On the two types of steady hard X-ray states of GRS 1915+105

Using the data of 5 years of RXTE observations we investigate the X-ray spectral and timing properties of GRS 1915+105 during the hard steady states. According to the results of our simultaneous X-ray spectral and timing analysis the behavior the source during the hard steady states can be reduced to a couple of major distinct types. i) Type I states: The dominant hard component of the energy spectrum has characteristic quasi- exponential cut-off at 50-120 keV. The broad-band power density spectrum of the source shows significant high frequency noise component with a cut-off at 60-80 Hz. ii) Type II states: The hard spectral component has a break in its slope at ~12-20 keV. The high frequency part of the power density spectrum fades quickly lacking significant variability at frequencies higher than ~30 Hz. These two types of the X-ray hard states are also clearly distinguished by their properties in the radio band: while during the type I observations the source tends to be 'radio-quiet', the type II observations are characterized by high level of radio flux ('plateau' radio states). In this work we demonstrate aforementioned differences using the data of 12 representative hard steady state observations. We conclude that the difference between these two types can be probably explained in terms of different structure of the accretion flow in the immediate vicinity of the compact object due to presence of relativistic outflow of matter.Comment: 16 pages, including 3 figures, submitted to Astrophysical Journal Letter

Detection of a 5-Hz QPO from X-ray Nova GRS 1739-278

The X-ray nova GRS1739-278 flared up near the Galactic center in the spring of 1996. Here we report on the discovery of a ~5-Hz quasi-periodic oscillations (QPO) in RXTE/PCA observations of GRS1739-278. The QPO were only present when the source was in its very high state, and disappeared later, when it made a transition down into the high state. We present the energy spectra of this black hole candidate measured in both high and very high states, and discuss the similarities between this system and other X-ray transients.Comment: 12 pages, 4 figures, accepted for publication in ApJ Letter

Observations of the X-ray Afterglows of GRB011211 and GRB001025 by XMM-Newton

We present the XMM-Newton observations of X-ray afterglows of the gamma-ray bursts GRB 011211 and GRB 001025. For GRB 011211 XMM detected fading X-ray object with an average flux in 0.2-10 keV declining from 2.7$\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$ during the first 5 ks of 27-ks observation to 1.0$\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$ toward the end of the observation. The spectrum of the afterglow can be fit to a power law with alpha=2.16$\pm$0.03 modified for the Galactic absorption. No significant evolution of spectral parameters has been detected during the observation. Similar X-ray spectrum with alpha=2.01$\pm$0.09 has been observed by the XMM from the GRB 001025. The non-detection of any extra absorption in these spectra above the Galactic value is an interesting fact and may impose restrictions to the favorable GRB models involving burst origin in star-forming regions. Finally we discuss soft X-ray lines from GRB 011211 reported by Reeves et al.(2002) and conclude that there is no definitive evidence for the presense of these lines in the spectrum.Comment: submitted to ApJL (7 pages, 4 figures, 2 tables, emulateapj.sty