Search

We report the discovery of a bright pulse having a dispersion measure (DM) equal to 134.4 \pm 2 pc cm^{-3}, a peak flux density (S_p) equal to 20 \pm 4 Jy and a half-width (W_e) equal to 211 \pm 6 ms. The excessive DM of the pulse, after taking into account the Milky Way contribution, is 114 pc cm^{-3} that indicates its extragalactic origin. Such value of DM corresponds to the luminosity distance 713 Mpc. The above parameters make the pulse to be a reliable candidate to the fast radio burst (FRB) event, and then it is the second FRB detected at such a large \lambda \sim 2.7 m wavelength and the first one among non-repeating FRBs. The normalized luminosity L_\nu of the event, which we have designated as FRB 20190203, estimated under assumption that the whole excessive DM is determined by the intergalactic environment toward the host galaxy, is equal to \simeq 10^{34} erg s^{-1} Hz{-1}. In addition to the study of radio data we analyzed data from the quasi-simultaneous observations of the sky in the high energy (\ge 80 keV) band by the omnidirectional detector SPI/ACS aboard the INTEGRAL orbital observatory (in order to look for a possible gamma-ray counterpart of FRB 20190203). We did not detect any transient events exceeding the background at a statistically significant level. In the INTEGRAL archive, the FRB 20190203 localization region has been observed many times with a total exposure of \sim 73.2 days. We have analyzed the data but were unable to find any reliable short gamma-ray bursts from the FRB 20190203 position. Finally we note that the observed properties of FRB 20190203 can be reproduced well in the framework of a maser synchrotron model operating in the far reverse shock (at a distance of \sim 10^{15} cm) of a magnetar. However, triggering the burst requires a high conversion efficiency (at the level of 1%) of the shock wave energy into the radio emission., Comment: submitted to PASA, 11 pages, 7 figures

We present the largest optical photometry compilation of Gamma-Ray Bursts (GRBs) with redshifts ($z$). We include 64813 observations of 535 events (including upper limits) from 28 February 1997 up to 18 August 2023. We also present a user-friendly web tool \textit{grbLC} which allows users the visualization of photometry, coordinates, redshift, host galaxy extinction, and spectral indices for each event in our database. Furthermore, we have added a Gamma Ray Coordinate Network (GCN) scraper that can be used to collect data by gathering magnitudes from the GCNs. The web tool also includes a package for uniformly investigating colour evolution. We compute the optical spectral indices for 138 GRBs for which we have at least 4 filters at the same epoch in our sample and craft a procedure to distinguish between GRBs with and without colour evolution. By providing a uniform format and repository for the optical catalogue, this web-based archive is the first step towards unifying several community efforts to gather the photometric information for all GRBs with known redshifts. This catalogue will enable population studies by providing light curves (LCs) with better coverage since we have gathered data from different ground-based locations. Consequently, these LCs can be used to train future LC reconstructions for an extended inference of the redshift. The data gathering also allows us to fill some of the orbital gaps from Swift in crucial points of the LCs, e.g., at the end of the plateau emission or where a jet break is identified., Comment: 20 pages, 16 figures, 2 tables. Submitted to MNRAS, this version matches the third revision. The Online Materials and data will be available after the publication

The results of a study of the short gamma-ray burst GRB 231115A in the X-ray and gamma-ray ranges are presented, based on data from the INTEGRAL and Fermi space observatories. The source of the burst is localized by the IBIS/ISGRI telescope of INTEGRAL observatory with an accuracy of $\leq$ 1.5 arcmin, it is located in the Cigar Galaxy (M 82). Early follow-up observations of the burst localization region were carried out in the optical range with the 36-cm telescope of the ISON-Kitab observatory and the 70-cm telescope AS-32 of the Abastumani Astrophysical Observatory, the optical emission has not been detected. The proximity of the host galaxy ($D_L \simeq 3.5$ Mpc) significantly limits energetics of the event ($E_{iso}\ \sim\ 10^{45}$ erg) and allows us to interpret the burst as a giant flare of a previously unknown soft gamma repeater (SGR) which is an extreme manifestation of the activity of a highly magnetized neutron star (magnetar). This conclusion is confirmed by the energy spectrum atypically hard for cosmological gamma-ray bursts, as well as the absence of optical afterglow and gravitational wave signal, which should have been detected in the LIGO/Virgo/KAGRA experiments if the burst was caused by a merger of binary neutron stars. The location of the burst in the $E_{p,i}$ -- $E_{iso}$ and $T_{90,i}$ -- $EH$ diagrams also suggests that GRB 231115A was a magnetar giant flare. This is the first well-localized giant flare of an extragalactic SGR., Comment: 21 pages, 14 figures, accepted to Astronomy Letters at 2023 November 21

