XMM-Newton Slew Survey Research Articles

Identification of three cataclysmic variables detected by the ART-XC and eROSITA telescopes on board the SRG during the all-sky X-ray survey

We report the discovery of three cataclysmic variables in the data of the first year of the all-sky X-ray survey by the SRG orbital observatory. The sources were selected for their brightness in the 4-12 keV band in the data of the Mikhail Pavlinsky ART-XC telescope. They are also detected by the eROSITA telescope, which provides accurate localizations and spectral data for a broadband spectral analysis. All three objects were previously known as X-ray sources from the ROSAT all-sky survey and XMM-Newton slew survey, but their nature remained unknown. The X-ray spectra obtained by eROSITA and ART-XC are consistent with optically thin thermal emission with a temperature kT ≳ 18 keV for SRGA J194638.9+704552 and SRGA J225412.8+690658 and kT ≳ 5 keV for SRGAJ204547.8+672642. Together with the inferred high X-ray luminosities (2 × 1032-3 × 1033 erg s-1), this strongly suggests that all three sources are cataclysmic variables (CVs). We have obtained optical photometry and spectroscopy for these objects using the AZT-33IK 1.6 m telescope of the Sayan Observatory. The optical properties confirm the CV nature of the objects. We conclude that SRGA J194638.9+704552 is an intermediate polar, SRGA J204547.8+672642 is likely a polar or intermediate polar, and SRGA J225412.8+690658 is either a magnetic or nonmagnetic CV. We have also measured an orbital period of 2.98 h for SRGA J204547.8+672642 based on TESS data. Three out of the planned eight SRG all-sky surveys have now been completed. We expect to find many new CVs, in particular, magnetic systems, during the survey, and we plan to continue our optical follow-up program.

Populations of highly variable X-ray sources in theXMM–Newtonslew survey

ABSTRACTWe present the identifications of a flux-limited sample of highly variable X-ray sources on long time-scales from the second catalogue of the XMM–Newton SLew survey (XMMSL2). The carefully constructed sample, comprising 265 sources (2.5 per cent) selected from the XMMSL2 clean catalogue, displayed X-ray variability of a factor of more than 10 in 0.2–2 keV compared to the ROSAT All Sky Survey. Of the sample sources, 94.3 per cent are identified. The identification procedure follows a series of cross-matches with astronomical data bases and multiwavelength catalogues to refine the source position and identify counterparts to the X-ray sources. Assignment of source type utilizes a combination of indicators including counterparts offset, parallax measurement, spectral colours, X-ray luminosity, and light-curve behaviour. We identified 40 per cent of the variables with stars, 10 per cent with accreting binaries, and at least 30.4 per cent with active galactic nuclei. The rest of the variables are identified as galaxies. It is found that the mean effective temperatures of the highly variable stars are lower than those of less variable stars. Our sample of highly variable AGN tend to have lower black hole masses, redshifts, and marginally lower soft X-ray luminosities compared to the less variable ones, while no difference was found in the Eddington ratio distributions. Five flaring events are tidal disruption events published previously. This study has significantly increased the number of variable sources in XMMSL2 with identifications and provides greater insight on the nature of many o f the sources, enabling further studies of highly variable X-ray sources.

Multiwavelength Study of an X-Ray Tidal Disruption Event Candidate in NGC 5092

Abstract We present multiwavelength studies of a transient X-ray source, XMMSL1 J131952.3+225958, associated with the galaxy NGC 5092 at z = 0.023 detected in the XMM-Newton SLew survey (XMMSL). The source brightened in the band by a factor of in 2005 as compared with previous flux limits and then faded by a factor of >200 as observed with XMM-Newton in 2013 and with Swift in 2018. At the flaring state the X-ray spectrum can be modeled with a blackbody at a temperature of ∼60 eV and an overall luminosity of erg s−1. A UV flare and optical flare were also detected with the Galaxy Evolution Explorer and the Sloan Digital Sky Survey, respectively, within several months of the X-ray flare, whose nonstellar UV–optical spectrum can be described with a blackbody at a temperature of K and a luminosity of erg s−1. Interestingly, mid-infrared monitoring observations of NGC 5092 with the Wide-field Infrared Survey Explorer 5–13 yr later show a continuous flux decline. These dramatic variability properties, from the X-ray through UV and optical to infrared, appear to be orderly, suggestive of a stellar tidal disruption event (TDE) by a massive black hole, confirming the postulation by Kanner et al. This TDE candidate belongs to a rare sample with contemporaneous bright emission detected in the X-ray, UV, and optical, which are later echoed by dust-reprocessed light in the mid-infrared. The black hole has a mass of 10 , residing in a galaxy that is dominated by a middle-aged stellar population of 2.5 Gyr.

