|
|
| XMM-Newton spectroscopy of the cluster of galaxies 2A 0335+096 |
| We present here the results of a deep (130 ks) XMM-Newton observation of the cluster of galaxies 2A 0335+096. The deep exposure allows us to study in detail its temperature structure and its elemental abundances. We fit three different thermal models and find that the multi-temperature wdem model fits our data best. We find that the abundance structure of the cluster is consistent with a scenario where the relative number of type Ia supernovae contributing to the enrichment of the intra-cluster medium is ~25%, while the relative number of core collapse supernovae is ~75%. Comparison of the observed abundances to the supernova yields does not allow us to put any constrains on the contribution of Pop III stars to the enrichment of the ICM. Radial abundance profiles show a strong central peak of both type Ia and core collapse supernova products. Both the temperature and iron abundance maps show an asymmetry in the direction of the elongated morphology of the surface brightness. In particular the temperature map shows a sharp change over a brightness edge on the southern side of the core, which was identified as a cold front in the Chandra data. This suggests that the cluster is in the process of a merger with a subcluster. Moreover, we find that the blobs or filaments discovered in the core of the cluster by Chandra are, contrary to the previous results, colder than the ambient gas and they appear to be in pressure equilibrium with their environment. |
| Publication date: 15 Apr 2006 |
|
|
| Spectral changes during dipping in low-mass X-ray binaries due to highly-ionized absorbers |
| X-ray observations have revealed that many microquasars and low-mass X-ray binaries (LMXBs) exhibit narrow absorption features identified with resonant absorption from FeXXV and FeXXVI and other abundant ions. In many well studied systems there is evidence for blue-shifts, indicating outflowing plasmas. The changes in both the X-ray continuum and the Fe absorption features during dips from the LMXB XB 1323-619 have been modeled as resulting primarily from an increase in column density and a decrease in the ionization state of a highly-ionized absorber. We successfully fit the same ionized absorber model to the persistent and dipping emission from all the other bright dipping LMXBs observed by XMM-Newton (EXO 0748-676, XB 1254-690, X 1624-490, MXB 1659-298, 4U 1746-371 and XB 1916-053) and find similar changes in the properties of the ionized absorber as for XB 1323-619. This implies that the complex spectral changes in the X-ray continua observed from the dip sources as a class can be most simply explained primarily by changes in the highly ionized absorbers present in these systems. There is no need to invoke unusual abundances or partial covering of extended emission regions. Outside of the dips, the absorption line properties do not vary strongly with orbital phase. This implies that the ionized plasma has a cylindrical geometry with a maximum column density close to the plane of the accretion disk. Since dipping sources are simply normal LMXBs viewed from close to the orbital plane this implies that ionized plasmas are a common feature of LMXBs. |
| Publication date: 01 Apr 2006 |
|
|
| Polar Outflows in Six Broad Absorption Line Quasars |
| Using radio observations by FIRST and NVSS, we build a sample of 151 radio-variable quasars selected from the Sloan Digital Sky Survey Data Release 3 (SDSS DR3). Six (and probably another two) of these objects are classified as broad absorption line (BAL) quasars and show radio flux variations of a few tens of percent within 1.5-5 yr. Such large amplitudes of variations imply brightness temperatures much higher than the inverse Compton limits (1012 K) in all these BAL quasars, suggesting the presence of relativistic jets beaming toward the observer. The angles between the outflow and the jet are constrained to be less than ~20°. Such BAL quasars with polar outflows are beyond the simple unification models of BAL and non-BAL quasars, which hypothesize BAL quasars as otherwise normal quasars seen nearly edge-on. |
| Publication date: 10 Mar 2006 |
|
|
| Disc precession in the M31 dipping X-ray binary Bo 158? |
