XMM observations of the high-redshift quasar RX J1028.6 – 0844 at z= 4.276 : soft X-ray spectral flattening

We present results from a new XMM–Newton observation of the high-redshift quasar RX J1028.6 – 0844 at a redshift of 4.276. The soft X-ray spectral flattening, as reported by a previous study with ASCA , is confirmed to be present, with, however, a reduced column density when modelled by absorption. The inferred column density for absorption intrinsic to the quasar is  2.1(^+0.4_−0.3) × 10²²  cm⁻²  for cold matter, and higher for ionized gas. The spectral flattening shows remarkable similarity with that of two similar object, namely GB 1428 + 4217 and PMN J0525 − 3343. The results improve upon those obtained from a previous short-exposure observation for RX J1028.6 – 0844 with XMM–Newton . A comparative study of the two XMM–Newton observations reveals a change in the power-law photon index from  Γ≃ 1.3  to 1.5 on time-scales of about one year. A tentative excess emission feature in the rest-frame 5–10 keV band is suggested, which is similar to that marginally suggested for GB 1428 + 4217.     

Comparison of high- and low-state X-ray spectra in the type 1.5 quasi-stellar object 2MASS 0918+2117

When observed by XMM–Newton in 2003, the type 1.5 quasi-stellar object 2MASS 0918+2117 was found to be in a low state, with an X-ray flux approximately four to five times fainter than during an earlier Chandra observation. The 2–6 keV spectrum was unusually hard (photon index  Γ∼ 1.25  ), with evidence for a reflection-dominated continuum, while a soft excess visible below ∼1 keV prevented confirmation of the anticipated low energy absorber. In a second XMM–Newton observation in 2005, the X-ray flux is found to have recovered, with a 2–10 keV continuum spectrum now typical of a broad-line active galaxy  (Γ∼ 2)  and a deficit of flux below ∼1 keV indicative of continuum absorption in a column   N _H∼ 4 × 10²¹ cm⁻²  . We find the preferred ionization state of the absorbing gas to be low, which then leaves a residual soft excess of similar spectral form and flux to that found in the 2003 XMM–Newton observation. Although observed at different epochs, we note that dust in the absorbing column could also explain the red nucleus and strong optical polarization of 2MASS 0918+2117.     

The ASCA spectrum of the z = 4.72 blazar GB 1428+4217

The X-ray-luminous quasar GB 1428+4217 at redshift 4.72 has been observed with ASCA . The observed 0.5–10 keV flux is 3.2 Å– 10⁻¹² erg cm⁻² s⁻¹. We report here on the intrinsic 4 − 57 keV X-ray spectrum, which is very flat (photon index 1.29). We find no evidence for flux variability within the ASCA data set or between it and ROSAT data. We show that the overall spectral energy distribution of GB 1428+4217 is similar to that of lower redshift MeV blazars, and present models that fit the available data. The Doppler beaming factor is likely to be at least 8. We speculate on the number density of such high-redshift blazars, which must contain rapidly formed massive black holes.     

An absorption event in the X-ray light curve of NGC 3227

We have monitored the Seyfert galaxy NGC 3227 with the Rossi X-ray Timing Explorer ( RXTE ) since 1999 January. During late 2000 and early 2001 we observed an unusual hardening of the 2–10 keV X-ray spectrum which lasted several months. The spectral hardening was not accompanied by any correlated variation in flux above 8 keV. We therefore interpret the spectral change as transient absorption by a gas cloud of column density 2.6 × 10²³ cm⁻² crossing the line of sight to the X-ray source. A spectrum obtained by XMM–Newton during an early phase of the hard-spectrum event confirms the obscuration model and shows that the absorbing cloud is only weakly ionized. The XMM–Newton spectrum also shows that ∼10 per cent of the X-ray flux is not obscured, but this unabsorbed component is not significantly variable and may be scattered radiation from a large-scale scattering medium. Applying the spectral constraints on the cloud ionization parameter and assuming that the cloud follows a Keplerian orbit, we constrain the location of the cloud to be   R ∼ 10–100  light-days from the central X-ray source, and its density to be   n _H∼ 10⁸ cm⁻³  , implying that we have witnessed the eclipse of the X-ray source by a broad line region cloud.     

