XMM Observations Research Articles

A variable Quasi-Periodic Oscillation in M82 X-1. Timing and spectral analysis of XMM-Newton and RossiXTE observations

We report results from a spectral and timing analysis of M82 X-1, one of the brightest known ultraluminous X-ray sources. Data from a new 105-ks XMM-Newton observation of M82 X-1, performed in 2004 April, and of archival RossiXTE observations are presented. A very soft thermal component is present in the XMM spectrum. Although it is not possible to rule out a residual contamination from the host galaxy, modelling it with a standard accretion disc would imply a black hole (BH) mass of ≈ 10 3 M ⊙ . An emission line was also detected at an energy typical for fluorescent Fe emission. The power density spectrum of the XMM observation shows a variable Quasi-Periodic Oscillation (QPO) at frequency of 113 mHz with properties similar to those discovered by Strohmayer and Mushotzky. The QPO was also found in seven archival RXTE observations, that include those analysed by Strohmayer and Mushotzky, and Fiorito and Titarchuk. A comparison of the properties of this QPO with those of the various types of QPOs observed in Galactic black hole candidates strongly suggests an association with the type-C, low-frequency QPOs. Scaling the frequency inversely to the BH mass, the observed QPO frequency range (from 50 to 166 mHz) would yield a BH mass anywhere in the interval few tens to 1000 M ⊙ .

The hard X-ray emission from the Vela pulsar wind nebula

We present the results of a preliminary spectral analysis performed on the BeppoSAX and XMM observations of the Vela plerion. The broad energy range covered by the instruments on board the two observatories allows an evaluation of the spectral parameters of the high energy emission model and provides an indication on the morphology of the source emission above 10 keV. We confirm the softening of the PWN spectrum (3–10 keV band) at distances greater than 4′ from the pulsar and estimate the diameter of the high energy (>10 keV) emission region to be on the order of 25′–30′.

ROSAT observations of the soft X-ray background and of the cluster soft excess emission in the Hercules supercluster

Recent observations with the XMM-Newton satellite confirmed the existence of the soft excess phenomenon in galaxy clusters, earlier discovered in several EUVE, ROSAT and BeppoSAX observations. Among the clusters for which XMM has reported detection of soft excess emission are MKW03s and A2052, two clusters in the Hercules concentration. The Hercules supercluster lies along the southern extension of the North Polar Spur, a region of bright soft X-ray emission clearly visible in ROSAT All-Sky Survey images. We analyze 11 pointed ROSAT PSPC observations toward 3 clusters in the Hercule concentration, MKW03s, A2052 and A2063, and 8 neighboring fields in order to investigate the soft X-ray emission in that region of the sky. We find that the soft X-ray emission varies by a factor of few on scales of few degrees, rendering the background subtraction a complex task. If the Noth Polar Spur emission is of local origin, we find that only A2052 and A2063 have evidence of cluster soft excess emission, and that the OVII emission lines detected in XMM observations of A2052 and MKW03s are not associated with the cluster. If part or all of the North Polar Spur soft X-ray enhancement is of extragalactic nature, the three clusters feature strong soft excess emission, and the OVII emission lines observed by XMM are genuinely associated with the clusters. We interpret the soft excess emission with the presence of warm gas, either intermixed with the hot intra-cluster medium or in filamentary structures located around the clusters, and estimate that the warm gas is approximately as massive as the hot intra-cluster medium.

IGR J16320–4751 as seen by simultaneous INTEGRAL and XMM observations

We present the preliminary results of simultaneous XMM-Newton and INTEGRAL observations of the highly absorbed INTEGRAL source IGR J16320-4751. We refine the X-ray position with XMM-Newton, and then examine the spectral properties of the source using both satellites, separating two periods visible in the lightcurves, an initial flare and a more steady period. We show that the source spectrum and its behaviour are compatible with IGR J16320-4751 being a pulsar accreting from a high mass companion.