SDSS-IV/SPIDERS: A catalogue of X-ray selected AGN properties

This work presents the catalogue of optical spectral properties for all X-ray selected SPIDERS active galactic nuclei (AGN) up to SDSS DR14. SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV programme that is currently conducting optical spectroscopy of the counterparts to the X-ray selected sources detected in the ROSAT all-sky survey and the XMM-Newton slew survey in the footprint of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). The SPIDERS DR14 sample is the largest sample of X-ray selected AGN with optical spectroscopic follow-up to date. The catalogue presented here is based on a clean sample of 7344 2RXS (z¯ = 0.5) and 1157 XMM-Newton slew survey (z¯ = 0.4) type 1 AGN with spectroscopic coverage of the Hβ and/or MgII emission lines. Visual inspection results for each object in this sample are available from a combination of literature sources and the SPIDERS group, which provide both reliable redshifts and source classifications. The spectral regions around the Hβ and MgII emission lines have been fit in order to measure both line and continuum properties, estimate bolometric luminosities, and provide black hole mass estimates using the single-epoch (or photoionisation) method. The use of both Hβ and MgII allows black hole masses to be estimated up to z ≃ 2.5. A comparison is made between the spectral properties and black hole mass estimates derived from Hβ and MgII using the subsample of objects which have coverage of both lines in their spectrum. These results have been made publicly available as an SDSS-IV DR14 value added catalogue.

The stellar content of the XMM-Newton slew survey

Aims. We present a detailed analysis of the stellar content of the current version of the XMM-Newton slew survey (XMMSL2). Methods. Since stars emit only a small fraction of their total luminosity in the X-ray band, the stellar XMMSL2 sources ought to have relatively bright optical counterparts. Therefore the stellar identifications were obtained by an automatic crossmatch of the XMMSL2 catalog with the first Gaia data release (Gaia DR1), 2MASS, and Tycho2 catalogs. The reliability of this procedure was verified by a comparison with the individually classified Einstein Observatory medium sensitivity survey X-ray sources and by a crossmatch with the Chandra Source Catalog. Results. We identify 6815 of the 23 252 unique XMMSL2 sources to be stellar sources, while 893 sources are flagged as unreliable. For every counterpart a matching probability is estimated based upon the distance between the XMMSL2 source and the counterpart. Given this matching probability the sample is expected to be reliable to 96.7 % and complete to 96.3 % . The sample contains stars of all spectral types and luminosity classes, and late-type dwarfs have the largest share. For many stellar sources the fractional contribution of the X-ray band to the total energy output is found above the saturation limit of previous studies (Lx/Lbol = 10−3), because the XMMSL2 sources are more affected by flares owing to their short exposure times of typically 6 s. A comparison with the second ROSAT all-sky survey (2RXS) source catalog shows that about 25 % of the stellar XMMSL2 sources are previously unknown X-ray sources. The results of our identification procedure can be accessed via VizieR.

SPIDERS: selection of spectroscopic targets using AGN candidates detected in all-sky X-ray surveys

SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV survey running in parallel to the eBOSS cosmology project. SPIDERS will obtain optical spectroscopy for large numbers of X-ray-selected AGN and galaxy cluster members detected in wide area eROSITA, XMM-Newton and ROSAT surveys. We describe the methods used to choose spectroscopic targets for two sub-programmes of SPIDERS: X-ray selected AGN candidates detected in the ROSAT All Sky and the XMM-Newton Slew surveys. We have exploited a Bayesian cross-matching algorithm, guided by priors based on mid-IR colour-magnitude information from the WISE survey, to select the most probable optical counterpart to each X-ray detection. We empirically demonstrate the high fidelity of our counterpart selection method using a reference sample of bright well-localised X-ray sources collated from XMM-Newton, Chandra and Swift-XRT serendipitous catalogues, and also by examining blank-sky locations. We describe the down-selection steps which resulted in the final set of SPIDERS-AGN targets put forward for spectroscopy within the eBOSS/TDSS/SPIDERS survey, and present catalogues of these targets. We also present catalogues of ~12000 ROSAT and ~1500 XMM-Newton Slew survey sources which have existing optical spectroscopy from SDSS-DR12, including the results of our visual inspections. On completion of the SPIDERS program, we expect to have collected homogeneous spectroscopic redshift information over a footprint of ~7500 deg$^2$ for >85 percent of the ROSAT and XMM-Newton Slew survey sources having optical counterparts in the magnitude range 17<r<22.5, producing a large and highly complete sample of bright X-ray-selected AGN suitable for statistical studies of AGN evolution and clustering.