| We present results from three XMM-Newton observations of the M31 low mass X-ray binary (LMXB) XMMU J004314.4+410726.3 (Bo 158), spaced over 3 days in 2004 July. Bo 158 was the first dipping LMXB to be discovered in M31. Periodic intensity dips were previously seen to occur on a 2.78-h period, due to absorption in material that is raised out of the plane of the accretion disc. The report of these observations stated that the dip depth was anticorrelated with source intensity. In light of the 2004 XMM-Newton observations of Bo 158, we suggest that the dip variation is due to precession of the accretion disc. This is to be expected in LMXBs with a mass ratio 0.3 (period 4 h), as the disc reaches the 3:1 resonance with the binary companion, causing elongation and precession of the disc. A smoothed particle hydrodynamics simulation of the disc in this system shows retrograde rotation of a disc warp on a period of 11Porb, and prograde disc precession on a period of 29 ± 1Porb. This is consistent with the observed variation in the depth of the dips. We find that the dipping behaviour is most likely to be modified by the disc precession, hence we predict that the dipping behaviour repeats on an 81 ± 3 h cycle. |
| Publication date: 15 Feb 2006 |
|
|
| XMM-Newton Observations of the sigma Ori Cluster |
| We present the results of an XMM-Newton observation of the young (~2-4 Myr) cluster around the hot star sigma Orionis. In a previous paper we presented the analysis of the RGS spectrum of the central hot star; here we discuss the results of the analysis of the full EPIC field. We have detected 175 X-ray sources, 88 of which have been identified with cluster members, including very low-mass stars down to the substellar limit. We detected also eleven new possible candidate members from the 2MASS catalogue. We find that late-type stars have a median log L_X/L_bol ~ -3.3, i.e. very close to the saturation limit. We detected significant variability in ~40% of late-type members or candidates, including 10 flaring sources; rotational modulation is detected in one K-type star and possibly in other 3 or 4 stars. Spectral analysis of the brightest sources shows typical quiescent temperatures in the range T_1~ 0.3-0.8 keV and T_2~ 1-3 keV, with subsolar abundances Z~ 0.1-0.3 Z_sol, similarly to what is found in other star-forming regions and associations. We find no significant difference in the spectral properties of classical and weak-lined T Tauri stars, although classical T Tauri stars tend to be less X-ray luminous than weak-lined T~Tauri stars. |
| Publication date: 02 Feb 2006 |
|
|
| A compact flare eclipsed in the corona of SV Cam |
| The eclipsing active binary SV Cam (G0V/K6V, Porb=0.593071 d) was observed with XMM-Newton during two campaigns in 2001 and 2003. No eclipses in the quiescent emission are clearly identified, but a flare was eclipsed during the 2001 campaign, allowing us to strongly constrain, from purely geometrical considerations, the position and size of the event: the flare is compact and it is formed at a latitude below 65deg. The size, temperature and Emission Measure of the flare imply an electron density of log n_e (cm^-3)~10.6-13.3 and a magnetic field of ~65-1400 G in order to confine the plasma, consistently with the measurements that are obtained from density-sensitive line ratios in other similar active stars. Average emission seems to come from either extended or polar regions because of lack of eclipses. The Emission Measure Distribution, coronal abundances, and characteristics of variability are very similar to other active stars such as AB~Dor (K1V). |
| Publication date: 11 Jan 2006 |
|
|
| A long look at the BALQSO LBQS 2212-1759 with XMM-Newton |