The soft and hard X-ray emission of 3C 273 from 1996 to 2004 with BeppoSAX and XMM- Newton

We present the results of a long monitoring of the quasar 3C 273 with BeppoSAX (1996–2001) and XMM- Newton (2000–2004). Our dataset is composed of nine BeppoSAX and 15 XMM observations for a total exposure time of 855 ks (∼492 ks for BeppoSAX and ∼363 ks for XMM). In the soft X-ray domain, we investigate the 2–10 keV continuum with MECS and PN and the presence of an Fe line with MECS. The hard X-ray emission of 3C 273 is analyzed using PDS (15–220 keV) on board BeppoSAX. Two particular flux states are observed in our dataset with a flare of non-thermal emission from the jet in January 1997, whereas the X-ray flux reaches its lowest value in June 2000 and in particular in June 2004. We confirm the detection of an Fe line in one observation performed with BeppoSAX in July 1996. In addition, we report two new detection with MECS of a relatively broad Fe line in June 1998 (also detected by ASCA) and in June 2001. Presence or lack of correlation between different spectral parameters allow us to distinguish the influence of the two emission processes (non-thermal + thermal) on the observed X-ray emission of 3C 273.

Possible AGN Shock Heating in the Cool‐Core Galaxy Cluster Abell 478

We present a detailed X-ray study of the intracluster medium (ICM) of the nearby, cool-core galaxy cluster Abell 478, with Chandra and XMM observations. Using a wavelet smoothing hardness analysis, we derive detailed temperature maps of A478, revealing a surprising amount of temperature structure. The broad band Chandra spectral fits yield temperatures which are significantly hotter than those from XMM, but the Fe ionization temperature shows good agreement. We show that the temperature discrepancy is slightly reduced when comparing spectra from regions selected to enclose nearly isothermal gas. However, by simulating multi-temperature spectra and fitting them with a single temperature model, we find no significant difference between Chandra and XMM, indicating that non-isothermality cannot fully explain the discrepancy. We have discovered 4 hot spots located between 30--50 kpc from the cluster center, where the gas temperature is roughly a factor of 2 higher than in the surrounding material. We estimate the combined excess thermal energy present in these hot spots to be (3+/-1)x10^59 erg. The location of and amount of excess energy present in the hot spots are suggestive of a common origin within the cluster core, which hosts an active galactic nucleus. This cluster also possesses a pair of X-ray cavities coincident with weak radio lobes, as reported in a previous analysis, with an associated energy <10% of the thermal excess in the hot spots. The presence of these hot spots could indicate strong-shock heating of the ICM from the central radio source -- one of the first such detections in a cool core cluster. We also probe the mass distribution in the core and find it to be characterized by a logarithmic slope of -0.35+/-0.22, which is significantly flatter than an NFW cusp of -1. (abridged)

XMM observations of high redshift X-ray clusters and cosmological interpretation

We present the preliminary results of the Ω project, a large XMM program devoted to observe distant SHARC clusters. For the first time a measurement of the L– T evolution with XMM is presented. We found clear evidence for a positive evolution of the L– T relation, in agreement with most previous analysis based on ASCA and Chandra observations. Its cosmological implication is also discussed based on a new analysis of different X-ray surveys: EMSS, RDCS, MACS, SHARC, 160 deg 2. It is found that a high matter density model fits remarkably well all these surveys, in agreement with all existing previous analyzes following the same strategy. Concordance models produce far more faint clusters than observed counts. This failure could be the indication of a deviation from the expected scaling of the M– T relation with redshift. However, no signature of such possibility is found in existing data.

