Discovery of a Peculiar Dip from GX 301-2

We present temporal and spectral properties of a unique X-ray dip in GX 301-2 as seen with Rossi X-ray Timing Explorer in May 2010. The X-ray pulsation from the source gradually declined prior to the dip, disappears for one spin cycle during the dip and is abruptly restored in the spin cycle immediately after the dip. Moreover, the phase-integrated spectrum of the source becomes softer before and during the dip and it quickly hardens again following the dip. Our findings indicate the fact that the mechanism for pulsations gradually turned off briefly and underlying dim and softer emission likely from the accretion column became observable in the brief absence of high level emission due to wind accretion.Comment: Accepted for publication in A&A Letter

A transient high-coherence oscillation in 4U 1820-30

We re-analyzed two Rossi X-Ray Timing Explorer archival observations of the atoll source 4U 1820-30 in order to investigate the detailed time-frequency properties of the source during the intervals when a ~7 Hz QPO was detected by Wijnands et al. (1999, ApJ, 512, L39). We find that in both observations, in addition to a QPO signal lasting a couple of minutes as previously reported, there is a much narrower transient oscillation with a life time of only a few seconds. Within this time, the oscillation is consistent with being coherent. Its integrated fractional rms is around 10% and its frequency 7.3 Hz and 5.7 Hz in the two observations. We discuss the possible association of this QPO with other oscillations known both in Neutron-Star and Black-Hole systems, concentrating on the similarities with the narrow 5-7 Hz oscillations observed at high flux in Black-Hole Candidates.Comment: 5 pages, 3 figures, accepted for publication in A&A. FIgure 1 is reduced in resolution, full-resolution version of this text available at http://www.merate.mi.astro.it/~belloni/ms0335.ps.g

ASCA observations of the galactic bulge hard x-ray source GRS 1758--258

GRS 1758-258 is one of the few persistent hard X-ray emitters (E>100 keV) in the Galaxy. Using the ASCA satellite, we have obtained the first detailed data on GRS 1758-258 in the 1-10 keV range, where previous observations were affected by confusion problems caused by the nearby strong source GX5-1. The spectrum is well described by a power law with photon index 1.7 without strong Fe emission lines. A prominent soft excess, as observed with ROSAT when the hard X-ray flux was in a lower intensity state, was not detected. However, the presence of a soft spectral component, accounting for at most 5% of the 0.1-300 keV flux, cannot be excluded. The accurate measurement of interstellar absorption (N_H=(1.5+-0.1) x 10^22 cm -2) corresponds to an optical extinction which definitely excludes the presence of a massive companion.Comment: 7 pages, AAS latex [11pt,aaspptwo,flushrt,tighten], + 1.ps figure Accepted for pubblication in ApJ, 09 02 96 Also available at http://fy.chalmers.se/~haardt/personal/curr.html Figures 1 and 2 available upon request at [email protected]

Kinematics of Black Hole X-ray Binary GRS 1915+105

The space velocity of a stellar black hole encodes the history of its formation and evolution. Here we measure the 3-dimensional motion of the microquasar GRS 1915+105, using a decade of astrometry with the NRAO Very Long Baseline Array, together with the published radial velocity. The velocity in the Galactic Plane deviates from circular rotation by 53-80 +_ 8 km/s, where the range covers any specific distance from 6-12 kpc. Perpendicular to the plane, the velocity is only 10 +_ 4 km/s. The peculiar velocity is minimized at a distance 9-10 kpc, and is then nearly in the radial direction towards the Galactic Center. We discuss mechanisms for the origin of the peculiar velocity, and conclude that it is most likely a consequence of Galactic velocity diffusion on this old binary, rather than the result of a supernova kick during the formation of the 14 Mo black hole. Finally, a brief comparison is made with 4 other BH binaries whose kinematics are well determined.Comment: 16 pages, 4 figures. ApJ accepte

Discovery of a Peculiar Dip from GX 301-2

We present temporal and spectral properties of a unique X-ray dip in GX 301-2 as seen with Rossi X-ray Timing Explorer in May 2010. The X-ray pulsation from the source gradually declined prior to the dip, disappears for one spin cycle during the dip and is abruptly restored in the spin cycle immediately after the dip. Moreover, the phase-integrated spectrum of the source becomes softer before and during the dip and it quickly hardens again following the dip. Our findings indicate the fact that the mechanism for pulsations gradually turned off briefly and underlying dim and softer emission likely from the accretion column became observable in the brief absence of high level emission due to wind accretion.Comment: Accepted for publication in A&A Letter

Wigner quasi-probability distribution for the infinite square well: energy eigenstates and time-dependent wave packets

We calculate the Wigner quasi-probability distribution for position and momentum, P_W^(n)(x,p), for the energy eigenstates of the standard infinite well potential, using both x- and p-space stationary-state solutions, as well as visualizing the results. We then evaluate the time-dependent Wigner distribution, P_W(x,p;t), for Gaussian wave packet solutions of this system, illustrating both the short-term semi-classical time dependence, as well as longer-term revival and fractional revival behavior and the structure during the collapsed state. This tool provides an excellent way of demonstrating the patterns of highly correlated Schrodinger-cat-like `mini-packets' which appear at fractional multiples of the exact revival time.Comment: 45 pages, 16 embedded, low-resolution .eps figures (higher resolution, publication quality figures are available from the authors); submitted to American Journal of Physic

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

Strong Aperiodic X-ray Variability and Quasi-Periodic Oscillation in X-ray Nova XTE J1550-564

We report the discovery of strong aperiodic X-ray variability and quasi-periodic oscillation (QPO) in the X-ray light curves of a new X-ray Nova, XTE J1550-564, and the evolution of the observed temporal properties during the rise of the recent X-ray outburst. The power spectral analysis of the first observation reveals strong aperiodic X-ray variability of the source (~28%), as well as the presence of a QPO at ~82 mHz with fractional rms amplitude ~14% over the 2-60 keV energy range. Also apparent is the first harmonic of the QPO with the amplitude ~9%. As the X-ray flux increases, the source tends to become less variable, and the QPO frequency increases rapidly, from 82 mHz to 4 Hz, over the flux (2-50 keV) range of 1.73-5.75 x 10^{-8} ergs cm^{-2} s^{-1}. The amplitude of the fundamental component of the QPO varies little, while that of the harmonic follows a decreasing trend. The fundamental component strengthens toward high energies, while its harmonic weakens. Initially, the power spectrum is roughly flat at low frequencies and turns into a power law at high frequencies, with the QPO harmonic sitting roughly at the break. In later observations, however, the high-frequency portion of the continuum can actually be better described by a broken power law (as opposed to a simple power law). This effect becomes more apparent at higher energies. The overall amplitude of the continuum shows a similar energy dependence to that of the fundamental component of the QPO. Strong rapid X-ray variability, as well as hard energy spectrum, makes XTE J1550-564 a good black hole candidate. We compare its temporal properties with those of other black hole candidates.Comment: 12 pages, including 5 figures. To appear in ApJ Letters, vol. 512 (1999

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