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G. Beskin

Publications and source records attributed to G. Beskin.

At least 19 recordsLinked to original sources
arXiv2017

Transition from Fireball to Poynting-flux-dominated Outflow in Three-Episode GRB 160625B

The ejecta composition is an open question in gamma-ray bursts (GRB) physics. Some GRBs possess a quasi-thermal spectral component in the time-resolved spectral analysis, suggesting a hot fireball origin. Others show a featureless non-thermal spectrum known as the "Band" function, consistent with a synchrotron radiation origin and suggesting that the jet is Poynting-flux-dominated at the central engine and likely in the emission region as well. There are also bursts showing a sub-dominant thermal component and a dominant synchrotron component suggesting a likely hybrid jet composition. Here we report an extraordinarily bright GRB 160625B, simultaneously observed in gamma-rays and optical wavelengths, whose prompt emission consists of three isolated episodes separated by long quiescent intervals, with the durations of each "sub-burst" being $\sim$ 0.8 s, 35 s, and 212 s, respectively. Its high brightness (with isotropic peak luminosity L$_{\rm p, iso}\sim 4\times 10^{53}$ erg/s) allows us to conduct detailed time-resolved spectral analysis in each episode, from precursor to main burst and to extended emission. The spectral properties of the first two sub-bursts are distinctly different, allowing us to observe the transition from thermal to non-thermal radiation between well-separated emission episodes within a single GRB. Such a transition is a clear indication of the change of jet composition from a fireball to a Poynting-flux-dominated jet.

astro-ph.HE↗
arXiv2017

Discovery of the subsecond linearly polarized spikes of synchrotron origin in the UV Ceti giant optical flare

During our optical monitoring of UV Ceti, iconic late-type flaring star, with high temporal resolution using the Russian 6-m telescope in 2008 we detected a giant flare with the amplitude of about 3 magnitudes in $U$-band. Near flare maximum more than a dozen of spike bursts have been discovered with triangular shapes and durations from 0.6 to 1.2 s and maximal luminosities in the range $(1.5-8)\times10^{27}$ erg~s$^{-1}$. For the half of these events the linear polarization exceeds 35% with significance better than $5σ$. We argue that these events are synchrotron emission of electron streams with the energies of several hundred MeV moving in the magnetic field of about 1.4 kG. Emission from such ultrarelativistic (with energies far exceeding 10 MeV) particles is being routinely observed in solar flares, but has never been detected from UV Ceti type stars. This is the first ever detection of linearly polarized optical light from the UV Ceti-type stars which indicates that at least some fraction of the flaring events on these stars are powered by a non-thermal synchrotron emission mechanism.

astro-ph.SR↗
arXiv2016

Meteor observations with Mini-MegaTORTORA wide-field monitoring system

Here we report on the results of meteor observations with 9-channel Mini-MegaTORTORA (MMT-9) wide-field optical monitoring system with high temporal resolution. During first 1.5 years of operation more than 90 thousands of meteors have been detected, at a rate of 300-350 per night, with durations from 0.1 to 2.5 seconds and angular velocities up to 38 degrees per second. The faintest detected meteors has the peak brightness about 10 mag, while the majority - from 4 to 8 mag. Some of the meteors have been observed in BVR filters simultaneously. Color variations along the trail for them are determined. All parameters of detected meteors are published online. The database also includes the information on 10 thousands meteors detected by our previous FAVOR camera in 2006-2009 years.

astro-ph.EP↗
arXiv2015

On the Atmospheric Extinction Reduction Procedure in Multiband Wide-Field Photometric Surveys

We propose an improved method for the atmospheric extinction reduction within optical photometry. Our method is based on the simultaneous multicolor observations of photometric standards. Such data are now available within the modern wide-field sky surveys and contain a large amount of information about instant atmospheric conditions. So, it became possible to estimate the extinction parameters on the basis of a quite short observational dataset and, hence, to trace the rapid stars twinkling accurately. Having been developed for a new MiniMegaTORTORA observational system, the proposed method can be adopted for a wide range of modern observational programs.

astro-ph.IM↗
arXiv2015

The first light of Mini-MegaTORTORA wide-field monitoring system

Here we describe the first light of the novel 9-channel wide-field optical monitoring system with sub-second temporal resolution, Mini-MegaTORTORA, which is being tested now at Special Astrophysical Observatory on Russian Caucasus. The system is able to observe the sky simultaneously in either wide (~900 square degrees) or narrow (~100 square degrees) fields of view, either in clear light or with any combination of color (Johnson B, V or R) polarimetric filters installed, with exposure times ranging from 100 ms to 100 s. The primary goal of the system is the detection of rapid -- with sub-second characteristic time-scales -- optical transients, but it may be also used for studying the variability of the sky objects on longer time scales.