XMM–Newton and Suzaku analysis of the Fe K complex in the type 1 Seyfert galaxy Mrk 509

We report on partially overlapping XMM–Newton (∼260 ks) and Suzaku (∼100 ks) observations of the iron K band in the nearby, bright type 1 Seyfert galaxy Mrk 509. The source shows a resolved neutral Fe K line, most probably produced in the outer part of the accretion disc. Moreover, the source shows further emission bluewards of the 6.4 keV line due to ionized material. This emission is well reproduced by a broad line produced in the accretion disc, while it cannot be easily described by scattering or emission from photoionized gas at rest. The summed spectrum of all XMM–Newton observations shows the presence of a narrow absorption line at 7.3 keV produced by highly ionized outflowing material. A spectral variability study of the XMM–Newton data shows an indication for an excess of variability at 6.6–6.7 keV. These variations may be produced in the red wing of the broad ionized line or by variation of a further absorption structure. The Suzaku data indicate that the neutral Fe K α line intensity is consistent with being constant on long time-scales (of a few years), and they also confirm as most likely the interpretation of the excess blueshifted emission in terms of a broad ionized Fe line. The average Suzaku spectrum differs from the XMM–Newton one in the disappearance of the 7.3 keV absorption line and around 6.7 keV, where the XMM–Newton data alone suggested variability.     

Correlated multiwavelength emission from the X-ray-bright Seyfert galaxy III Zw 2

The X-ray-bright Seyfert 1 galaxy III Zw 2 was observed with XMM–Newton in 2000 July. Its X-ray spectrum can be described by a power law of photon index Γ= 1.7 and an extremely broad (FWHM∼ 140 000 km  s⁻¹  ) Fe Kα line at 6.44 keV. The iron line has an equivalent width of ∼800 eV. To study the long-term X-ray behaviour of the source we have analysed 25 yr of data, from 1975 to 2000. There is no evidence of significant intrinsic absorption within the source or of a soft X-ray excess in the XMM or archival data. We do not detect rapid X-ray variability (a few  × 10³ s  ) during any of the individual observations; however, on longer time-scales (a few years) the X-ray light curve shows 10-fold flux variations. We infer a black hole mass of  ∼10⁹ M_⊙  (from Hβ FWHM) for III Zw 2 which is much higher than some previous estimates.
A comparison of X-ray variability with light curves at other wavelengths over a 25-yr period reveals correlated flux variations from radio to X-ray wavelengths. We interpret the variable radio to optical emission as synchrotron radiation, self-absorbed in the radio/millimetre region, and the X-rays mainly as a result of Compton up-scattering of low-energy photons by the population of high-energy electrons that give rise to the synchrotron radiation.     

An XMM–Newton observation of Ton S180: constraints on the continuum emission in ultrasoft Seyfert galaxies

We present an XMM–Newton observation of the bright, narrow-line, ultrasoft type 1 Seyfert galaxy Ton S180. The  0.3–10 keV  X-ray spectrum is steep and curved, showing a steep slope above 2.5 keV  (Γ∼ 2.3)  and a smooth, featureless excess of emission at lower energies. The spectrum can be adequately parametrized using a simple double power-law model. The source is strongly variable over the course of the observation but shows only weak spectral variability, with the fractional variability amplitude remaining approximately constant over more than a decade in energy. The curved continuum shape and weak spectral variability are discussed in terms of various physical models for the soft X-ray excess emission, including reflection off the surface of an ionized accretion disc, inverse Compton scattering of soft disc photons by thermal electrons, and Comptonization by electrons with a hybrid thermal/non-thermal distribution. We emphasize the possibility that the strong soft excess may be produced by dissipation of accretion energy in the hot, upper atmosphere of the putative accretion disc.     

