ABSTRACT
We present a catalogue of point sources detected with the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory during a wide-field survey of the Galactic Bulge that was conducted ...as part of the mission’s calibration and performance verification phase in 2019. The survey consisted of nearly 18 d of consecutive scanning observations of the sky region |l| < 6 deg, |b| < 2.5 deg with the median sensitivity of 4 × 10−13 erg s−1 cm−2 in the 4–12 keV energy band, which allows the detection of sources down to a luminosity of 3 × 1033 erg s−1 near the Galactic Centre. Using a maximum-likelihood-based algorithm, 172 sources were detected. Of these, 153 are registered on the average 4–12 keV map and 18 sources are either extremely hard (detected only at energies above 7 keV) or highly variable (detected only in individual scans shorter than a day). For 121 sources, there are plausible counterparts in other X-ray source catalogues, including 43 with known classification. The remaining 51 sources are previously unknown objects, discovered by ART-XC during the Galactic Bulge survey.
We present an updated catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope aboard the Spektrum-Roentgen-Gamma (SRG) observatory during its all-sky survey. It is based on the data of ...the first four and the partially completed fifth scans of the sky (ARTSS1-5). The catalog comprises 1545 sources detected in the 4–12 keV energy band. The achieved sensitivity ranges between ~4 × 10 −12 erg s −1 cm −2 near the ecliptic plane and ~7 × 10 −13 erg s −1 cm −2 near the ecliptic poles, which is a ~30–50% improvement over the previous version of the catalog based on the first two all-sky scans (ARTSS12). There are ~130 objects, excluding the expected contribution of spurious detections, that were not known as X-ray sources before the SRG/ART-XC all-sky survey. We provide information, partly based on our ongoing follow-up optical spectroscopy program, on the identification and classification of the majority of the ARTSS1-5 sources (1463), of which 173 are tentative at the moment. The majority of the classified objects (964) are extragalactic, a small fraction (30) are located in the Local Group of galaxies, and 469 are Galactic. The dominant classes of objects in the catalog are active galactic nuclei (911) and cataclysmic variables (192).
The MVN (Monitor Vsego Neba, all-sky monitor) experiment onboard the International Space Station for high-accuracy measurement of the cosmic X-ray background by the aperture modulation method being ...planned in 2022–2025 is considered. The technique that allows the measurement error within the MVN experiment to be minimized is described. Simulations of the main results of the experiment have been performed. They have shown that a record accuracy of measuring the cosmic X-ray background can be achieved. The main MVN systems are considered, and the results of the flight and ground-based experiments to measure the parameters of these systems are presented.
The article describes the MVN experiment (MVN – Monitor Vsego Neba in Russian transliteration) – All Sky Monitor onboard the ISS, which will start in 2021. The main scientific task of the experiment ...is to measure the cosmic X-ray background in energy range of 6 – 70 keV with unprecedented high absolute and spectral accuracy (about 1%). To reach this goal, Space Research Institute of the Russian Academy of Sciences has developed scientific payload called MVN. The main instrument of MVN is the SPIN-X1-MVN X-ray monitor, which is equipped with four CdTe based semiconductor detectors. The X-ray monitor will be mounted on the external surface of the ISS with zenith orientation. The structure of the monitor including the key systems (detectors, gears, thermal control system) is considered. Measuring of the cosmic X-ray background is carried out by the aperture modulation method described in detail in this article. Also we describe an optimal algorithm of the obtained in experiment data filtering, which will provide us with highest quality of the CXB measurement.
An analytical review of the systems for ensuring the thermal mode of current and prospective space astrophysical instruments has been performed, which showed that, in order to solve most of the ...current important problems of extra-atmospheric astronomy, the exact thermal stabilization of the mirror system and the radiation receiver of space telescopes has almost the same value as the level of their basic functional characteristics.
The models and results of the experimental studies of the characteristics of objects that are new for domestic instrumentation are presented: an X-ray mirror system and a CdTe strip semiconductor ...detector that are used in the first Russian ART-XC reflecting X-ray telescope. This telescope is a part of the Spektr-RG international space observatory, which started to the L2 libration point in July 2019.
