ABSTRACT
The examination of long-term (1979–2020) photometric observations of SS433 enabled us to discover a non-zero orbital eccentricity of e = 0.05 ± 0.01. We have also found evidence for a ...secular increase in the orbital period at a rate of $\dot{P}_\mathrm{b}=(1.0\pm 0.3)\times 10^{-7}$ s s−1. The binary orbital period increase rate makes it possible to improve the estimate of the binary mass ratio q = MX/MV > 0.8, where MX and MV are the masses of the relativistic object and the optical star, respectively. For an optical star mass of 10 M⊙, the mass of the relativistic object (a black hole) is MX > 8 M⊙. A neutron star in SS433 is reliably excluded because in that case the orbital period should decrease, in contradiction to observations. The derived value of $\dot{P}_\mathrm{b}$ sets a lower limit on the mass-loss rate in the Jeans mode from the binary system ≳7 × 10−6 M⊙ yr−1. The discovered orbital ellipticity of SS433 is consistent with the model of the slaved accretion disc tracing the precession of the misaligned optical star’s rotational axis.
ABSTRACT
We present the first sample of tidal disruption events (TDEs) discovered during the SRG all-sky survey. These 13 events were selected among X-ray transients detected in the 0° < l < 180° ...hemisphere by eROSITA during its second sky survey (2020 June 10 to December 14) and confirmed by optical follow-up observations. The most distant event occurred at z = 0.581. One TDE continued to brighten at least 6 months. The X-ray spectra are consistent with nearly critical accretion on to black holes of a few ×103 to $10^8\, \mathrm{ M}_\odot$, although supercritical accretion is possibly taking place. In two TDEs, a spectral hardening is observed 6 months after the discovery. Four TDEs showed an optical brightening apart from the X-ray outburst. The other nine TDEs demonstrate no optical activity. All 13 TDEs are optically faint, with Lg/LX < 0.3 (Lg and LX being the g band and 0.2–6 keV luminosity, respectively). We have constructed a TDE X-ray luminosity function, which can be fit by a power law with a slope of −0.6 ± 0.2, similar to the trend observed for optically selected TDEs. The total rate is estimated at (1.1 ± 0.5) × 10−5 TDEs per galaxy per year, an order of magnitude lower than inferred from optical studies. This suggests that X-ray bright events constitute a minority of TDEs, consistent with models predicting that X-rays can only be observed from directions close to the axis of a thick accretion disc formed from the stellar debris. Our TDE detection threshold can be lowered by a factor of ∼2, which should allow a detection of ∼700 TDEs by the end of the SRG survey.
We propose a novel method for observing the gravitational wave signature of supermassive black hole (SMBH) mergers. This method is based on the detection of a specific type of gravitational waves, ...namely gravitational wave burst with memory (BWM), using pulsar timing. We study the unique signature produced by BWM in anomalous pulsar timing residuals. We show that the present-day pulsar timing precision allows one to detect BWM due to SMBH mergers from distances of up to 1 Gpc (for the case of equal mass of 108 M⊙ SMBH). Improvements in the precision of pulsar timing together with an increase in the number of observed pulsars should eventually lead to the detection of a BWM signal due to the SMBH merger, thereby making the proposed technique complementary to the capabilities of the planned LISA mission.
Primordial stellar-mass black holes, which may contribute to dark matter and to the observed LIGO binary black hole coalescences, are expected to be born with very low spins. Here we show that ...accretion mass gain by the components of a primordial black hole binary from the surrounding matter could lead to noticeable spins of the components prior to the coalescence provided high initial orbital eccentricities.
Fast radio bursts Popov, S B; Postnov, K A; Pshirkov, M S
Physics Uspekhi,
10/2018, Volume:
61, Issue:
10
Journal Article
Peer reviewed
Open access
First discovered in 2007, fast radio bursts (FRBs) are highly luminous (10−1−102 Jy), millisecond-scale, highly dispersive single radio pulses whose record high brightness temperatures suggest a ...nonthermal emission mechanism. As of March 2018, a total of 32 FRBs have been recorded. There is also one repeating source, from which hundreds of bursts have already been detected. The rate of events is estimated to be several thousand per day per sky (disregarding bursts from the repeater), and their isotropic distribution in the sky suggests a likely cosmological origin. While numerous hypotheses have been proposed for FRBs since their discovery, the origin of these transients is not yet known. The most promising models either relate them to burst-type radiation from magnetars (neutron stars powered by the dissipation of their magnetic energy) or consider them analogous to giant pulses from some radio pulsars (strongly magnetized rotating neutron stars). The increasing statistics on the observed bursts and improvements in characterizing the FRB population will allow FRBs to become another tool for probing the intergalactic medium, estimating the cosmological parameters, and testing fundamental physical theories.