Characterization of AGN from the XMM–Newton Slew Survey

We present optical spectroscopy of candidate AGN pinpointed by a Swift follow-up campaign on unidentified transients in the XMM-Newton Slew Survey, increasing the completeness of the identifications of AGN in the Survey. Our Swift follow-up campaign identified 17 XRT-detected candidate AGN, of which nine were selected for optical follow-up and a further two were confirmed as AGN elsewhere. Using data obtained at the William Herschel Telescope, Very Large Telescope and New Technology Telescope, we find AGN features in seven of the candidates. We classify six as Seyfert types 1.0 to 1.5, with broad-line region velocities spanning 2000--12000 km s$^{-1}$, and identify one as a possible Type II AGN, consistent with the lack of a soft band X-ray detection in the Slew Survey. The Virial black hole mass estimates for the sample lie between 1$\times$10$^{8}$ M$_{\odot}$ and 3$\times$10$^9$ M$_{\odot}$, with one source likely emitting close to its Eddington rate, $L_{\rm Bol}/L_{\rm Edd} \sim 0.9$. We find a wide redshift range of $0.08<z<0.9$ for the nine now confirmed AGN drawn from the unidentified Slew Survey sample. One source remaining unclassified shows outbursts rarely seen before in AGN. We conclude that AGN discovered in this way are consistent with the largely non-varying, Slew-selected, known AGN population. We also find parallels with XMM-Newton Bright Serendipitous Survey AGN selected from pointed observations, and postulate that shallow X-ray surveys select AGN drawn from the same populations that have been characterised in deeper X-ray selected samples.

IPTF Discovery of the Rapid “Turn-on” of a Luminous Quasar

Abstract We present a radio-quiet quasar at z = 0.237 discovered “turning on” by the intermediate Palomar Transient Factory (iPTF). The transient, iPTF 16bco, was detected by iPTF in the nucleus of a galaxy with an archival Sloan Digital Sky Survey spectrum with weak narrow-line emission characteristic of a low-ionization nuclear emission-line region (LINER). Our follow-up spectra show the dramatic appearance of broad Balmer lines and a power-law continuum characteristic of a luminous ( erg s−1) type 1 quasar 12 yr later. Our photometric monitoring with PTF from 2009–2012 and serendipitous X-ray observations from the XMM-Newton Slew Survey in 2011 and 2015 constrain the change of state to have occurred less than 500 days before the iPTF detection. An enhanced broad Hα/[O iii] λ5007 line ratio in the type 1 state relative to other changing-look quasars also is suggestive of the most rapid change of state yet observed in a quasar. We argue that the &gt;10 increase in Eddington ratio inferred from the brightening in UV and X-ray continuum flux is more likely due to an intrinsic change in the accretion rate of a preexisting accretion disk than an external mechanism such as variable obscuration, microlensing, or the tidal disruption of a star. However, further monitoring will be helpful in better constraining the mechanism driving this change of state. The rapid “turn-on” of the quasar is much shorter than the viscous infall timescale of an accretion disk and requires a disk instability that can develop around a black hole on timescales less than 1 yr.

Tidal disruption events seen in the XMM-Newton slew survey

AbstractXMM-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.

The detection and X-ray view of the changing look AGN HE 1136-2304

We report the detection of high-amplitude X-ray flaring of the AGN HE 1136-2304, which is accompanied by a strong increase in the flux of the broad Balmer lines, changing its Seyfert type from almost type 2 in 1993 down to 1.5 in 2014. HE 1136-2304 was detected by the XMM-Newton slew survey at >10 times the flux it had in the ROSAT all-sky survey, and confirmed with Swift follow-up after increasing in X-ray flux by a factor of 30. Optical spectroscopy with SALT shows that the AGN has changed from a Seyfert 1.95 to a Seyfert 1.5 galaxy, with greatly increased broad line emission and an increase in blue continuum AGN flux by a factor of > 4. The X-ray spectra from XMM-Newton and NuSTAR reveal moderate intrinsic absorption and a high energy cutoff at 100 keV. We consider several different physical scenarios for a flare, such as changes in obscuring material, tidal disruption events, and an increase in the accretion rate. We find that the most likely cause of the increased flux is an increase in the accretion rate, although it could also be due to a change in obscuration.

