We report on the detection of type-C quasi-periodic oscillations during the initial stages of the outburst of Swift J1727.8-1613 in 2023. Using data of the INTEGRAL observatory along with the data of the SRG/ART-XC and Swift/XRT telescopes the fast growth of the QPO frequency was traced. We present a hard X-ray lightcurve that covers the initial stages of the 2023 outburst - the fast rise and plateau - and demonstrate that the QPO frequency was stable during the plateau. The switching from type-C to type-B QPO was detected with the beginning of the source flaring activity. We have constructed a broad-band spectrum of Swift J1727.8-1613 and found an additional hard power-law spectral component extending at least up to 400 keV. Finally, we have obtained an upper limit on the hard X-ray flux at the beginning of the optical outburst and estimated the delay of the X-ray outburst with respect to the optical one.

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 similar to 4 x 10(-1)2 erg s(-1) cm(-2) near the ecliptic plane and similar to 7 x 10(-13) erg s(-1) cm(-2) near the ecliptic poles, which is a similar to 30-50% improvement over the previous version of the catalog based on the first two all-sky scans (ARTSS12). There are similar to 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).

ABSTRACT We describe an X-ray source detection method entirely based on the maximum likelihood analysis, in application to observations with the ART-XC telescope onboard the Spectrum Roentgen Gamma observatory. The method optimally combines the data taken at different conditions, a situation commonly found in scanning surveys or mosaic observations with a telescope with a significant off-axis PSF distortion. The method can be naturally extended to include additional information from the X-ray photon energies, detector grades, etc. The likelihood-based source detection naturally results in an optimal use of available information for the sources detection and stable and uniform definition of detection thresholds under different observing conditions (PSF, background level). This greatly simplifies the statistical calibration of the survey needed to, e.g. obtain the $\log N - \log S$ distribution of detected sources or their luminosity function. The method can be applied to the data from any imaging X-ray telescope.

We report on Konus-WIND (KW) and Mikhail Pavlinsky Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) observations and analysis of a nearby GRB 221009A, the brightest γ -ray burst (GRB) detected by KW for >28 yr of observations. The prompt, pulsed phase of the burst emission lasts for ∼600 s and is followed by a steady power-law decay lasting for more than 25 ks. From the analysis of the KW and ART-XC light curves and the KW spectral data, we derive time-averaged spectral peak energy of the burst E _p ≈ 2.6 MeV, E _p at the brightest emission peak ≈ 3.0 MeV, the total 20 keV–10 MeV energy fluence of ≈0.22 erg cm ^−2 , and the peak energy flux in the same band of ≈0.031 erg cm ^−2 s ^−1 . The enormous observed fluence and peak flux imply, at redshift z = 0.151, huge values of isotropic energy release E _iso ≈ 1.2 × 10 ^55 erg (or ≳6.5 solar rest mass) and isotropic peak luminosity L _iso ≈ 3.4 × 10 ^54 erg s ^−1 (64 ms scale), making GRB 221009A the most energetic and one of the most luminous bursts observed since the beginning of the GRB cosmological era in 1997. The isotropic energetics of the burst fit nicely both “Amati” and “Yonetoku” hardness–intensity correlations for >300 KW long GRBs, implying that GRB 221009A is most likely a very hard, super-energetic version of a “normal” long GRB.

We present a catalog of sources detected by theMikhail Pavlinsky ART-XC telescope onboardthe SRG space observatory during the observations of the Galactic plane region near a longitude l 20◦(L20 field) in October 2019. The L20 field was observed four times in the scanning mode, which provideda uniform coverage of the sky region with a total area of 24 sq. deg with a median sensitivity of 8 ×10−13 erg s−1 cm−2 (at 50% detection completeness) in the 4–12 keV energy band. As a result, we havedetected 29 X-ray sources at a statistically significant level, 11 of which have not been detected previouslyby other X-ray observatories. Preliminary estimates show that four of themcan presumably be extragalacticin nature. We also show that the source SRGA J183220.1−103508 (CXOGSG J183220.8−103510) ismost likely a galaxy cluster containing a bright radio galaxy at redshift z 0.121.

