1,476 research outputs found
RAPTOR observations of delayed explosive activity in the high-redshift gamma-ray burst GRB 060206
The RAPid Telescopes for Optical Response (RAPTOR) system at Los Alamos
National Laboratory observed GRB 060206 starting 48.1 minutes after gamma-ray
emission triggered the Burst Alert Telescope (BAT) on-board the Swift
satellite. The afterglow light curve measured by RAPTOR shows a spectacular
re-brightening by ~1 mag about 1 h after the trigger and peaks at R ~ 16.4 mag.
Shortly after the onset of the explosive re-brightening the OT doubled its flux
on a time-scale of about 4 minutes. The total R-band fluence received from GRB
060206 during this episode is 2.3e-9 erg/cm2. In the rest frame of the burst (z
= 4.045) this yields an isotropic equivalent energy release of ~0.7e50 erg in
just a narrow UV band 130 +/- 22 nm. We discuss the implications of RAPTOR
observations for untriggered searches for fast optical transients and studies
of GRB environments at high redshift.Comment: Submitted to ApJ Letter
The Optical Gravitational Lensing Experiment. Monitoring of QSO 2237+0305
We present results from 2 years of monitoring of Huchra's lens (QSO
2237+0305) with the 1.3 m Warsaw telescope on Las Campanas, Chile. Photometry
in the V band was done using a newly developed method for image subtraction.
Reliable subtraction without Fourier division removes all complexities
associated with the presence of a bright lensing galaxy. With positions of
lensed images adopted from HST measurements it is relatively easy to fit the
variable part of the flux in this system, as opposed to modeling of the
underlying galaxy. For the first time we observed smooth light variation over a
period of a few months, which can be naturally attributed to microlensing. We
also describe automated software capable of real time analysis of the images of
QSO 2237+0305. It is expected that starting from the next observing season in
1999 an alert system will be implemented for high amplification events (HAE) in
this object. Time sampling and photometric accuracy achieved should be
sufficient for early detection of caustic crossings.Comment: 8 pages (including 4 figures and table), latex, emulateapj, submitted
to ApJ, revised version - minor change
Limits on I-band microvariability of the Galactic Bulge Miras
We search for microvariability in a sample of 485 Mira variables with high
quality I-band light curves from the second generation Optical Gravitational
Lensing Experiment (OGLE-II). Rapid variations with amplitudes in the ~0.2-1.1
mag range lasting hours to days were discovered in Hipparcos data by de Laverny
et al. (1998). Our search is primarily sensitive to events with time-scales of
about 1 day, but retains a few percent efficiency (per object) for detecting
unresolved microvariability events as short as 2 hours. We do not detect any
candidate events. Assuming that the distribution of the event time profiles is
identical to that from the Hipparcos light curves we derive the 95% confidence
level upper limit of 0.038 per year per star for the rate of such events (1 per
26 years per average object of the ensemble). The high event rates of the order
of 1 per year per star implied by the Hipparcos study in the H_P band are
excluded with high confidence by the OGLE-II data in the I band. Our
non-detection could still be explained by much redder spectral response of the
I filter compared to the H_P band or by population differences between the
bulge and the solar neighborhood. In any case, the OGLE-II I-band data provide
the first limit on the rate of the postulated microvariability events in Mira
stars and offer new quantitative constraints on their properties. Similar
limits are obtained for other pulse shapes and a range of the assumed
time-scales and size-frequency distributions.Comment: Accepted for publication in Ap
Numerical Study of Modular 5.56 mm Standard Assault Rifle Referring to Dynamic Characteristics
The paper describes investigations carried out to verify a loading mechanism of a newly designed modular assault rifle MSBS-5.56. A complex character of interaction between its elements during a reloading process encouraged the authors implement a numerical approach based on the multibody system to specify the essential dynamic characteristics. The achieved results were compared to the data recorded during the experimental tests on the shooting range. Owing to the proposed modelling methodology, a good agreement between experimental and numerical studies has been achieved.A numerical model presented in the paper will be applied in further investigations to analyse strength parameters of the reloading mechanism and to conduct additional optimisation studies
The first direct detection of a gravitational micro-lens toward the Galactic bulge
We present a direct detection of the gravitational lens that caused the
microlensing event MACHO-95-BLG-37. This is the first fully resolved
microlensing system involving a source in the Galactic bulge, and the second
such system in general. The lens and source are clearly resolved in images
taken with the High Resolution Channel of the Advanced Camera for Surveys on
board the Hubble Space Telescope (HST) ~9 years after the microlensing event.