We present full photometric coverage and spectroscopic data for soft GRB 201015A with a redshift z = 0.426. Our data spans a time range of 85 days following the detection of GRB. These observations revealed an underlying supernova SN 201015A with a maximum at $8.54 \pm $1.48 days (rest frame) and an optical peak absolute magnitude $-19.45_{-0.47}^{+0.85}$ mag. The supernova stands out clearly, since the contribution of the afterglow at this time is not dominant, which made it possible to determine SN's parameters. A comparison of these parameters reveals that the SN 201015A is the earliest (the minimum $T_{max}$) known supernova associated with gamma-ray bursts. Spectroscopic observations during the supernova decay stage showed broad lines, indicating a large photospheric velocity, and identified this supernova as a type Ic-BL. Thus, the SN 201015A associated with the GRB 201015A becomes the 27th SN/GRB confirmed by both photometric and spectroscopic observations. Using the results of spectral analysis based on the available data of Fermi-GBM experiment, the parameters $E_\text{p,i} = 20.0 \pm 8.5$ keV and $E_\text{iso} = (1.1 \pm 0.2) \times 10^{50}$ erg were obtained. According to the position of the burst on the $E_\text{p,i}$-$E_\text{iso}$ correlation, GRB 201015A was classified as a Type II (long) gamma-ray burst, which was also confirmed by the $T_\text{90,i}$-$EH$ diagram., Comment: 15 pages, 10 figures

We have carried out a systematic analysis of the gamma-ray bursts' (GRBs) light curves detected in the SPI-ACS experiment onboard the INTEGRAL observatory aimed to search extended emission. The emission occasionally recorded after the prompt active phase of a GRB in the form of an emission that is longer than the active phase and less intense is called the extended one. Out of the 739 brightest GRBs recorded from 2002 to 2017, extended emission has been detected in $\sim20\%$ of the individual light curves; its maximum duration reaches $\sim 10000$ s. Two different types of extended emission have been revealed. One of them is an additional component of the light curve and is described by a power law (PL) with an index $\alpha \sim -1$ close to the PL index of the afterglow in the optical and X-ray bands. The second type can be described by a steeper PL decay of the light curve typical of the active burst phase. Extended emission has also been found in the combined light curve of long GRBs in the individual curves of which no extended emission has been detected. The PL index of the extended emission in the combined light curve is $\alpha \sim -2.4$. It is most likely associated with the superposition of light curves at the active phase; its total duration is $\sim 800$ s.

SPI-ACS/INTEGRAL is one of the most sensitive orbital gamma-ray detectors in energy range above 80 keV. Since 2002 it registered several thousands of gamma-ray bursts, including the bursts associated with LIGO-Virgo gravitational wave events GW 170817 and GW 190425. No dedicated in-flight calibrations were performed for SPI-ACS/INTEGRAL, complicating estimation of spectral and energetic characteristics of an event. Using data of GBM/Fermi we perform cross-calibration of SPI-ACS/INTEGRAL, based on 1032 bright GRBs registered by both experiments. We find the conversion factor between instrumental counts from SPI-ACS and energy units from GBM to be dependent on hardness of GRB spectrum (defined as the characteristic energy value, $E_{p}$) and on location of a source in spacecraft based coordinate system. We determine the corresponding analytical model to calculate the conversion factor and estimate its accuracy empirically. Sensitivity of SPI-ACS/INTEGRAL to detect gamma-ray transients is also investigated. Using the calibration we re-estimate energetics of GRB/GW 190425, detected by SPI-ACS/INTEGRAL alone. We constrain possible range of the characteristic energy $E_{p}$ and isotropic equivalent of total energy, emitted in gamma-rays $E_{iso}$ for GRB 190425, using the $ E_{p,i} $ -- $ E_{iso} $ (Amati) correlation. The calibration model could be applied to any transients with energy spectrum, analogous to gamma-ray bursts., Comment: 11 pages, 11 figures, Accepted to MNRAS 2023 August 3, in original form 2023 June 23

