Effects of Resonance in Quasiperiodic Oscillators of Neutron Star Binaries

Using a large quantity of Rossi X-ray Timing Explorer data presented in the literature I offer a detailed investigation into the accuracy of quasiperiodic oscillations (QPO) frequency determination. The QPO phenomenon seen in X-ray binaries is possibly a result of the resonance of the intrinsic (eigen) oscillations and harmonic driving forces of the system. I show that the resonances, in the presence of the damping of oscillations, occur at the frequencies which are systematically and randomly shifted with respect to the eigenfrequencies of the system. The shift value strongly depends on the damping rate which is measured by the halfwidth of the QPO feature. Taking into account this effect I analyze the QPO data for four Z-sources: Sco X-1, GX 340+0, GX 5-1, GX 17+2 and two atoll sources: 4U 1728-34, 4U 0614+09. The transition layer model (TLM) predicts the existence of the invariant quantity: delta, an inclination angle of the magnetospheric axis with respect to the normal to the disk. I calculate delta and the error bars of delta using the resonance shift and I find that the inferred delta-values are consistent with constants for these four Z-sources, where horizontal branch oscillation and kilohertz frequencies have been detected and correctly identified. It is shown that the inferred delta are in the range between 5.5 and 6.5 degrees. I conclude that the TLM seems to be compatible with data.Comment: 9 pages and 2 figures. Accepted for publication in the Astrophysical Journal Letters 2002 August 2

Correlations of Power-law Spectral and QPO Features In Black Hole Candidate Sources

Recent studies have shown that strong correlations are observed between low frequency QPO`s and the spectral power law index for a number of black hole candidate sources (BHC's), when these sources exhibit quasi-steady hard x-ray emission states. The dominant long standing interpretation of QPO's is that they are produced in and are the signature of the thermal accretion disk. Paradoxically, strong QPO`s are present even in the cases where the thermal component is negligible. We present a model which identifies the origin of the QPO's and relates them directly to the properties of a compact coronal region which is bounded by the adjustment from Keplerian to sub-Keplerian inflow into the BH and which is primarily responsible for the observed power law spectrum. The model also predicts the relationship between high and low frequency QPO's and shows how BH's can be unique identified from observations of the soft states of NS's and BHC's.Comment: 2 pages, to be published in Proc. of International Conference on Stellar Mass, Intermediate Mass and Super Massive Black Holes, Oct. 28-31, 2003, Kyoto, Japa

Scaling of the photon index vs mass accretion rate correlation and estimate of black hole mass in M101 ULX-1

We report the results of Swift and Chandra observations of an ultra-luminous X-ray source, ULX-1 in M101. We show strong observational evidence that M101 ULX-1 undergoes spectral transitions from the low/hard state to the high/soft state during these observations. The spectra of M101 ULX-1 are well fitted by the so-called bulk motion Comptonization (BMC) model for all spectral states. We have established the photon index (\Gamma) saturation level, \Gamma_{sat}=2.8 +/- 0.1, in the \Gamma vs. mass accretion rate (\dot M) correlation. This \Gamma-\dot M correlation allows us to evaluate black hole (BH) mass in M101 ULX-1 to be M_{BH}~(3.2 - 4.3)x10^4 solar masses assuming the spread in distance to M101 (from 6.4+/- 0.5 Mpc to 7.4+/-0.6 Mpc). For this BH mass estimate we use the scaling method taking Galactic BHs XTE~J1550-564, H~1743-322 and 4U~1630-472 as reference sources. The Gamma vs. \dot M correlation revealed in M101~ULX-1 is similar to that in a number of Galactic BHs and exhibits clearly the correlation along with the strong \Gamma saturation at ~2.8. This is robust observational evidence for the presence of a BH in M101 ULX-1. We also find that the seed (disk) photon temperatures are quite low, of order of 40-100 eV which is consistent with high BH mass in M101~ULX-1. Thus, we suggest that the central object in M101 ULX-1 has intermediate BH mass of order 10^{4} solar massesComment: 12 pages, 9 figures, accepted by Astronomy & Astrophysic

Correlations between kHz QPO and Low Frequency Features Attributed to Radial Oscillations and Diffusive Propagation in the Viscous Boundary Layer Around a Neutron Star

