1,608 research outputs found
Common Patterns in the Evolution between the Luminous Neutron Star Low-Mass X-ray Binary Subclasses
The X-ray transient XTE J1701-462 was the first source observed to evolve
through all known subclasses of low-magnetic-field neutron star low-mass X-ray
binaries (NS-LMXBs), as a result of large changes in its mass accretion rate.
To investigate to what extent similar evolution is seen in other NS-LMXBs we
have performed a detailed study of the color-color and hardness-intensity
diagrams (CDs and HIDs) of Cyg X-2, Cir X-1, and GX 13+1 -- three luminous
X-ray binaries, containing weakly magnetized neutron stars, known to exhibit
strong secular changes in their CD/HID tracks. Using the full set of Rossi
X-ray Timing Explorer Proportional Counter Array data collected for the sources
over the 16 year duration of the mission, we show that Cyg X-2 and Cir X-1
display CD/HID evolution with close similarities to XTE J1701-462. Although GX
13+1 shows behavior that is in some ways unique, it also exhibits similarities
to XTE J1701-462, and we conclude that its overall CD/HID properties strongly
indicate that it should be classified as a Z source, rather than as an atoll
source. We conjecture that the secular evolution of Cyg X-2, Cir X-1, and GX
13+1 -- illustrated by sequences of CD/HID tracks we construct -- arises from
changes in the mass accretion rate. Our results strengthen previous suggestions
that within single sources Cyg-like Z source behavior takes place at higher
luminosities and mass accretion rates than Sco-like Z behavior, and lend
support to the notion that the mass accretion rate is the primary physical
parameter distinguishing the various NS-LMXB subclasses.Comment: 20 pages, 14 figures, 5 tables -- matches published version in Ap
On the geometric nature of low-frequency quasi-periodic oscillations in neutron-star low-mass X-ray binaries
We report on a detailed analysis of the so-called ~1 Hz quasi-periodic
oscillation (QPO) in the eclipsing and dipping neutron-star low-mass X-ray
binary EXO 0748-676. This type of QPO has previously been shown to have a
geometric origin. Our study focuses on the evolution of the QPO as the source
moves through the color-color diagram, in which it traces out an
atoll-source-like track. The QPO frequency increases from ~0.4 Hz in the hard
state to ~25 Hz as the source approaches the soft state. Combining power
spectra based on QPO frequency reveals additional features that strongly
resemble those seen in non-dipping/eclipsing atoll sources. We show that the
low-frequency QPOs in atoll sources and the ~1 Hz QPO in EXO 0748-676 follow
similar relations with respect to the noise components in their power spectra.
We conclude that the frequencies of both types of QPOs are likely set by (the
same) precession of a misaligned inner accretion disk. For high-inclination
systems, like EXO 0748-676, this results in modulations of the neutron-star
emission due to obscuration or scattering, while for lower-inclination systems
the modulations likely arise from relativistic Doppler boosting and
light-bending effects.Comment: Updated to published version (ApJ, 812, 80
Discovery of the near-infrared counterpart to the luminous neutron-star low-mass X-ray binary GX 3+1
Using the High Resolution Camera onboard the Chandra X-ray Observatory, we
have measured an accurate position for the bright persistent neutron-star X-ray
binary and atoll source GX 3+1. At a location that is consistent with this new
position we have discovered the near-infrared (NIR) counterpart to GX 3+1 in
images taken with the PANIC and FourStar cameras on the Magellan Baade
Telescope. The identification of this K_s=15.8+-0.1 mag star as the counterpart
is based on the presence of a Br-gamma emission line in a NIR spectrum taken
with the FIRE spectrograph on the Baade Telescope. The absolute magnitude
derived from the best available distance estimate to GX 3+1 indicates that the
mass donor in the system is not a late-type giant. We find that the NIR light
in GX 3+1 is likely dominated by the contribution from a heated outer accretion
disk. This is similar to what has been found for the NIR flux from the brighter
class of Z sources, but unlike the behavior of atolls fainter (Lx ~ 1e36 to
1e37 erg/s) than GX 3+1, where optically-thin synchrotron emission from a jet
probably dominates the NIR flux.Comment: Accepted for publication in Ap
Simbol untuk Menunjang Sistem Informasi Desain Kemasan Makanan dan Minuman Plastik
The use of plastic as packaging food and beverages has increased along with the development of technological and cultural changes in society. But this change has not been followed by an adequate understanding of the various types of plastic and usefulness. Symbols and information system on packaging become important information for consumer and visual communication designer. Based on field research, literature research and desktop research, the author summarizes that the information in the form of significant symbols are important to be put on the design of plastic packaging for food or beverage. During this time, several foods and beverages in plastic packaging have included the plastic code. But generally consumers do not have enough knowledge about these codes. This is where the role of visual communication designers becomes an important. Symbols and information systems which prepared in well design will be more easily to understand. With easily understandable symbol and information systems, consumer certainly would be wiser to choose and avoid the negative impact during the bad use of food and beverage plastics packaging
