V. Kornilov

Prompt, early, and afterglow optical observations of five gamma-ray bursts (GRBs 100901A, 100902A, 100905A, 100906A, and 101020A)

We present results of the prompt, early, and afterglow optical observations of five gamma-ray bursts, GRBs 100901A, 100902A, 100905A, 100906A, and 101020A, made with the Mobile Astronomical System of TElescope-Robots in Russia (MASTER-II net), the 1.5-m telescope of Sierra-Nevada Observatory, and the 2.56-m Nordic Optical Telescope. For two sources, GRB 100901A and GRB 100906A, we detected optical counterparts and obtained light curves starting before cessation of gamma-ray emission, at 113 s and 48 s after the trigger, respectively. Observations of GRB 100906A were conducted with two polarizing filters. Observations of the other three bursts gave the upper limits on the optical flux; their properties are briefly discussed. More detailed analysis of GRB 100901A and GRB 100906A supplemented by Swift data provides the following results and indicates different origins of the prompt optical radiation in the two bursts. The light curves patterns and spectral distributions suggest a common production site of the prompt optical and high-energy emission in GRB 100901A. Results of spectral fits for GRB 100901A in the range from the optical to X-rays favor power-law energy distributions with similar values of the optical extinction in the host galaxy. GRB 100906A produced a smoothly peaking optical light curve suggesting that the prompt optical radiation in this GRB originated in a front shock. This is supported by a spectral analysis. We have found that the Amati and Ghirlanda relations are satisfied for GRB 100906A. An upper limit on the value of the optical extinction on the host of GRB 100906A is obtained.

Significant and variable linear polarization during the prompt optical flash of GRB 160625B

Newly formed black holes of stellar mass launch collimated outflows (jets) of ionized matter that approach the speed of light. These outflows power prompt, brief and intense flashes of γ-rays known as γ-ray bursts (GRBs), followed by longer-lived afterglow radiation that is detected across the electromagnetic spectrum. Measuring the polarization of the observed GRB radiation provides a direct probe of the magnetic fields in the collimated jets. Rapid-response polarimetric observations of newly discovered bursts have probed the initial afterglow phase, and show that, minutes after the prompt emission has ended, the degree of linear polarization can be as high as 30 per cent—consistent with the idea that a stable, globally ordered magnetic field permeates the jet at large distances from the central source. By contrast, optical and γ-ray observations during the prompt phase have led to discordant and often controversial results, and no definitive conclusions have been reached regarding the origin of the prompt radiation or the configuration of the magnetic field. Here we report the detection of substantial (8.3 ± 0.8 per cent from our most conservative simulation), variable linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt γ-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the jet, closer to its central black hole, and show that the prompt phase is produced via fast-cooling synchrotron radiation in a large-scale magnetic field that is advected from the black hole and distorted by dissipation processes within the jet.

MASTER Optical Detection of the First LIGO/Virgo Neutron Star Binary Merger GW170817

Following the discovery of the gravitational-wave source GW170817 by three Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo antennae (Abbott et al., 2017a), the MASTER Global Robotic Net telescopes obtained the first image of the NGC 4993 host galaxy. An optical transient, MASTER OTJ130948.10-232253.3/SSS17a was later found, which appears to be a kilonova resulting from the merger of two neutron stars (NSs). Here we describe this independent detection and photometry of the kilonova made in white light, and in B, V, and R filters. We note that the luminosity of this kilonova in NGC 4993 is very close to those measured for other kilonovae possibly associated with gamma-ray burst (GRB) 130603 and GRB 080503.

MASTER OPTICAL POLARIZATION VARIABILITY DETECTION IN THE MICROQUASAR V404 CYG/GS 2023+33

On 2015 June 15 the Swift space observatory discovered that the Galactic black hole candidate V404 Cyg was undergoing another active X-ray phase, after 25 years of inactivity (Barthelmy et al. 2015). Twelve telescopes of the MASTER Global Robotic Net located at six sites across four continents were the first ground based observatories to start optical monitoring of the microquasar after its gamma-ray wakeup at 18h 34m 09s U.T. on 2015 June 15 (Lipunov et al. 2015). In this paper we report, for the first time, the discovery of variable optical linear polarization, changing by 4-6% over a timescale of approximately 1 h, on two different epochs. We can conclude that the additional variable polarization arisies from the relativistic jet generated by the black hole in V404Cyg. The polarization variability correlates with optical brightness changes, increasing when the flux decreases.

