5,016 research outputs found
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
- …