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- ItemThe eROSITA X-ray telescope on SRG(Les Ulis : EDP Sciences, 2021) Predehl, P.; Andritschke, R.; Arefiev, V.; Babyshkin, V.; Batanov, O.; Becker, W.; Böhringer, H.; Bogomolov, A.; Boller, T.; Borm, K.; Bornemann, W.; Bräuninger, H.; Brüggen, M.; Brunner, H.; Brusa, M.; Bulbul, E.; Buntov, M.; Burwitz, V.; Burkert, W.; Clerc, N.; Churazov, E.; Coutinho, D.; Dauser, T.; Dennerl, K.; Doroshenko, V.; Eder, J.; Emberger, V.; Eraerds, T.; Finoguenov, A.; Freyberg, M.; Friedrich, P.; Friedrich, S.; Fürmetz, M.; Georgakakis, A.; Gilfanov, M.; Granato, S.; Grossberger, C.; Gueguen, A.; Gureev, P.; Haberl, F.; Hälker, O.; Hartner, G.; Hasinger, G.; Huber, H.; Ji, L.; Kienlin, A. v.; Kink, W.; Korotkov, F.; Kreykenbohm, I.; Lamer, G.; Lomakin, I.; Lapshov, I.; Liu, T.; Maitra, C.; Meidinger, N.; Menz, B.; Merloni, A.; Mernik, T.; Mican, B.; Mohr, J.; Müller, S.; Nandra, K.; Nazarov, V.; Pacaud, F.; Pavlinsky, M.; Perinati, E.; Pfeffermann, E.; Pietschner, D.; Ramos-Ceja, M. E.; Rau, A.; Reiffers, J.; Reiprich, T. H.; Robrade, J.; Salvato, M.; Sanders, J.; Santangelo, A.; Sasaki, M.; Scheuerle, H.; Schmid, C.; Schmitt, J.; Schwope, A.; Shirshakov, A.; Steinmetz, M.; Stewart, I.; Strüder, L.; Sunyaev, R.; Tenzer, C.; Tiedemann, L.; Trümper, J.; Voron, V.; Weber, P.; Wilms, J.; Yaroshenko, V.eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the primary instrument on the Spectrum-Roentgen-Gamma (SRG) mission, which was successfully launched on July 13, 2019, from the Baikonour cosmodrome. After the commissioning of the instrument and a subsequent calibration and performance verification phase, eROSITA started a survey of the entire sky on December 13, 2019. By the end of 2023, eight complete scans of the celestial sphere will have been performed, each lasting six months. At the end of this program, the eROSITA all-sky survey in the soft X-ray band (0.2-2.3 keV) will be about 25 times more sensitive than the ROSAT All-Sky Survey, while in the hard band (2.3-8 keV) it will provide the first ever true imaging survey of the sky. The eROSITA design driving science is the detection of large samples of galaxy clusters up to redshifts z > 1 in order to study the large-scale structure of the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGNs, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars, and diffuse emission within the Galaxy. Results from early observations, some of which are presented here, confirm that the performance of the instrument is able to fulfil its scientific promise. With this paper, we aim to give a concise description of the instrument, its performance as measured on ground, its operation in space, and also the first results from in-orbit measurements.