We present a dimensional analysis of two characteristic time scales in the boundary layer where the disk adjusts to the rotating neutron star (NS). The boundary layer is treated as a transition region between the NS surface and the first Keplerian orbit. The radial transport of the angular momentum in this layer is controlled by a viscous force defined by the Reynolds number, which in turn is related to the mass accretion rate. We show that the observed low-Lorentzian frequency is associated with radial oscillations in the boundary layer, where the observed break frequency is determined by the characteristic diffusion time of the inward motion of the matter in the accretion flow. Predictions of our model regarding relations between those two frequencies and frequencies of kHz QPO's compare favorably with recent observations for the source 4U 1728-34. This Letter contains a theoretical classification of kHz QPO's in NS binaries and the related low frequency features. Thus, results concerning the relationship of the low-Lorentzian frequency of viscous oscillations and the break frequency are presented in the framework of our model of kHz QPO's viewed as Keplerian oscillations in a rotating frame of reference.Comment: 10 pages, 4 figures, it it will appear in ApJLetter

On the Nature of the Compact Object in SS~433. Observational Evidence of X-ray Photon Index Saturation

We present an analysis of the X-ray spectral properties observed from black hole candidate (BHC) binary SS~433. We have analyzed RXTE data from this source, coordinated with Green Bank Interferometer/RATAN-600. We show that SS~433 undergoes a X-ray spectral transition from the low hard state (LHS) to the intermediate state (IS). We show that the X-ray broad-band energy spectra during all spectral states are well fit by a sum of so called ``Bulk Motion Comptonization (BMC) component'' and by two (broad and narrow) Gaussians for the continuum and line emissions respectively. In addition to these spectral model components we also find a strong feature that we identify as a "blackbody-like (BB)" component which color temperature is in the range of 4-5 keV in 24 IS spectra during the radio outburst decay in SS~433. Our observational results on the "high temperature BB" bump leads us to suggest the presence of gravitationally redshifted annihilation line emission in this source. I\ We have also established the photon index saturation at about 2.3 in index vs mass accretion correlation. This index-mass accretion correlation allows us to evaluate the low limit of black hole (BH) mass of compact object in SS~433, M_{bh}> 2 solar masses, using the scaling method using BHC GX 339-4 as a reference source. Our estimate of the BH mass in SS 433 is consistent with recent BH mass measurement using the radial-velocity measurements of the binary system by Hillwig & Gies who find that M_{x}=(4.3+/-0.8 solar masses. This is the smallest BH mass found up to now among all BH sources. Moreover, the index saturation effect versus mass accretion rate revealed in SS~433, like in a number of other BH candidates, is the strong observational evidence for the presence of a BH in SS~433.Comment: 29 pages, 14 figures. Accepted for the ApJ, 2010, October 1, v. 721 (2

The Observed Galactic Annihilation Line. Possible Signature of the Cluster for Accreting Small Mass Black Holes

Compton Gamma Ray Observatory, OSSE, SMM, TGRS, balloon and recent INTEGRAL data reveal a feature of the 0.511 MeV annihilation radiation of the Galactic Center with a flux of approximately 5x 10^{-4}~0.511 MeV photons cm^{-2} s^{-1}. We argue that e+e- pairs can be generated when the X-ray radiation photons and ~10-30 MeV photons interact with each other in the compact region in the proximity of the Galactic Center black hole. In fact, disks formed near black holes of 10^{17} g mass should emit the ~ 10 MeV temperature blackbody radiation. If positron e+ sources are producing about 10^{42} e+ s^{-1} near the Galactic Center they would annihilate on the way out and result in 0.511 MeV emission. We suggest that the annihilation radiation can be an observational consequence of the interaction of the accretion disk radiation of the SMall Mass Black Holes (SMMBHs) with X-ray radiation in the Galactic Center. This is probably the only way to identify and observe these SMMBHs.Comment: 21 pages, 1 figure, to appear in the ApJ, 10 March 2006, v 639 2 issu

ESO 243-49 HLX-1: scaling of X-ray spectral properties and black hole mass determination

