Sergey Karpov

From TORTORA to MegaTORTORA—Results and Prospects of Search for Fast Optical Transients

To study short stochastic optical flares of different objects (GRBs, SNs, etc.) of unknown localizations as well as NEOs it is necessary to monitor large regions of sky with high-time resolution. We developed a system consisting of widefield camera with field of view of 400–600 sq.deg. which uses TV-CCD with 0.13 s temporal resolution to record and classify optical transients, and a fast robotic telescope aimed to perform their spectroscopic and photometric investigation just after detection. Such two-telescope complex, combining wide-field camera TORTORA and robotic telescope REM, operated from May 2006 at La Silla ESO observatory. Some results of its operation, including first high time resolution study of optical transient accompanying GRB and discovery of its fine time structure, are presented. Also, prospects for improving the efficiency of such observations are given, and a project of a next generation wide field monitoring system, the MegaTORTORA, is described.

GRB sky distribution puzzles

We analyze the randomness of the sky distribution of cosmic gamma-ray bursts. These events are associated with massive galaxies, spiral or elliptical, and therefore their positions should trace the large-scale structure, which, in turn, could show up in the sky distribution of fluctuations of the cosmicmicrowave background (CMB). We test this hypothesis by mosaic correlation mapping of the distributions of CMB peaks and burst positions, find the distribution of these two signals to be correlated, and interpret this correlation as a possible systematic effect.

Detection of regular low-amplitude photometric variability of the magnetic dwarf WD0009+501. on the possibility of photometric investigation of exoplanets on the basis of 1-meter class telescopes of the special and crimean astrophysical observatories

We present the results of photometric observations of the weak magnetic white dwarf WD 0009+501. The observations were carried out for two years with the 1-m telescopes of the Special and Crimean Astrophysical Observatories. As a result of these observations, we detected regular V -band luminosity variations with a period of P ≈ 8 hours. The amplitude of the variability is stable on timescales greater than two years and amounts to 11 ± 1 mmag. The difference in the variability amplitude from observations with different telescopes is 1–3 mmag. The result is interpreted within the concept of a rotation-modulated variability of magnetic properties of the star’s atmosphere. We also discuss a possible variability due to the presence of planetary companions around stars of this type. The results of monitoring were used to explore the capabilities of the telescopes for exoplanet investigation. We studied the dependences between the characteristic times of exposures, magnitudes of the objects, and a threshold level of the expected variability amplitudes for all the telescopes involved in our program. A program of exoplanet monitoring with the mentioned telescopes was drawn up for the next few years based on the results of the study.

Cross-Identification of Large Surveys for Finding Interstellar Extinction

The publication of large photometric surveys and the tools for the cross-identification of their objects open up a possibility for obtaining multicolor photometry of hundreds of millions of objects. This, in turn, makes it possible not only to classify the objects and determine their parameters, but also to measure the interstellar extinction towards them and produce an extinction map for the Milky Way. The aim of this study is to develop a tool for the cross identification of objects in the most well-known surveys and test it in several sky areas. To this end, we implemented an algorithm of fast positional matching of large astronomical catalogs in small (up to one degree) sized areas with filtering of false identification. As a result, we drew in seven 0.1-degree radius areas samples of objects from the DENIS, 2MASS, SDSS, GALEX, and UKIDSS surveys, and performed the cross-identification of these surveys. We compiled the corresponding subcatalogs in the VO Table format. The tool developed as a result of this work can be used to cross-identify objects in arbitrary sky areas for the further classification and determination of stellar parameters, including the measurement of the amount of interstellar extinction.

Wide and Fast: Monitoring the Sky in Subsecond Domain with the FAVOR and TORTORA Cameras

In order to detect and investigate short stochastic optical flares from a number of variable astrophysical objects (GRBs, SNe, flare stars, CVs, X-Ray binaries) of unknown localizations as well as near-earth objects (NEOs), both natural and artificial, it is necessary to perform the systematic monitoring of large regions of the sky with high temporal resolution. Here we discuss the criteria for a system that is able to perform such a task and describe two cameras we created for wide-field monitoring with high temporal resolution—FAVOR and TORTORA. Also, we describe basic principles of real-time data processing for the high frame rates needed to achieve subsecond temporal resolution on a typical hardware.