AnXMM-Newtonview of M101 - II. Global X-ray source properties

We present the global X-ray properties of the point source population in the grand-design spiral galaxy M101, as seen with XMM‐Newton. 108 X-ray sources are detected within the D25 ellipse of M101, of which ∼24 are estimated to be background galaxies. Multiwavelength cross-correlations show that 20 sources are coincident with H II regions and/or supernova remnants (SNRs), seven have identified/candidate background galaxy counterparts, six are coincident with foreground stars and one has a radio counterpart. While the spectral and timing properties of the brightest sources were presented by Jenkins et al., here we apply an X-ray colour classification scheme to split the entire source population into different types, i.e. X-ray binaries (XRBs), SNRs, absorbed sources, background sources and supersoft sources (SSSs). Approximately 60 per cent of the population can be classified as XRBs, although there is source contamination from background active galactic nuclei (AGN) in this category as they have similar spectral shapes in the X-ray regime. 15 sources have X-ray colours consistent with SNRs, three of which correlate with known SNR/H II radio sources. Another two are promising new candidates for SNRs, one is unidentified, and the remainder are a mixture of foreground stars, bright soft XRBs and AGN candidates. We also detect 14 candidate SSSs, with significant detections in the softest X-ray band (0.3‐1 keV) only. 16 sources display short-term variability during the XMM‐Newton observation, twelve of which fall into the XRB category, giving additional evidence of their accreting nature. Using archival Chandra and ROSAT High Resolution Imager data, we find that ∼40 per cent of the XMM sources show long-term variability over a baseline of up to ∼10 yr, and eight sources display potential transient behaviour between observations. Sources with significant flux variations between the XMM and Chandra observations show a mixture of softening and hardening with increasing luminosity. The spectral and timing properties of the sources coincident with M101 confirm that its X-ray source population is dominated by accreting XRBs.

Dynamical state and star formation properties of the merging galaxy cluster Abell 3921

We present the analysis and results of a new VRI photometric and spectroscopic survey of the central ~ region of the galaxy cluster A3921 (). We detect the presence of two dominant clumps of galaxies with a mass ratio of ~5: a main cluster centred on the Brightest Cluster Galaxy (BCG) (A3921-A), and an NW sub-cluster (A3921-B) hosting the second brightest cluster galaxy. The distorted morphology of the two sub-clusters suggests that they are interacting, while the velocity distribution of 104 confirmed cluster members does not reveal strong signatures of merging. By applying a two-body dynamical formalism to the two sub-clusters of A3921, and by comparing our optical results to the X-ray analysis of A3921 based on XMM observations (Belsole et al. [CITE]), we conclude that A3921-B is probably tangentially traversing the main cluster along the SW/NE direction. The two sub-clusters are observed in the central phase of their merging process (±0.3 Gyr), with a collision axis nearly perpendicular to the line of sight. Based on the spectral features of the galaxies belonging to A3921 we estimate the star formation properties of the confirmed cluster members. Substantial fractions of both emission-line (~13%) and post-star-forming objects (so called k+a's, ~16%) are detected, comparable to those measured at intermediate redshifts. Our analysis reveals a lack of bright post-star-forming objects in A3921 with respect to higher redshift clusters, while the fraction of k+a's increases towards fainter magnitudes (). Similar results were obtained in the Coma cluster by Poggianti et al. ([CITE]), but at still fainter magnitudes, suggesting that the maximum mass of actively star-forming galaxies increases with redshift (“downsizing effect”). The spatial and velocity distributions of k+a galaxies do not show significant differences to those of the passive population, and to the whole cluster. Most of these objects show relatively red colours and moderate Balmer absorption lines, which suggest that star formation has ceased ∼ Gyr ago. Their presence is therefore difficult to relate to the on-going merging event. We find that star-forming galaxies share neither the kinematics nor the projected distribution of the passive cluster members. Moreover, most emission-line galaxies are concentrated in A3921-B and in the region between the two sub-clusters. We therefore suggest that the ongoing merger may have triggered a star-formation episode in at least a fraction of the observed emission-line galaxies.

Thermal emission from isolated neutron stars and their surface magnetic field: Going quadrupolar?

