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The curious Galactic features near G357.2$-$0.2 were observed with the MeerKAT radio interferometer array in the UHF and L bands (0.56--1.68 GHz). There are two possibly related features: a newly identified faint heart-shaped partial shell (the "Heart"), and a series of previously known but now much better imaged narrow, curved features (the "Worm") interior to the heart. Polarized emission suggests that much of the emission is nonthermal and is embedded in a dense plasma. The filaments of the worm appear to be magnetic structures powered by embedded knots that are sites of particle acceleration. The morphology of the worm broadly resembles some known pulsar wind nebulae (PWNe) but there is no known pulsar or PWN which could be powering this structure. We also present eROSITA observations of the field; no part of the nebula is detected in X-rays, but the current limits do not preclude the existence of a pulsar/PWN of intermediate spin-down luminosity., Comment: 14 pages, 14 figures

The orbital observatory Spectrum-Roentgen-Gamma (SRG), equipped with the grazing-incidence X-ray telescopes Mikhail Pavlinsky ART-XC and eROSITA, was launched by Roscosmos to the Lagrange L2 point of the Sun-Earth system on July 13, 2019. The launch was carried out from the Baikonur Cosmodrome by a Proton-M rocket with a DM-03 upper stage. The German telescope eROSITA was installed on SRG under an agreement between Roskosmos and the DLR, the German Aerospace Agency. In December 2019, SRG started to perform its main scientific task: scanning the celestial sphere to obtain X-ray maps of the entire sky in several energy ranges (from 0.2 to 8 keV with eROSITA, and from 4 to 30 keV with ART-XC). By mid-June 2021, the third six-month all-sky survey had been completed. Over a period of four years, it is planned to obtain eight independent maps of the entire sky in each of the energy ranges. The sum of these maps will provide high sensitivity and reveal more than three million quasars and over one hundred thousand massive galaxy clusters and galaxy groups. The availability of eight sky maps will enable monitoring of long-term variability (every six months) of a huge number of extragalactic and Galactic X-ray sources, including hundreds of thousands of stars with hot coronae. The rotation of the satellite around the axis directed toward the Sun with a period of four hours enables tracking the faster variability of bright X-ray sources during one day every half year. The chosen strategy of scanning the sky leads to the formation of deep survey zones near both ecliptic poles. The paper presents sky maps obtained by the telescopes on board SRG during the first survey of the entire sky and a number of results of deep observations performed during the flight to the L2 point in the frame of the performance verification program.(Abriged), Comment: 30 pages, 46 figures. Astronomy & Astrophysics, 656, A132, 2021. Abstract abridged

We examine the X-ray, optical, and radio properties for the members clusters of a new supercluster discovered during the SRG/eROSITA Performance Verification phase. In the 140 deg2 eROSITA Final Equatorial Depth Survey (eFEDS) field we detect a previously unknown supercluster consisting of a chain of eight galaxy clusters at z=0.36. The redshifts of these members are determined through HSC photometric measurements. We examine the X-ray morphological and dynamical properties, gas and total mass out to R500 of the members and compare them with the general population of clusters detected in the eFEDS field. We further investigate the gas in the bridge region between the cluster members for a potential WHIM detection. Radio follow-up observations with LOFAR and uGMRT are used to search for diffuse emission and constrain the dynamic state of the system. We do not find significant differences in the morphological parameters and properties of the intra-cluster medium of the clusters embedded in this large-scale filament compared to eFEDS clusters. We also provide upper limits on the electron number density and mass of the warm-hot intergalactic medium as provided by the eROSITA data. These limits are consistent with previously reported values for the detections in the vicinity of clusters of galaxies. In LOFAR and uGMRT follow-up observations of the northern part of this supercluster we find two new radio relics that are the result of major merger activity in the system. These early results show the potential of eROSITA to probe large-scale structures such as superclusters and the properties of their members. Our forecasts show that we will be able to detect 450 superclusters with 3000 member clusters located in the eROSITA_DE region at the final eROSITA all-sky survey depth, enabling statistical studies of the properties of superclusters and their constituents embedded in the cosmic web., 19 pages, 13 figures, accepted for publication by A&A

We report the results of two Chandra ACIS-S observations from February and August 2003 of the highly X-ray variable Narrow-Line Seyfert 1 galaxy RX J2217.9--5941. Observations spanning the time from the ROSAT All Sky Survey (RASS) through an ASCA observation in 1998 indicate apparently monotonically decreasing flux by a factor of 30. The Chandra observations reveal increased emission over that seen in ASCA, supporting a persistent variability rather than an X-ray outburst event. However, the cause of the strong X-ray variability remains unclear. Our Chandra observations confirm the steep soft X-ray spectrum in the 0.2-2.0 keV band found during the ROSAT All-Sky Survey observation (\ax=2.7). The spectral shape of the source appears to be variable with the spectrum becoming softer when the source becomes fainter. Best fitting models to the data include an absorbed broken power law, a blackbody plus power law, and a power law with partial covering absorption. The latter model suggests a variable partial-covering absorber in the line of sight which can explain in part the variability seen in RX J2217.9--5941. We suggest that there might be a population of Narrow Line Seyfert 1 galaxies which are at least at times highly absorbed.

