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.
We present the low-resolution spectroscopic and UBVRI broad-band photometric investigations of the Type IIb supernova (SN) 2011fu, discovered in UGC 01626. The photometric follow-up of this event was ...initiated a few days after the explosion and covers a period of about 175 d. The early-phase light curve shows a rise, followed by steep decay in all bands, and shares properties very similar to that seen for SN 1993J, with a possible detection of the adiabatic cooling phase. Modelling of the quasi-bolometric light curve suggests that the progenitor had an extended (∼1 × 1013 cm), low-mass (∼0.1 M) H-rich envelope on top of a dense, compact (∼2 × 1011 cm), more massive (∼1.1 M) He-rich core. The nickel mass synthesized during the explosion was found to be ∼0.21 M, slightly larger than that seen for other Type IIb SNe. The spectral modelling performed with synow suggests that the early-phase line velocities for H and Fe ii features were ∼16 000 and ∼14 000 km s−1, respectively. Then, the velocities declined up to day +40 and became nearly constant at later epochs.
We present photometry and spectroscopy of the Type IIP supernova (SN IIP) 2009bw in UGC 2890 from a few days after the outburst to 241 d. The light curve of SN 2009bw during the photospheric phase is ...similar to that of normal SNe IIP but with a brighter peak and plateau (
mag,
mag). The luminosity drop from the photospheric to the nebular phase is one of the fastest ever observed, ∼2.2 mag in about 13 d. The radioactive tail of the bolometric light curve indicates that the amount of ejected 56Ni is ≈0.022 M⊙. The photospheric spectra reveal high-velocity lines of Hα and Hβ until about 105 d after the shock breakout, suggesting a possible early interaction between the SN ejecta and pre-existent circumstellar material, and the presence of CNO elements. By modelling the bolometric light curve, ejecta expansion velocity and photospheric temperature, we estimate a total ejected mass of ∼8-12 M⊙, a kinetic energy of ∼0.3 foe and an initial radius of ∼3.6-7 × 1013 cm.
ABSTRACT
Optical, near-infrared (NIR) photometric and spectroscopic studies, along with the optical imaging polarimetric results for SN 2012au, are presented in this article to constrain the nature ...of the progenitor and other properties. Well-calibrated multiband optical photometric data (from –0.2 to +413 d since B-band maximum) were used to compute the bolometric light curve and to perform semi-analytical light-curve modelling using the minim code. A spin-down millisecond magnetar-powered model explains the observed photometric evolution of SN 2012au reasonably. Early-time imaging polarimetric follow-up observations (–2 to +31 d) and comparison with other similar cases indicate signatures of asphericity in the ejecta. Good spectral coverage of SN 2012au (from –5 to +391 d) allows us to trace the evolution of layers of SN ejecta in detail. SN 2012au exhibits higher line velocities in comparison with other SNe Ib. Late nebular phase spectra of SN 2012au indicate a Wolf–Rayet star as the possible progenitor for SN 2012au, with oxygen, He-core, and main-sequence masses of ∼1.62 ± 0.15 M⊙, ∼4–8 M⊙, and ∼17–25 M⊙, respectively. There is a clear absence of a first overtone of carbon monoxide (CO) features up to +319 d in the K-band region of the NIR spectra. Overall analysis suggests that SN 2012au is one of the most luminous slow-decaying Type Ib SNe, having comparatively higher ejecta mass (∼ 4.7–8.3 M⊙) and kinetic energy (∼ 4.8–5.4 × 1051 erg). Detailed modelling using mesa and the results obtained through stella and snec explosions also strongly support spin-down of a magnetar with mass of around 20 M⊙ and metallicity Z = 0.04 as a possible powering source of SN 2012au.
