Observations of GRB 060526 Optical Afterglow with Russian-Turkish 1.5-m Telescope

We present the results of the photometric multicolor observations of GRB 060526 optical afterglow obtained with Russian-Turkish 1.5-m Telescope (RTT150, Mt. Bakirlitepe, Turkey). The detailed measurements of afterglow light curve, starting from about 5 hours after the GRB and during 5 consecutive nights were done. In addition, upper limits on the fast variability of the afterglow during the first night of observations were obtained and the history of afterglow color variations was measured in detail. In the time interval from 6 to 16 hours after the burst, there is a gradual flux decay, which can be described approximately as a power law with an index of -1.14+-0.02. After that the variability on the time scale \delta t < t is observed and the afterglow started to decay faster. The color of the afterglow, V-R=~0.5, is approximately the same during all our observations. The variability is detected on time scales up to \delta t/t =~ 0.0055 at \Delta F_\nu/F_\nu =~ 0.3, which violates some constraints on the variability of the observed emission from ultrarelativistic jet obtained by Ioka et al. (2005). We suggest to explain this variability by the fact that the motion of the emitting shell is no longer ultrarelativistic at this time.Comment: 6 pages, 7 figures, Astronomy Letters, 2007, 33, 797, The on-line data tables and the original text in Russian can be found at http://hea.iki.rssi.ru/grb/060526/indexeng.htm

Optical Identifications of Five INTEGRAL Hard X-ray Sources in the Galactic Plane Region

The results of optical identifications of five hard X-ray sources in the Galactic plane region from the INTEGRAL all-sky survey are presented. The X-ray data on one source (IGRJ20216+4359) are published for the first time. The optical observations were performed with 1.5-m RTT-150 telescope (TUBITAK National Observatory, Antalya, Turkey) and 6-m BTA telescope (Special Astrophysical Observatory, Nizhny Arkhyz, Russia). A blazar, three Seyfert galaxies, and a high-mass X-ray binary are among the identified sources.Comment: 7 pages, 10 figures, Astronomy Letters, v. 34, p. 65

Optical Identification of Four Hard X-ray Sources from the Swift All-Sky Survey

We present the results of our optical identifications of four hard X-ray sources from the Swift all-sky survey. We obtained optical spectra for each of the program objects with the 6-m BTA telescope (Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz), which allowed their nature to be established. Two sources (SWIFT J2237.2+6324} and SWIFT J2341.0+7645) are shown to belong to the class of cataclysmic variables (suspected polars or intermediate polars). The measured emission line width turns out to be fairly large (FWHM ~ 15-25 A), suggesting the presence of extended, rapidly rotating (v~400-600 km/s) accretion disks in the systems. Apart from line broadening, we have detected a change in the positions of the line centroids for SWIFT J2341.0+7645, which is most likely attributable to the orbital motion of the white dwarf in the binary system. The other two program objects (SWIFT J0003.3+2737 and SWIFT J0113.8+2515) are extragalactic in origin: the first is a Seyfert 2 galaxy and the second is a blazar at redshift z=1.594. Apart from the optical spectra, we provide the X-ray spectra for all sources in the 0.6-10 keV energy band obtained from XRT/Swift data.Comment: 9 pages, 6 figures, will be published in Astronomy Letters, 38, No.5, pp.281-289 (2012

Additional spectroscopic redshift measurements for galaxy clusters from the First Planck Catalogue

We present the results of spectroscopic redshift measurements for the galaxy clusters from the first all-sky Planck catalogue of the Sunyaev-Zeldovich sources, that have been mostly identified by means of the optical observations performed previously by our team (Planck Collaboration, 2015a). The data on 13 galaxy clusters at redshifts from z=~0.2 to z=~0.8, including the improved identification and redshift measurement for the cluster PSZ1 G141.73+14.22 at z=0.828, are provided. The measurements were done using the data from Russian-Turkish 1.5-m telescope (RTT-150), 2.2-m Calar Alto Observatory telescope, and 6-m SAO RAS telescope (Bolshoy Teleskop Azimutalnyi, BTA).Comment: published in Astronomy Letter

