First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z < 0.6

High Energy Astrophysic

Redshift Measurements for Galaxies in Clusters by Multislit Spectroscopy at the 1.5-m Telescope RTT150

© 2020, Pleiades Publishing, Inc. Abstract: An example of simultaneous spectroscopic redshift measurements for a large number of galaxies in a cluster by multiobject spectroscopy with the medium- and low-resolution TFOSC spectrograph at the RussianTurkish 1.5-m telescope (RTT150) is presented. The redshifts of galaxies in the cluster 0301.6+0156 at z=0.17057\pm 0.0004 detected previously by the SunyaevZeldovich signal in the Planck all-sky survey have been measured. The spectra of 16 cluster galaxies, 9 of which were determined as ellipticals, were taken in one observation with an exposure time of 3 h and high-quality redshift measurements were made for them. We show that the redshifts of galaxies with magnitudes to mr=20.0, whose number in the TFOSC field can reach dozens, depending on the cluster richness and distance, can be measured in one observation with the TFOSC spectrograph using multiobject masks. Such measurements may be required to refine the redshifts of clusters and to estimate their masses by the dynamical method

Spectroscopic Redshift Measurements for Galaxy Clusters Detected in the Planck All-Sky Survey

© 2020, Pleiades Publishing, Ltd. Abstract: We present the results of spectroscopic redshift measurements for galaxy clusters from the catalogue compiled previously from Planck all-sky survey data in combination with Sloan Digital Sky Survey (SDSS) and WISE data in the optical and infrared ranges. Most of these clusters are massive objects that will also be detected in future all-sky surveys, such as the eROSITA all-sky X-ray survey onboard the Spectrum–Roentgen–Gamma (SRG) space observatory. The spectroscopic observations of these galaxy clusters have been carried out with the 1.5-m Russian–Turkish telescope (RTT150), the 1.6-m Sayan Observatory AZT-33IK telescope, and the 6-m SAO RAS telescope (Bolshoi Teleskop Azimutalnyi, BTA). The spectroscopic redshift measurements have been obtained for 67 galaxy clusters, including 12 galaxy clusters from the second Planck catalogue of Sunyaev–Zeldovich sources

Spectroscopic Redshift Measurements for Galaxy Clusters from the Planck Survey and Observations of These Clusters in the SRG/eROSITA Survey

Abstract: We present the results of our spectroscopic redshift measurements for galaxy clusters detected previously from Planck all-sky survey data as well as Sloan Digital Sky Survey and WISE all-sky survey data. The redshifts have been measured for 23 clusters, including four galaxy clusters from the second Planck catalogue of Sunyaev–Zeldovich sources. The main spectroscopic observations were carried out during 2019–early 2020 at the 1.6-m AZT-33IK telescope of the Sayan Observatory and the 1.5-m Russian–Turkish telescope (RTT-150). Some of the data have been obtained previously at the 3.5-m Calar Alto telescope. Out of the 23 clusters in this sample, 14 objects are located in the half of the sky where the rights to the data from the eROSITA sky survey onboard the SRG orbital X-ray observatory belong to the Russian side. All these clusters were detected with the eROSITA telescope in the course of the sky survey during 2020. On the whole, we have measured the spectroscopic redshifts for 220 galaxy clusters within our program of optical identifications of galaxy clusters from the Planck catalogue during several years. Many of them have already been detected in the SRG/eROSITA survey; a significant fraction of these objects are among the most massive galaxy clusters of the eROSITA sky survey and will most likely enter into cosmological samples of clusters from this survey

Optical Identifications of High-Redshift Galaxy Clusters from the Planck Sunyaev–Zeldovich Survey

International audienceWe present the results of optical identifications and spectroscopic redshift measurements for galaxy clusters from the second Planck catalogue of Sunyaev–Zeldovich sources (PSZ2) located at high redshifts, z ≈ 0.7−0.9. We used the data of optical observations with the Russian–Turkish 1.5-mtelescope (RTT-150), the Sayan Observatory 1.6-m telescope, the Calar Alto 3.5-m telescope, and the 6-m SAO RAS telescope (BTA). The spectroscopic redshift measurements were obtained for seven galaxy clusters, including one cluster, PSZ2 G126.57+51.61, from the cosmological sample of the PSZ2 catalogue. In the central regions of two clusters, PSZ2 G069.39+68.05 and PSZ2 G087.39−34.58, we detected arcs of strong gravitational lensing of background galaxies, one of which is at redshift z = 4.262. The data presented below roughly double the number of known galaxy clusters in the second Planck catalogue of Sunyaev–Zeldovich sources at high redshifts, z ≈ 0.8

Optical Identification of Candidates for Active Galactic Nuclei Detected by the Mikhail Pavlinsky ART-XC Telescope Onboard the SRG Observatory during an All-Sky X-ray Survey