In the last few years considerable observational resources have been devoted to study the thermal emission from isolated neutron stars. Detailed XMM and Chandra observations revealed a number of features in the X-ray pulse profile, like asymmetry, energy dependence, and possible evolution of the pulse profile over a time scale of months or years. Here we show that these characteristics may be explained by a patchy surface temperature distribution, which is expected if the magnetic field has a complex structure in which higher order multipoles contribute together with the dipole. We reconsider these effects from a theoretical point of view, and discuss their implications to the observational properties of thermally emitting neutron stars.

XMM-Newtonobservations of three poor clusters: Similarity in dark matter and entropy profiles down to low mass

We present an analysis of the mass and entropy profiles of three poor galaxy clusters (A1991, A2717 and MKW9) observed with XMM-Newton. The clusters have very similar temperatures (, 2.53 and 2.58 keV), and similar redshifts (). We trace the surface brightness, temperature, entropy and integrated mass profiles with excellent precision up to ~ kpc (A1991 and A2717) and ~ kpc (MKW9). This corresponds to , where r200 is the radius corresponding to a density contrast of 200 with respect to the critical density at the cluster redshifts. None of the surface brightness profiles is well fitted with a single β-model. Double isothermal β-models provide reasonable fits, and in all cases the value of the external β parameter is consistent with the value found for richer clusters. The temperature profiles have central dips but are approximately flat at the exterior, up to the detection limit. The integrated mass profiles are very similar in physical units and are reasonably well fitted with the NFW mass model with concentration parameters in the range and . A King model is inconsistent with these mass data. The entropy profiles are very similar at large scale, but there is some scatter in the very central region ( kpc). However, none of the clusters has an isentropic core. We then discuss the structural and scaling properties of cluster mass and entropy profiles, including similar quality data on the slightly cooler cluster A1983 ( keV), and on the massive cluster A1413 ( keV). We find that the mass profiles scaled in units of M200 and r200 nearly coincide, with 20 per cent dispersion in the radial range , where we could compare the profiles without excessive extrapolation. We provide a quantitative test of mass profile shapes by combining the concentration parameters of these poor clusters with other values of similar precision from the literature, and comparing with the relation derived from numerical simulations for a ΛCDM cosmology. The data are fully consistent with the predictions, taking into account the measurement errors and expected intrinsic scatter, in the mass range . This excellent agreement with theoretical predictions – a quasi universal cusped mass profile with concentration parameters as expected – shows that the physics of the dark matter collapse is basically understood. Scaling the entropy profiles using the self-similar relation , we find a typical scatter of ~30 per cent in scaled entropy in the radial range . The dispersion is reduced (~22 per cent) if we use the empirical relation . The scatter is nearly constant with radius, indicating a genuine similarity in entropy profile shape. The averaged scaled profile is well fitted by a power law for , with a slope slightly lower than expected from pure shock heating (), and a normalisation at consistent with previous ROSAT/ASCA studies. These precise XMM observations confirm that the entropy profiles of clusters are self-similar down to low mass (), but that the entropy temperature relation is shallower than in the purely gravitational model. This self-similarity of shape is a strong constraint, allowing us to rule out simple pre-heating models. The gas history thus probably depends not only on gravitational processes, but also on the interplay between cooling and various galaxy feedback mechanisms.

Supersoft X‐Ray Sources in M31. I. AChandraSurvey and an Extension to Quasi‐soft Sources

