We present the results of the prompt, early and afterglow optical observations of five gamma-ray bursts (GRBs): GRB 100901A, GRB 100902A, GRB 100905A, GRB 100906A and GRB 101020A. These observations ...were made with the Mobile Astronomical System of TElescope-Robots in Russia (MASTER-II Net), the 1.5-m telescope of the Sierra Nevada Observatory and the 2.56-m Nordic Optical Telescope. For two sources, GRB 100901A and GRB 100906A, we detected optical counterparts and obtained light curves starting before the cessation of gamma-ray emission, at 113 and 48 s after the trigger, respectively. Observations of GRB 100906A were conducted in two polarizing filters. Observations of the other three bursts gave the upper limits on the optical flux; their properties are briefly discussed. A more detailed analysis of GRB 100901A and GRB 100906A, supplemented by Swift data, provides the following results and indicates different origins for the prompt optical radiation in the two bursts. The light-curve patterns and spectral distributions suggest that there is a common production site for the prompt optical and high-energy emission in GRB 100901A. The results of the spectral fits for GRB 100901A in the range from optical to X-ray favour power-law energy distributions and a consistent value of the optical extinction in the host galaxy. GRB 100906A produced a smoothly peaking optical light curve, suggesting that the prompt optical radiation in this GRB originated in a front shock. This is supported by a spectral analysis. We have found that the Amati and Ghirlanda relations are satisfied for GRB 100906A. We obtain an upper limit on the value of the optical extinction on the host of GRB 100906A. PUBLICATION ABSTRACT
Aims. We address the task of modeling soft X-ray and optical light curves of X-ray novae in the high/soft state. Methods. The analytic model of viscous evolution of an externally truncated accretion ...alpha-disk is used. Relativistic effects near a Kerr black hole and self-irradiation of an accretion disk are taken into account. Results. The model is applied to the outbursts of X-ray nova Monocerotis 1975 (A 0620-00) and X-ray nova Muscae 1991 (GRS 1124-68). Comparison of observational data with the model yields constraints on the angular momentum (the Kerr parameter) of the black holes in A 0620-00 and GRS 1124-68: 0.3-0.6 and leq0.4, and on the viscosity parameter alpha of the disks: 0.7-0.95 and 0.55-0.75. We also conclude that the accretion disks should have an effective geometrical thickness 1.5-2 times greater than the theoretical value of the distance between the photometric layers.
We examine the jets and the disc of SS 433 at super-Eddington luminosities with by time-dependent two-dimensional radiation hydrodynamical calculations, assuming an α-model for the viscosity. ...One-dimensional supercritical accretion disc models with mass loss or advection are used as the initial configurations of the disc. As a result, from the initial advective disc models with α= 0.001 and 0.1, we obtain total luminosities ∼2.5 × 1040 and 2.0 × 1040 erg s−1. The total mass-outflow rates are ∼4 × 10−5 and 10−4 M⊙ yr−1, and the rates of the relativistic axial outflows in a small half opening angle of ∼1° are about 10−6 M⊙ yr−1: the values are generally consistent with the corresponding observed rates of the wind and the jets, respectively. From the initial models with mass loss but without advection, we obtain total mass-outflow and axial outflow rates smaller than or comparable to the observed rates of the wind and the jets, respectively, depending on α. In the advective disc model with α= 0.1, the initially radiation-pressure-dominant, optically thick disc evolves to a gas-pressure-dominated, optically thin state in the inner region of the disc, and the inner disc is unstable. Consequently, we find remarkable modulations of the disc luminosity and the accretion rate through the inner edge. These modulations manifest themselves as recurrent hot blobs with high temperatures and low densities at the disc plane, which develop outwards and upwards and produce quasi-periodic oscillations (QPOs) of the total luminosity with an amplitude of a factor of ∼2 and quasi-periods of ∼10–25 s. This may explain the massive jet ejection and the QPO phenomena observed in SS 433.
•For GRB100906A, GRB110422A, GRB121011A the dimensionless Stokes parameter is obtained.•The polarization of SN 2012bh at the early stage of the envelope expansion was <3%.•Polarization measurements ...for the blazars OC 457, 3C 454.3 are presented.•Polarization degree for the blazars QSOB1215+303, 87GB 165943.2+395846 are presented.•MASTER telescopes can safely register linear polarization in excess of 10%.