High temporal resolution coordinate-sensitive detector with gallium-arsenide photocathode

We present a coordinate-sensitive detector with a gallium-arsenide photocathode—a vacuum photoelectronic device featuring microchannel gain and a multi-element collector—which had several prototypes manufactured. Quantum efficiency of the photocathode amounts to 48% at maximum, its sensitivity range spans from 350 to 900 nm. The microchannel gain unit consists of two plates with an ion barrier film at the entrance. The coordinates of electron avalanches are determined using a 16-element collector. The spatial resolution, diameter of the working field, and temporal resolution of the detector are equal to 25 µm, 18 mm, and about 1 µs, respectively.

High-temporal resolution multimode photospectropolarimeter

A hardware and software complex of the MANIA experiment designed to search for and study the photometric variability of astrophysical objects with a temporal resolution of 10−6 s is described. The panoramic photospectropolarimeter uses interchangeable optical units, which allow the observations to be performed in four modes—spectroscopic, spectropolarimetric, photometric, and polarimetric. A coordinate—sensitive detector equipped with a set of microchannel plates is capable of recording flux fluctuations from objects and comparison stars simultaneously in different photometric bands and in different polarization planes. The Quantochron 4–48 data acquisition facility operating on line with a computer acquires observational data with a temporal resolution of 1microsecond. The methods of analysis of panoramic data with high temporal resolution are discussed.

Wide-field optical monitoring with Mini-MegaTORTORA (MMT-9) multichannel high temporal resolution telescope

We describe the properties of Mini-MegaTORTORA (MMT-9) nine-channel wide-field optical sky monitoring system with subsecond temporal resolution. This instrument can observe sky areas as large as 900 deg2, perform photometry in three filters close to Johnson BV R system and polarimetry of selected objects or areas with 100–300 deg2 sizes. The limiting magnitude of the system is up to V = 11m for 0.1 s temporal resolution, and reaches V = 15m in minute-long exposures. The system is equipped with a powerful computing facility and dedicated software pipeline allowing it to perform automatic detection, real-time classification, and investigation of transient events of different nature located both in the near- Earth space and at extragalactic distances. The objects routinely detected by MMT-9 include faint meteors and artificial Earth satellites.We discuss astronomical tasks that can be solved using MMT-9, and present the results of the first two years of its operation. In particular, we report the parameters of the optical flare detected on June 25, 2016, which accompanied the gamma-ray burst GRB160625B.

Devices and software for optical panoramic observations with microsecond time resolution

The set of equipment and software of MANIA experiment for search for and study of astrophysical objects variability with time resolution of 1 us is described. Observations are carried out at the Russian 6‐meter telescope by means of universal photospectropolarimeter. This device is equipped with different optical units which implement four observational modes—spectroscopic, spectropolarimetric, photometric, and photopolarimetric. The use of position‐sensitive detector with set of microchannel plates gives possibility to register object photon fluxes in different colour bands and for different orientations of polarizer simultaneously. Acquisition system “Quantochron 4‐48” on line with computer accumulates observational data with time resolution of 1 microsecond. The features of software intended for processing of panoramic data of high time resolution are discussed.

Search for the event horizon by means of optical observations with high temporal resolution

The critical property of the black hole is the presence of the event horizon. It may be detected only by means of the detailed study of the emission features of its surroundings. The temporal resolution of such observations has to be better than ∼ rg/c, and it lies in the 10−6–10 s range depending on the black hole mass. In SAO RAS we have developed the MANIA hardware and software complex based on the panoramic photon counter and use it in observations on 6m telescope for the search and investigation of the optical variability on the time scales of 10−6–103 s of various astronomical objects. We present the hardware and methods used for these photometrical, spectroscopic and polarimetrical observations, the principles and criteria of the object selection. The list of the latter includes objects with featureless optical spectra (DC white dwarfs, blazars) and long microlensing events. We present the results of the observations of two objects-candidates – long MACHO event MACHO-1999-BLG-22 and radio-loud x-ray source with featureless optical spectrum J1942+10 – on the 6-m telescope in June-July 2006.