The XMM–Newton/2dF survey – VIII. The extended X-ray sources

We present a sample of eight extended X-ray sources detected in the wide-field (∼2.3 deg²), bright (2–10 ks) XMM–Newton /2dF survey, reaching a flux limit of  ∼2 × 10⁻¹⁴ erg s⁻¹ cm⁻²  . Of these, seven are identified as secure X-ray clusters in the soft 0.3–2 keV band using a standard wavelet algorithm on either the PN or the MOS images. Spectroscopic or photometric redshifts are available for five clusters, spanning a range between 0.12 and 0.68. The X-ray spectral fittings show temperatures between 1 and 4.6 keV, characteristic of poor clusters and groups of galaxies. We derive for the first time the XMM–Newton cluster number count  log  N –log  S   distribution albeit with poor statistics. Both the  log  N –log  S   and the luminosity–temperature relation are in good agreement with previous ROSAT results.     

Fe K emission in the ultraluminous infrared galaxy Arp 220

Prominent Fe Kα line emission is detected in the XMM–Newton spectrum of the ultraluminous infrared galaxy Arp 220. The centroid of the line is found at an energy of 6.7 keV and the equivalent width of the line is  EW ∼ 1.9 keV  (at 3.5σ significance). A few other spectral features are found at various degrees of significance in the lower energy range on a hard 2.5–10 keV continuum  (Γ∼ 1)  . The large EW of the Fe K line poses a problem with interpreting the hard X-ray emission as integrated X-ray binary emission. A thermal emission spectrum with a temperature of   kT ∼ 7 keV  modified by absorption of   N _H≃ 3 × 10²² cm⁻²  , can describe the 2.5–10 keV continuum shape and the Fe K emission. A hot bubble that is shocked internally in a starburst region would have a similar temperature and gives a good explanation for the observed X-ray properties with a high star formation rate. An ensemble of radio supernovae in a dense environment, as suggested from VLBI imaging, could be another possibility, if such powerful supernovae are produced continuously at a high rate. However, the apparent lack of emission from X-ray binaries is incompatible with the high supernova rate (∼2 SNe yr⁻¹) required by both interpretations. Highly photoionized, low-density gas illuminated by a hidden Compton-thick active galactic nucleus is a possible alternative for the hard X-ray emission, which can be tested by examining whether radiative recombination continua from highly ionized Ca and Fe are present in better quality data from a forthcoming observation.     

The X-ray properties of optically selected z > 0.6 clusters in the European Southern Observatory Distant Cluster Survey

We present XMM–Newton observations of three optically selected   z > 0.6  clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and – unlike other high-redshift, optically selected clusters – are consistent with the T –σ and   L _X–σ  relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by   z ∼ 0.8  .     

The warm absorber of the type 1 Seyfert galaxy H1419+480

The bright type 1 Seyfert galaxy H1419+480  ( z ∼ 0.072)  , whose X-ray colours from earlier HEAO-1 and ROSAT missions suggested a complex X-ray spectrum, has been observed with XMM–Newton . The EPIC spectrum above 2 keV is well fitted by a power law with photon index  Γ= 1.84 ± 0.01  and an Fe Kα line of equivalent width ∼250 eV. At softer energies, a decrement with respect to this model extending from 0.5 to 1 keV is clearly detected. After trying a number of models, we find that the best fit corresponds to O vii absorption at the emission redshift, plus a 2σ detection of O viii absorption. A photoionized gas model fit yields  log ξ∼ 1.15–1.30  (ξ in erg cm s⁻¹) with   N _H∼ 5 × 10²¹ cm⁻²  for solar abundances. We find that the ionized absorber was weaker or absent in an earlier ROSAT observation. An International Ultraviolet Explorer spectrum of this source obtained two decades before shows a variable (within a year) C iv absorber outflowing with a velocity ∼1800 km s⁻¹. We show that both X-ray and ultraviolet absorptions are consistent with arising in the same gas, with varying ionization.     