Angular correlation of the stellar scintillation for large telescopes

The stellar scintillation is one of the fundamental limitation to the precision of groundbased photometry. The paper examines the problem of correlation of the scintillation of two close stars at the focus of a large telescope. The derived correlation functions were applied to data of the long-term study of the optical turbulence (OT) in the Northern Caucasus with MASS (Multi-Aperture Scintillation Sensor) instrument to predict the angular correlation of the scintillation at the Sternberg institute 2.5 m telescope currently in construction. A median angular radius of the correlation as large as 20 arcsec was found for the case of Kolmogorov OT. On the basis of the obtained relations we also analyze the correlation impact in ensemble photometry and conjugate plane photometry. It is shown that a reduction of the scintillation noise up to 8 times can be achieved when using a crowded ensemble of comparison stars. The calculation of the angular correlation can be repeated for any large telescope at the site where the OT vertical profiles are known.

Comparison of the scintillation noise above different observatories measured with MASS instruments

Aims. Scintillation noise is a major limitation of ground-based photometric precision. Methods. An extensive dataset of stellar scintillation collected at 11 astronomical sites world-wide with MASS instruments was used to estimate the scintillation noise of large telescopes in the fast photometry and traditional long-exposure regime. Results. Statistical distributions of the corresponding parameters are given. The scintillation noise is mostly determined by turbulence and wind in the upper atmosphere and is comparable at all sites, with slightly lower values at Mauna Kea and the highest noise at Tolonchar in Chile. We show that the classical Young’s formula underestimates the scintillation noise. The temporal variations of the scintillation noise are also similar at all sites, showing short-term variability at time scales of 1 − 2 h and slower variations, including marked seasonal trends (stronger scintillation and less clear sky during local winter). Some correlation was found between nearby observatories.

A statistical description of the non-linearity of photon counts

A new description of the registration of events by a counter with a dead time based on a nonclassical, quasi-binomial distribution is proposed. A description of the type of dead time via the continuous parameter y is introduced. It is shown based on this approach that the distribution of events registered by an non-extendable counter (y = 1) can be described by a generalized Poisson distribution. It is shown for various types of counters that the distribution of registered events will be indistinguishable from a generalized Poisson distribution if the number of measurements is ≲ 106. Formulas that can be used to determine the initial flux of events from the detected flux and vice versa are derived. The behavior of the non-Poisson coefficient as a function of the non-linearity is discussed. All the analytical results obtained are tested using numerical simulations.

Project “Universat-SOCRAT” of Multiple Small Satellites for Monitoring of Natural and Technogenic Space Hazards

Abstract The new space project of M. V. Lomonosov Moscow State University on elaboration of multiple satellites for real time monitoring in the near-Earth space of radiation environment, natural (asteroids, meteoroids) and artificial (space debris) potentially dangerous objects, electromagnetic transients, such as cosmic gamma ray bursts, terrestrial gamma ray flashes, optical and ultraviolet bursts in the Earth atmosphere is presented. It is intended to install on the satellites the following instruments for space monitoring of dangerous objects and hazards: spectrometers of electrons and protons, complex of instruments for study of transient electromagnetic phenomena including gamma ray spectrometer, detectors of ultraviolet and optical emission and wide-field optical cameras. Successful implementation of the project for the first time in the world allows realization of a space system prototype for monitoring and preventing of space hazards for both ongoing and planned space missions, and also for aircraft flying in the upper atmosphere. There are also discussed results of experiments on-board Lomonosov in view of good experience of wide field camera use for monitor observations in space. These results formed the base of scientific program for the new project Universat- SOCRAT.

Observations of Near-Earth Optical Transients with the Lomonosov Space Observatory

The results of observations with the MASTER-SHOK robotic wide-field optical cameras onboard the Lomonosov Space Observatory carried out in 2016 are presented. In all, the automated transient detection system transmitted 22 181 images of moving objects with signal-to-noise ratios greater than 5 to the Earth. Approximately 84% of these images are identified with well-known artificial Earth satellites (including repeated images of the same satellite) and fragments of such satellites (space debris), according to databases of known satellites. The remaining 16% of the images are relate to uncatalogued objects. This first experience in optical space-based monitoring of near-Earth space demonstrates the high efficiency and great potential of using large-aperture cameras in space, based on the software and technology of the MASTER robotic optical complexes (the Mobile Astronomical System of TElescope- Robots (MASTER) global network of robotic telescopes of Lomonosov Moscow State University).

Comparison cosmic ray irradiation simulation and particle beam test on UFFO Burst Alert & Trigger telescope(UBAT) detectors

Ultra-Fast Flash Observatory pathfinder(UFFO-p) was launched onboard Lomonosov on 28th of April, 2016, and now is under various types of calibration for detection of Gamma Ray Bursts (GRBs). Since last September UFFO-p has taken X-ray data in space with UFFO Burst Alert & Trigger telescope (UBAT), those X-rays are mostly diffused backgrounds however, the rate turns out to be higher than expected by a factor of three. We assumed cosmic rays can contribute by making the count rate higher. We did such a simulation to investigate the effect of cosmic rays. In December 2016, we irradiated fragmented high energy heavy ions at CERN on the UBAT detector. We will report the result of comparison between simulation and beam test.