We have performed calibration tests of a spare CdTe detector unit of the ART-XC/SRG telescope at the Space Research Institute’s 60-m-long X-ray test facility. During the tests, we illuminated the ...detector with a quasi-parallel X-ray beam generated by interchangeable X-ray tubes with different targets. To monitor the X-ray flux, we used two commercial detectors Amptek XR-100T-CdTe and XR-100SDD. We present some features of the ART-XC detectors operation, limitations of reducing the lower energy thresholds for photon detection and results of verification of the detector’s flat field characteristics at different energies. We estimate the ART-XC X-ray detector efficiency based on data obtained by the Amptek detectors and the ratio of their model efficiency. Using the measured detector efficiency, we have updated the ART-XC telescope’s on-axis effective area for the sum of doubly and singly reflected events. The ART-XC effective area reaches a maximum of 410 ± 16 cm
2
at 9.6 keV.
From October 2016 to September 2017, we performed tests of the ART-XC /SRG spare mirror system and detector unit at the 60-m-long IKI X-ray test facility. We describe some technical features of this ...test facility. We also present a brief description of the ART-XC mirror system and focal detectors. The nominal focal length of the ART-XC optics is 2700 mm. The field of view is determined by the combination of the mirror system and the detector unit and is equal to
∼
0.31 square degrees. The declared operating energy range is 5–30 keV. During the tests, we illuminated the detector with a
55
Fe+
241
Am calibration source and also with a quasi-parallel X-ray beam. The calibration source is integrated into the detector’s collimator. The X-ray beam was generated by a set of Oxford Instruments X-ray tubes with Cr, Cu and Mo targets and an Amptek miniature X-ray tube (Mini-X) with Ag transmission target. The detector was exposed to the X-ray beam either directly or through the mirror system. We present the obtained results on the detector’s energy resolution, the muon on-ground background level and the energy dependence of the W90 value. The accuracy of a mathematical model of the ART-XC mirror system, based on ray-tracing simulations, proves to be within 3.5% in the main energy range of 4–20 keV and 5.4% in the “hard” energy range of 20–40 keV.
We have performed tests of the SRG project’s ART-XC telescope’s flight spare units of the mirror system (MS) and the URD focal plane X-ray detector. During the tests, the MS was illuminated by a ...quasi-parallel X-ray beam from a microfocus tube. By changing the angle between the MS optical axis and the incoming beam we obtained data on vignetting of the effective area of the MS–URD pair at the energies of Cu K-lines. The measurements are in good agreement with our model. Using the model vignetting of the effective area, we determined the ART-XC grasp as a function of energy for singly and doubly reflected events. The grasp reaches ∼31 cm
2
deg
2
for singly reflected events at 7.2 keV, ∼44 cm
2
deg
2
for doubly reflected events at 8.6 keV and ∼74 cm
2
deg
2
for the sum of singly and doubly reflected events at 7.6 keV. The grasp values at 8.1 keV are ∼29.9 cm
2
deg
2
for singly reflected events, ∼43.8 cm
2
deg
2
for doubly reflected events and ∼73.7 cm
2
deg
2
for all events. The ART-XC field of view is ∼2 deg
2
. In its central ∼0.3 deg
2
, sources are imaged and the instrument works in a “telescope” mode. The outer ∼1.7 deg
2
do not have an imaging capability and the instrument works as a “concentrator” there. We also discuss the possibility of using ART-XC for monitoring bright transient X-ray sources when the observatory will be operating in the survey mode.
The results of the broadband spectral and timing study of the recently discovered transient X-ray pulsar MAXI J0903–531 in a wide range of luminosities that differ by a factor of ~30 are reported. ...The observed X-ray spectrum in both states can be described as a classical pulsar-like spectrum consisting of a power law with a high-energy cutoff. We argue that the absence of the spectrum transformation to the two-hump structure that is expected at low fluxes indicates that the magnetic field of the neutron star is relatively weak below (2–3) × 10
12
G. This estimate is consistent with other indirect constraints and non-detection of any absorption features that might be interpreted as a cyclotron absorption line. The timing analysis of the
NuSTAR
data revealed only slight variations of a single-peaked pulse profile of the source as a function of the energy band and mass accretion rate. In both intensity states, the pulsed fraction increases from 40% to roughly 80% with the energy. Finally, we were also able to obtain the orbital solution for the binary system using data from the
Fermi/GBM
, NICER, and
NuSTAR
instruments.
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