arXiv subjects

A. Tsvetkova

Publications and source records attributed to A. Tsvetkova.

24 records · Page 2Linked to original sources

arXiv2021

A peculiar hard X-ray counterpart of a Galactic fast radio burst

Fast radio bursts are bright, millisecond-scale radio flashes of yet unknown physical origin. Recently, their extragalactic nature has been demonstrated and an increasing number of the sources have been found to repeat. Young, highly magnetized, isolated neutron stars - magnetars - have been suggested as the most promising candidates for fast radio burst progenitors owing to their energetics and high X-ray flaring activity. Here we report the detection with the Konus-Wind of a hard X-ray event of April 28, 2020, temporarily coincident with a bright, two-peak radio burst from the Galactic magnetar SGR~1935+2154 with properties remarkably similar to those of fast radio bursts. We show that two peaks of the double-peaked X-ray burst coincide in time with the radio peaks, confirming that the X-ray and radio emission most likely have a common origin. Thus, this is the first simultaneous detection of a fast radio burst from a Galactic magnetar and its high-energy counterpart. The total energy emitted in X-rays in this burst is typical of bright short magnetar bursts, but an unusual hardness of its energy spectrum strongly distinguish the April 28 event among multiple "ordinary" flares detected from SGR~1935+2154 previously. This, and a recent non-detection of radio emission from about one hundred typical soft bursts from SGR 1935+2154 favors the idea that bright, FRB-like magnetar signals are associated with rare, hard-spectrum X-ray bursts, which implied rate ($\sim$ 0.04 yr$^{-1}$ magnetar$^{-1}$) appears consistent with the rate estimate of SGR 1935+2154-like radio bursts (0.007 - 0.04 yr$^{-1}$ magnetar$^{-1}$).

astro-ph.HE↗

arXiv2021

A bright gamma-ray flare interpreted as a giant magnetar flare in NGC 253

Magnetars are young, highly magnetized neutron stars that produce extremely rare giant flares of gamma-rays, the most luminous astrophysical phenomena in our Galaxy. The detection of these flares from outside the Local Group of galaxies has been predicted, with just two candidates so far. Here we report on the extremely bright gamma-ray flare GRB 200415A of April 15, 2020, which we localize, using the Interplanetary Network, to a tiny (20 sq. arcmin) area on the celestial sphere, that overlaps the central region of the Sculptor galaxy at 3.5 Mpc from the Milky Way. From the Konus-Wind detections, we find a striking similarity between GRB 200415A and GRB 051103, the even more energetic flare that presumably originated from the M81/M82 group of galaxies at nearly the same distance (3.6 Mpc). Both bursts display a sharp, millisecond-scale, hard-spectrum initial pulse, followed by an approximately 0.2 s long steadily fading and softening tail. Apart from the huge initial pulses of magnetar giant flares, no astrophysical signal with this combination of temporal and spectral properties and implied energy has been reported previously. At the inferred distances, the energy released in both flares is on par with that of the December 27, 2004 superflare from the Galactic magnetar SGR 1806-20, but with a higher peak luminosity. Taken all together, this makes GRB 200415A and its twin GRB 051103 the most significant candidates for extragalactic magnetar giant flares, both a factor of five more luminous than the brightest Galactic magnetar flare observed previously, thus providing an important step towards a better understanding of this fascinating phenomenon.

astro-ph.HE↗

arXiv2021

The Konus-Wind catalog of gamma-ray bursts with known redshifts. II. Waiting mode bursts simultaneously detected by Swift/BAT

In the Second part of The Konus-Wind Catalog of Gamma-Ray Bursts with Known Redshifts (first part: Tsvetkova et al. 2017; T17), we present the results of a systematic study of gamma-ray bursts (GRBs) with reliable redshift estimates detected simultaneously by the Konus-Wind (KW) experiment (in the waiting mode) and by the Swift/BAT (BAT) telescope during the period from 2005 January to the end of 2018. By taking advantage of the high sensitivity of BAT and the wide spectral band of KW we were able to constrain the peak spectral energies, the broadband energy fluences, and the peak fluxes for the joint KW-BAT sample of 167 weak, relatively soft GRBs (including four short bursts). Based on the GRB redshifts, which span the range $0.04 \leq z \leq 9.4$, we estimate the rest-frame, isotropic-equivalent energy, and peak luminosity. For 14 GRBs with reasonably constrained jet breaks, we provide the collimation-corrected values of the energetics. This work extends the sample of KW GRBs with known redshifts to 338 GRBs, the largest set of cosmological GRBs studied to date over a broad energy band. With the full KW sample, accounting for the instrumental bias, we explore GRB rest-frame properties, including hardness-intensity correlations, GRB luminosity evolution, luminosity and isotropic-energy functions, and the evolution of the GRB formation rate, which we find to be in general agreement with those reported in T17 and other previous studies.

astro-ph.HE↗

arXiv2019

On Hamiltonian systems integrable in elliptic functions that describe waves over underwater banks and ridges

We discuss the 4-dimensional Hamiltonian systems that describe waves over underwater banks and ridges. The systems are exactly integrable in terms of elliptic functions and of solutions to nontrivial transcendental equations involving the elliptic integrals (Weierstrass' $ζ$-function).

nlin.SI↗

arXiv2019

GRB observations with Konus-WIND experiment

We give a short review of gamma-ray burst (GRB) observations with the Konus-WIND (KW) experiment, which has been providing a continuous all-sky coverage in the 20 keV-15 MeV band during the period from 1994 to present. The recent results include a systematic study of GRBs with known redshifts and a search for ultra-long GRBs in the KW archival data. We also discuss the KW capabilities for multi-messenger astronomy.

astro-ph.HE↗

arXiv2017

The Konus-Wind catalog of gamma-ray bursts with known redshifts. I. Bursts detected in the triggered mode

In this catalog, we present the results of a systematic study of gamma-ray bursts (GRBs) with reliable redshift estimates detected in the triggered mode of the Konus-Wind (KW) experiment during the period from 1997 February to 2016 June. The sample consists of 150 GRBs (including twelve short/hard bursts) and represents the largest set of cosmological GRBs studied to date over a broad energy band. From the temporal and spectral analyses of the sample, we provide the burst durations, the spectral lags, the results of spectral fits with two model functions, the total energy fluences, and the peak energy fluxes. Based on the GRB redshifts, which span the range 0.1 <= z <= 5, we estimate the rest-frame, isotropic-equivalent energy and peak luminosity. For 32 GRBs with reasonably-constrained jet breaks we provide the collimation-corrected values of the energetics. We consider the behavior of the rest-frame GRB parameters in the hardness-duration and hardness-intensity planes, and confirm the "Amati" and "Yonetoku" relations for Type II GRBs. The correction for the jet collimation does not improve these correlations for the KW sample. We discuss the influence of instrumental selection effects on the GRB parameter distributions and estimate the KW GRB detection horizon, which extends to z ~ 16.6, stressing the importance of GRBs as probes of the early Universe. Accounting for the instrumental bias, we estimate the KW GRB luminosity evolution, luminosity and isotropic-energy functions, and the evolution of the GRB formation rate, which are in general agreement with those obtained in previous studies.

astro-ph.HE↗