astro-ph.IM↗
arXiv2011

Monotonic and cyclic components of radio pulsars spin-down

In this article we revise the problem of anomalous values of pulsars' braking indices n_{obs} and frequency second derivatives F2 arising in observations. The intrinsic evolutionary braking is buried deep under superimposed irregular processes, that prevent direct estimations of its parameters for the majority of pulsars. We re-analyze the distribution of "ordinary" radio pulsars on a F2-F1, F2-F0, F1-F0 and n_{obs}-tau_{ch} diagrams assuming their spin-down to be the superposition of a "true" monotonous term and a symmetric oscillatory term. We demonstrate that their effects may be clearly separated using simple ad hoc arguments. Using maximum likelihood estimator we derive the parameters of both components. We find characteristic timescales of such oscillations to be of the order of 1e3-1e4 years, while its amplitudes are large enough to modulate the observed spin-down rate up to 0.5-5 times and completely dominate the second frequency derivatives. On the other hand, pulsars' secular evolution is consistent with classical magnetodipolar model with braking index n ~ 3. So, observed pulsars' characteristic ages (and similar estimators that depend on the observed F1) are also affected by long term cyclic process and differ up to 0.5-5 times from their monotonous values. This fact naturally resolves the discrepancy of characteristic and independently estimated physical ages of several objects, as well as explains very large, up to 1e8 years, characteristic ages of some pulsars. We discuss the possible physical connection of long term oscillation with a complex neutron star rotation relative its magnetic axis due to influence of the near-field part of magnetodipolar torque.

astro-ph.HE↗
arXiv2011

Evidence of Deterministic Components in the Apparent Randomness of GRBs: Clues of a Chaotic Dynamic

Prompt γ-ray emissions from gamma-ray bursts (GRBs) exhibit a vast range of extremely complex temporal structures with a typical variability time-scale significantly short - as fast as milliseconds. This work aims to investigate the apparent randomness of the GRB time profiles making extensive use of nonlinear techniques combining the advanced spectral method of the Singular Spectrum Analysis (SSA) with the classical tools provided by the Chaos Theory. Despite their morphological complexity, we detect evidence of a non stochastic short-term variability during the overall burst duration - seemingly consistent with a chaotic behavior. The phase space portrait of such variability shows the existence of a well-defined strange attractor underlying the erratic prompt emission structures. This scenario can shed new light on the ultra-relativistic processes believed to take place in GRB explosions and usually associated with the birth of a fast-spinning magnetar or accretion of matter onto a newly formed black hole.

astro-ph.HE↗
arXiv2009

Analysis of the Prompt Optical Emission of the Naked-Eye GRB 080319B

We present the observed/intrinsic optical parameters and the variability analysis of the Naked-Eye Burst, GRB 080319B, observed by the TORTORA wide-field optical monitoring system. The event is extreme not only in observed properties but also intrinsically: it is the most luminous event ever recorded at optical wavelengths. The temporal properties suggest short-lived periodic activities of the internal engine. This is the fastest optically variable source detected at cosmological distances.

astro-ph.HE↗
arXiv2009

Fast optical variability of Naked-Eye Burst - manifestation of periodic activity of internal engine

We imaged the position of the Naked-Eye Burst, GRB080319B, before, during and after its gamma-ray activity with sub-second temporal resolution and discovered the fast variability of its prompt optical emission. Its characteristics and similarity with properties of gamma emission temporal structure suggest that it reflects the behaviour of internal engine -- supposedly, a hyperaccreting solar-mass black hole formed in the collapse of a massive stellar core.

astro-ph.HE↗
arXiv2007

Pulse variation of the optical emission of Crab pulsar

The stability of the optical pulse of the Crab pulsar is analyzed based on the 1 $μ$s resolution observations with the Russian 6-meter and William Hershel telescopes equipped with different photon-counting detectors. The search for the variations of the pulse shape along with its arrival time stability is performed. Upper limits on the possible short time scale free precession of the pulsar are placed. The evidence of pulse time of arrival (TOA) variations on 1.5-2 hours time scale is presented, along with evidence of small light curve (shape and separation of main and secondary peaks) changes between data sets, on time scale of years. Also, the fine structure of the main pulse is studied.

astro-ph↗
arXiv2007

Observational appearances of isolated stellar-mass black hole accretion - theory and observations