We present the results of our analysis of multiwavelength observations for the long gamma-ray burst GRB 200829A. The burst redshift $z \approx 1.29 \pm 0.04$ has been determined photometrically at the afterglow phase. In gamma rays the event is one of the brightest (in isotropic equivalent), $E_{iso} \gtrsim 10^{54}$ erg. The multicolor light curve of the GRB 200829A afterglow is characterized by chromatic behavior and the presence of a plateau gradually transitioning into a power-law decay that can also be interpreted as a quasi-synchronous inhomogeneity (flare). We assume that the presence of a chromatic inhomogeneity in the early afterglow is consistent with the model of a structured jet., Comment: 18 pages, 14 figures

The RELEC scientific instrumentation onboard the Vernov spacecraft launched on July 8, 2014, included the DRGE gamma-ray and electron spectrometer. This instrument incorporates a set of scintillation phoswich detectors, including four identical X-ray and gamma-ray detectors in the energy range from 10 keV to 3 MeV with a total area of $\sim$500 $cm^{2}$ directed toward the nadir, and an electron spectrometer containing three mutually orthogonal detector units with a geometry factor of $\sim$2 $cm^{2} sr$, which is also sensitive to X-rays and gamma-rays. The goal of the space experiment with the DRGE instrument was to investigate phenomena with fast temporal variability, in particular, terrestrial gamma-ray flashes (TGFs) and magnetospheric electron precipitations. However, the detectors of the DRGE instrument could record cosmic gamma-ray bursts (GRBs) and allowed one not only to perform a detailed analysis of the gamma-ray variability but also to compare the time profiles with the measurements made by other instruments of the RELEC scientific instrumentation (the detectors of optical and ultraviolet flashes, the radio-frequency and low-frequency analyzers of electromagnetic field parameters). We present the results of our observations of cosmic GRB 141011A and GRB 141104A, compare the parameters obtained in the GBM/Fermi and KONUSWind experiments, and estimate the redshifts and Eiso for the sources of these GRBs. The detectability of GRBs and good agreement between the independent estimates of their parameters obtained in various experiments are an important factor of the successful operation of similar detectors onboard the Lomonosov spacecraft., Comment: 19 pages, 8 figures

Multi-pulsed GRB 190530A, detected by the GBM and LAT onboard \fermi, is the sixth most fluent GBM burst detected so far. This paper presents the timing, spectral, and polarimetric analysis of the prompt emission observed using \AstroSat and \fermi to provide insight into the prompt emission radiation mechanisms. The time-integrated spectrum shows conclusive proof of two breaks due to peak energy and a second lower energy break. Time-integrated (55.43 $\pm$ 21.30 \%) as well as time-resolved polarization measurements, made by the Cadmium Zinc Telluride Imager (CZTI) onboard \AstroSat, show a hint of high degree of polarization. The presence of a hint of high degree of polarization and the values of low energy spectral index ($\alpha_{\rm pt}$) do not run over the synchrotron limit for the first two pulses, supporting the synchrotron origin in an ordered magnetic field. However, during the third pulse, $\alpha_{\rm pt}$ exceeds the synchrotron line of death in few bins, and a thermal signature along with the synchrotron component in the time-resolved spectra is observed. Furthermore, we also report the earliest optical observations constraining afterglow polarization using the MASTER (P $<$ 1.3 \%) and the redshift measurement ($z$= 0.9386) obtained with the 10.4m GTC telescopes. The broadband afterglow can be described with a forward shock model for an ISM-like medium with a wide jet opening angle. We determine a circumburst density of $n_{0} \sim$ 7.41, kinetic energy $E_{\rm K} \sim$ 7.24 $\times 10^{54}$ erg, and radiated $\gamma$-ray energy $E_{\rm \gamma, iso} \sim$ 6.05 $\times 10^{54}$ erg, respectively., Comment: 28 pages, 17 figures, accepted for publication in MNRAS