Optical identification of hard X-ray source IGRJ18257-0707

We present the results of the optical identification of hard X-ray source IGRJ18257-0707 trough the spectroscopic observations of its optical counterpart with RTT150 telescope. Accurate position of the X-ray source, determined using Chandra observations, allowed us to associate this source with the faint optical object (m_R=~20.4), which shows broad H_\alpha emission line in its optical spectrum. Therefore we conclude that the source IGRJ18257-0707 is a type 1 Seyfert galaxy at redshift z=0.037.Comment: 4 pages, 3 figures, accepted for publication in Astronomy Letters, the original text in Russian can be found at http://hea.iki.rssi.ru/~rodion/pigrj18257-0707.pd

X-ray surface brightness and gas density profiles of galaxy clusters up to 3*R500c with SRG/eROSITA

Using the data of the SRG/eROSITA all-sky survey, we stacked a sample of ~40 galaxy cluster images in the 0.3--2.3 keV band, covering the radial range up to $10\times R_{\rm 500c}$. The excess emission on top of the galactic and extragalactic X-ray backgrounds and foregrounds is detected up to $\sim 3\times R_{\rm 500c}$. At these distances, the surface brightness of the stacked image drops below $\sim 1$% of the background. The density profile reconstructed from the X-ray surface brightness profile agrees well (within $\sim30$%) with the mean gas profile found in numerical simulations, which predict the local gas overdensity of $\sim$ 20--30 at $3\times R_{\rm 500c}$ and the gas fraction close to the universal value of $\frac{\Omega_b}{\Omega_m}\approx 0.15$ in the standard $\Lambda$CDM model. Taking at face value, this agreement suggests that up to $\sim 3\times R_{\rm 500c}$ the X-ray signal is not strongly boosted by the gas clumpiness, although a scenario with a moderately inhomogeneous gas cannot be excluded. A comparison of the derived gas density profile with the electron pressure profile based on the SZ measurements suggests that by $r\sim 3\times R_{\rm 500c}$ the gas temperature drops by a factor of $\sim$ 4--5 below the characteristic temperature of a typical cluster in the sample within $R_{\rm 500c}$, while the entropy keeps growing up to this distance. Better constraints on the gas properties just beyond $3\times R_{\rm 500c}$ should be possible with a sample larger than used for this pilot study.Comment: accepted by MNRA

First hours of the GRB 030329 optical afterglow

We present the first results of the observations of the extremely bright optical afterglow of gamma-ray burst (GRB) 030329 with the 1.5m Russian-Turkish telescope RTT150 (TUBITAK National Observatory, Bakyrlytepe, Turkey). RTT150 was one of the first 1.5m-class telescopes pointed to the afterglow. Observations were started approximately 6 hours after the burst. During the first 5 hours of our observations the afterglow faded exactly as a power law with index -1.19+-0.01 in each of the BVRI Bessel filters. After that, in all BVRI filters simultaneously we observe a steepening of the power law light curve. The power law decay index smoothly approaches the value ~= -1.9, observed by other observatories later. This power law break occurs at t-t_0 =0.57 days and lasts for +-0.1 days. We observe no variability above the gradual fading with the upper limits 10--1% on time scales 0.1--1000s. Spectral flux distribution in four BVRI filters corresponds to the power law spectrum with spectral index \alpha=0.66+-0.01. The change of the power law decay index in the end of our observations can be interpreted as a signature of collimated ultrarelativistic jet. The afterglow flux distribution in radio, optical and x-rays is consistent with synchrotron spectrum. We continue our observations of this unique object with RTT150.Comment: Astronomy Letters, Vol. 29, No. 9, p. 573; 6 pages, 5 figures; pagination corrected; the original Russian version can be found at http://hea.iki.rssi.ru/~br/030329/pfh030329.pd