We present a new statistical method for constructing background subtracted measurements from event list data gathered by X-ray and gamma ray observatories. This method was initially developed specifically to construct images that account for the high background fraction and low overall count rates observed in survey data from the Mikhail Pavlinsky ART-XC telescope aboard the Spektrum Röntgen Gamma (SRG) mission, although the mathematical underpinnings are valid for data taken with other imaging missions and analysis applications. This method fully accounts for the expected Poisson fluctuations in both the sky photon and non X-ray background count rates in a manner that does not result in unphysical negative counts. We derive the formulae for arbitrary confidence intervals for the source counts and show that our new measurement converges exactly to the standard background subtraction calculation in the high signal limit. Utilizing these results, we discuss several variants of images designed to optimize different science goals for both pointed and slewing telescopes. Using realistic simulated data of a galaxy cluster as observed by ART-XC we show that our method provides a more significant and robust detection of the cluster emission as compared to a standard background subtraction. We also demonstrate its advantages using real observations of a point source from the ART-XC telescope. These calculations may have widespread applications for a number of source classes observed with high energy telescopes.

We present a first catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope on board the SRG observatory in the 4-12 keV energy band during its ongoing all-sky survey. The catalog comprises 867 sources detected on the combined map of the first two 6-month scans of the sky (December 2019 - December 2020). The achieved sensitivity to point sources varies between ~4x10^-12 erg/s/cm2 near the ecliptic plane and ~8x10^-13 erg/s/cm2 (4-12 keV) near the ecliptic poles, and the typical localization accuracy is ~15 arcsec. Of the 750 sources of known or suspected origin in the catalog, 56% are extragalactic (mostly active galactic nuclei, AGN; and clusters of galaxies) and the rest are Galactic (mostly cataclysmic variables, CVs; and low- and high-mass X-ray binaries). For 114 sources, ART-XC has detected X-rays for the first time. Although the majority of these (~80) are expected to be spurious (given the adopted detection threshold), there can be a significant number of newly discovered astrophysical objects. We have started a program of optical follow-up observations of the new and previously unidentified X-ray sources, which has already led to the identification of several AGN and CVs. With the SRG all-sky survey planned to continue for a total of four years, we can expect the ART-XC survey in the 4-12 keV band to significantly surpass previous surveys that were carried out in similar (medium X-ray) energy bands in terms of the combination of angular resolution, sensitivity, and sky coverage.

ABSTRACT The Spectrum-Roentgen-Gamma (SRG) observatory is currently conducting its 4-yr all-sky X-ray survey, started on 2019 December 12. The survey is periodically interrupted for technological operations with the spacecraft. These time intervals are usually used by the Mikhail Pavlinsky ART-XC telescope to perform calibrations. In this context, SRG carried out scanning observations of the Puppis A supernova remnant (SNR) with the aim to check the imaging performance of ART-XC and to optimize the technique of image reconstruction for extended objects. Using the unique imaging capabilities of ART-XC and its uniform coverage of the entire Puppis A region, we attempted to investigate the morphology of this SNR at energies ≳ 4 keV, and to search for previously unknown X-ray sources. Puppis A was observed in 2019–2020, conducting 1.5° × 1.5° shallow surveys with an exposure of 36 h. Additional deep pointed observations of the central part of Puppis A were carried out in 2021 lasted 31 h to highlight the morphology of the extended emission. The X-ray emission of the Puppis A was significantly detected as an extended structure in the 4–6 keV energy band. The morphology of the emission is in general agreement with that observed in soft X-rays previously. The deep sky image of Puppis A obtained with the ART-XC telescope is characterized by a typical SNR shell rim morphology, an extended emission and a bright emission knot in the north-eastern part of the supernova shell. Also, four point X-ray sources have been detected, including three objects identified in catalogues, and one newly discovered X-ray emitter.

The SRG observatory, equipped with the X-ray telescopes Mikhail Pavlinsky ART-XC and eROSITA, was launched by Roscosmos to the L2 point on July 13, 2019. The launch was carried out from Baikonur by a Proton-M rocket with a DM-03 upper stage. The German telescope eROSITA was installed on SRG under agreement between Roskosmos and DLR. In December 2019, SRG started to scan the celestial sphere in order to obtain X-ray maps of the entire sky in several energy bands (from 0.3 to 8 keV, eROSITA, and from 4 to 30 keV, ART-XC). By mid-December 2020, the second full-sky scan had been completed. Over 4 years, 8 independent maps of the sky will be obtained. Their sum will reveal more than three million quasars and over one hundred thousand galaxy clusters and groups. The availability of 8 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. Rotation of the satellite around the axis directed toward the Sun with a period of 4 hours makes it possible to track faster variability of bright X-ray sources. The chosen scanning strategy leads to the formation of deep survey zones near both ecliptic poles. We present sky maps obtained by the telescopes aboard SRG during the first scan of the sky and a number of results of deep observations performed during the flight to L2, demonstrating the capabilities of the Observatory in imaging, spectroscopy and timing. In December 2023 the Observatory will switch for at least two years to observations of the most interesting sources in the sky in triaxial orientation mode and deep scanning of selected fields with an area of up to 150 sq. deg. These modes of operation were tested during the Performance Verification phase. Every day, SRG data are dumped onto the largest antennae of the Russian Deep Space Network in Bear Lakes and near Ussuriysk.