A new superwind galaxy: XMM–Newton observations of NGC 6810

We present the first imaging X-ray observation of the highly inclined  ( i = 78°)  Sab Seyfert 2 galaxy NGC 6810 using XMM–Newton , which reveals soft X-ray emission that extends out to a projected height of ∼7 kpc away from the plane of the galaxy. The soft X-ray emission beyond the optical disc of the galaxy is most plausibly extraplanar, although it could instead come from large galactic radius. This extended X-ray emission is spatially associated with diffuse Hα emission, in particular with a prominent 5-kpc-long Hα filament on the north-west of the disc. A fraction ≲35 per cent of the total soft X-ray emission of the galaxy arises from projected heights  | z | ≥ 2 kpc  . Within the optical disc of the galaxy the soft X-ray emission is associated with the star-forming regions visible in ground-based Hα and XMM–Newton optical monitor near-UV imaging. The temperature, supersolar α-element-to-iron abundance ratio, soft X-ray/Hα correlation, and X-ray to far-infrared (FIR) flux ratio of NGC 6810 are all consistent with local starbursts with winds, although the large base radius of the outflow would make NGC 6810 one of the few 'disc-wide' superwinds currently known. Hard X-ray emission from NGC 6810 is weak, and the total   E = 2–10 keV  luminosity and spectral shape are consistent with the expected level of X-ray binary emission from the old and young stellar populations. The X-ray observations provide no evidence of any active galactic nucleus activity. We find that the optical, IR and radio properties of NGC 6810 are all consistent with a starburst galaxy, and that the old classification of this galaxy as a Seyfert 2 galaxy is probably incorrect.     

The ultraluminous X-ray source population of NGC 4485/4490

We report the results of spectral and temporal variability studies of the ultraluminous X-ray sources (ULXs) contained within the interacting pair of galaxies NGC 4485/4490, combining Chandra and XMM–Newton observations. Each of the four separate observations provide at least modest quality spectra and light curves for each of the six previously identified ULXs in this system; we also note the presence of a new transient ULX in the most recent observation. No short-term variability was observed for any ULX within our sample, but three out of five sources show correlated flux/spectral changes over longer time-scales, with two others remaining stable in spectrum and luminosity over a period of at least 5 yr. We model the spectra with simple power-law and multicolour disc blackbody models. Although the data are insufficient to statistically distinguish models in each epoch, those better modelled (in terms of their  χ²  fit) by a multicolour disc blackbody appear to show a disc-like correlation between luminosity and temperature, whereas those modelled by a power-law veer sharply away from such a relationship. The ULXs with possible correlated flux/spectral changes appear to change spectral form at  ∼2 × 10³⁹ erg s⁻¹  , suggestive of a possible change in spectral state at high luminosities. If this transition is occurring between the very high state and a super-Eddington ultraluminous state, it indicates that the mass of the black holes in these ULXs is around  10–15 M_⊙  .     

Multi-epoch spectroscopy of the globular cluster black hole in NGC 4472

We present a study of the X-ray spectral properties of the highly variable X-ray emitting black hole in a globular cluster in the elliptical galaxy NGC 4472. The X-ray Multiple Mirror–Newton ( XMM–Newton ) spectrum of the source in its bright epoch is well described by a multiple blackbody model with a characteristic temperature   kT _in≈  0.2 keV. The spectrum of an archival Chandra observation of the source obtained 3.5 yr before the XMM data gives similar estimates for the blackbody parameters. We confirm that the fainter interval of the XMM–Newton observation has a spectrum that is consistent with the brighter epoch, except for an additional level of foreground absorption. We also consider other possible mechanisms for the variability. Based on the time-scale of the X-ray flux decline and the estimated size of the X-ray emission region, we argue that an eclipsing companion is highly unlikely. We find the most likely means of producing the absorption changes on the observed time-scale is through partial obscuration by a precessing warped accretion disc.     