Gamma-ray bursts (GRBs) are classified as long and short events. Long GRBs (LGRBs) are associated with the end states of very massive stars, while short GRBs (SGRBs) are linked to the merger of compact objects. GRB 200826A was a peculiar event, because by definition it was a SGRB, with a rest-frame duration of ~ 0.5 s. However, this event was energetic and soft, which is consistent with LGRBs. The relatively low redshift (z = 0.7486) motivated a comprehensive, multi-wavelength follow-up campaign to characterize its host, search for a possible associated supernova (SN), and thus understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) and optical imaging together with spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution is in agreement with several LGRB-SNe. Analysis of the prompt GRB shows that this event follows the $E_{\rm p,i}-E_{\rm iso}$ relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical for LGRBs, but with one of the highest star-formation rates (SFR), especially with respect to its mass ($\log M_\ast/M_\odot = 8.6$, SFR $\sim 4.0 \,M_\odot$/yr). We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs. These findings support theoretical predictions that events produced by collapsars can be as short as 0.5 s in the host frame and further confirm that duration alone is not an efficient discriminator for the progenitor class of a GRB., Comment: 19 pages, 11 figures, 2 tables. Accepted for publication in ApJ

This paper is based on a proposal submitted for a BRICS astronomy flagship program, which was presented at the 2019 meeting of the BRICS Astronomy Working Group, held in Rio de Janeiro from 29 September to 2 October 2019. The future prospects for the detection and study of transient phenomena in the Universe heralds a new era in time domain astronomy. The case is presented for a dedicated BRICS-wide flagship program to develop a network of ground-based optical telescopes for an all-sky survey to detect short lived optical transients and to allow follow-up of multi-wavelength and multi-messenger transient objects. This will leverage existing and planned new facilities within the BRICS countries and will also draw on the opportunities presented by other multi-wavelength space- and ground-based facilities that exist within the BRICS group. The proposed optical network would initially perform followup observations on new transients using existing telescopes. This would later expand to include a new global network of $\sim$70 wide-field 1-m telescopes which will cover the entire sky, simultaneously, with a cadence of less than a few hours. This realization would represent a ground-breaking and unique global capability, presenting many scientific opportunities and associated spin-off benefits to all BRICS countries., Comment: 39 pages, 5 figures. Accepted for publication in the Journal "Annals of the Brazilian Academy of Sciences" as part of the Proceedings for the BRICS Astronomy Workshop - BAWG 2019 -, held in Rio de Janeiro, 29 Sep - 2 Oct 2019

A detailed analysis of the GBM/Fermi experiment data is carried out to classify GRB 200415A. It is shown that, on the one hand, this event exhibits typical for type I (short) gamma-ray bursts (GRBs) properties, such as duration, variability, and the character of spectral evolution (lag). On the other hand, the localization of the event source on the celestial plane, obtained by the triangulation method (IPN), indicates the nearby ($ D_L $ = 3.5 Mpc) galaxy NGC 253 (Sculptor) as a possible host galaxy for this burst. It introduces significant restrictions on the energetics of the event ($ E_{iso} $ $ \sim $ $ 10^{46} $ erg) and gives an alternative interpretation of GRB 200415A as a giant flare (GF) of a soft gamma repeater (SGR). This interpretation is supported by the atypically hard energy spectrum. In addition, according to the position of the burst on the $ E_{p, i} $ -- $ E_{iso} $ (the position of the maximum in the energy spectrum $ \nu F_{\nu} $ in the source frame depending on the isotropic equivalent of the total energy, emitted in gamma rays) and $ T_{90, i} $ -- $ EH $ (duration in the source frame depending on the combination of parameters $ EH = E_{p,i,2} ~ E_{iso,51}^{ ~ -0.4} $) diagrams, GRB 200415A is unambiguously classified as a giant flare of a magnetar, assuming its association with the galaxy NGC 253. In these diagrams, known giant flares in the Galaxy and candidates for giant flares in nearby galaxies form a well-defined group, which includes the GRB 200415A., Comment: 22 pages, 7 figures, Accepted for publication in Astronomy Letters