| Very long (172 ks effective exposure time) observations of the BALQSO LBQS 2212-1759 with XMM-Newton yield a stringent upper-limit on its 0.2-10 keV (rest- frame 0.64-32.2 keV) flux, F < 6 E-17 erg/cm2/s, while simultaneous UV and optical observations reveal a rather blue spectrum extending to 650 A in the source rest frame. These results are used to set a tight upper-limit on its optical to X-ray spectral index alpha_{ox} < -2.56. Given the HI-BAL nature of LBQS 212-1759, its X-ray weakness is most likely due to intrinsic absorption. If this is the case, and assuming that the intrinsic alpha_{ox} of LBQS 2212-1759 is -1.63 - a value appropriate for a radio-quiet quasar of this luminosity - one can set a lower limit on the X-ray absorbing column N_{H} > 3.4 E25 cm-2. Such a large column has a Thomson optical depth to electron scattering tau > 23, sufficient to extinguish the optical and UV emission. The problem only gets worse if the gas is neutral since the opacity in the Lyman continuum becomes extremely large, > 2 E8, conflicting with the source detection below 912 A. This apparent contradiction probably means that our lines-of-sight to the X-ray and to the UV emitting regions are different, such that the gas covers completely the compact X-ray source but only partially the more extended source of ultraviolet photons. An extended (~ 1) X-ray source is detected 2 to the south-east of the QSO. Given its thermal spectrum and temperature (1.5 < T < 3.0 keV}, it is probably a foreground (0.29 < z < 0.46) cluster of galaxies. |
| Publication date: 04 Jan 2006 |
|
|
| Light echoes from ancient supernovae in the Large Magellanic Cloud |
| The light from historical supernovae could in principle still be visible as scattered-light echoes centuries after the explosion. The detection of light echoes could allow us to pinpoint the supernova event both in position and age and, most importantly, permit the acquisition of spectra to determine the 'type' of the supernova centuries after the direct light from the explosion first reached Earth. Although echoes have been discovered around some nearby extragalactic supernovae, targeted searches have not found any echoes in the regions of historical Galactic supernovae. Here we report three faint variable-surface-brightness complexes with high apparent proper motions pointing back to three of the six smallest (and probably youngest) previously catalogued supernova remnants in the Large Magellanic Cloud, which are believed to have been thermonuclear (type Ia) supernovae. Using the distance and apparent proper motions of these echo arcs, we estimate ages of 610 and 410 years for two of them. |
| Publication date: 22 Dec 2005 |
|
|
| Low-energy absorption towards the ultra-compact X-ray binary 4U 1850-087 located in the globular cluster NGC6712 |
| We report the results of two XMM-Newton observations of the ultra-compact low-mass X-ray binary 4U 1850-087 located in the galactic globular cluster NGC6712. A broad emission feature at 0.7 keV was detected in an earlier ASCA observation and explained as the result of an unusual Ne/O abundance ratio in the absorbing material local to the source. We find no evidence for this feature and derive Ne/O ratios in the range 0.14-0.21, consistent with that of the interstellar medium. During the second observation, when the source was ~10% more luminous, there is some evidence for a slightly higher Ne/O ratio and additional absorption. Changes in the Ne/O abundance ratio have been detected from another ultra-compact binary, 4U 1543-624. We propose that these changes result from an X-ay induced wind which is evaporated from an O and Ne rich degenerate donor. As the source X-ray intensity increases so does the amount of evaporation and hence the column densities and abundance ratio of Ne and O. |
| Publication date: 21 Nov 2005 |
|
|
| Flares observed with XMM-Newton and the VLA |
| We present lightcurves obtained in X-ray by the XMM-Newton EPIC cameras and simultaneous radio lightcurves obtained with the VLA for five active M-type flare stars. A number of flare events were observed, and by comparing radio with X-ray data, we consider various possible flare mechanisms. In cases where there seems to be a clear correlation between radio and X-ray activity, we use an energy budget argument to show that the heating which leads to the X-ray emission could be due to the same particles emitting in the radio. In cases where there is radio activity without corresponding X-ray activity, we argue that the radio emission is likely to arise from coherent processes involving comparatively few particles. In one case, we are able to show from polarization of the radio emission that this is almost certainly the case. Cases for which X-ray activity is seen without corresponding radio activity are more difficult to explain. We suggest that the heating particles may be accelerated to very high energy, and the resulting synchrotron radio emission may be beamed in directions other than the line of sight. |
