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 110 MHz. The Chilescope observatory detected an optical transient of ∼19m 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 × 104 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 ∼2 s with respect to the LIGO signal and softer thermal pulse with T ∼ 10 keV lasting for another ∼2 s. 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 ∼10−2 M , 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.
ABSTRACT
Studies of the pulsar B0823+26 have been carried out using the Large Phased Array (LPA) radio telescope. At a time span of 5.5 yr, the amplitudes of the main pulse (MP), postcursor (PC), and ...interpulse (IP) were evaluated in daily sessions lasting 3.7 min. It is shown that the ratio of the average amplitudes of MP in the bright (B) and quiet (Q) modes is 60. For B-mode, the average ratio of MP amplitudes to IP amplitudes is 65, and the ratio of MP amplitudes to PC amplitudes is 28. The number of sessions with a nulling is 4 per cent of the total number of sessions. Structure function (SF) and correlation function analysis of MP, IP, and PC amplitude variations of over a long-time interval allowed us to detect typical time scales 37 ± 5 d and one year. The analysis of time variations shows that the time scale of 37 d is well explained by refraction on inhomogeneities of interstellar plasma, which is distributed mostly quasi-uniformly in the line of sight. This scintillation makes the main contribution to the observed variability. Analysis of the structure function showed that there may be a few days variability. This time scale does not have an unambiguous interpretation but is apparently associated with the refraction of radio waves on the interstellar medium. One-year variability time scale has not been previously detected. We associate its appearance with the presence of a scattering layer on a closely located screen at a distance of about 50–100 pc from the Earth.
Sun-sized Water Vapor Masers in Cepheus A Sobolev, A. M.; Moran, J. M.; Gray, M. D. ...
Astrophysical journal/The Astrophysical journal,
03/2018, Letnik:
856, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present the first VLBI observations of a Galactic water maser (in Cepheus A) made with a very long baseline interferometric array involving the RadioAstron Earth-orbiting satellite station as one ...of its elements. We detected two distinct components at −16.9 and 0.6 km s−1 with a fringe spacing of 66 as. In total power, the 0.6 km s−1 component appears to be a single Gaussian component of strength 580 Jy and width of 0.7 km s−1. Single-telescope monitoring showed that its lifetime was only eight months. The absence of a Zeeman pattern implies the longitudinal magnetic field component is weaker than 120 mG. The space-Earth cross power spectrum shows two unresolved components smaller than 15 as, corresponding to a linear scale of 1.6 × 1011 cm, about the diameter of the Sun, for a distance of 700 pc, separated by 0.54 km s−1 in velocity and by 160 35 as in angle. This is the smallest angular structure ever observed in a Galactic maser. The brightness temperatures are greater than 2 × 1014 K, and the line widths are 0.5 km s−1. Most of the flux (about 87%) is contained in a halo of angular size of 400 150 as. This structure is associated with the compact H ii region HW3diii. We have probably picked up the most prominent peaks in the angular size range of our interferometer. We discuss three dynamical models: (1) Keplerian motion around a central object, (2) two chance overlapping clouds, and (3) vortices caused by flow around an obstacle (i.e., von Kármán vortex street) with a Strouhal number of about 0.3.
Status of UCN supersource at WWR-M reactor Serebrov, A P; Lyamkin, V A; Fomin, A K ...
Journal of physics. Conference series,
11/2019, Letnik:
1390, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The WWR-M reactor at NRC «Kurchatov Institute» - PNPI is going to be equipped with high-density ultracold neutron source. Method of UCN production is based on their accumulation in the superfluid ...helium at 1.2 K temperature. Thus, the source will provide the UCN density at EDM spectrometer equals to ρ = 1.3⋅104 cm−3 which is 2 order magnitude greater than the output density of existing UCN source in the world. An extensive program of fundamental researches such as measuring of neutron lifetime and searching of neutron-antineutron oscillation is planned. In addition, CN and VCN beams are going to be equipped with condensed matter physics experimental setups. The design of the UCN source has been completed, complex tests at full-scale model showed that is possible to maintain superfluid helium under reactor heat load; calculations of an UCN source passive shielding, which ensures source safe operation, is completed. At the moment the process of UCN source manufacturing is taking place.
Detection of Two New RRATs at 111 MHz Samodurov, V. A.; Tyul’bashev, S. A.; Toropov, M. O. ...