The presently available data are not sufficient for the final, unambiguous
identification of the gravitational lens and the microlensed source. While the
light curve models combined with the high resolution photometry for individual
objects indicate that the source is red and the lens is blue, the
color-magnitude diagram for the line of sight and the observed proper motions
strongly support the opposite case. The first scenario points to a metal-poor
lens with mass M = ~0.6 M_Sun at the distance D_l = ~4 kpc. In the second
scenario the lens could be a main-sequence star with M = 0.8 - 0.9 M_Sun about
half-way to the Galactic bulge or in the foreground disk, depending on the
extinction.Comment: Accepted for publication in Ap
Analysis of RR Lyrae Stars in the Northern Sky Variability Survey
We use data from the Northern Sky Variability Survey (NSVS), obtained from
the first generation Robotic Optical Transient Search Experiment (ROTSE-I), to
identify and study RR Lyrae variable stars in the solar neighborhood. We
initially identified 1197 RRab (RR0) candidate stars brighter than the ROTSE
median magnitude V = 14. Periods, amplitudes, and mean V magnitudes are
determined for a subset of 1188 RRab stars with well defined light curves.
Metallicities are determined for 589 stars by the Fourier parameter method and
by the relationship between period, amplitude, and [Fe/H]. We comment upon the
difficulties of clearly classifying RRc (RR1) variables in the NSVS dataset.
Distances to the RRab stars are calculated using an adopted
luminosity-metallicity relation with corrections for interstellar extinction.
The 589 RRab stars in our final sample are used to study the properties of the
RRab population within 5 kpc of the Sun. The Bailey diagram of period versus
amplitude shows that the largest component of this sample belongs to Oosterhoff
type I. Metal-rich ([Fe/H] > -1) RRab stars appear to be associated with the
Galactic disk. Our metal-rich RRab sample may include a thin disk as well as a
thick disk population, although the uncertainties are too large to establish
this. There is some evidence among the metal-rich RRab stars for a decline in
scale height with increasing [Fe/H], as was found by Layden (1995). The
distribution of RRab stars with -1 < [Fe/H] < -1.25 indicates that within this
metallicity range the RRab stars are a mixture of stars belonging to halo and
disk populations.Comment: 68 pages, 26 figures, 9 tables, accepted to A
The Optical Gravitational Lensing Experiment. Short Distance Scale to the LMC
We present {\it UBVI} photometry of the eclipsing binary HV2274 - the system
which has been recently used for distance determination to the LMC by Guinan et
al. (1998). We determine the interstellar reddening to the star,
E(B-V)=0.149+/-0.015 mag, based on observed colors of the star. This value is
in excellent agreement with the mean reddening towards HV2274 obtained from
photometry of the red clump stars in the surrounding field. The reddening is
almost twice as large as determined by Guinan et al. (1998).
We discuss the consequences of reddening underestimate. Most likely HV2274 is
located much closer with the distance modulus to the star and the LMC: m-M =
18.22+/-0.13 mag supporting the short distance scale to the LMC. Such a
distance modulus is in excellent agreement with the recent distance
determinations with RR Lyr and red clump stars.Comment: 11 pages, Latex, 2 Figures. Accepted for publication in Astrophysical
Journal Letters. New version - trimmed to fit ApJL. Additional determination
of the reddening towards HV2274 with OB star
RAPTOR observations of the early optical afterglow from GRB 050319
The RAPid Telescopes for Optical Response (RAPTOR) system at Los Alamos
National Laboratory observed GRB 050319 starting 25.4 seconds after gamma-ray
emission triggered the Burst Alert Telescope (BAT) on-board the Swift
satellite. Our well sampled light curve of the early optical afterglow is
composed of 32 points (derived from 70 exposures) that measure the flux decay
during the first hour after the GRB. The GRB 050319 light curve measured by
RAPTOR can be described as a relatively gradual flux decline (power-law index
alpha = -0.37) with a transition, at about 400 s after the GRB, to a faster
flux decay (alpha = -0.91). The addition of other available measurements to the
RAPTOR light curve suggests that another emission component emerged after 10^4
s. We hypothesize that the early afterglow emission is powered by extended
energy injection or delayed reverse shock emission followed by the emergence of
forward shock emission.Comment: Accepted for publication in ApJ Letters. To see a short movie of
fading GRB 050319 go to
http://www.raptor.lanl.gov/images/GRB050319/grb050319_movie_annotated.gi