| Publication date: 15 Jun 2005 |
|
|
| Tentative detection of warm intervening gas towards PKS 0548-322 with XMM-Newton |
| We present the results of a long (~93 ks) XMM-Newton observation of the bright BL-Lac object PKS 0548-322 (z= 0.069). Our Reflection Grating Spectrometer (RGS) spectrum shows a single absorption feature at an observed wavelength lambda= 23.33 +/- 0.01 Å, which we interpret as OVI Kalpha absorption at z= 0.058, i.e. ~3000 km s-1 from the background object. The observed equivalent width of the absorption line, ~30 mÅ, coupled with the lack of the corresponding absorption edge in the EPIC pn data, implies a column density of NOVI ~ 2 x 1016 cm-2 and turbulence with a Doppler velocity parameter b > 100 km s-1. Within the limitations of our RGS spectrum, no OVII or OV Kalpha absorption are detected. Under the assumption of ionization equilibrium by both collisions and the extragalactic background, this is only marginally consistent if the gas temperature is ~2.5 x 105 K, with significantly lower or higher values being excluded by our limits on OV or OVII. If confirmed, this would be the first X-ray detection of a large amount of intervening warm absorbing gas through OVI absorption. The existence of such a high column density absorber, much stronger than any previously detected one in OVI, would place stringent constraints on the large-scale distribution of baryonic gas in the Universe. |
| Publication date: 15 Jun 2005 |
|
|
| XMM-Newton RGS Detector Performance Tools |
| The two Reflection Grating Spectrometers on board ESA's XMM-Newton X-ray satellite are designed to perform high resolution X-ray spectroscopy in the range [0.3-2.1] keV. The most-commonly used operation mode for scientific observations with the RGS is the Spectroscopy Mode. It includes on-board thresholds, hot pixel and column rejection using look-up tables and rejection of cosmic events. In Diagnostic Mode, this on-board data processing is completely by-passed and full images of the CCDs are transferred to ground. These data are then used for dark current, system noise level calibration and hot pixel / column detection. Diagnostic images are also normally obtained during Spectroscopy observations interleaved at a low frequency. We have developed IDL based interactive tools for Diagnostic data analysis, with the main aims of establishing system noise calibration and hot pixel and columns detection, as well as for instrument health monitoring purposes. The RGS Diagnostic Tools can be run individually on single diagnostic images, but are mostly used in batch mode per revolution for populating a database. Interactive analysis and batch tools then interact with the database for parameter extraction and temporal analysis. The Tools produce also several graphical and numerical outputs, which are used on a web-based integrated system for fast diagnostic and trend monitoring. In addition IDL tools are available for the monitoring of the quality of the science data in spectroscopy mode. Data from the onboard calibration source is extracted and used to monitor the gain and contamination of the instrument. These tools build also a database to monitor long term changes in the instrument response. |
| Publication date: 01 Jun 2005 |
|
|
| An XMM-Newton survey of M 31 |
| In an analysis of XMM-Newton archival observations of the bright Local Group spiral galaxy M 31 we study the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2-4.5 keV luminosity of 4.4 x 1034 . EPIC hardness ratios and optical and radio information are used to distinguish between different source classes. The survey detects 856 sources in an area of 1.24 square degrees. We correlate our sources with earlier M 31 X-ray catalogues and use information from optical, infra-red and radio wavelengths. As sources within M 31 we detect 21 supernova remnants (SNR) and 23 SNR candidates, 18 supersoft source (SSS) candidates, 7 X-ray binaries (XRBs) and 9 XRB candidates, as well as 27 globular cluster sources (GlC) and 10 GlC candidates, which most likely are low mass XRBs within the GlC. Comparison to earlier X-ray surveys reveal transients not detected with XMM-Newton, which add to the number