We present very early ground-based optical follow-up observations of GRB~140423A, which was discovered by \emph{Swift}/BAT and by {\it Fermi}/GBM. Its broadband afterglow was monitored by {\it Swift}/XRT and ground-based optical telescopes from $T_0+$70.96~s to 4.8~d after the {\it Swift}/BAT trigger. This is one more case of prompt optical emission observation. The temporal and spectral joint fit of the multiwavelength light curves of GRB 140423A reveals that achromatic behavior is consistent with the external shock model including a transition from a stellar wind to the interstellar medium (ISM) and energy injection. In terms of the optical light curves, there is an onset bump in the early afterglow with a rising index $\alpha_{\rm O,I} = -0.59 \pm 0.04$ (peaking at $t_{\rm peak}-T_0 \approx 206$~s). It then decays with a steep index $\alpha_{\rm O,II} = 1.78 \pm 0.03$, and shows a steeper to flatter "transition" with $\alpha_{\rm O,III} = 1.13 \pm 0.03$ at around $T_0 + 5000$~s. The observed X-ray afterglow reflects an achromatic behavior, as does the optical light curve. There is no obvious evolution of the spectral energy distribution between the X-ray and optical afterglow, with an average value of the photon index $\Gamma \approx 1.95$. This "transition" is consistent with an external shock model having the circumburst medium transition from a wind to the ISM, by introducing a long-lasting energy injection with a Lorentz factor stratification of the ejecta. The best parameters from Monte Carlo Markov Chain fitting are $E_{\rm K,iso} \approx 2.14\times10^{55}$ erg, $\Gamma_0 \approx 162$, $\epsilon_e \approx 0.02$, $\epsilon_B \approx 1.7\times10^{-6}$, $A_\ast \approx 1.0$, $R_t \approx 4.1\times10^{17}$ cm, $n \approx 11.0 \rm\ cm^{-3}$, $L_0 \approx 3.1\times10^{52} \rm\ erg\ s^{-1}$, $k \approx 1.98$, $s \approx 1.54$, and $\theta_j > 0.3$ rad., Comment: 30 pages, 6 fiures; Accepted for publication in ApJ

A systematic search for cosmic gamma-ray bursts (GRBs) and other short hard X-ray events in the archival data from the IBIS/ISGRI telescope of the INTEGRAL observatory over 2003-2018 has been carried out. Seven previously unknown GRBs have been recorded in the telescope field of view; all of them have been localized with an accuracy < 2 arcmin. These events were not revealed by the INTEGRAL burst alert system (IBAS) designed for an automatic GRB search and alert. Four more such localized events missed by IBAS, but known previously, i.e., observed in other experiments, have been found. Eight hundred and eighty six GRBs outside the field of view that arrived at large angles to the IBIS/ISGRI axis have also been recorded. All of them were previously recorded in other experiments, primarily by the anticoincidence shield (ACS) of the SPI gamma-ray spectrometer onboard INTEGRAL, the PICsIT detector of the IBIS gamma-ray telescope, and the KONUS/WIND monitor. An order of magnitude more events without any confirmations in other experiments have been recorded. Both GRBs and solar flares or magnetospheric transient events can be among them. Catalogs with the basic parameters of confirmed and previously unknown GRBs recorded by IBIS/ISGRI have been compiled. The statistical distributions of bursts in various parameters have been constructed and investigated., Comment: 19 pages, 12 figures, 4 tables

Observations of the gravitational-wave (GW) event S190425z registered by the LIGO/Virgo detectors with the Anti-Coincidence Shield (ACS) of the gamma-ray spectrometer SPI aboard the INTEGRAL observatory are presented. With a high probability (>99%) it was associated with a neutron star (NS) merger in a close binary system. This is only the second event of such type in the history of GW observations (after GW170817). A weak gamma-ray burst, GRB190425, consisting of two pulses in ~0.5 and ~5.9 s after the NS merging in S190425z was detected by SPI-ACS. The pulses had a priori reliability of 3.5 and 4.4 sigma as single events and 5.5 sigma as a combined event. Analysis of the SPI-ACS count rate history recorded these days (~125 ks in total) has shown that the rate of appearance of two close pulses with characteristics of GRB190425 by chance does not exceed 6.4 x 10^{-5} s^{-1}. We note that the time profile of GRB190425 has a lot in common with the profile of the GRB170817A burst accompanying the GW170817 event; that both the NS mergers were the closest (<150 Mpc) of all the events registered by the LIGO/Virgo detectors; and that there were no confident excesses of gamma-ray emission over the background detected in any of >30 black hole merger events recorded to the moment by these detectors. No hard X-ray flares were detected in the field of view of the SPI and IBIS-ISGRI gamma-ray telescopes aboard INTEGRAL. This, as well as the lack of detection of gamma-ray emission from GRB190425 by the GBM monitor of the Fermi observatory assuming its occultation by the Earth, can significantly reduce the localization area for the source of this GW event. The estimates of the parameters E_{iso} and E_{p} for GRB190425 are obtained and compared with the similar parameters for GRB170817A., Comment: 16 pages, 7 figures, 2 tables