Microlensing optical depth toward the Galactic Bulge using bright sources from OGLE-II
We present a measurement of the microlensing optical depth toward the
Galactic Bulge based on 4 years of the OGLE-II survey using Red Clump Giant
(RCG). Using 32 events we find tau=2.55_{-0.46}^{+0.57}* 10^{-6} at
(l,b)=(1.16, -2.75). Taking into account the measured gradient along the
Galactic latitude b, tau = [ (4.48+/- 2.37) + (0.78+/- 0.84)* b]* 10^{-6}, this
value is consistent with previous measurements using RCG sources and recent
theoretical predictions. We determine the microlensing parameters and select
events using a model light curve with the flux blending. We find that ~38% of
the OGLE-II events which appear to have RCG sources are actually due to much
fainter stars blended with a bright companion. We show explicitly that model
fits without blending result in similar tau estimates through partial
cancellation of contributions from higher detection efficiency, underestimated
time-scales and larger number of selected events. This approach, however, leads
to biased time-scale distributions and event rates. Consequently, microlensing
studies should carefully consider source confusion effects even for bright
stars.Comment: 49 pages and 18 figures, ApJ in press, the value changed due to the
systematic correctio
The initial zones of the atrioventricular node: really neglected anatomical features of potential clinical significance?
The constant evolution of medical knowledge and accompanying development
of diagnostic and treatment possibilities for arrhythmias and conduction disturbances
has reawakened interest in the structure and function of the conduction
system of the human heart, especially in the region of the atrioventricular (AV)
junction and within the junction itself. Of the large number of studies dealing
with the AV junction few focus on the initial zones of the AV node. These were
described for the first time by Tawara in 1906. Similarly, Anderson et al. distinguished
two origins of the AV node, the left one running towards the basis of
the mitral valve and the right one leading towards the tricuspid valve. The differences
in length and scale could be the result of the adoption of different reference
points.
The study was carried out on the material of 50 human hearts, of both sexes
and ranging in age from 22 to 93, which were fixed in 10% formalin and 98%
ethanol solution. The tissue obtained was fixed in the 10% formalin solution
and, after being sunk in the paraffin, was cut into layers of about 10 μm thick.
According to the age of the hearts, every 10th or 6th section was stained by the
Masson-Goldner method. The preparations were examined under a LEICA 2000
and BIOLAR 2 microscope at magnifications of 2× to 400×.
Each of the 50 examined hearts contained the atrioventricular node and its initial
parts. We observed that the initial zone of the AV node is created by an
assembly of cells typical for a conduction system that can create three groups
that are initially independent of each other and are always arranged around the
AV nodal artery. In all the hearts examined we found at least two initial parts of
the node: the superior and inferior. These two groups were present in 45 hearts
(90%). In the last 5 cases (10%) there was also a middle group. No cases were
found either with a single initial group or without any initial groups. In the
sections examined the superior group appeared to be first in 27 hearts (54%),
while in 23 cases (46%) the inferior group was first. The length of each group
was measured from its first appearance to its first direct contact with the second
part. The length of the superior part varied from 0.15 to 2.91 mm (mean 0.90 ± 0.6 mm), the inferior from 0.11 to 2.41 mm (mean 0.88 ± 0.6 mm) and the middle from 0.67 to 2.21 mm (mean 1.04 ± 0.7 mm). As mentioned above, in
all 50 hearts there was a direct connection between the atrial muscle and the
upper origin of AV node. Furthermore, in all sections (100%) the same part of
the interatrial septal muscle was connected to the compact part of the node.
Additionally, in 3 cases (6%) we were able to observe direct connections between
the muscle fibres running from the fasciculus limbicus inferior to the
initial zone of the AV node: in 2 cases (4%) with the superior group and in
1 case (2%) with the inferior group. In 8% of the material the atrial muscle of
the supra-orificial zone made direct contact with the superior initial group and
the compact zone of the node and in 10% there was contact between the
suborificial muscle and the inferior group and the compact part of the node.
This configuration was not observed in relation to the middle and inferior groups
- …