of M 31 XRBs. There are 567 sources classified as hard, which may either be XRBs or Crab-like SNRs in M 31 or background AGN. The number of 44 SNRs and candidates more than doubles the X-ray-detected SNRs. 22 sources are new SNR candidates in M 31 based on X-ray selection criteria. Another SNR candidate may be the first plerion detected outside the Galaxy and the Magellanic Clouds. On the other hand, six sources are foreground stars and 90 foreground star candidates, one is a BL Lac-type active galactic nucleus (AGN) and 36 are AGN candidates, one source coincides with the Local Group galaxy M 32, one with a background galaxy cluster (GCl) and another is a GCl candidate, all sources not connected to M 31. |
| Publication date: 15 May 2005 |
|
|
| Five Years of Newton Science |
| On 10 December 2004, it was five years since ESA's XMM-Newton observatory was successfully put into orbit. It is therefore time to stand back and ask where we stand with the scientific results and what new perspectives the mission has brought us. The answers are to be found in more than 700 publications in the refereed literature and the manifold oversubscription for every observing Announcement of Opportunity for the mission. |
| Publication date: 15 May 2005 |
|
|
| XMM-Newton observations of two transient millisecond X-ray pulsars in quiescence |
| We report on XMM-Newton observations of two X-ray transient millisecond pulsars (XRTMSPs). We detected XTE J0929-314 with an unabsorbed luminosity of ~ 7x 1031 erg s-1 (0.5-10 keV) at a fiducial distance of 10 kpc. The quiescent spectrum is consistent with a simple power law spectrum. The upper limit on the flux from a cooling neutron star atmosphere is about 20% of the total flux. XTE J1807-294 instead was not detected. We can put an upper limit on the source quiescent 0.5-10 keV unabsorbed luminosity ~< 4x1031 erg s-1 at 8 kpc. These observations strenghten the idea that XRTMSPs have quiescent luminosities significantly lower than classical neutron star transients. |
| Publication date: 15 May 2005 |
|
|
| On the Polar Caps of the Three Musketeers |
| XMM-Newton EPIC observations of PSR B0656+14, PSR B1055-52, and Geminga have substantially increased the collection of statistics available for these three isolated neutron stars, so apparently similar to deserve the nickname of the Three Musketeers, given to them by Becker & Trumper. Here we take advantage of the EPIC statistics to perform phase-resolved spectroscopy for all three objects. The phase-averaged spectrum of the Three
Musketeers is best described by a three-component model. This includes two blackbody components -a cooler one, possibly originating from the bulk of the star surface, and a hotter one, coming from a smaller portion of the star surface (a "hot spot") -plus a power law. The relative contributions of the three components are seen to vary as a function of phase, as the stars' rotation brings into view different emitting regions. The hot spots, which have very different apparent dimensions (in spite of the similarity of the three neutron stars polar cap radii) are responsible for the bulk of the phase variation. The amplitude of the observed phase modulation is also markedly different for the
three sources. Another striking aspect of our phase-resolved phenomenology is the apparent lack of any common phase alignment between the observed modulation patterns for the two blackbody components. They are seen to
vary in phase in the case of PSR B1055-52 but in antiphase in the case of PSR B0656+14. These findings do not support standard and simplistic models of neutron star magnetic field configuration and surface temperature
distribution. |
| Publication date: 20 Apr 2005 |
|
|
| The XMM-Newton view of three X-ray weak quasars iron emission and strong ionized absorption |
