X-ray Observation of SS 433 with RXTE

Apart from regular monitoring by ASM, the compact object SS 433 was observed with RXTE several times last two/three years. We present the first analysis of these observations. We also include the results of the recent exciting TOO campaign made during donour inferior (orbital phase $\phi=0$) and superior ($\phi=0.5$) conjunctions which took place on Oct. 2nd, 2003, and on March 13th, 2004 respectively, when the jet itself was directly pointing towards us (i.e., precessional phase $\psi \sim 0$). Generally, we found that two distinct lines fit the spectra taken on all these days. We present some of the light-curves and the X-ray spectra, and show that the Doppler shifts of the emitted lines roughly match those predicted by the kinematic model for the jets. We find that the line with a higher energy can be best identified with a FeXXVI Ly-$\alpha$ transition while the line with lower energy can be identified with a FeXXV (1s2p - 1s$^2$) transition. We observe that the X-ray flux on March 13th, 2004 (when the base of the jet is exposed) is more than twice compared to that on Oct. 2nd, 2003 (when the base is covered by the companion). We find the flux to continue to remain high at least till another orbital period. We believe that this is because SS 433 was undergoing a weak flaring activity during the recent observation.Comment: 15 pages, 6 figures, submitted for publication in MNRAS (April, 2004

S-matrix elements for gauge theories with and without implemented constraints

We derive an expression for the relation between two scattering transition amplitudes which reflect the same dynamics, but which differ in the description of their initial and final state vectors. In one version, the incident and scattered states are elements of a perturbative Fock space, and solve the eigenvalue problem for the `free' part of the Hamiltonian --- the part that remains after the interactions between particle excitations have been `switched off'. Alternatively, the incident and scattered states may be coherent states that are transforms of these Fock states. In earlier work, we reported on the scattering amplitudes for QED, in which a unitary transformation relates perturbative and non-perturbative sets of incident and scattered states. In this work, we generalize this earlier result to the case of transformations that are not necessarily unitary and that may not have unique inverses. We discuss the implication of this relationship for Abelian and non-Abelian gauge theories in which the `transformed', non-perturbative states implement constraints, such as Gauss's law.Comment: 8 pages. Invited contribution to Foundation of Physics for an issue honoring Prof. Lawrence Horwitz on his 65th Birthda

A Disk--Jet interaction model for the X--Ray Variability in Microquasars

We propose a simple dynamical model that may account for the observed spectral and temporal properties of GRS 1915+105 and XTE J1550-5634. The model is based on the assumption that a fraction of the radiation emitted by a hot spot lying on the accreting disk is dynamically Comptonized by the relativistic jet that typically accompanies the microquasar phenomenon. We show that scattering by the jet produces a detectable modulation of the observed flux. In particular, we found that the phase lag between hard and soft photons depends on the radial position of the hot spot and, if the angle between the jet and the line of sight is sufficiently large, the lags of the fundamental and its harmonics may be either positive or negative.Comment: 14 pages, 4 figures, accepted for publication in ApJ Part

On the modulation of low frequency Quasi-Periodic Oscillations in black-hole transients

We studied the properties of the low-frequency quasi-periodic oscillations detected in a sample of six black hole candidates (XTE J1550-564, H 1743-322, XTE J1859+226, 4U 1630-47,GX 339-4, XTE J1650-500) observed by the Rossi XTE satellite. We analyzed the relation between the full width half maximum and the frequency of all the narrow peaks detected in power density spectra where a type-C QPO is observed. Our goal was to understand the nature of the modulation of the signal by comparing the properties of different harmonic peaks in the power density spectrum. We find that for the sources in our sample the width of the fundamental and of the first harmonic are compatible with a frequency modulation, while that of the sub-harmonic is independent of frequency, possibly indicating the presence of an additional modulation in amplitude. We compare our results with those obtained earlier from GRS 1915+105 and XTE J1550-564.Comment: 8 pages, 3 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