Batch discovery of nine z∼ 1 clusters using X-ray and K or R, z' images

We present the results of an initial search for clusters of galaxies at z ∼ 1 and above, using data from 2.9 square degrees of XMM–Newton images. By selecting weak potentially extended X-ray sources with faint or no identifications in deep, ground-based optical imaging, we have constructed a starting sample of 19 high-redshift cluster candidates. Near-IR and R , z ' imaging of these fields identified nine of them as high-redshift systems. Six of these were confirmed spectroscopically, three at z ∼ 1.0 and the other three in the  0.8 < z < 0.92  range. The remaining three systems have solid photometric evidence to be at   z _phot∼ 0.8, 1.0  and 1.3. The present sample significantly increases the number of such clusters. The measured density of z ≳ 1 clusters, after discarding 'low'-redshift systems at z ≲ 0.92 is about 1.7 deg⁻² (with 68 per cent confidence interval equal to [1.0, 2.9]) for   f_X ≳ 2.5  10⁻¹⁵ erg cm⁻² s⁻¹  ([0.5–2] keV) and this is a lower limit, having screened not all potential z ∼ 1 candidate clusters. Coordinates, X-ray measures and evidence for nine X-ray-selected high-redshift clusters is given.     

Suzaku observations of Markarian 335: evidence for a distributed reflector

We report on a 151-ks net exposure Suzaku observation of the narrow-line Seyfert 1 galaxy Mrk 335. The 0.5–40 keV spectrum contains a broad Fe line, a strong soft excess below about 2 keV and a Compton hump around 20–30 keV. We find that a model consisting of a power law and two reflectors provides the best fit to the time-averaged spectrum. In this model, an ionized, heavily blurred, inner reflector produces most of the soft excess, while an almost neutral outer reflector (outside ∼ 40 r _g) produces most of the Fe line emission. The spectral variability of the observation is characterized by spectral hardening at very low count rates. In terms of our power-law + two-reflector model it seems like this hardening is mainly caused by pivoting of the power law. The rms spectrum of the entire observation has the curved shape commonly observed in active galactic nuclei, although the shape is significantly flatter when an interval which does not contain any deep dip in the light curve is considered. We also examine a previous 133-ks XMM–Newton observation of Mrk 335. We find that the XMM–Newton spectrum can be fitted with a similar two-reflector model as the Suzaku data and we confirm that the rms spectrum of the observation is flat. The flat rms spectra, as well as the high-energy data from the Suzaku PIN detector, disfavour an absorption origin for the soft excess in Mrk 335.     

The blazar GB 1428+4217: a warm absorber at z=4.72?

BeppoSAX observations of the high-redshift ( z =4.72) blazar GB 1428+4217 confirm the presence of a complex soft X-ray spectrum first seen with the ROSAT PSPC. Flattening below a rest-frame energy of 5 keV can be accounted for by absorption from an equivalent column density of (cold) gas with N _H∼8×10²² cm⁻² . Below 2 keV a (variable) excess of a factor of ∼20 above the extrapolated absorbed spectrum is also detected. These findings are consistent with and extend to higher redshifts the correlation between increasing soft X-ray flattening and increasing z , previously pointed out for large samples of radio-loud quasars. We propose that such features, including X-ray absorption and soft excess emission as well as absorption in the optical spectra, can be satisfactorily accounted for by the presence of a highly ionized nuclear absorber with column N _H∼10²³ cm⁻² , with properties possibly related to the conditions in the nuclear regions of the host galaxy. High-energy X-ray emission consistent with the extrapolation of the medium-energy spectrum is detected up to ∼300 keV (rest frame).     