We report on very soft X-ray sources (VSSs) in M31. In a survey that was most sensitive to soft sources in four 8' × 8' regions covered by Chandra's ACIS-S S3 CCD, we find 33 VSSs that appear to belong to M31. Fifteen VSSs have spectral characteristics mirroring the supersoft X-ray sources studied in the Magellanic Clouds and Milky Way (kTeff ≤ 100 eV); we therefore call these "classical" supersoft sources, or simply supersoft sources (SSSs). Eighteen VSSs may have either small (<10%) hard components or slightly higher effective temperatures (but still less than 350 eV). We refer to these VSSs as quasi-soft sources (QSSs). While hot white dwarf models may apply to SSSs, the effective temperatures of QSSs are too high, unless, e.g., the radiation emanates from only a small portion of surface. Two of the SSSs were first detected and identified as such through ROSAT observations. One SSS and one QSS may be identified with symbiotics and two SSSs with supernova remnants. Both SSSs and QSSs in the disk are found near star-forming regions, possibly indicating that they are young. VSSs in the outer disk and halo are likely to be old systems; in these regions, there are more QSSs than SSSs, which is opposite to what is found in fields closer to the galaxy center. The largest density of bright VSSs is in the bulge; some of the bulge sources are close enough to the nucleus to be remnants of the tidal disruption of a giant by the massive central black hole. By using Chandra data in combination with ROSAT and XMM observations, we find most VSSs to be highly variable, fading from or brightening toward detectability on timescales of months. There is evidence for VSSs with low luminosities (~1036 ergs s-1).

XMM Observations of Polars from the SDSS

AbstractWe condueted XMM observations of 5 faint Polars discovered by the Sloan Digital Sky Survey. The X-ray fluxes and spectra show a variety of shock regimes. The lowest accretor has X-ray properties consistent with an origin on the secondary star. The light curves of all systems show large variability, with one showing a deep eclipse, and with some evidence for orbital-related variations in 2 others.

The XMM/BeppoSAX observation of Mkn 841

Mkn 841 has been observed simultaneously by XMM and BeppoSAX in January 2001. Due to an operational contingency, the 30 ks XMM observation was split into two parts, separated by about 15 hours. We first report the presence of a narrow iron line which appears to be rapidly variable between the two pointings, requiring a non-standard interpretation. We then focus on the analysis of the broad band (0.3-200 keV) continuum using the XMM/EPIC, RGS and SAX/PDS data. The Mkn 841 spectrum is well fitted by a comptonization model in a geometry more photon-fed than a simple slab geometry above a passive disk. It presents a relatively large reflection (R≳2) which does not agree with an apparently weak iron line. It also shows the presence of a strong soft excess well fitted by a comptonized spectrum in a cool plasma, suggesting the presence of a multi-temperature corona.

Ultralow Iron Abundances in the Distant Hot Gas in Galaxy Groups

A new XMM observation of the outer regions of the galaxy group NGC 5044 indicates hot gas iron abundances of only ZFe/Z☉ ~ 0.15 between r = 0.2rvir and 0.4rvir. While the total baryon mass within the virial radius may be close to the cosmic mean value observed in rich clusters, the ratio of total iron mass to optical light in NGC 5044 is about 3 times lower than that in rich clusters. The remarkably low iron abundance over a large volume of the intergroup gas in the outer regions of NGC 5044 cannot be easily understood in terms of the outflow of enriched gas in a group wind during its early history or by the long-term enrichment by the group member galaxies that currently occupy this region. It is possible that the stars in NGC 5044 did not produce iron with the same efficiency as in clusters, or that the iron resides in nonluminous clouds or stars, or that the entropy of the iron-enriched gas created in early galactic starburst winds was too high to penetrate the group gas of lower entropy.

XMM‐NewtonObservations of an Intermediate X‐Ray Object in NGC 2276

We present the results from a approx. 53 ksec XMM observation of NGC 2276. This galaxy has an unusual optical morphology with the disk of this spiral appearing to be truncated along the western edge. This XMM observation shows that the X-ray source at the western edge is a bright Intermediate X-ray Object (IXO). Its spectrum is well fit by a multi-color disk blackbody model used to fit optically thick standard accretion disks around black holes. The luminosity derived for this IXO is 1.1 x 10(exp 41) erg/s in the 0.5 - 10 keV band making it one of the most luminous discovered to date. The large source luminosity implies a large mass black hole if the source is radiating at the Eddington rate. On the other hand, the inner disk temperature determined here is too high for such a massive object given the standard accretion disk model. In addition to the IXO we find that the nuclear source in this galaxy has dimmed by at least a factor of several thousand in the eight years since the ROSAT HRI observations.