- ItemThe XMM-Newton serendipitous survey : IX. The fourth XMM-Newton serendipitous source catalogue(Les Ulis : EDP Sciences, 2020) Webb, N.A.; Coriat, M.; Traulsen, I.; Ballet, J.; Motch, C.; Carrera, F.J.; Koliopanos, F.; Authier, J.; de la Calle, I.; Ceballos, M.T.; Colomo, E.; Chuard, D.; Freyberg, M.; Garcia, T.; Kolehmainen, M.; Lamer, G.; Lin, D.; Maggi, P.; Michel, L.; Page, C.G.; Page, M.J.; Perea-Calderon, J.V.; Pineau, F.-X.; Rodriguez, P.; Rosen, S.R.; Santos Lleo, M.; Saxton, R.D.; Schwope, A.; Tomás, L.; Watson, M.G.; Zakardjian, A.Context. Sky surveys produce enormous quantities of data on extensive regions of the sky. The easiest way to access this information is through catalogues of standardised data products. XMM-Newton has been surveying the sky in the X-ray, ultra-violet, and optical bands for 20 years. Aims. The XMM-Newton Survey Science Centre has been producing standardised data products and catalogues to facilitate access to the serendipitous X-ray sky. Methods. Using improved calibration and enhanced software, we re-reduced all of the 14 041 XMM-Newton X-ray observations, of which 11 204 observations contained data with at least one detection and with these we created a new, high quality version of the XMM-Newton serendipitous source catalogue, 4XMM-DR9. Results. 4XMM-DR9 contains 810 795 detections down to a detection significance of 3σ, of which 550 124 are unique sources, which cover 1152 degrees2 (2.85%) of the sky. Filtering 4XMM-DR9 to retain only the cleanest sources with at least a 5σ detection significance leaves 433 612 detections. Of these detections, 99.6% have no pileup. Furthermore, 336 columns of information on each detection are provided, along with images. The quality of the source detection is shown to have improved significantly with respect to previous versions of the catalogues. Spectra and lightcurves are also made available for more than 288 000 of the brightest sources (36% of all detections).
- ItemSynthetic simulations of the extragalactic sky seen by eROSITA : I. Pre-launch selection functions from Monte-Carlo simulations(Les Ulis : EDP Sciences, 2018) Clerc, N.; Ramos-Ceja, M.E.; Ridl, J.; Lamer, G.; Brunner, H.; Hofmann, F.; Comparat, J.; Pacaud, F.; Käfer, F.; Reiprich, T.H.; Merloni, A.; Schmid, C.; Brand, T.; Wilms, J.; Friedrich, P.; Finoguenov, A.; Dauser, T.; Kreykenbohm, I.Context. Studies of galaxy clusters provide stringent constraints on models of structure formation. Provided that selection effects are under control, large X-ray surveys are well suited to derive cosmological parameters, in particular those governing the dark energy equation of state. Aims. We forecast the capabilities of the all-sky eROSITA (extended ROentgen Survey with an Imaging Telescope Array) survey to be achieved by the early 2020s. We bring special attention to modelling the entire chain from photon emission to source detection and cataloguing. Methods. The selection function of galaxy clusters for the upcoming eROSITA mission is investigated by means of extensive and dedicated Monte-Carlo simulations. Employing a combination of accurate instrument characterisation and a state-of-the-art source detection technique, we determine a cluster detection efficiency based on the cluster fluxes and sizes. Results. Using this eROSITA cluster selection function, we find that eROSITA will detect a total of approximately 105 clusters in the extra-galactic sky. This number of clusters will allow eROSITA to put stringent constraints on cosmological models. We show that incomplete assumptions on selection effects, such as neglecting the distribution of cluster sizes, induce a bias in the derived value of cosmological parameters. Conclusions. Synthetic simulations of the eROSITA sky capture the essential characteristics impacting the next-generation galaxy cluster surveys and they highlight parameters requiring tight monitoring in order to avoid biases in cosmological analyses.
