We aim to identify new intermediate polars (IPs) in XMM-Newton observations from a list of promising candidates. By selecting targets not previously known to be X-ray bright we aim to uncover ...evidence for an X-ray underluminous IP subpopulation. We performed period searches on the XMM-Newton X-ray and optical data of our targets to seek both the spin and orbital periods, which differ in IPs. We also investigated the X-ray spectra to find the hot plasma emission shown by these objects. With archival Swift data we coarsely investigated the long-term X-ray variability, and with archival optical data from a variety of catalogues, we compared the optical to X-ray luminosity to identify X-ray faint objects. This paper presents the first XMM-Newton observation of the prototype IP, DQ Her. We find firm evidence for HZ Pup, V349 Aqr, and IGR J18151-1052 being IPs, with likely white dwarf spin periods of 1552, 390, and 390 s, respectively. The former two have luminosities typical of IPs, and the latter is strongly absorbed and with unknown distance. GI Mon and V1084 Her are apparently non-magnetic CVs with interesting short-term variability unrelated to WD spin. V533 Her is probably a magnetic CV and remains a good IP candidate, while V1039 Cen is possibly a polar. The remaining candidates were too faint to allow for any firm conclusions.
Aims. We aim to study the temporal and spectral behaviour of the eclipsing polar CSS081231:071126+440405 from the infrared to the X-ray regimes. Methods. We obtained phase-resolved XMM-Newton X-ray ...observations on two occasions in 2012 and 2013 in different states of accretion. In 2013 the XMM-Newton X-ray and UV data were complemented by optical photometric and spectroscopic observations. Results. CSS081231 displays two-pole accretion in the high state. The magnetic fields of the two poles are 36 and 69 MG, indicating a non-dipolar field geometry. The X-ray spectrum of the main accreting pole with the lower field comprises a hot thermal component from the cooling accretion plasma, kTplas of a few tens of keV, and a much less luminous blackbody-like component from the accretion area with kTbb ~ 50–100 eV. The high-field pole, which was located opposite to the mass-donating star, accretes at a low rate and has a plasma temperature of about 4 keV. On both occasions the X-ray eclipse midpoint precedes the optical eclipse midpoint by 3.2 s. The centre of the X-ray bright phase shows accretion-rate-dependent longitudinal motion of ~20 deg. Conclusions. CSS081231 is a bright polar that escaped detection in the RASS survey because it was in a low accretion state. Even in the high state it lacks the prominent soft component previously thought to be ubiquitous in polars. Such an excess may still be present in the unobserved extreme ultraviolet. All polars discovered in the XMM-Newton era lack the prominent soft component. The intrinsic spectral energy distribution of polars still awaits characterisation by future X-ray surveys such as eROSITA. The trajectory taken by material to reach the second pole is still uncertain.
Context.
Ultraluminous X-ray sources (
L
X
≳ ×10
39
erg s
−1
, ULXs) are excellent probes for extreme accretion physics, star formation history in galaxies, and intermediate-mass black holes ...searches. As the sample size of X-ray data from modern observatories such as
XMM-Newton
and
Chandra
increases, producing extensive catalogues of ULXs and studying their collective properties has become both a possibility and a priority.
Aims.
Our aim is to build a clean updated ULX catalogue based on one of the most recent
XMM-Newton
X-ray serendipitous survey data releases, 4XMM-DR9, and the most recent and exhaustive catalogue of nearby galaxies, HECATE. We performed a preliminary population study to test if the properties of the expanded
XMM-Newton
ULX population are consistent with previous findings.
Methods.
We performed positional cross-matches between
XMM-Newton
sources and HECATE objects to identify host galaxies, and we used distance and luminosity arguments to identify ULX candidates. We flagged interlopers by finding known counterparts in external catalogues and databases such as
Gaia
DR2, SSDS, Pan-STARRS1, the NASA/IPAC Extragalactic Database, and SIMBAD. Source, galaxy and variability parameters from 4XMM-DR9, HECATE, and 4XMM-DR9s were used to study the spectral, abundance, and variability properties of the ULX sample.
Results.
We identify 779 ULX candidates, 94 of which hold
L
X
≳ 5 × 10
40
erg s
−1
. Spiral galaxies are more likely to host ULXs. For early spiral galaxies the number of ULX candidates per star-forming rate is consistent with previous studies, while a significant ULX population in elliptical and lenticular galaxies also exists. Candidates hosted by late-type galaxies tend to present harder spectra and to undergo more extreme inter-observation variability than those hosted by early-type galaxies. Approximately 30 candidates with
L
X
> 10
41
erg s
−1
are also identified, constituting the most interesting candidates for intermediate-mass black hole searches.
Conclusions.