An X-ray and UV flare from the galaxy XMMSL1 J061927.1-655311

New high variability extragalactic sources may be identified by comparing the flux of sources seen in the XMM-Newton Slew Survey with detections and upper limits from the ROSAT All Sky Survey. In November 2012, X-ray emission was detected from the galaxy XMMSL1 J061927.1-655311 (a.k.a. 2MASX 06192755-6553079), a factor 140 times higher than an upper limit from 20 years earlier. Both the X-ray and UV flux subsequently fell, over the following year, by factors of 20 and 4 respectively. Optically, the galaxy appears to be a Seyfert I with broad Balmer lines and weak, narrow, low-ionisation emission lines, at a redshift of 0.0729. The X-ray luminosity peaks at Lx ~ 8x10^43 ergs/s with a typical Sy I-like power-law X-ray spectrum of index ~ 2. The flare has either been caused by a tidal disruption event or by an increase in the accretion rate of a persistent AGN.

Low-luminosity X-ray sources and the Galactic ridge X-ray emission

Using the XMM-Newton Slew Survey, we construct a hard-band selected sample of low-luminosity Galactic X-ray sources. Two source populations are represented, namely coronally-active stars and binaries (ASBs) and cataclysmic variables (CVs), with X-ray luminosities collectively spanning the range 10^(28-34) erg/s (2-10 keV). We derive the 2-10 keV X-ray luminosity function (XLF) and volume emissivity of each population. Scaled to the local stellar mass density, the latter is found to be 1.08 +/- 0.16 x 10^28 erg/s/M and 2.5 +/- 0.6 x 10^27 erg/s/M, for the ASBs and CVs respectively, which in total is a factor 2 higher than previous estimates. We employ the new XLFs to predict the X-ray source counts on the Galactic plane at l = 28.5 deg and show that the result is consistent with current observational constraints. The X-ray emission of faint, unresolved ASBs and CVs can account for a substantial fraction of the Galactic ridge X-ray emission (GRXE). We discuss a model in which roughly 80 per cent of the 6-10 keV GRXE intensity is produced in this way, with the remainder attributable to X-ray scattering in the interstellar medium and/or young Galactic source populations. Much of the hard X-ray emission attributed to the ASBs is likely to be produced during flaring episodes.

Discovery of SXP 265, a Be/X-ray binary pulsar in the Wing of the Small Magellanic Cloud★

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 OGLE I-band light curve. The optical counterpart has been classified spectroscopically, with data obtained at the SAAO 1.9 m telescope, and photometrically, with data obtained using GROND 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 = (264.516+-0.014) s. The source likely shows a persistent X-ray luminosity of a few 10^35 erg/s 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.

X-RAY TRANSIENTS IN THE ADVANCED LIGO/VIRGO HORIZON

Advanced LIGO and Advanced Virgo will be all-sky monitors for merging compact objects within a few hundred Mpc. Finding the electromagnetic counterparts to these events will require an understanding of the transient sky at low red-shift (z<0.1). We performed a systematic search for extragalactic, low red-shift, transient events in the XMM-Newton Slew Survey. In a flux limited sample, we found that highly-variable objects comprised 10% of the sample, and that of these, 10% were spatially coincident with cataloged optical galaxies. This led to 4x10^-4 transients per square degree above a flux threshold of 3x10^-12 erg cm-2 s-1 [0.2-2 keV] which might be confused with LIGO/Virgo counterparts. This represents the first extragalactic measurement of the soft X-ray transient rate within the Advanced LIGO/Virgo horizon. Our search revealed six objects that were spatially coincident with previously cataloged galaxies, lacked evidence for optical AGNs, displayed high luminosities around 10^43 erg s-1, and varied in flux by more than a factor of ten when compared with the ROSAT All-Sky Survey. At least four of these displayed properties consistent with previously observed tidal disruption events.

TheXMM-Newtonslew survey in the 2–10 keV band

The XMM-Newton Slew Survey (XSS) covers 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. We investigate the source content of the XSS, focussing on detections in the 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 3e-12 erg/cm2/s (2-10 keV). Our starting point was a sample of 487 sources detected in the XMMSL1d2 XSS at high galactic latitude in the hard band. Through cross-correlation with published source catalogues from surveys spanning the electromagnetic spectrum from radio to gamma-rays, we find that 45% of the sources have likely identifications with normal/active galaxies, 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 hard band sample comprised of 219 galaxies and active galaxies. We investigate the properties of this extragalactic sample including its X-ray logN-logS distribution. We find that in the low-count limit, the XSS is 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 logN-logS 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.