Optical and X-ray analysis of the galaxy cluster A3921

We present the analysis and results of a new spectroscopic and photometric survey of the central 1.5 4-5: a main cluster centered on the BCG (A3921-A), and a NW sub-cluster (A3921-B) hosting the second brightest cluster object. By comparing optical results to the X-ray analysis of XMM observations (Belsole et al. 2004), we find that A3921-B is tangentially traversing the main cluster along a SW/NE direction. The analysis of stellar populations of more than one hundred cluster members reveals that the merger event has probably affected the kinematics and spectral properties of the active galaxies in A3921.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

XMM-NewtonObservations of Two High-Redshift Quasars: RX J1028-0844 and BR 0351-1034

We report the results of XMM-Newton observations of two high-redshift quasars, one radio-loud, RX J1028.6-0844 (z = 4.276) and one radio-quiet, BR 0351-1034 (z = 4.351). We find that the evidence for strong excess absorption toward RX J1028-0844 is marginal at best, contrary to previous claims. The superior sensitivity and broader, softer energy range of XMM-Newton (0.2–10 keV) allows better determination of spectral parameters than much deeper ASCA observations (0.8–7 keV). Our XMM-Newton observations call into question several other ASCA results of strong absorption toward high-redshift radio-loud quasars. RX J1028.6-0844 occupies the same parameter space in broadband spectral properties as the low-redshift BL Lac objects, showing no obvious evolution with redshift. The radio-quiet quasar BR 0351-1024 became fainter between ROSAT and XMM observations by a factor of at least 5, but with the present data we cannot determine whether there is an associated spectral change. These observations do not support previous claims of weaker X-ray emission from high-redshift, radio-quiet quasars. The soft X-ray spectral slope required to reconstruct the ROSAT PSPC hardness ratio of BR 0351-1034 is about αX = 3.5, the steepest X-ray slope ever observed in a high-redshift quasar and similar to that of low-redshift narrow-line Seyfert 1 galaxies.

Modeling Super-Eddington Active Galactic Nuclei: Optical–X-Ray Continuum Emission from Accretion Flows

Super-Eddington accretion onto supermassive black holes (BHs) seems to occur at narrow-line Seyfert 1 galaxies (NLS1s). We briefly describe some physical aspects that become important when an accretion rate becomes super-Eddington; electron scattering relativistic effect and self-gravity of accretion flows. It is found that the inner, non self-gravitating part of the disk emits UV to X-ray, while the outer, self-gravitating region radiates optical continuum. Then, a broadband spectral modeling for TonS180 is demonstrated. In order to test the theoretical models, we pick up one NLS1, PG1448+273, as the object with the highest Eddington ratio among AGNs. Preliminary results of our XMM observation on this object, together with spectral modeling, are briefly Presented.

XMM Observations of Abundances in the Intracluster Medium

Based on XMM-Newton observations of M 87 and the Centaurus cluster, abundance profiles of various elements of the intracluster medium (ICM) are derived. The abundances of Si and Fe show strong decreasing gradients. In contrast, the O and Mg abundances are about half of the Si abundance at the center.From the gas mass to stellar mass ratio and the comparison of Mg abundance with the stellar metallicity, the stellar mass loss from the central galaxies is indicated to be the main source of gas in the very central region of the clusters.The observed O, Si and Fe abundance pattern determines the contribution of supernova (SN) Ia and SN II, with the abundance pattern of ejecta of SN Ia. Most of the Si and Fe of the ICM in the central region of the clusters comes from SN Ia which occured in the central galaxies. In order to explain the observed O/Si ratio of a half solar, SN Ia products should have similar abundances of Si and Fe, which may reflect dimmer SN Ia observed in old stellar systems.