XMM–Newton observations of bright ROSAT selected active galactic nuclei with low intrinsic absorption

We present a sample of 21 ROSAT bright active galactic nuclei (AGNs), representing a range of spectral classes, and selected for follow-up snapshot observations with XMM–Newton . The typical exposure was between 5 and 10 ks. The objects were primarily selected on the bases of X-ray brightness and not on hardness ratio; thus the sample cannot be strictly defined as a 'soft'sample. One of the main outcomes from the XMM–Newton observations was that all of the AGN, including 11 type 1.8–2 objects, required low levels of intrinsic absorption  ( N _H≲ 10²¹ cm⁻²)  . The low absorption in type 2 systems is a challenge to account for in the standard orientation-based unification model, and we discuss possible physical and geometrical models which could elucidate the problem. Moreover, there does not appear to be any relation between the strength and shape of the soft excess, and the spectral classification of the AGN in this sample. We further identify a number of AGN which deserve deeper observations or further analysis: for example, the low-ionization nuclear emission regions (LINERs) NGC 5005 and NGC 7331, where optically thin thermal and extended emission is detected, and the narrow-line Seyfert 1 II Zw 177, which shows a broad emission feature at ∼ 5.8 keV.     

CENSORS: A Combined EIS–NVSS Survey Of Radio Sources – I. Sample definition, radio data and optical identifications

A new sample of radio sources, with the designated name CENSORS (A Combined EIS–NVSS Survey Of Radio Sources), has been defined by combining the National Radio Astronomy Observatory Very Large Array Sky Survey (NVSS) at 1.4 GHz with the ESO Imaging Survey (EIS) Patch D, a 3° by 2° region of sky centred at RA     , Dec. −21°00'00' (J2000). New radio observations of 199 NVSS radio sources with NVSS flux densities   S _{1.4 GHz} > 7.8 mJy  are presented, and are compared with the EIS I -band imaging observations which reach a depth of   I ∼ 23  ; optical identifications are obtained for over two-thirds of the ∼150 confirmed radio sources within the EIS field. The radio sources have a median linear size of 6 arcsec, consistent with the trend for lower flux density radio sources to be less extended. Other radio source properties, such as the lobe flux density ratios, are consistent with those of brighter radio source samples. From the optical information, 30–40 per cent of the sources are expected to lie at redshifts   z ≳ 1.5  .
One of the key goals of this survey is to accurately determine the high-redshift evolution of the radio luminosity function. These radio sources are at the ideal flux density level to achieve this goal; at redshifts   z ∼ 2  they have luminosities which are around the break of the luminosity function and so provide a much more accurate census of the radio source population at those redshifts than the existing studies of extreme, high radio power sources. Other survey goals include investigating the dual-population unification schemes for radio sources, studying the radio luminosity dependence of the evolution of radio source environments, and understanding the radio power dependence of the K – z relation for radio galaxies.     

Chandra X-ray observations of the 3C 295 cluster core

We examine the properties of the X-ray gas in the central regions of the distant ( z =0.46) , X-ray luminous cluster of galaxies surrounding the powerful radio source 3C 295, using observations made with the Chandra Observatory . Between radii of 50 and 500 kpc, the cluster gas is approximately isothermal with an emission-weighted temperature, kT ∼5 keV . Within the central 50-kpc radius this value drops to kT ∼3.7 keV . The spectral and imaging Chandra data indicate the presence of a cooling flow within the central 50-kpc radius of the cluster, with a mass deposition rate of approximately 280 M_⊙ yr⁻¹. We estimate an age for the cooling flow of 1–2 Gyr , which is approximately 1000 times older than the central radio source. We find no evidence in the X-ray spectra or images for significant heating of the X-ray gas by the radio source. We report the detection of an edge-like absorption feature in the spectrum for the central 50-kpc region, which may be caused by oxygen-enriched dust grains. The implied mass in metals seen in absorption could have been accumulated by the cooling flow over its lifetime. Combining the results on the X-ray gas density profile with radio measurements of the Faraday rotation measure in 3C 295, we estimate the magnetic field strength in the region of the cluster core to be B ∼12 μG .