Abstract: We present the results of our identification of eight objects from the preliminary catalogue of X-ray sources detected in the 4–12 keV energy band by the Mikhail Pavlinsky ART-XC telescope onboard the SRG observatory during the first all-sky survey. Three of them (SRGA J005751.0+210846, SRGA J014157.0-032915, SRGA J232446.8+440756) have been discovered by the ART-XC telescope, while five have already been known previously as X-ray sources, but their nature has remained unestablished. The last five sources have also been detected in soft X-rays by the eROSITA telescope of the SRG observatory. Our optical observations have been carried out at the 1.6-m AZT-33IK telescope of the Sayan Observatory and the 1.5-m Russian–Turkish telescope (RTT-150). All of the investigated objects have turned out to be active galactic nuclei (AGNs) at redshifts from 0.019 to 0.283. Six of them are Seyfert 2 galaxies (including one Seyfert 1.9 galaxy), one (SRGA J005751.0+210846) is a ‘‘hidden’’ AGN (in an edge-on galaxy), and one (SRGA J224125.9+760343) is a narrow-line Seyfert 1 galaxy. The latter object is characterized by a high X-ray luminosity (~(2-13) × 1044 erg s-1 in the 4–12 keV band) and, according to our black hole mass estimate (~2 × 107Mꙩ), an accretion rate close to the Eddington limit. All three AGNs discovered by the ART-XC telescope (which are not detected by the eROSITA telescope) are characterized by a high absorption column density (Formula presented.). The results obtained confirm the expectations that the ART-XC telescope is an efficient instrument in searching for heavily obscured and other interesting AGNs in the nearby (Formula presented.) Universe. The SRG sky survey will last for another 3 years or more, which must allow many such objects to be discovered

Modelling of 35-d superorbital cycle of B and V light curves of IMXB HZ Her/Her X-1

© 2020 The Author(s). The X-ray binary Her X-1 consists of an accreting neutron star and the optical component HZ Her. The 35-d X-ray superorbital variability of this system is known, since its discovery in 1972 by the Uhuru satellite and is believed to be caused by forced precession of a warped accretion disc tilted to the orbital plane. We argue that the observed features of the 35-d optical variability of HZ Her can be explained by free precession of the neutron star with a period close to that of the forced disc. The model parameters include (a) the X-ray luminosity of the neutron star; (b) the optical flux from the accretion disc; and (c) the tilt of the inner and outer edges of the accretion disc. A possible synchronization mechanism based on the coupling between the neutron star free precession and the dynamical action of non-stationary gas streams is discussed

Multi-object spectroscopy in the observational complex of the RTT150

The multi-object spectroscopy technique was implemented on the Russian-Turkish 1.5m optical telescope (aka. RTT150) by modifying the slit wheel of its main instrument TFOSC (TÜBİTAK Faint Object Spectrograph and Camera). Remotelycontrolled rotating holders of the multi object masks were installed in the two nests of the slit wheel. The accuracy of the mask unit’s rotation is the order of 1 arcmin, in which the image plane for 2 sources located at a separation of 5 arcmin corresponds to a positional accuracy of 0.1 arcsec. To investigate the quality of the MOS technique in RTT150, the well-known merging galaxy cluster Abell 1914 was observed spectroscopically. The dispersion of the differences between known and RTT150 redshift estimations is 0.0006, which is good enough for cosmological studies

Spectroscopic Redshift Determination for a Sample of Distant Quasars Detected by the SRG Observatory Based on RTT-150 Observations. II

Abstract: Results of the spectroscopic observations at the 1.5-m Russian–Turkish telescope for another group of 12 X-ray sources discovered by the eROSITA telescope onboard the SRG space observatory and identified by the SRGz machine learning system as candidates for distant X-ray quasars are presented. Ten objects have been confirmed as quasars at redshifts z=2.6{-}3.2 and two sources have turned out to be active galactic nuclei (AGNs) at z=0.42 and 1.02

Observation of a Very Massive Galaxy Cluster at z = 0.76 in the SRG/eROSITA All-Sky Survey

Abstract: The results of multiwavelength observations of the very massive galaxy cluster SRGe CL2305.2–2248 detected in X-rays during the first SRG/eROSITA all-sky survey are discussed. This galaxy cluster has also been detected previously in the millimeter band in the South Pole Telescope (SPT-CL J2305–2248) and Atacama Cosmology Telescope (ACT-CL J2305.1–2248) surveys through the observation of the Sunyaev–Zeldovich effect. The spectroscopic redshift has been measured at the 6-m BTA telescope, z=0.7573. In addition, deep photometric measurements of galaxies have been performed at the Russian–Turkish 1.5-m telescope (RTT-150). The mass of the cluster is estimated from the eROSITA data to be (Formula presented.). We show that this cluster is among several tens of the most massive clusters in the observable Universe and among only a few most massive galaxy clusters at z>0.6