| We present the analysis of XMM-Newton observations of three X-ray weak quasars: PG 1001+054, PG1535+547 and PG 2112+059. All objects are absorbed by ionized material showing high column densities, NH = 2.9 x 1022 cm-2 to NH = 1.9 x 1023 cm-2, and ionization parameters, xi = 147 erg cm s-1 to xi = 542 erg cm s-1. The spectra of PG1535+547 requires an additional partial covering by neutral material with a column density of NH approx 9 x 1022 cm-2 at a covering factor of approx 0.96. The spectra of PG1535+547 show systematic residuals in the energy range from sim 4 keV to sim 6 keV, which are inconsistent with Kalpha-fluorescence-emission of neutral or ionized iron under the assumption of a Gaussian line profile. They can be described with a relativistic disk line (Laor) and establish therefore the second X-ray weak quasar with such a spectral characteristic. Our results together with the findings of Brinkmann et al. (2004) and Piconcelli et al. (2004a), indicate that warm absorbers characterized by high column densities and ionization parameters are typical of X-ray weak quasars. The occurrence of a variable relativistic broad Fe Kalpha fluorescence line in two out of the five well studied X-ray weak quasars might indicate a second general characteristic of the entire object class. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. |
| Publication date: 06 Apr 2005 |
|
|
| The XMM-Newton spectrum of the high-z optically-obscured QSO RXJ1343.4+0001 |
| We present a 30 ks XMM-Newton observation of the z = 2.35 Type II radio quiet quasar RXJ1343.4+0001. These data provide the first good quality X--ray spectrum for this object. We measured a continuum slope Gamma = 1.85+/-0.10 with only an upper limit on the column density of the absorbing material of Nh <~ 10e22 cm-2 as well as a Fe K_alpha emission line at the 3sigma confidence level. We do not find therefore a highly absorbed object neither a truly flat spectrum as suggested on the basis of previous less sensitive ROSAT and ASCA measurements. |
| Publication date: 20 Mar 2005 |
|
|
| The XMM-Newton view of PG quasars. I. X-ray continuum and absorption |
| We present results of a systematic analysis of the XMM-Newton spectra of 40 quasars (QSOs) (z<~1.72) from the Palomar-Green (PG) Bright Quasar Survey sample (MB<-23). The sample includes 35 radio-quiet quasars (RQQs) and 5 radio-loud quasars (RLQs). The analysis of the spectra above 2 keV reveals that the hard X-ray continuum emission can be modeled with a power law component with = 1.89+/-0.11 and = 1.63(+0.02,-0.01) for the RQQs and RLQs, respectively. Below 2 keV, a strong, broad excess is present in most QSO spectra. This feature has been fitted with four different models assuming several physical scenarios. All tested models (blackbody, multicolor blackbody, bremsstrahlung and power law) satisfactorily fitted the majority of the spectra. However, none of them is able to provide an adequate parameterization for the soft excess emission in all QSOs, indicating the absence of an universal shape for this spectral feature. An additional cold absorption component was required only in three sources. On the other hand, as recently pointed out by Porquet et al. (2004) for a smaller sample of PG QSOs, warm absorber features are present in ~50% of the QSO spectra in contrast with their rare occurrence (~5-10%) found in previous studies. The XMM-Newton view of optically-selected bright QSOs therefore suggests that there are no significant difference in the X-ray spectral properties once compared with the low-luminosity Seyfert 1 galaxies. Properties of the Fe Kalpha emission lines are presented in a companion paper. |
| Publication date: 10 Mar 2005 |
|
|
| Solar control on Jupiter's equatorial X-ray emissions |
| During Nov. 26-29, 2003 XMM-Newton observed soft
(0.2-2 keV) X-ray emission from Jupiter for 69 hours. The low-latitude X-ray disk emission of Jupiter is observed to be almost uniform in intensity with brightness that is consistent with a solar-photon driven process. The simultaneous light curves of Jovian equatorial X rays and solar X rays (measured by the TIMED/SEE and GOES satellites) show similar day-to-day variability. A large solar X-ray flare occurring on the Jupiter-facing side of the Sun is found to have a corresponding feature in the Jovian X rays. These results support the hypothesis that X-ray emission from Jovian low-latitudes are solar X rays scattered from the planet's upper atmosphere, and suggest that the Sun directly controls the non-auroral X rays from Jupiter's disk. Our study also suggests that Jovian equatorial X rays can be used to monitor the solar X-ray flare activity on the hemisphere of the Sun that is invisible to space weather satellites. |
| Publication date: 18 Jan 2005 |
|
|