Abstract
A minor population of antistars in galaxies has been predicted by some of non-standard models of baryogenesis and
nucleosynthesis in the early Universe, and their presence is not yet ...excluded by the currently available observations. Detection of an unusually high abundance of antinuclei in cosmic rays can probe the baryogenesis scenarios in the early Universe.
Recent report of the
AMS-02
collaboration on the tentative detection of a few antihelium nuclei in GeV cosmic rays provided a great hope on the progress in this issue. We discuss possible sources of antinuclei in cosmic rays from antistars which are predicted in a modified Affleck-Dine baryogenesis scenario by Dolgov and Silk (1993).
The model allows us to estimate the expected fluxes and isotopic content of
antinuclei in the GeV cosmic rays produced in scenarios involving antistars. We show that
the flux of antihelium CRs reported by the
AMS-02
experiment can be explained by Galactic anti-nova outbursts, thermonuclear anti-SN Ia explosions, a collection of flaring antistars, or an extragalactic source with abundances not violating existing gamma-ray and microlensing constraints on the antistar population.
Using RXTE/ASM archival data, we investigate the behaviour of the spectral hardness ratio as a function of X-ray luminosity in a sample of six transient X-ray pulsars (EXO 2030+375, GX 304−1, 4U ...0115+63, V 0332+63, A 0535+26 and MXB 0656−072). In all sources we find that the spectral hardness ratio defined as F
5−12 keV/F
1.33−3 keV increases with the ASM flux (1.33–12 keV) at low luminosities and then saturates or even slightly decreases above some critical X-ray luminosity falling into the range ∼(3–7) × 1037 erg s−1. Two-dimensional structure of accretion columns in the radiation–diffusion limit is calculated for two possible geometries (filled and hollow cylinder) for mass accretion rates
$\dot{M}$
ranging from 1017 to 1.2 × 1018 g s−1. The observed spectral behaviour in the transient X-ray pulsars with increasing
$\dot{M}$
can be reproduced by a Compton-saturated sidewall emission from optically thick magnetized accretion columns with taking into account the emission reflected from the neutron star atmosphere. At
$\dot{M}$
above some critical value
$\dot{M}_{\rm cr}\sim (6{\rm -}8)\times 10^{17}$
g s−1, the height of the column becomes such that the contribution of the reflected component to the total emission starts decreasing, which leads to the saturation and even slight decrease of the spectral hardness. Hollow-cylinder columns have a smaller height than the filled-cylinder ones, and the contribution of the reflected component in the total emission does not virtually change with
$\dot{M}$
(and hence the hardness of the continuum monotonically increases) up to higher mass accretion rates than
$\dot{M}_{\rm cr}$
for the filled columns.
On masses of the components in SS433 Cherepashchuk, A M; Postnov, K A; Belinski, A A
Monthly notices of the Royal Astronomical Society,
10/2018, Volume:
479, Issue:
4
Journal Article
Evidence of Fermi bubbles around M31 Pshirkov, M. S; Vasiliev, V. V; Postnov, K. A
Monthly notices of the Royal Astronomical Society. Letters,
06/2016, Volume:
459, Issue:
1
Journal Article
Peer reviewed
Open access
Gamma-ray haloes can exist around galaxies due to the interaction of escaping galactic cosmic rays with the surrounding gas. We have searched for such a halo around the nearby giant spiral Andromeda ...galaxy M31 using almost 7 yr of Fermi LAT data at energies above 300 MeV. The presence of a diffuse gamma-ray halo with total photon flux 2.6 ± 0.6 × 10−9 cm−2 s−1, corresponding to a luminosity (0.3–100 GeV) of (3.2 ± 0.6) × 1038 erg s−1 (for a distance of 780 kpc) was found at a 5.3σ confidence level. The halo form does not correspond to the extended baryonic H i disc of M31, as would be expected in hadronic production of gamma photons from cosmic ray interaction, nor it is spherically symmetric, as could be in the case of dark matter annihilation. The best-fitting halo template corresponds to two 6–7.5 kpc bubbles symmetrically located perpendicular to the M31 galactic disc, similar to the ‘Fermi bubbles’ found around the Milky Way centre, which suggests the past activity of the central supermassive black hole or a star formation burst in M31.
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