The Complex Phase Lag Behavior of the 3-12 Hz Quasi-Periodic Oscillations during the Very High State of XTE J1550-564
We present a study of the complex phase lag behavior of the low-frequency
(<20 Hz) quasi-periodic oscillations (QPOs) in the X-ray transient and
black-hole candidate XTE J1550-564 during its very high state. We distinguish
two different types of low-frequency QPOs, based on their coherence and
harmonic content. The first type is characterized by a 6 Hz QPO with a Q (the
QPO frequency divided by the QPO width) of <3 and with a harmonic at 12 Hz. The
second type of QPO is characterized by a 6 Hz QPO with a Q value of >6 and with
harmonics at 3, 12, 18, and possibly at 9 Hz. Not only the Q values and the
harmonic content of the two types are different, but also their phase lag
behavior. For the first type of QPO, the low energy photons (<5 keV) of both
the 6 Hz QPO and its harmonic at 12 Hz lag the hard energy photons (>5 keV) by
as much as 1.3 radian. The phase lags of the second type of QPO are more
complex. The soft photons (<5 keV) of the 3 and the 12 Hz QPOs lag the hard
photons (>5 keV) by as much as 1.0 radian. However, the soft photons of the 6
Hz QPO precede the hard ones by as much as 0.6 radian. This means that
different harmonics of this type of QPO have different signs for their phase
lags. This unusual behavior is hard to explain when the lags are due to
light-travel-time differences between the photons at different energies, e.g.,
in a Comptonizing region surrounding the area where the QPOs are formed.Comment: Accepted for publication in ApJ Letters, 29 September 199
MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VI. Kinematics Analysis of a Complete Sample of Blazar Jets
We discuss the jet kinematics of a complete flux-density-limited sample of
135 radio-loud active galactic nuclei (AGN) resulting from a 13 year program to
investigate the structure and evolution of parsec-scale jet phenomena. Our
analysis is based on new 2 cm Very Long Baseline Array (VLBA) images obtained
between 2002 and 2007, but includes our previously published observations made
at the same wavelength, and is supplemented by VLBA archive data. In all, we
have used 2424 images spanning the years 1994-2007 to study and determine the
motions of 526 separate jet features in 127 jets. The data quality and temporal
coverage (a median of 15 epochs per source) of this complete AGN jet sample
represents a significant advance over previous kinematics surveys. In all but
five AGNs, the jets appear one-sided, most likely the result of differential
Doppler boosting. In general the observed motions are directed along the jet
ridge line, outward from the optically thick core feature. We directly observe
changes in speed and/or direction in one third of the well-sampled jet
components in our survey. While there is some spread in the apparent speeds of
separate features within an individual jet, the dispersion is about three times
smaller than the overall dispersion of speeds among all jets. This supports the
idea that there is a characteristic flow that describes each jet, which we have
characterized by the fastest observed component speed. The observed maximum
speed distribution is peaked at ~10c, with a tail that extends out to ~50c.
This requires a distribution of intrinsic Lorentz factors in the parent
population that range up to ~50. We also note the presence of some rare
low-pattern speeds or even stationary features in otherwise rapidly flowing
jets... (abridged)Comment: 19 pages, 10 figures, 2 tables, accepted by the Astronomical Journal;
online only material is available from
http://www.cv.nrao.edu/2cmVLBA/pub/MOJAVE_VI_suppl.zi
MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. VII. Blazar Jet Acceleration
We discuss acceleration measurements for a large sample of extragalactic
radio jets from the MOJAVE program which studies the parsec-scale jet structure
and kinematics of a complete, flux-density-limited sample of Active Galactic
Nuclei (AGN). Accelerations are measured from the apparent motion of individual
jet features or "components" which may represent patterns in the jet flow. We
find that significant accelerations are common both parallel and perpendicular
to the observed component velocities. Parallel accelerations, representing
changes in apparent speed, are generally larger than perpendicular acceleration
that represent changes in apparent direction. The trend for larger parallel
accelerations indicates that a significant fraction of these changes in
apparent speed are due to changes in intrinsic speed of the component rather
than changes in direction to the line of sight. We find an overall tendency for
components with increasing apparent speed to be closer to the base of their
jets than components with decreasing apparent speed. This suggests a link
between the observed pattern motions and the underlying flow which, in some
cases, may increase in speed close to the base and decrease in speed further
out; however, common hydro-dynamical processes for propagating shocks may also
play a role. About half of the components show "non-radial" motion, or a
misalignment between the component's structural position angle and its velocity
direction, and these misalignments generally better align the component motion
with the downstream emission. Perpendicular accelerations are closely linked
with non-radial motion. When observed together, perpendicular accelerations are
usually in the correct direction to have caused the observed misalignment.Comment: 17 pages, 11 figures, 1 table, accepted by the Astrophysical Journa
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