We report results of the first broadband observation of the transient X-ray pulsar GRO J1008−57 performed in the quiescent state. Observations were conducted quasi-simultaneously with NuSTAR and the Mikhail Pavlinsky ART-XC telescope on board SRG right before the beginning of a Type I outburst. GRO J1008−57 was detected in the state with the lowest observed luminosity around several ×10 34 erg s −1 and consequently accreting from the cold disk. Timing analysis allowed us to detect pulsations during this state for the first time. The observed pulsed fraction of about 20% is, however, almost three times lower than in brighter states when the accretion proceeds through the standard disk. We traced the evolution of the broadband spectrum of the source on a scale of three orders of magnitude in luminosity and found that at the lowest luminosities the spectrum transforms into the double-hump structure similarly to other X-ray pulsars accreting at low luminosities (X Persei, GX 304–1, and A 0535+262) reinforcing the conclusion that this spectral shape is typical for these objects.

ART-XC (Astronomical Roentgen Telescope - X-ray Concentrator) is the hard X-ray instrument with grazing incidence imaging optics on board the Spektr-Roentgen-Gamma (SRG) observatory. The SRG observatory is the flagship astrophysical mission of the Russian Federal Space Program, which was successively launched into orbit around the second Lagrangian point (L2) of the Earth-Sun system with a Proton rocket from the Baikonur cosmodrome on 13 July 2019. The ART-XC telescope will provide the first ever true imaging all-sky survey performed with grazing incidence optics in the 4-30 keV energy band and will obtain the deepest and sharpest map of the sky in the energy range of 4-12 keV. Observations performed during the early calibration and performance verification phase as well as during the on-going all-sky survey that started on 12 Dec. 2019 have demonstrated that the in-flight characteristics of the ART-XC telescope are very close to expectations based on the results of ground calibrations. Upon completion of its 4-year all-sky survey, ART-XC is expected to detect 5000 sources ( 3000 active galactic nuclei, including heavily obscured ones, several hundred clusters of galaxies, 1000 cataclysmic variables and other Galactic sources), and to provide a high-quality map of the Galactic background emission in the 4-12 keV energy band. ART-XC is also well suited for discovering transient X-ray sources. In this paper, we describe the telescope, results of its ground calibrations, major aspects of the mission, the in-flight performance of ART-XC and first scientific results.

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. In addition, 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, demonstrating the capabilities of the observatory in imaging, spectroscopy, and timing of X-ray sources. It is planned that in December 2023, the observatory will for at least two years switch to observations of the most interesting sources in the sky in triaxial orientation mode and deep scanning of selected celestial fields with an area of up to 150 square degrees. These modes of operation were tested during the performance verification phase. Every day, data from the SRG observatory are dumped onto the largest antennas of the Russian Deep Space Network in Bear Lakes and near Ussuriysk.

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. In addition, 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, demonstrating the capabilities of the observatory in imaging, spectroscopy, and timing of X-ray sources. It is planned that in December 2023, the observatory will for at least two years switch to observations of the most interesting sources in the sky in triaxial orientation mode and deep scanning of selected celestial fields with an area of up to 150 square degrees. These modes of operation were tested during the performance verification phase. Every day, data from the SRG observatory are dumped onto the largest antennas of the Russian Deep Space Network in Bear Lakes and near Ussuriysk.

ART-XC is an X-ray grazing incidence mirror telescopes array onboard the Spectrum-Roentgen-Gamma (SRG) mission, that is currently scheduled for launch in March 2019. This instrument was developed by the Space Research Institute (IKI) and the All-Russian Scientific Research Institute for Experimental Physics (VNIIEF). The NASA Marshall Space Flight Center (MSFC) has developed and fabricated flight X-ray mirror modules. Each mirror module is aligned with a focal plane CdTe double-sided strip detector which will operate over the energy range of 4−30 keV, with an angular resolution of <1′, a field of view of ~0.3 deg2 in double reflection and an expected energy resolution of about 9% at 14 keV. The ART-XC instrument will be used to perform an all-sky survey simultaneously with the other instrument of the SRG mission, eROSITA, operational in a softer energy range 0.3-10 keV. We present an overview of the ARTXC/SRG instrument and an update on the current status of the project.