Astronomy reports,
06/2023, Letnik:
67, Številka:
6
Journal Article
Recenzirano
Odprti dostop
At the LPA LPI radio telescope, a search was conducted for pulse signals in a specific area with declinations
. The processing involved ten months of observations recorded in six frequency channels, ...each with a channel width of 415 kHz and a total bandwidth of 2.5 MHz. The analysis of the data revealed 22 000 events, exhibiting a pronounced dispersion delay of signals over the frequency channels, which are indicative of pulsar pulses. These pulses were found to belong to four known pulsars and two new rotating radio transients (RRAT). Additional pulse search was carried out in 32-channel data with a channel width of 78 kHz. This led to the discovery of 8 pulses for the transient J0249+52 and 7 pulses for the transient J0744+55. No periodic emission of transients was detected. The analysis of the observations indicates a high probability that the identified RRATs are pulsars with nullings, where the fraction of nullings is greater than 99.9%.
A search for pulse signals was carried out in a new sky area included in the monitoring program for the search for pulsars and transients. Processing of several months data recorded in six frequency ...channels with a total bandwidth of 2.5 MHz showed that, on average, 4 pulses per hour are observed in each of the 24 connected stationary beams. Of these pulses, 18.3% are similar to those of pulsars. They are visible in one or two neighboring beams and have a pronounced dispersion shift, that is, they are recorded first at a high and then at a low frequency, which indicates the possible passage of the signal through the interstellar medium. Almost 68% of such detected pulses belong to six known pulsars with dispersion measures from 9 to 141 pc/cm
3
, and almost all of the remaining pulses are either noise of an unknown nature or artifacts of the proposed pulse separation technique. An additional study of the selected array of 3650 obvious pulsar pulses revealed 13 pulses belonging to four rotating radio transients (RRATs). Their dispersion measures are in the range of 17–51 pc/cm
3
. A search for regular (periodic) RRAT emission was carried out using power spectra summed over 121 days. Periodic radiation was not detected, but for two RRATs, upper estimates of the periods were obtained from measurements of the time intervals between pulses. The upper estimates of the integrated flux density of the detected RRATs are in the range 2–4 mJy at the frequency 111 MHz.
The WWR-M reactor at PNPI is going to be equipped with an ultracold neutron source of high density. Method of UCN production is based on their accumulation in the super fluid helium due to particular ...qualities of that quantum liquid. The satisfying storage time of UCN at WWR-M reactor in the super fluid helium exists at a temperature below 1.2 K. Our source aims at obtaining a density of UCN equals to 104 n/cm3, two orders of magnitude exceeding that in existing sources presently available in the world. Increase in the density of UCN will raise the accuracy of the measurement of the neutron electric dipole moment (EDM) of an order of magnitude, which is fundamentally important for the problem of CP violation. The most intense sources of UCN allows PNPI become the centre of fundamental researches with ultracold neutrons.
In the process of astronomical observations vast amounts of data are collected. BSA (Big Scanning Antenna) LPI used in the study of impulse phenomena, daily logs 87.5 GB of data (32 TB per year). ...This data has important implications for both short-and long-term monitoring of various classes of radio sources (including radio transients of different nature), monitoring the Earth's ionosphere, the interplanetary and the interstellar plasma, the search and monitoring of different classes of radio sources. In the framework of the studies discovered 83096 individual pulse events (in the interval of the study highlighted July 2012 - October 2013), which may correspond to pulsars, twinkling springs, and a rapid radio transients. Detected impulse events are supposed to be used to filter subsequent observations. The study suggests approach, using the creation of the multilayered artificial neural network, which processes the input raw data and after processing, by the hidden layer, the output layer produces a class of impulsive phenomena.
A method for searching for new periodic radio sources is described. The method is based on the spectral analysis of data from daily monitoring of the sky on the Large Phased Antenna (LPA) of the ...Pushchino Radio Astronomy Observatory at 111 MHz in a 2.5-MHz band. The 96-beam directivity pattern of the LPA is used. The signal is received in six 0.42-MHz frequency channels with a sampling rate of 0.1 s. The duration of the processed survey is four months. The particulars of detecting periodic sources with the LPA are considered. In total, 16 such radio sources have been detected, for which equatorial and Galactic coordinates, periods, and dispersion measures are given.
The results of calculation of fluxes of ultracold (UCNs), very cold, and cold neutrons at the output of neutron guides of the UCN source with superfluid helium at the WWR-M reactor are presented. UCN ...density ρ
35L
= 1.3 × 10
4
n/cm
3
in the trap of the electric dipole moment (EDM) spectrometer was obtained by optimizing source parameters. This UCN density in the EDM spectrometer is two orders of magnitude higher than the UCN density at the output of the available UCN sources. The flux density of cold neutrons with a wavelength of 2–20 Å at the output of a neutron guide with a cross section of 30 × 200 mm
2
should be as high as 1.1 × 10
8
n/(cm
2
s), while the flux density of very cold neutrons (50–100 Å) at the output of the same neutron guide should be 2.3 × 10
5
n/(cm
2
s). An extensive program of fundamental and applied physical research was mapped out for this source.
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