The Role of Wide Field X-ray Surveys in Astronomy

AbstractWe review the history of X-ray sky surveys from the early experiments to the catalogues of 105 sources produced by ROSAT, Chandra and XMM-Newton. At bright fluxes the X-ray sky is shared between stars, accreting binaries and extragalactic sources while deeper surveys are dominated by AGN and clusters of galaxies. The X-ray background, found by the earliest missions, has been largely resolved into discrete sources at soft (0.3-2 keV) energies but at higher energies an important fraction still escapes detection. The possible identification of the missing flux with Compton-thick AGN has been probed in recent years by Swift and Integral.Variability seen in objects observed at different epochs has proved to be an excellent discriminator for rare classes of objects. The comparison of ROSAT All Sky Survey (RASS) and ROSAT pointed observations identified several Novae and high variability AGN as well as initiating the observational study of Tidal Disruption events. More recently the XMM-Newton slew survey, in conjunction with archival RASS data, has detected further examples of flaring objects which have been followed-up in near-real time at other wavelengths.

TYC 8380-1953-1: Discovery of an RS CVn Binary Through the XMM-Newton Slew Survey

ABSTRACTIn this article we report the discovery of the chromospherically active (RS CVn type) binary TYC 8380-1953-1 through the XMM-Newton slew survey and present results of our optical and X-ray follow-up. With a flux limit of 6 × 10-13 ergs cm-2 s-1 in the soft band (0.2–2 keV), the XMM-Newton slew has a similar sensitivity to the ROSAT All Sky Survey, allowing interesting sources to be identified by their long-term variability. Two different types of stellar sources are detected in shallow X-ray surveys: young stars (both pre–main- and main-sequence stars) and chromospherically active binaries (BY Dra and RS CVn-type systems). The discovery of stars in such surveys and the study of their nature through optical follow-ups is valuable to determine their spatial distribution and scale height in the Galaxy. Our analysis shows that TYC 8380-1953-1 is a double-lined spectroscopic binary, with both components having similar spectral type (likely K0/2 + K3/5) and luminosity. With a typical coronal temperature for an RS CVn system (kT ∼ 1.15 keV) and an X-ray luminosity in the 0.3–10 keV energy band higher than 4 × 1031 erg s-1, TYC 8380-1953-1 lies among the most X-ray luminous RS CVn binaries.

ON THE NATURE OF HARD X-RAY EXTRAGALACTIC SOURCES OBSERVED WITHXMM-NEWTON

Over the last decade, X-ray surveys have provided outstanding new results due to the lack of the common selection effects present at other wavelengths. Here, we have selected a sample of unidentified sources from the XMM-Newton Slew Survey Catalog, likely to be extragalactic. Five of them were observed with the XMM-Newton observatory. In this work, we present the results of the spectral analysis of these objects in the X-ray and optical bands. Only three of them had useful spectroscopic X-ray data, and follow up observations were carried out in the optical range to determine their coordinates, classification, and redshift. The sources are different types of active galactic nuclei (AGNs) with redshifts ranging from 0.059 to 0.386. The properties at both spectral ranges (X-rays and optical) are compatible with the common properties of their types of AGNs. Although the sources were selected by their hard X-ray properties, none of the three detected objects turned out to be an obscured AGN.

Tidal disruption events from the first XMM-Newton slew survey

Observations over the past decade have revealed that supermassive black holes (SMBHs) likely reside at the centres of most or all bulge galaxies. Confirmation of their dormant presence in non-active galaxies is difficult to obtain. An unavoidable consequence of the existence of remnant SMBHs is the detection of a tidal disruption event. This is discovered as flaring radiation produced when a star is tidally disrupted and subsequently accreted by the black hole. Two of these exceptional events have been discovered by XMM-Newton in the first slew catalogue, NGC 3599 and SDSS J132341.97+482701.3. Here we show their evolution up to four years after the peak of the outburst including a detailed analysis of NGC 3599, for which novel follow-up observations are presented here.

A well-monitored, X-ray selected, tidal disruption event

We report on a candidate tidal disruption event detected in the XMM-Newton slew survey from the nucleus of SDSS J120136.02+300305.5 (z = 0.146; hereafter SDSS J1201+30). The source, monitored by Swift and XMM-Newton, was highly variable on timescales of a week, reaching a peak X-ray luminosity of 3 × 1044 ergs/s. The light curve is reminiscent of the variations seen in SWIFT J1644+57, although in this case the absence of radio flux rules out a jet mechanism for the emission. The X-ray spectrum is steep, (spectral index = 3–5) and softens with diminishing flux. It is inconsistent with a single or multi-temperature black-body model but may be fit with Bremsstrahlung or comptonised thermal emission.