We present the most extensive sample of 45 type I (short) and 275 type II (long) gamma-ray bursts (GRB) with known redshift to investigate the correlation between the rest frame peak energy, Ep,i and the total isotropic equivalent energy, Eiso of the prompt emission (Amati relation). The Ep,i - Eiso correlation for type I bursts is found to be well-distinguished from the one constructed for type II bursts and has a similar power-law index value, a = 0.4, which possibly indicates the same emission mechanism of both GRB types. We show that the initial pulse complex (IPC) of type I bursts with an extended emission and regular type I bursts follow the same correlation. We obtain similar results for type II bursts associated with Ic supernovae and for regular type II bursts. Three possible outliers from the Ep,i - Eiso correlation for type II subsample are detected. Significant evolution of the Ep,i - Eiso correlation with redshift for type II bursts is not found. We suggest the new classification method, based on the Ep,i - Eiso correlation and introduce two parameters, EH and EHD. EHD is found to be the most reliable parameter for the blind type I - type II classification, which can be used to classify GRBs with no redshift., Comment: 20 pages, 6 figures, Accepted to MNRAS 2019 December 18, in original form 2019 October 24

We propose a new method to detect gravitational waves, based on spatial coherence interferometry with stellar light, as opposed to the conventional temporal coherence interferometry with laser sources. The proposed method detects gravitational waves by using two coherent beams of light from a single distant star measured at separate space-based detectors with a long baseline. This method can be applied to either the amplitude or intensity interferometry. This experiment allows for the search of gravitational waves in the lower frequency range of $10^{-6}$ to $10^{-4}$ Hz. In this work, we present the detection sensitivity of the proposed stellar interferometer by taking the detector response and shot and acceleration noises into account. Furthermore, the proposed experimental setup is capable of searching for primordial black holes and studying the size of the target neutron star, which are also discussed in the paper., Comment: 12 pages, 7 figures

We investigate the prompt emission and the afterglow properties of short duration gamma-ray burst (sGRB) 130603B and another eight sGRB events during 2012-2015, observed by several multi-wavelength facilities including the GTC 10.4m telescope. Prompt emission high energy data of the events were obtained by INTEGRAL/SPI/ACS, Swift/BAT and Fermi/GBM satellites. The prompt emission data by INTEGRAL in the energy range of 0.1-10 MeV for sGRB 130603B, sGRB 140606A, sGRB 140930B, sGRB 141212A and sGRB 151228A do not show any signature of the extended emission or precursor activity and their spectral and temporal properties are similar to those seen in case of other short bursts. For sGRB130603B, our new afterglow photometric data constraints the pre jet-break temporal decay due to denser temporal coverage. For sGRB 130603B, the afterglow light curve, containing both our new as well as previously published photometric data is broadly consistent with the ISM afterglow model. Modeling of the host galaxies of sGRB 130603B and sGRB 141212A using the LePHARE software supports a scenario in which the environment of the burst is undergoing moderate star formation activity. From the inclusion of our late-time data for 8 other sGRBs we are able to; place tight constraints on the non-detection of the afterglow, host galaxy or any underlying kilonova emission. Our late-time afterglow observations of the sGRB 170817A/GW170817 are also discussed and compared with the sub-set of sGRBs., Comment: 24 pages, 22 figures, Accepted to MNRAS, 2019 February 19. Received 2019 February 19; in original form 2018 August 30

We discuss the inhomogeneous behavior of gamma-ray burst afterglow light curves in optic. We use well-sampled light curves based on mostly our own observations to find and identify deviations (inhomogeneities) from broken power law. By the inhomogeneous behavior we mean flashes, bumps,slow deviations from power law (wiggles) in a light curve. In particular we report parameters of broken power law, describe phenomenology, compare optical light curves with X-ray ones and classify the inhomogeneities. We show that the duration of the inhomogeneities correlates with their peak time relative to gamma-ray burst (GRB) trigger and the correlation is the same for all types of inhomogeneities., Comment: 5 pages, 4 figures, 3 tables