We report the results of Swift/XRT observations (2008-2015) of a hyper-luminous X-ray source, ESO 243-49 HLX-1. We found a strong observational evidence that ESO 243-49 HLX-1 underwent spectral transitions from the low/hard state to the high/soft state during these observations. The spectra of ESO 243-49 HLX-1 are well fitted by the so-{called} bulk motion Comptonization model for all spectral states. We have established the photon index Gamma saturation level, Gamma_{sat}$=3.0+/-0.1, in the correlation of Gamma versus mass accretion rate dot M. This Gamma-dot M correlation allows us to estimate the black hole (BH) mass in ESO 243-49 HLX-1 to be M_{BH}~ 7x 10^4 solar masses, assuming the distance to ESO 243-49 of 95 Mpc. For the BH mass estimate we used the scaling method, taking Galactic BHs XTE~J1550-564, H~1743-322 and 4U~1630-472, and an extragalactic BH source, M101 ULX-1 as reference sources. The Gamma-dot M correlation revealed in ESO 243-49 HLX-1 is similar to those in a number of Galactic and extragalactic BHs and it clearly shows the correlation along with the strong Gamma saturation at ~ 3. This is a reliable observational evidence of a BH in ESO 243-49 HLX-1. We also found that the seed (disk) photon temperatures are quite low, of order of 50-140 eV which are consistent with a high BH mass in ESO 243-49 HLX-1.Comment: 21 pages, 8 figures, accepted by Astronomy and Astrophysics on August 29, 201

delta-invariant for Quasi-periodic Oscillations and Physical Parameters of 4U 0614+09 binary

The recently formulated Two Oscillator (TO) model interprets the lowest of the kilohertz frequencies of the twin peak quasi-periodic oscillations in X -ray binaries as the Keplerian frequency nu_K. The high twin frequency nu_h in this model holds the upper hybrid frequency relation to the rotational frequency of the neutron star's magnetosphere Omega: nu_h^2=nu_K^2+ 4(Omega/2pi)^2. The vector Omega is assumed to have an angle delta with the normal to the disk. The first oscillator in the TO model allows one to interpret the horizontal branch observed below 100 Hz as the lower mode of the Keplerian oscillator under the influence of the Coriolis force, with frequency nu_L being dependent on nu_h, nu_K and delta. For some stars such as 4U 0614+09, Sco X-1 and 4U 1702-42, nu_h, nu_K and nu_L have been observed simultaneously providing the opportunity to check the central prediction of the TO model: the constancy of delta for a particular source. Given the considerable variation of each of these three frequencies, the existence of an observational invariant with a clear physical interpretation as a global parameter of the neutron star magnetosphere is an important test of the TO model. Using the results of recent observations of 4U 0614+09 we verify the existence of this invariant and determine the angle delta=15^o.6+/- 0.^o5 for this star. The second oscillator in the model deals with a radial (presumably sound) oscillation and diffuse process in the viscous layer surrounding the neutron star. Our analysis of the viscous oscillation frequency nu_V and the break frequency nu_b of the diffusion shows that the spin value of the inner boundary of the transition layer for 4U 0614+09 is at least two times more than values for 4U 1728-34 and Sco X-1.Comment: 13 pages, 4 figures, accepted for publications in ApJ Letter

Rayleigh - Taylor Gravity Waves and Quasiperiodic Oscillation Phenomenon in X-ray Binaries

Accretion onto compact objects in X-ray binaries [black hole, neutron star (NS), white dwarf] is characterized by non-uniform flow density profiles. Such an effect of heterogeneity in presence of gravitational forces and pressure gradients exhibits Raylegh-Taylor gravity waves (RTGW). They should be seen as quasioperiodic wave oscillations (QPO). In this paper I show that the main QPO frequency, which is very close to the Keplerian frequency, is split into separate frequencies (hybrid and low branch) under the influence of the gravitational forces in the rotational frame of reference. The observed low and high QPO frequencies are an intrinsic signature of the RTGW. I elaborate the conditions for the density profile when the RTGW oscillations are stable. A comparison of the inferred QPO frequencies with QPO observations is presented. I find that hectohertz frequencies detected from NS binaries can be identified as the RTGW low branch frequencies. I also predict that an observer can see the double NS spin frequency during the NS long (super) burst events when the pressure gradients and buoyant forces are suppressed. The Coriolis force is the only force which acts in the rotational frame of reference and its presence causes perfect coherent pulsations with a frequency twice of the NS spin.Comment: 14 pages and 2 figures, ApJ in pres