We report the early discovery of the optical afterglow of gamma-ray burst (GRB) 140801A in the 137 deg... 3-... error-box of the Fermi Gamma-ray Burst Monitor (GBM). MASTER is the only observatory ...that automatically reacts to all Fermi alerts. GRB 140801A is one of the few GRBs whose optical counterpart was discovered solely from its GBM localization. The optical afterglow of GRB 140801A was found by MASTER Global Robotic Net 53 s after receiving the alert, making it the fastest optical detection of a GRB from a GBM error-box. Spectroscopy obtained with the 10.4-m Gran Telescopio Canarias and the 6-m Big Telescope Alt-azimuth of the Special Astrophysical Observatory of the Russian Academy of Sciences reveals a redshift of z = 1.32. We performed optical and near-infrared photometry of GRB 140801A using different telescopes with apertures ranging from 0.4 to 10.4 m. GRB 140801A is a typical burst in many ways. The rest-frame bolometric isotropic energy release and peak energy of the burst are ... erg and ..., respectively, which is consistent with the Amati relation. The absence of a jet break in the optical light curve provides a lower limit on the half-opening angle of the ... The observed ... is consistent with the limit derived from the Ghirlanda relation. The joint Fermi GBM and Konus-Wind analysis show that GRB 140801A could belong to the class of intermediate duration. The rapid detection of the optical counterpart of GRB 140801A is especially important regarding the upcoming experiments with large coordinate error-box areas. (ProQuest: ... denotes formulae/symbols omitted.)
We present a wide data set of gamma-ray, X-ray, UV/Opt/IR (UVOIR), and radio observations of the Swift GRB100814A. At the end of the slow decline phase of the X-ray and optical afterglow, this burst ...shows a sudden and prominent rebrightening in the optical band only, followed by a fast decay in both bands. The optical rebrightening also shows chromatic evolution. Such a puzzling behaviour cannot be explained by a single component model. We discuss other possible interpretations, and we find that a model that incorporates a long-lived reverse shock and forward shock fits the temporal and spectral properties of GRB100814 the best.
ABSTRACT
We present full photometric coverage and spectroscopic data for soft gamma-ray burst GRB 201015A with a redshift z = 0.426. Our data span a time range of 85 d following the detection of GRB. ...These observations revealed an underlying supernova SN 201015A with a maximum at 8.54 ± 1.48 d (rest frame) and an optical peak absolute magnitude $-19.45_{-0.47}^{+0.85}$ mag. The SN 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 Tmax) known SN associated with GRBs. Spectroscopic observations during the SN decay stage showed broad lines, indicating a large photospheric velocity, and identified this SN 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 Ep,i = 20.0 ± 8.5 keV and Eiso = (1.1 ± 0.2) × 1050 erg were obtained. According to the position of the burst on the Ep,i–Eiso correlation, GRB 201015A was classified as a type II (long) GRB, which was also confirmed by the T90,i–EH diagram.
We have analyzed our photometric and spectroscopic observations of the new eclipsing cataclysmic variable MLS120126:042313+212951. We have found the system’s orbital period
day (
h) corresponding to ...the gap
h in the distribution of cataclysmic variables. A Doppler tomogram in the H
line demonstrates a bright spot that is formed in the accretion stream–outer accretion disk interaction region. Based on known calibrations of the secondary mass versus period, eclipse duration, and emission line peak separation, we have estimated the orbital inclination and the white-dwarf mass:
and
. These estimates are consistent with the position of the hot spot on the Doppler tomogram.
Chromatic Afterglow of GRB 200829A Pankov, N. S.; Pozanenko, A. S.; Minaev, P. Yu ...
Astronomy letters,
03/2023, Letnik:
49, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present the results of our analysis of multiwavelength observations for the long gamma-ray burst GRB 200829A. The burst redshift
has been determined photometrically at the afterglow phase. In ...gamma rays the event is one of the brightest (in isotropic equivalent),
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.
We present a study of the influence of magnetically induced control of external convection in stars of different types, in particular white dwarfs, on their thermal evolution. In the work preceding ...this study, we argued that for the cooling down white dwarf stars that have exhausted the sources of thermonuclear combustion, cessation of convection by a magnetic field significantly slows down their cooling. To test this asertion, we performed an observational program to search for new highly magnetized white dwarfs. The program is described in detail in the same issue of the journal. Our observations, together with the observations of other researchers, allowed us to construct the observed luminosity function of strongly magnetized white dwarfs with stopped convection and compare it with the well-known similar luminosity function of white dwarfs with weak fields that allow effective convective heat removal from their insides. As a result of the model analysis of these functions, the hypothesis that strongly magnetized white dwarfs cool down slower than weakly magnetic ones is confirmed. The article also qualitatively examines the effect of magnetic braking of convection in solar-type stars and cool M-dwarf stars of the Main Sequence on the periodicity of their radiation activity. The geophysical aspect of the problem and the practical application of magnetic field control of the heat removal in electrically conductive media are discussed.
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