General properties of accretion onto isolated stellar mass black holes in the Galaxy are discussed. An analysis of plasma internal energy growth during the infall is performed. Adiabatic heating of collisionless accretion flow due to magnetic adiabatic invariant conservation is 25% more efficient than in the standard non-magnetized gas case. It is shown that magnetic field line reconnections in discrete current sheets lead to significant nonthermal electron component formation, which leads to a formation of a hard (UV, X-ray, up to gamma), highly variable spectral component in addition to the standard synchrotron optical component first derived by Shvartsman generated by thermal electrons in the magnetic field of the accretion flow. Properties of accretion flow emission variability are discussed. Observation results of two single black hole candidates - gravitational lens MACHO-1999-BLG-22 and radio-loud x-ray source with featureless optical spectrum J1942+10 - in optical band with high temporal resolution are presented and interpreted in the framework of the proposed model.

astro-ph↗
arXiv2007

GRBs with optical afterglow and known redshift: a statistical study

We present a correlation between two intrinsic parameters of GRB optical afterglows. These are the isotropic luminosity at the maximum of the light curve (Lpeak) and the time-integrated isotropic energy (Eiso) radiated after the observed maximum. We test the correlation between the logarithms of (Eiso) and (Lpeak) and finally we value the effect of the different samples of GRBs in according with the first optical observation reduced to proper time.

astro-ph↗
arXiv2006

On the peculiarities in the rotational frequency evolution of isolated neutron stars

The measurements of pulsar frequency second derivatives have shown that they are $10^2-10^6$ times larger than expected for standard pulsar spin-down law, and are even negative for about half of pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters $ν$, $\dot ν$ and $\ddot ν$ of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between $\ddot ν$ and $\dot ν$ for both $\ddotν> 0$ and $\ddotν< 0$, as well as between $ν$ and $\dotν$. We interpret these dependencies as evolutionary ones due to $\dotν$ being nearly proportional to the pulsars' age. The derived statistical relations as well as "anomalous" values of $\ddotν$ are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore, consists of secular change of $ν_{ev}(t)$, $\dotν_{ev}(t)$ and $\ddotν_{ev}(t)$ according to the power law with $n \approx 5$, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that timespan -- several tens of years.

astro-ph↗
arXiv2006

Search for optical activity of SGR 1806-20

The region of SGR 1806-20 localization was observed during its gamma-ray activity in 2001. The observations have been performed on the 6-meter telescope of the Special Astrophysical Observatory, using the Panoramic Photometer-Polarimeter (PPP). The search for variability was performed on the $10^{-6}$ - 10 s time scale, and its results were compared to the properties of corresponding x-ray flares.

astro-ph↗
arXiv2006

Short time scale pulse stability of the Crab pulsar in the optical band

The fine structure and the variations of the optical pulse shape and phase of the Crab pulsar are studied on various time scales. The observations have been carried out on 4-m William Hershel and 6-m BTA telescopes with APD photon counter, photomultiplier based 4-channel photometer and PSD based panoramic spectrophotopolarimeter with 1$μ$s time resolution in 1994, 1999, 2003 and 2005-2006 years. The upper limit on the pulsar precession on Dec 2, 1999 is placed in the 10 s - 2 hours time range. The evidence of a varying from set to set fine structure of the main pulse is found in the 1999 and 2003 years data. No such fine structure is detected in the integral pulse shape of 1994, 1999 and 2003 years. The drastic change of the pulse shape in the 2005-2006 years set is detected along with the pulse shape variability and quasi-periodic phase shifts.

astro-ph↗
arXiv2006

Cyclic evolution of radio pulsars on the time scale of hundreds of years

The recent massive measurements of pulsar frequency second derivatives have shown that they are 100-1000 times larger than expected for standard pulsar slowdown low. Moreover, the second derivatives as well as braking indices are even negative for about half of pulsars. We explain these paradoxical results on the basis of the statistical analysis of the rotational parameters $ν$, $\dot ν$ and $\ddot ν$ of the subset of 295 pulsars taken mostly from the ATNF database. We have found strong correlation of $\ddot ν$ and $\dot ν$ either for $\ddotν> 0$ (correlation coefficient $r\approx0.9$) and $\ddotν< 0$ ($r\approx0.85$), and of $ν$ and $\dotν$ ($r\approx0.7$). We interpret these dependencies as evolutionary ones due to $\dotν$ being nearly proportional to characteristic age $τ_{ch}$. The derived statistical relations as well as "anomalous" values of $\ddotν$ are well explained in the framework of the simple model of cyclic evolution of the rotational frequency of the pulsars. It combines the secular change of $ν_{tr}(t)$, $\dotν_{tr}(t)$ and $\ddotν_{tr}(t)$ according to the power law with $n\approx5$ and harmonic oscillations of 100--1000 years period with an amplitude from $10^{-3}$ Hz for young pulsars to $10^{-10}$ Hz for elder ones. The physical nature of these cyclic variations of the rotational frequency may be similar to the well-known red timing noise, however, with much larger characteristic time scale.

astro-ph↗