We have built the largest ULX catalogue to date. Our results on the spectral and abundance properties of ULXs confirm the findings made by previous studies based on
XMM-Newton
and
Chandra
data, while our population-scale study on variability properties is unprecedented. Our study, however, provides limited insight into the properties of the brightest ULX candidates due to the small sample size. The expected growth of X-ray catalogues and potential future follow-ups will aid in drawing a clearer picture.
Aims. We aim to incorporate background subtraction into the Bayesian Blocks algorithm so that transient events can be timed accurately and precisely even in the presence of a substantial, rapidly ...variable background. Methods. We developed several modifications to the algorithm and tested them on a simulated XMM-Newton observation of a bursting and eclipsing object. Results. We found that bursts can be found to good precision for almost all background-subtraction methods, but eclipse ingresses and egresses present problems for most methods. We found one method that recovered these events with precision comparable to the interval between individual photons, in which both source- and background-region photons are combined into a single list and weighted according to the exposure area. We also found that adjusting the Bayesian Blocks change points nearer to blocks with higher count rate removes a systematic bias towards blocks of low count rate.
Aims.
We look to provide a detailed description of the SPectroscopic IDentification of ERosita Sources (SPIDERS) survey, an SDSS-IV programme aimed at obtaining spectroscopic classification and ...redshift measurements for complete samples of sufficiently bright X-ray sources.
Methods.
We describe the SPIDERS X-ray Point Source Spectroscopic Catalogue, considering its store of 11 092 observed spectra drawn from a parent sample of 14 759 ROSAT and XMM sources over an area of 5129 deg
2
covered in SDSS-IV by the eBOSS survey.
Results.
This programme represents the largest systematic spectroscopic observation of an X-ray selected sample. A total of 10 970 (98.9%) of the observed objects are classified and 10 849 (97.8%) have secure redshifts. The majority of the spectra (10 070 objects) are active galactic nuclei (AGN), 522 are cluster galaxies, and 294 are stars.
Conclusions.
The observed AGN redshift distribution is in good agreement with simulations based on empirical models for AGN activation and duty cycle. Forming composite spectra of type 1 AGN as a function of the mass and accretion rate of their black holes reveals systematic differences in the H-beta emission line profiles. This study paves the way for systematic spectroscopic observations of sources that are potentially to be discovered in the upcoming eROSITA survey over a large section of the sky.
Peculiar groups of X‐ray emitting isolated neutron stars, which include magnetars, the “magnificent seven”, and central compact objects in supernova remnants, escape detection in standard pulsar ...surveys. Yet, they constitute a key element in understanding the neutron star evolution and phenomenology. Their use in population studies in the galactic scale has been hindered by the rarity of their detection. The all‐sky survey of the extended Roentgen Survey with an Imaging Telescope Array (eROSITA) on‐board the forthcoming Spectrum‐Roentgen‐Gamma (SRG) mission has the unique potential to unveil the X‐ray faint part of the population and constrain evolutionary models. To create a forecast for the 4‐year all‐sky survey, we perform Monte Carlo simulations of a population synthesis model, where we follow the evolutionary tracks of thermally emitting neutron stars in the Milky Way and test their detectability. In this paper, we discuss strategies for pinpointing the most promising candidates for follow‐up observing campaigns using current and future facilities.
Aims. We aimed to identify the variable X-ray source 3XMM J000511.8+634018, which was serendipitously discovered through routine inspections while the 3XMM catalogue was compiled. Methods. We ...analysed the archival XMM-Newton observation of the source, obtained BUSCA photometry in three colours, and performed optical spectroscopy with the LBT. These data were supplemented by archival observations from the Zwicky Transient Facility. Results. Based on its optical and X-ray properties, 3XMM J000511.8+634018 is classified as a magnetic cataclysmic variable, or polar. The flux is modulated with a period of 2.22 h (8009.1 ± 0.2 s), which we identify with the orbital period. The bright phases are highly variable in X-ray luminosity from one cycle to the next. The source shows a thermal plasma spectrum typical of polars without evidence of a luminous soft blackbody-like component. It is non-eclipsing and displays one-pole accretion. The X-ray and BUSCA light curves show a stream absorption dip, which suggests an inclination 50° < i < 75°. The phasing of this feature, which occurs at the end of the bright phase, requires a somewhat special accretion geometry with a stream running far around the white dwarf before it is magnetically channelled. The period of this polar falls within the period gap of the cataclysmic variables (2.15−3.18 h), but appears to fall just below the minimum period when only polars are considered.