We demonstrate the feasibility of transmission grating spectroscopy in the 10 keV range. The diffraction efficiency of a 5000 l/mm free-standing gold transmission grating was measured at the three photon energies of 1.49, 5.4, and 8.04 keV (Kα of Al, Cr, and Cu). At 1.49 keV, the measured efficiencies agree well with efficiencies calculated by standard grating theory. At 5.4 and 8.04 keV, the measured efficiencies significantly exceed the theoretical ones. For Cu Kα, the absolute efficiency into first order is still as high as 3.3%. We present spectra of fs laser plasmas generated by irradiating Al, Cr, and Cu targets.

The Galactic supernova remnant Cas A is believed to be the result of a recent (∼ 300 yrs) and nearby (D ∼ 3 kpc) explosion of a massive star. The discovery of gamma-ray line emission due to radioactive 44 Ti with COMPTEL supports the massive star origin of Cas A. However, the ejection of 44 Ti should be accompanied by large amounts of 56 Ni and 57 Ni, which would have made this a very bright supernova. No 17th century sightings of this event exist, with the notable exception of the ∼ 6th mag star 3 Cas reported by Sir John Flamsteed. This mystery may be solved by assuming that the supernova was enshrouded by a dusty envelope, perhaps provided by a pre-supernova wind. X-ray observations with ROSAT provide evidence for this scenario through the simultaneous analysis of absorption along the line of sight and the extended X-ray scattering halo around Cas A. The supernova shock destroyed the dust, reducing the line-of-sight opacity to a value consistent with a 3 kpc path through an average ISM. ROSAT detects the evaporated dust as excess absorption.

The interaction of X-rays with interstellar dust leads to small angle scattering. X-ray sources behind sufficiently dense dust columns are therefore surrounded by haloes of faint and diffuse X-ray emission. Since these X-ray sources are also highly absorbed, X-ray observations offer the unique opportunity to measure both components of interstellar extinction simultaneously. This method provides an excellent means of determining interstellar gas to dust ratios, a differentiation between interstellar and circumstellar matter, and, last but not least, a clue to the physical nature of dust itself. In particular we have a plausible explanation why the supernova- explosion in Cassiopaea 300 years ago, of which we know today the remnant Cas A, has not been seen. Furthermore, we find that dust grains must be ‘fluffy’ or porous with voids up to 70%.

We report on the development of a generic X‐ray instrument simulator to be used in simulations of future X‐ray missions. Based on a Monte Carlo approach the code generates photon events for sources in an X‐ray source catalogue such as the ROSAT all sky survey or the XMM‐Newton slew surveys and then models the imaging and detection process based on the available calibration files (e.g., point spread functions for the imaging). The output of the program are event lists, which can be analysed using standard software such as xselect. Due to its modular concept the simulation software can be easily adapted to different concepts of imaging detectors.As examples for the potential use of the simulation we present our studies for eROSITA and show results of simulations of the detector performance for the High Time Resolution Spectrometer and the Wide Field Imager on the International X‐ray Observatory.

The ART-XC instrument is an X-ray grazing-incidence telescope system in an ABRIXAS-type optical configuration optimized for the survey observational mode of the Spectrum-RG astrophysical mission which is scheduled to be launched in 2011. ART-XC has two units, each equipped with four identical X-ray multi-shell mirror modules. The optical axes of the individual mirror modules are not parallel but are separated by several degrees to permit the four modules to share a single CCD focal plane detector, 1/4 of the area each. The 450-micron-thick pnCCD (similar to the adjacent eROSITA telescope detector) will allow the detection of X-ray photons up to 15 keV. The field of view of the individual mirror module is about 18×18 arcminutes2 and the sensitivity of the ART-XC system for 4 years of survey will be better than 10-12 erg s-1 cm-2 over the 4-12 keV energy band. This will allow the ART-XC instrument to discover several thousands new AGNs.

Rontgenstrahlung wird an den kleinen Staubkornern des interstellaren Mediums gestreut. Im Gegensatz zum sichtbaren Licht erfolgt diese Streuung in Vorwartsrichtung, so das helle Rontgenquellen hinter genugend tiefen Staubschichten von einem Halo schwacher, diffuser Strahlung umgeben sind. Mit ROSAT wurden die Halos einer Reihe von Rontgenquellen gemessen. Erstmalig konnte damit das Verhaltnis zwischen Absorption und Streuung von kosmischer Rontgenstrahlung ermittelt werden. Dies ist eine neue Methode zur direkten Bestimmung des Staubanteils der interstellaren Materie.

The ROSAT telescope is equipped with two different kinds of X-ray image converters: two redundant position sensitive proportional counters (PSPC) and one high resolution imager (HRI), based on microchannel plates. The detectors and part of their front-end electronics as well as the gas supply system for the PSPC's are mounted onto a carrousel, which allows positioning of the desired imager in the focus of the telescope. All instruments, electronics, mechanisms, etc. are accommodated in the focal plane housing, which is mounted to the optical bench of the mirror system. We will give an overview of the focal plane instrumentation and present the performance of the X-ray image converters.

The primary scientific objective of the ROSAT mission is to perform the first all sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. Consequently a large number of new sources (> 105) will be discovered and located with an accuracy of 1 arcmin. After completion of the survey which will take about half a year the instrument will be used for detailed observations of selected targets.