A Unified Description of the Timing Features of Accreting X-ray Binaries

We study an empirical model for a unified description of the power spectra of accreting neutron stars and black holes. This description is based on a superposition of multiple Lorentzians and offers the advantage that all QPO and noise components are dealt with in the same way, without the need of deciding in advance the nature of each component. This approach also allows us to compare frequencies of features with high and low coherences in a consistent manner and greatly facilitates comparison of power spectra across a wide range of source types and states. We apply the model to six sources, the low-luminosity X-ray bursters 1E 1724-3045, SLX 1735-269 and GS 1826-24, the high-latitude transient XTE J1118+480, the bright system Cir X-1, and the Z source GX 17+2. We find that it provides a good description of the observed spectra, without the need for a scale-free (1/f) component. We update previously reported correlations between characteristic frequencies of timing features in the light of this new approach and discuss similarities between different types of systems which may point towards similar underlying physics.Comment: 13 pages, to appear in The Astrophysical Journa

Observations of Rapid Disk-Jet Interaction in the Microquasar GRS 1915+105

We present evidence that ~ 30 minute episodes of jet formation in the Galactic microquasar GRS 1915+105 may sometimes entirely be a superposition of smaller, faster phenomena. We base this conclusion on simultaneous X-ray and infrared observations in July 2002, using the Rossi X-ray Timing Explorer and the Palomar 5 meter telescope. On two nights, we observed quasi-periodic infrared flares from GRS 1915+105, each accompanied by a set of fast oscillations in the X-ray light curve (indicating an interaction between the jet and accretion disk). In contrast to similar observations in 1997, we find that the duration of each X-ray cycle matches the duration of its accompanying infrared flare, and we observed one instance in which an isolated X-ray oscillation occurred at the same time as a faint infrared "subflare" (of duration ~ 150 seconds) superimposed on one of the main flares. From these data, we are able to conclude that each X-ray oscillation had an associated faint infrared flare and that these flares blend together to form, and entirely comprise, the ~ 30 minute events we observed. Part of the infrared emission in 1997 also appears to be due to superimposed small flares, but it was overshadowed by infrared-bright ejections associated with the appearance of a sharp "trigger" spike in each X-ray cycle that were not present in 2002. We also study the evolution of the X-ray spectrum and find significant differences in the high energy power law component, which was strongly variable in 1997 but not in 2002. Taken together, these observations reveal the diversity of ways in which the accretion disk and jet in black hole systems are capable of interacting and solidify the importance of the trigger spike for large ejections to occur on ~ 30 minute timescales in GRS 1915+105.Comment: 17 pages, 9 figures; accepted for publication in The Astrophysical Journa

Anti-correlated hard X-ray time lags in Galactic black hole sources

We investigate the accretion disk geometry in Galactic black hole sources by measuring the time delay between soft and hard X-ray emissions. Similar to the recent discoveries of anti-correlated hard X-ray time lags in Cyg X-3 and GRS 1915+105, we find that the hard X-rays are anti-correlated with soft X-rays with a significant lag in another source: XTE J1550-564. We also find the existence of pivoting in the model independent X-ray spectrum during these observations. We investigate time-resolved X-ray spectral parameters and find that the variation in these parameters is consistent with the idea of a truncated accretion disk. The QPO frequency, which is a measure of the size of truncated accretion disk, too changes indicating that the geometric size of the hard X-ray emitting region changes along with the spectral pivoting and soft X-ray flux. Similar kind of delay is also noticed in 4U 1630-47.Comment: 14 pages, 7 figures, accepted for publication in Ap

Evidence of Class Transitions in GRS 1915+105 from IXAE Data

GRS 1915+105 shows at least twelve distinct classes of light curves. By analysing the data obtained from Indian X-ray Astronomy Experiment (IXAE) instrument aboard IRS-P3 satellite, we show that in at least two days, transitions between one class to another were observed. In these days the so-called $\kappa$ class went to $\rho$ class and $\chi$ class went to $\rho$ class. In the frequency-time plane such transitions exhibited change in quasi-periodic oscillation (QPO) frequency. We could detect that low-frequency QPOs can occur in anticipation of a class transition several hundred minutes before the actual transitionComment: 14 pages, 3 figures, Astrophysical Journa