We present results of optical polarization observations performed with the MASTER robotic net (Lipunov et al., 2004, 2010; Kornilov et al., 2012) for three types of objects: gamma-ray bursts, supernovae, and blazars. For the gamma-ray bursts GRB100906A, GRB110422A, GRB121011A, polarization observations were obtained Shift during very early stages of optical emission. For GRB100906A it was the first prompt optical polarization observation in the world. Photometry in polarizers is presented for Type Ia Supernova 2012bh during 20days, starting on March 27, 2012. We find that the linear polarization of SN 2012bh at the early stage of the envelope expansion was less than 3%. Polarization measurements for the blazars OC 457, 3C 454.3, QSO B1215+303, 87GB 165943.2+395846 at single nights are presented. We infer the degree of the linear polarization and polarization angle. The blazars OC 457 and 3C 454.3 were observed during their periods of activity. The results show that MASTER is able to measure substantially polarized light; at the same time it is not suitable for determining weak polarization (less than 5%) of dim objects (fainter than 16m). Polarimetric observations of the optical emission from gamma-ray bursts and supernovae are necessary to investigate the nature of these transient objects.
We study statistical properties of long gamma-ray bursts (GRBs) produced by the collapsing cores of WR stars in binary systems. Fast rotation of the cores enables a two-stage collapse scenario, ...implying the formation of a spinar-like object. A burst produced by such a collapse consists of two pulses, whose energy budget is enough to explain observed GRBs. We calculate models of spinar evolution using results from a population synthesis of binary systems (done by the ‘Scenario Machine’) as initial parameters for the rotating massive cores. Among the resulting bursts, events with a weaker first peak, namely precursor, are identified, and the precursor-to-main-pulse time separations fully agree with the range of the observed values. The calculated fraction of long GRBs with precursor (about 10 per cent of the total number of long GRBs) and the durations of the main pulses are also consistent with observations. Precursors with lead times greater by up to one order of magnitude than those observed so far are expected to be about a factor of 2 less numerous. Independently of the GRB model assumed, we predict the existence of precursors that arrive up to ≳103 s in advance of the main events of GRBs.
We derive the luminosity–temperature relation for the supercritically accreting black holes (BHs) and compare it to the data on ultraluminous X-ray sources (ULXs). At super-Eddington accretion rates, ...an outflow forms within the spherization radius. We construct the accretion disc model accounting for the advection and the outflow, and compute characteristic disc temperatures. The bolometric luminosity exceeds the Eddington luminosity LEdd by a logarithmic factor (where is the accretion rate in Eddington units) and the wind kinetic luminosity is close to LEdd. The apparent luminosity for the face-on observer is 2–7 times higher because of geometrical beaming. Such an observer has a direct view of the inner hot accretion disc, which has a peak temperature Tmax of a few keV in stellar mass BHs. The emitted spectrum extends as a power law FE∝E−1 down to the temperature at the spherization radius . We associate Tmax with a few keV spectral components and Tsp with the soft, 0.1–0.2 keV components observed in ULXs. An edge-on observer sees only the soft emission from the extended envelope, with the photosphere radius exceeding the spherization radius by orders of magnitude. The dependence of the photosphere temperature on luminosity is consistent with that observed in the super-Eddington accreting BHs SS 433 and V4641 Sgr. Strong outflows combined with the large intrinsic X-ray luminosity of the central BH explain naturally the presence of the photoionized nebulae around ULXs. An excellent agreement between the model and the observational data strongly argues in favour of ULXs being supercritically accreting, stellar mass BHs similar to SS 433, but viewed close to the symmetric axis.
The analytic investigation of time dependent accretion in disk is carried out. We consider a disk in a binary system at outburst which has fixed tidally truncated outer radius. The standard model ...(Shakura-Sunyaev 1973) of the disk is considered. The fully analytic solutions in two different opacity regimes are characterized by power-law variations of accretion rate with time. The solutions supply asymptotic description of the disk evolution after the peak of outburst while the disk is fully ionized. The X-ray flux of multicolor (black-body) α-disk is obtained to vary quasi-exponentially. The application to X-ray novae is briefly discussed concerning observed faster-than-power decays of X-ray light curves. The case of time dependent advective disk is mentioned.
Observations of X-ray binaries indicate substantial half-thicknesses for the accretion disks in these systems (up to h/R approximately 0.25, where h is the disk half-thickness and R its radius), ...while standard alpha accretion disks predict appreciably smaller half-thicknesses. We study the theoretical vertical structure of such disks using two independent numerical methods, and show that their maximum half-thicknesses in the subcritical regime cannot exceed h/R approximately 0.1. We consider various reasons for the apparent increase in the disk thickness, the most probable of which is the presence of matter above the disk in the form of a hot corona that scatters hard radiation from the central source and inner parts of the disk. As a result, the observed thickness of the disk and the illumination of its outer parts effectively increase. This mechanism can also explain both the optical-to-X-ray flux ratio in these systems and the observed parameters of eclipsing X-ray binaries.
PDF