- ItemFirst constraints on the AGN X-ray luminosity function at z 6 from an eROSITA-detected quasar(Les Ulis : EDP Sciences, 2021) Wolf, J.; Nandra, K.; Salvato, M.; Liu, T.; Buchner, J.; Brusa, M.; Hoang, D. N.; Moss, V.; Arcodia, R.; Brüggen, M.; Comparat, J.; de Gasperin, F.; Georgakakis, A.; Hotan, A.; Lamer, G.; Merloni, A.; Rau, A.; Rottgering, H. J. A.; Shimwell, T. W.; Urrutia, T.; Whiting, M.; Williams, W. L.Context. High-redshift quasars signpost the early accretion history of the Universe. The penetrating nature of X-rays enables a less absorption-biased census of the population of these luminous and persistent sources compared to optical/near-infrared colour selection. The ongoing SRG/eROSITA X-ray all-sky survey offers a unique opportunity to uncover the bright end of the high-z quasar population and probe new regions of colour parameter space. Aims. We searched for high-z quasars within the X-ray source population detected in the contiguous 140 deg2 field observed by eROSITA during the performance verification phase. With the purpose of demonstrating the unique survey science capabilities of eROSITA, this field was observed at the depth of the final all-sky survey. The blind X-ray selection of high-redshift sources in a large contiguous, near-uniform survey with a well-understood selection function can be directly translated into constraints on the X-ray luminosity function (XLF), which encodes the luminosity-dependent evolution of accretion through cosmic time. Methods. We collected the available spectroscopic information in the eFEDS field, including the sample of all currently known optically selected z > 5.5 quasars and cross-matched secure Legacy DR8 counterparts of eROSITA-detected X-ray point-like sources with this spectroscopic sample. Results. We report the X-ray detection of eFEDSU J083644.0+005459, an eROSITA source securely matched to the well-known quasar SDSS J083643.85+005453.3 (z = 5.81). The soft X-ray flux of the source derived from eROSITA is consistent with previous Chandra observations. The detection of SDSS J083643.85+005453.3 allows us to place the first constraints on the XLF at z > 5.5 based on a secure spectroscopic redshift. Compared to extrapolations from lower-redshift observations, this favours a relatively flat slope for the XLF at z 6 beyond L∗, the knee in the luminosity function. In addition, we report the detection of the quasar with LOFAR at 145 MHz and ASKAP at 888 MHz. The reported flux densities confirm a spectral flattening at lower frequencies in the emission of the radio core, indicating that SDSS J083643.85+005453.3 could be a (sub-) gigahertz peaked spectrum source. The inferred spectral shape and the parsec-scale radio morphology of SDSS J083643.85+005453.3 indicate that it is in an early stage of its evolution into a large-scale radio source or confined in a dense environment. We find no indications for a strong jet contribution to the X-ray emission of the quasar, which is therefore likely to be linked to accretion processes. Conclusions. Our results indicate that the population of X-ray luminous AGNs at high redshift may be larger than previously thought. From our XLF constraints, we make the conservative prediction that eROSITA will detect 90 X-ray luminous AGNs at redshifts 5.7 < z < 6.4 in the full-sky survey (De+RU). While subject to different jet physics, both high-redshift quasars detected by eROSITA so far are radio-loud; a hint at the great potential of combined X-ray and radio surveys for the search of luminous high-redshift quasars.
- ItemX-ray quasi-periodic eruptions from two previously quiescent galaxies(London [u.a.] : Nature Publ. Group, 2021) Arcodia, R.; Merloni, A.; Nandra, K.; Buchner, J.; Salvato, M.; Pasham, D.; Remillard, R.; Comparat, J.; Lamer, G.; Ponti, G.; Malyali, A.; Wolf, J.; Arzoumanian, Z.; Bogensberger, D.; Buckley, D.A.H.; Gendreau, K.; Gromadzki, M.; Kara, E.; Krumpe, M.; Markwardt, C.; Ramos-Ceja, M.E.; Rau, A.; Schramm, M.; Schwope, A.Quasi-periodic eruptions (QPEs) are very-high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central supermassive black holes of galactic nuclei1,2. It is currently unknown what triggers these events, how long they last and how they are connected to the physical properties of the inner accretion flows. Previously, only two such sources were known, found either serendipitously or in archival data1,2, with emission lines in their optical spectra classifying their nuclei as hosting an actively accreting supermassive black hole3,4. Here we report observations of QPEs in two further galaxies, obtained with a blind and systematic search of half of the X-ray sky. The optical spectra of these galaxies show no signature of black hole activity, indicating that a pre-existing accretion flow that is typical of active galactic nuclei is not required to trigger these events. Indeed, the periods, amplitudes and profiles of the QPEs reported here are inconsistent with current models that invoke radiation-pressure-driven instabilities in the accretion disk5–9. Instead, QPEs might be driven by an orbiting compact object. Furthermore, their observed properties require the mass of the secondary object to be much smaller than that of the main body10, and future X-ray observations may constrain possible changes in their period owing to orbital evolution. This model could make QPEs a viable candidate for the electromagnetic counterparts of so-called extreme-mass-ratio inspirals11–13, with considerable implications for multi-messenger astrophysics and cosmology14,15.