A non-perturbative proof of Bertrand's theorem

We discuss an alternative non-perturbative proof of Bertrand's theorem that leads in a concise way directly to the two allowed fields: the newtonian and the isotropic harmonic oscillator central fields.Comment: Latex file plus one eps figur

Generalized Flows around Neutron Stars

In this chapter, we present a brief and non-exhaustive review of the developments of theoretical models for accretion flows around neutron stars. A somewhat chronological summary of crucial observations and modelling of timing and spectral properties are given in sections 2 and 3. In section 4, we argue why and how the Two-Component Advective Flow (TCAF) solution can be applied to the cases of neutron stars when suitable modifications are made for the NSs. We showcase some of our findings from Monte Carlo and Smoothed Particle Hydrodynamic simulations which further strengthens the points raised in section 4. In summary, we remark on the possibility of future works using TCAF for both weakly magnetic and magnetic Neutron Stars.Comment: 15 pages, 7 figures. arXiv admin note: text overlap with arXiv:1901.0084

INTEGRAL observations of SS433, a supercritically accreting microquasar with hard spectrum

Observations of SS433 by INTEGRAL carried out in March -- May 2003 are presented. SS433 is evidently detected on the INTEGRAL images of the corresponding sky region in the energy bands 25-50 and 50-100 keV. The precessional variability of the hard X-ray flux is clearly seen. The X-ray eclipse caused by the binary orbital motion is also detected. A possible origin of the hard continuum is briefly discussed.Comment: 5 pages, 6 figures. Accepted to A&A INTEGRAL special volum

INTEGRAL Observations of SS433: Analysis of Precessional and Orbital X-ray Periodicities

Hard X-ray INT observations of SS 433 carried out during 2003-2005 years with an analysis of precessional and orbital variability is presented. The width of X-ray eclipse in the 25-50 keV range at the precessional phase $\psi=0.1$ (accretion disk is open to observer) is higher than that in the Ginga 18.4-27.6 keV range. This fact suggests existance the presence of hot extended corona around the supercritical accretion disk. Spectrum of hard X-rays in the range 10-200 keV does not change with the precessional phase which also suggests that hard X-ray flux is generated in the hot extended corona around the accretion disk. The parameters of this hot corona are: kT=23-25 keV, \tau = 1.8-2.8. Mass ratio estimated from the analysis of the ingress part of the eclipse light curve is in the range q=m_x/m_v=0.3-0.5.Comment: 5 pages, 10 figure

Coordinated integral and optical observations of SS433

Results of simultaneous INTEGRAL and optical observations of galactic microquasar SS433 in May 2003 are presented. The analysis of the X-ray and optical eclipse duration and hard X-ray spectra obtained by INTEGRAL together with optical spectroscopy obtained on the 6-m telescope allows us to construct a model of SS433 as a massive X-ray binary. X-ray eclipse in hard X-rays has a depth of ∼ 80% and extended wings. The optical spectroscopy allows us to identify the optical companion as a A5-A7 supergiant and to measure its radial velocity semiamplitude Kv = 132 km/s. A strong heating effect in the optical star atmosphere is discovered spectroscopically. The observed broadband X-ray spectrum 2-100 keV can be described by emission from optically thin thermal plasma with kT ∼ 15 - 20keV

INTEGRAL observations of SS433: Results of a coordinated campaign

Results of simultaneous INTEGRAL and optical observations of the galactic microquasar SS433 in May 2003 and INTEGRAL/RXTE observations in March 2004 are presented. Persistent precessional variability with a maximum to minimum uneclipsed hard X-ray flux ratio of ∼4 is discovered. The 18-60 keV X-ray eclipse is found to be in phase with optical and near infrared eclipses. The orbital eclipse observed by INTEGRAL in May 2003 is at least two times deeper and apparently wider than in the soft X-ray band. The broadband 2-100 keV X-ray spectrum simultaneously detected by RXTE/INTEGRAL in March 2004 can be explained by bremsstrahlung emission from optically thin thermal plasma with kT ∼ 30 keV. Optical spectroscopy with the 6-m SAO BTA telescope confirmed the optical companion to be an A5-A7 supergiant. For the first time, spectorscopic indications of a strong heating effect in the optical star atmosphere are found. The measurements of absorption lines which are presumably formed on the non-illuminated side of the supergiant yield its radial velocity semi-amplitude Kv = 132 ±9 km s-1. The analysis of the observed hard X-ray light curve and the eclipse duration, combined with the spectroscopically determined optical star radial velocity corrected for the strong heating effect, allows us to model SS433 as a massive X-ray binary. Assuming that the hard X-ray source in SS433 is eclipsed by the donor star that exactly fills its Roche lobe, the masses of the optical and compact components in SS433 are suggested to be Mv ≈ 30 M⊙ and Mx ≈ 9 M⊙, respectively. This provides further evidence that SS433 is a massive binary system with supercritical accretion onto a black hole. © ESO 2005

OJ 287: A new BH mass estimate of the secondary

We presented a study of outburst activity in the BL Lacertae source OJ~287, observed extensively with the X-ray telescope (XRT) onboard Neil Gehrels Swift Observatory. We demonstrated that the results of our analysis of X-ray flaring activity using the Swift/XRT data allow to refine the key characteristics of the OJ~287 secondary (its nature and mass). We discovered that the energy spectra in all spectral states can be fitted using the XSPEC Bulk Motion Comptonization (BMC) model. As a result we found that the X-ray photon index of the BMC model, Gamma correlates with the mass accretion rate, dot. We established that Gamma increases monotonically with dot from the low-hard state, Gamma~ 1.5 to the high-soft state, Gamma~2.8 and finally saturates. The index behavior was similar to that in a number of black hole (BH) candidates in which we showed that its saturation was an observational evidence of the presence of a BH. Based on this correlation, we applied a scaling method and determined that a secondary BH mass in OJ~287 is about ~1.25x10^8 solar masses, using the well-studied X-ray BH binaries XTE~1550--564, H~1743--322, 4U~1630--47, GRS~1915+105 as well as extragalactic BHs ESO~243--49 and M101~ULX--1, as reference sources. Also using the power spectrum analysis we inferred the size of the Compton cloud L_{CC}~ 10^{13} cm where X-ray spectra were formed. Using this value of L_{CC} we confirmed that a BH mass of the secondary in OJ~287 was of order of 10^8 solar masses as we derived using the index, Gamma-correlation (the scaling method) with respect of the mass accretion rate.Comment: 10 pages, 8 figure