We present our observations of electromagnetic transients associated with GW170817/GRB 170817A using optical telescopes of Chilescope observatory and Big Scanning Antenna (BSA) of Pushchino Radio Astronomy Observatory at 110MHz. The Chilescope observatory detected an optical transient of $\sim19^m$ on the third day in the outskirts of the galaxy NGC 4993; we continued observations following its rapid decrease. We put an upper limit of $1.5\times10^{4}$ Jy on any radio source with a duration of 10-60 s which may be associated with GW170817/GRB 170817A. The prompt gamma-ray emission consists of two distinctive components - a hard short pulse delayed by $\sim2$ seconds with respect to the LIGO signal and softer thermal pulse with $T\sim 10 $ keV lasting for another $\sim2$ seconds. The appearance of a thermal component at the end of the burst is unusual for short GRBs. Both the hard and the soft components do not satisfy the Amati relation, making GRB 170817A distinctively different from other short GRBs. Based on gamma-ray and optical observations, we develop a model for the prompt high-energy emission associated with GRB 170817A. The merger of two neutron stars creates an accretion torus of $\sim10^{-2} M_\odot$, which supplies the black hole with magnetic flux and confines the Blandford-Znajek-powered jet. We associate the hard prompt spike with the quasispherical breakout of the jet from the disk wind. As the jet plows through the wind with subrelativistic velocity, it creates a radiation-dominated shock that heats the wind material to tens of kiloelectron volts, producing the soft thermal component., Comment: 20 pages, 12 figures

We present optical observations of SN 2013dx, related to the Fermi burst GRB 130702A occurred at a redshift z = 0.145. It is the second-best sampled GRB-SN after SN~1998bw: the observational light curves contain more than 280 data points in uBgrRiz filters until 88 day after the burst, and the data were collected from our observational collaboration (Maidanak Observatory, Abastumani Observatory, Crimean Astrophysical Observatory, Mondy Observatory, National Observatory of Turkey, Observatorio del Roque de los Muchachos) and from the literature. We model numerically the multicolour light curves using the one-dimensional radiation hydrodynamical code STELLA, previously widely implemented for the modelling of typical non-GRB SNe. The best-fitted model has the following parameters: pre-supernova star mass M = 25 M_Sun, mass of a compact remnant M_CR = 6 M_Sun, total energy of the outburst E_oburst = 3.5 x 10^(52) erg, pre-supernova star radius R = 100 R_Sun, M_56Ni = 0.2 M_Sun which is totally mixed through the ejecta; M_O = 16.6 M_Sun, M_Si = 1.2 M_Sun, and M_Fe = 1.2 M_Sun, and the radiative efficiency of the SN is 0.1 per cent., Comment: 14 pages, 9 figures, 5 tables, accepted to MNRAS

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., Comment: Revised version reflecting the referees' comments. 27 pages, 11 figures, 5 tables. The final edited version will appear in Nature Astronomy

Electron-positron annihilation line from a Galactic center direction was discovered by the balloon-borne germanium gamma-ray telescope, and confirmed by OSSE experiment of CGRO mission. Extensive observations by INTEGRAL observatory permit to determine properties of the annihilation line from Galactic bulge. Possible sources of $e^{+}$ already discussed are supernovae explosions, microquasars, gamma-ray bursts, tidal disruption events, activity near black hole of Sgr A*, $e^{+}$ generation by subrelativistic cosmic rays, or even dark matter. One remarkable feature of the line emission is an absence of resolved point like sources. Any model should take into account this feature. We consider flares of low-mass stars as a possible cumulative $e^{+}$ source of the observed annihilation line from the bulge. Our estimations show that $e^{+}$ production by numerous flaring stars in Galaxy bulge can be significant, or even the main source of $e^{+}$ responsible for the annihilation line observed from the central part of our Galaxy.