Large-scale diffuse radio emission is observed in some clusters of galaxies. There is ample of evidence that the emission has its origin in synchrotron losses of relativistic electrons that have been ...accelerated in cluster mergers. In a cosmological simulation, we estimate the radio emission of structure formation shocks as follows: introducing a novel approach to identify strong shock fronts in an smoothed particle hydrodynamics (SPH) simulation, we determine the Mach number as well as the downstream density and temperature in the MareNostrum Universe simulation which has 2 × 10243 particles in a 500 h−1Mpc box. Then, we estimate the radio emission using the formalism derived in Hoeft & Brüggen to produce artificial radio maps of massive clusters and to derive a luminosity function of diffuse radio sources. Several of our clusters show radio objects with similar morphology to observed large-scale radio relics, whereas about half of the clusters show only very little radio emission. In agreement with observational findings, the maximum diffuse radio emission of our clusters depends strongly on their X-ray temperature. We find that the so-called accretion shocks cause only very little radio emission. We conclude that a moderate efficiency of shock acceleration, namely ξe= 0.005, and moderate magnetic fields in the region of the relics, namely 0.07–0.8 μG are sufficient to reproduce the number density and luminosity of radio relics.
Context. Galaxy clusters at high redshift are important to test cosmological models and models for the growth of structure. They are difficult to find in wide-angle optical surveys, however, leaving ...dedicated follow-up of X-ray selected candidates as one promising identification route. Aims. We aim to increase the number of galaxy clusters beyond the SDSS-limit, z ~ 0.75. Methods. We compiled a list of extended X-ray sources from the 2XMMp catalogue within the footprint of the Sloan Digital Sky Survey. Fields without optical counterpart were selected for further investigation. Deep optical imaging and follow-up spectroscopy were obtained with the Large Binocular Telescope, Arizona (LBT), of those candidates not known to the literature. Results. From initially 19 candidates, selected by visually screening X-ray images of 478 XMM-Newton observations and the corresponding SDSS images, 6 clusters were found in the literature. Imaging data through r,z filters were obtained for the remaining candidates, and 7 were chosen for multi-object (MOS) spectroscopy. Spectroscopic redshifts, optical magnitudes, and X-ray parameters (flux, temperature, and luminosity) are presented for the clusters with spectroscopic redshifts. The distant clusters studied here constitute one additional redshift bin for studies of the LX−T relation, which does not seem to evolve from high to low redshifts. Conclusions. The selection method of distant galaxy clusters presented here was highly successful. It is based solely on archival optical (SDSS) and X-ray (XMM-Newton) data. Out of 19 selected candidates, 6 of the 7 candidates selected for spectroscopic follow-up were verified as distant clusters, a further candidate is most likely a group of galaxies at z ~ 1.21. Out of the remaining 12 candidates, 6 were known previously as galaxy clusters, one object is a likely X-ray emission from an AGN radio jet, and for 5 we see no clear evidence for them to be high-redshift galaxy clusters.
Aims. We aim to confirm whether the eclipsing cataclysmic variable (CV) V902 Mon is an intermediate polar (IP), to characterise its X-ray spectrum and flux, and to refine its orbital ephemeris and ...spin period. Methods. We performed spectrographic observations of V902 Mon in 2016 with the 2.2 m Calar Alto telescope, and X-ray photometry and spectroscopy with XMM-Newton in October 2017. This data was supplemented by several years of AAVSO visual photometry. Results. We confirmed V902 Mon as an IP based on detecting the spin period, which has a value of 2208 s, at multiple epochs. Spectroscopy of the donor star and Gaia parallax yield a distance of 3.5−0.9+1.3 kpc3.5−0.9+1.3 kpc$$3.5_{ - 0.9}^{ + 1.3}\;{\rm{kpc}}$$, suggesting an X-ray luminosity one or two orders of magnitude lower than the 1033 erg s−1 typical of previously known IPs. The X-ray to optical flux ratio is also very low. The inclination of the system is more than 79°, and is most likely a value of around 82°. We have refined the eclipse ephemeris, stable over 14 000 cycles. The Hα line is present throughout the orbital cycle and is clearly present during eclipse, suggesting an origin distant from the white dwarf, and shows radial velocity variations at the orbital period. The amplitude and overall recessional velocity seem inconsistent with an origin in the disc. The XMM-Newton observation reveals a partially absorbed plasma model typical of magnetic CVs, that has a fluorescent iron line at 6.4 keV showing a large equivalent width of 1.4 keV. Conclusions. V902 Mon is an IP, and probably a member of the hypothesized X-ray underluminous class of IPs. It is likely to be a disc accretor, although the radial velocity behaviour of the Hα line remains puzzling. The large equivalent width of the fluorescent iron line, the small FX/Fopt ratio, and the only marginal detection of X-ray eclipses suggests that the X-ray emission arises from scattering.
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