galaxies), leaving 37% of the XSS sources with no current identification. We go on to define an XSS extragalactic sample comprised of 219 galaxies and active galaxies selected in the XSS hard band. We investigate the properties of this extragalactic sample including its X-ray log N-log S distribution. Results. We find that in the low-count limit, the XSS is, as expected, strongly affected by Eddington bias. There is also a very strong bias in the XSS against the detection of extended sources, most notably clusters of galaxies. A significant fraction of the detections at and around the low-count limit may be spurious. Nevertheless, it is possible to use the XSS to extract a reasonably robust sample of extragalactic sources, excluding galaxy clusters. The differential log N-log S relation of these extragalactic sources matches very well to the HEAO-1 A2 all-sky survey measurements at bright fluxes and to the 2XMM source counts at the faint end. Conclusions. The substantial sky coverage afforded by the XSS makes this survey a valuable resource for studying X-ray bright source samples, including those selected specifically in the hard 2-10 keV band. © ESO 2012.

Read A.M.,University of Leicester | Saxton R.D.,XMM SOC | Esquej P.,University of Leicester | Warwick R.S.,University of Leicester
AIP Conference Proceedings | Year: 2010

The data collected by XMM-Newton as it slews between pointings currently cover almost half the entire sky, and many familiar features and new sources are visible. The soft-band sensitivity limit of the Slew is close to that of the RASS, and a large-area Slew-RASS comparison now provides the best opportunity for discovering extremely rare high-variability objects. © 2010 American Institute of Physics.

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