We have analyzed the light curves of 519 short gamma-ray bursts (GRBs) detected in the SPI-ACS/INTEGRAL experiment from December 2002 to May 2014 to search for precursors. Both the light curves of 519 individual events and the averaged light curve of 372 brightest bursts have been analyzed. In a few cases, we have found and thoroughly studied precursor candidates based on SPI-ACS/INTEGRAL, GBM/Fermi, and LAT/Fermi data. A statistical analysis of the averaged light curve for the entire sample of short bursts has revealed no regular precursor. Upper limits for the relative intensity of precursors have been estimated. No convincing evidence for the existence of precursors of short GRBs has been found. We show that the fraction of short GRBs with precursors is less than 0.4% of all short bursts., Comment: 33 pages, 11 figures

How black holes accrete surrounding matter is a fundamental, yet unsolved question in astrophysics. It is generally believed that matter is absorbed into black holes via accretion disks, the state of which depends primarily on the mass-accretion rate. When this rate approaches the critical rate (the Eddington limit), thermal instability is supposed to occur in the inner disc, causing repetitive patterns of large-amplitude X-ray variability (oscillations) on timescales of minutes to hours. In fact, such oscillations have been observed only in sources with a high mass accretion rate, such as GRS 1915+105. These large-amplitude, relatively slow timescale, phenomena are thought to have physical origins distinct from X-ray or optical variations with small amplitudes and fast ($\lesssim$10 sec) timescales often observed in other black hole binaries (e.g., XTE J1118+480 and GX 339-4). Here we report an extensive multi-colour optical photometric data set of V404 Cygni, an X-ray transient source containing a black hole of nine solar masses (and a conpanion star) at a distance of 2.4 kiloparsecs. Our data show that optical oscillations on timescales of 100 seconds to 2.5 hours can occur at mass-accretion rates more than ten times lower than previously thought. This suggests that the accretion rate is not the critical parameter for inducing inner-disc instabilities. Instead, we propose that a long orbital period is a key condition for these large-amplitude oscillations, because the outer part of the large disc in binaries with long orbital periods will have surface densities too low to maintain sustained mass accretion to the inner part of the disc. The lack of sustained accretion -- not the actual rate -- would then be the critical factor causing large-amplitude oscillations in long-period systems., Comment: Published in Nature on January 7th, 2016

Gamma-ray bursts (GRBs) are the most luminous explosions in the universe, yet the nature and physical properties of their energy sources are far from understood. Very important clues, however, can be inferred by studying the afterglows of these events. We present optical and X-ray observations of GRB 130831A obtained by Swift, Chandra, Skynet, RATIR, Maidanak, ISON, NOT, LT and GTC. This burst shows a steep drop in the X-ray light-curve at $\simeq 10^5$ s after the trigger, with a power-law decay index of $\alpha \sim 6$. Such a rare behaviour cannot be explained by the standard forward shock (FS) model and indicates that the emission, up to the fast decay at $10^5$ s, must be of "internal origin", produced by a dissipation process within an ultrarelativistic outflow. We propose that the source of such an outflow, which must produce the X-ray flux for $\simeq 1$ day in the cosmological rest frame, is a newly born magnetar or black hole. After the drop, the faint X-ray afterglow continues with a much shallower decay. The optical emission, on the other hand, shows no break across the X-ray steep decrease, and the late-time decays of both the X-ray and optical are consistent. Using both the X-ray and optical data, we show that the emission after $\simeq 10^5$ s can be explained well by the FS model. We model our data to derive the kinetic energy of the ejecta and thus measure the efficiency of the central engine of a GRB with emission of internal origin visible for a long time. Furthermore, we break down the energy budget of this GRB into the prompt emission, the late internal dissipation, the kinetic energy of the relativistic ejecta, and compare it with the energy of the associated supernova, SN 2013fu., Comment: Accepted for publication by MNRAS. 21 pages, 3 figures, 8 tables. Extra table with magnitudes in the source

This paper describes outstanding issues in astrophysics and cosmology that can be solved by astronomical observations in a broad spectral range from far infrared to millimeter wavelengths. The discussed problems related to the formation of stars and planets, galaxies and the interstellar medium, studies of black holes and the development of the cosmological model can be addressed by the planned space observatory Millimetron (the "Spectr-M" project) equipped with a cooled 10-m mirror. Millimetron can operate both as a single-dish telescope and as a part of a space-ground interferometer with very long baseline., Comment: The translation of the original article in Physics Uspekhi http://ufn.ru/ru/articles/2014/12/c/