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In a recent outburst which lasted for 260 days, the black hole candidate GRO J1655-40 exhibited a behaviour similar to its last outburst observed almost eight years ago. We analyze a total of 150 observational spells in 122 days of data spreaded over the entire outburst phase of Feb. 2005 to Oct. 2005. From our study, a comprehensive understanding of the detailed behaviour of this black hole candidate has emerged. Based on the degree of importance of the black body and the power-law components we divide the entire episode in four spectral states, namely, hard, soft, very soft and intermediate. Quasi-Periodic oscillations (QPOs) were found in two out of these four states, namely, in the hard and the intermediate states. In the hard state, at the rising phase of the outburst, QPO frequency ranged from 0.034 - 17.78Hz and the spectra was fitted by a disk black body, power-law and iron emission line at 6.2 - 6.5 keV. In the intermediate state, QPOs vary from 13.17Hz to 19.04Hz and the QPO frequency modulation in this state was not significant. The spectra in this state are well fitted by the disk black body and the power-law components. In the hard state of the declining phase of the outburst, we found QPOs of decreasing frequency from 13.14 Hz to 0.034 Hz. The spectra of this state were fitted by a disk black body and power-law components, but in the initial few days a cooler Comptonized component was required for a better fit. In the soft/very soft states, the spectral states are mostly dominated by the strong disk black body component. [ABSTRACT FROM AUTHOR]

TAUVEX brings us a unique opportunity to explore the temporal variability of UV emitting objects in the sky. One of the questions that we intend to resolve with TAUVEX is whether the 'variabilities' detected in active galaxies and quasars and in radiations around massive black holes in general are just random variations of the intensities or these are intrinsic to the disk system, and possibly due to the quasi-periodic oscillations (QPOs) which are well known to be observed in smaller black holes (nano-quasars). In this article, we present a physical mechanism for the QPOs and show that this is a generic mechanism which should be manifested in all types of active compact objects, ranging from quasars to nano-quasars. We propose some tests by which we may be able to tell if these are QPOs, even without waiting for a large number of cycles to test the periodicity. We present a few examples to impress that perhaps we have already seen QPOs in some objects. Multi-wavelength observation capabilities in TAUVEX may be used to pinpoint the nature of the variable sources more accurately. [ABSTRACT FROM AUTHOR]

A knowledge of the recombination time on the grain surfaces has been a major obstacle in deciding the production rate of molecular hydrogen and other molecules in the interstellar medium. We present a numerical study to compute this time for molecular hydrogen for various cloud and grain parameters. We also find the time dependence, particularly when a grain is freshly injected into the system. Apart from the fact that the recombination times seem to be functions of the grain parameters such as the activation barrier energy, temperature etc, our result also shows the dependence on the number of sites in the grain S and the effective accretion rate per site as of atomic hydrogen. Simply put, the average time that a pair of atomic hydrogens will take to produce one molecular hydrogen depends on how heavily the grain is already populated by atomic and molecular hydrogens and how fast the hopping and desorption times are. We show that if we write the average recombination time as Tr ∼ Sa/AH, where, AH is the hopping rate, then α could be much greater than 1 for all astrophysically relevant accretion rates. Thus the average formation rate of H2 is also dependent on the grain parameters, temperature and the accretion rate. We believe that our result will affect the overall rate of the formation of complex molecules such as methanol which require successive hydrogenation on the grain surfaces in the interstellar medium. [ABSTRACT FROM AUTHOR]

We obtained a broadband radio spectrum of the galactic compact object SS433 through the multi-wavelength campaign using the Giant Meter Radio Telescope (GMRT) and the Effelsberg 100-m Radio Telescope. The observations took place from 2005 January 03 to 2005 February 08 using eight different frequencies. We observed a flare which appeared to have started prior to January 18 and lasted till February 08. The light curves show a progressively larger time-delay as the radio frequency goes down. The peak of the 6 cm lightcurve is delayed by ∼ 3 days with respect to the peak of the 9 mm lightcurve. There is an indication of the flattening of the spectrum and possibly a turnover at ∼ 1.5 GHz. If we interpret this to be due to synchrotron self-absorption, the required magnetic field would become too large, however, free-free absorption by hot thermal surrounding medium formed due to stellar winds is still a possibility. All sky monitor (ASM) aboard Rossi X-ray Timing Experiment (RXTE) showed very high X-ray count on 2005 January 25 when the flare was well underway. This may be due to slamming of the radio 'bullets' with previously ejected, relatively slowly moving material. [ABSTRACT FROM AUTHOR]

We study the efficiency of molecular hydrogen recombination on grain surfaces using both the rate equation (which tracks the average number of species) and the master equation (which tracks the expectation values of the species). We have incorporated Langmuir-Hinselwood rejection term in obtaining the efficiency. We vise this result to compute H2 production rates as a function of the grain temperature and accretion rate of atomic hydrogen. Our general conclusion is that the H2 formation efficiency is very much dependent on the grain temperature and the accretion rate of the atomic hydrogen on grains. We provide tables of H2 production rates which could be readily used for future calculation of production of more complex molecules in the gas phase. [ABSTRACT FROM AUTHOR]

We present a summary of the recent multiwavelength campaign made in September-October, 2002, to observe SS 433. We used the Giant Meter Radio Telescope (GMRT) for radio observation, 1.2 meter Physical Research Laboratory Infra-red telescope at Mt Abu for IR, 1 meter Telescope at the State Observatory, Nainital for Optical photometry, 2.3 meter optical telescope at the Vainu Bappu observatory for spectrum and Rossi X-ray Timing Explorer (RXTE) Target of Opportunity (TOO) for X-ray observations. Sharp variations in intensity in time-scales of a few minutes in X-rays, IR and radio wavelengths have been discovered. We also discover a delay of about two days between IR and Radio. Double Fe line profiles which corresponded to red and blue components of the relativistic jet have been found in X-ray data. We present the broadband spectrum averaged over the campaign duration. [ABSTRACT FROM AUTHOR]

It has been long thought that the rings of saturn are probably not thicker than a few hundreds of meters. By actually following the motion of particles inside the decaying bending waves of the Saturn's rings and matching the resulting damping length of the bending waves launched by a number of moons with the actual damping lengths observed by Voyagar-II, we show that the thickness of the rings need not be larger than a few meters at the most. We present a few of these results. [ABSTRACT FROM AUTHOR]