487 research outputs found
Spectral and Timing Nature of the Symbiotic X-ray Binary 4U 1954+319: The Slowest Rotating Neutron Star in an X-ray Binary System
The symbiotic X-ray binary 4U 1954+319 is a rare system hosting a peculiar
neutron star (NS) and an M-type optical companion. Its ~5.4h NS spin period is
the longest among all known accretion-powered pulsars and exhibited large (~7%)
fluctuations over 8 years. A spin trend transition was detected with Swift/BAT
around an X-ray brightening in 2012. The source was in quiescent and bright
states before and after this outburst based on 60 ks Suzaku observations in
2011 and 2012. The observed continuum is well described by a Comptonized model
with the addition of a narrow 6.4 keV Fe Kalpha line during the outburst.
Spectral similarities to slowly rotating pulsars in high-mass X-ray binaries,
its high pulsed fraction (~60-80%), and the location in the Corbet diagram
favor high B-field (>~1e+12 G) over a weak field as in low-mass X-ray binaries.
The observed low X-ray luminosity (1e+33-1e+35 erg/s), probable wide orbit, and
a slow stellar wind of this SyXB make quasi-spherical accretion in the subsonic
settling regime a plausible model. Assuming a ~1e+13 G NS, this scheme can
explain the ~5.4 h equilibrium rotation without employing the magnetar-like
field (~1e+16 G) required in the disk accretion case. The time-scales of
multiple irregular flares (~50 s) can also be attributed to the free-fall time
from the Alfven shell for a ~1e+13 G field. A physical interpretation of SyXBs
beyond the canonical binary classifications is discussed.Comment: 20 pages, 18 figures, 3 tables, accepted for publication in the
Astrophysical Journa
A Suborbital Payload for Soft X-ray Spectroscopy of Extended Sources
We present a suborbital rocket payload capable of performing soft X-ray
spectroscopy on extended sources. The payload can reach resolutions of
~100(lambda/dlambda) over sources as large as 3.25 degrees in diameter in the
17-107 angstrom bandpass. This permits analysis of the overall energy balance
of nearby supernova remnants and the detailed nature of the diffuse soft X-ray
background. The main components of the instrument are: wire grid collimators,
off-plane grating arrays and gaseous electron multiplier detectors. This
payload is adaptable to longer duration orbital rockets given its comparatively
simple pointing and telemetry requirements and an abundance of potential
science targets.Comment: Accepted to Experimental Astronomy, 12 pages plus 1 table and 17
figure
Design and Performance of the Wide-Field X-Ray Monitor on Board the High-Energy Transient Explorer 2
The Wide-field X-ray Monitor (WXM) is one of the scientific instruments
carried on the High Energy Transient Explorer 2 (HETE-2) satellite launched on
2000 October 9. HETE-2 is an international mission consisting of a small
satellite dedicated to provide broad-band observations and accurate
localizations of gamma-ray bursts (GRBs). A unique feature of this mission is
its capability to determine and transmit GRB coordinates in almost real-time
through the burst alert network. The WXM consists of three elements: four
identical Xe-filled one-dimensional position-sensitive proportional counters,
two sets of one-dimensional coded apertures, and the main electronics. The WXM
counters are sensitive to X-rays between 2 keV and 25 keV within a
field-of-view of about 1.5 sr, with a total detector area of about 350 cm.
The in-flight triggering and localization capability can produce a real-time
GRB location of several to 30 arcmin accuracy, with a limiting sensitivity of
erg cm. In this report, the details of the mechanical
structure, electronics, on-board software, ground and in-flight calibration,
and in-flight performance of the WXM are discussed.Comment: 28 pages, 24 figure
Termination of Electron Acceleration in Thundercloud by Intra/Inter-cloud Discharge
An on-ground observation program for high energy atmospheric phenomena in
winter thunderstorms along Japan Sea has been performed via measurements of
gamma-ray radiation, atmospheric electric field and low-frequency radio band.
On February 11, 2017, the radiation detectors recorded gamma-ray emission
lasting for 75 sec. The gamma-ray spectrum extended up to 20 MeV and was
reproduced by a cutoff power-law model with a photon index of
, being consistent with a Bremsstrahlung radiation from a
thundercloud (as known as a gamma-ray glow and a thunderstorm ground
enhancement). Then the gamma-ray glow was abruptly terminated with a nearby
lightning discharge. The low-frequency radio monitors, installed 50 km
away from the gamma-ray observation site recorded leader development of an
intra/inter-cloud discharge spreading over 60 km area with a 300 ms
duration. The timing of the gamma-ray termination coincided with the moment
when the leader development of the intra/inter-cloud discharge passed 0.7 km
horizontally away from the radiation monitors. The intra/inter-cloud discharge
started 15 km away from the gamma-ray observation site. Therefore, the
glow was terminated by the leader development, while it did not trigger the
lightning discharge in the present case.Comment: 12 pages, 4 figures, accepted for publication in Geophysical Research
Letter
Discovery of a Compact X-ray Source in the LMC Supernova Remnant N23 with Chandra
An X-ray compact source was discovered with Chandra in a supernova remnant
(SNR) N23, located in the Large Magellanic Cloud. The compact source (CXOU
J050552.3-680141) is seen in only the hard band (> 2 keV) image of N23, while
the soft band image (< 2 keV) shows diffuse emission of the SNR, with an extent
of ~60 arcsec times ~80 arcsec. The compact source is located at almost the
center of N23, and there is no identifiable object for the source from previous
observations at any other wavelength. The source spectrum is best explained by
a power-law model with a photon index of 2.2 (1.9-2.7) and an
absorption-corrected luminosity of 1.0 x 10^34 ergs s^-1 in the 0.5--10 keV
band for a distance of 50 kpc. Neither pulsation nor time variability of the
source was detected with this observation with a time resolution of 3.2 sec.
These results correspond with those of Hughes et al. (2006) who carried out
analysis independently around the same time as our work. Based on information
from the best-fit power-law model, we suggest that the source emission is most
likely from a rotation-powered pulsar and/or a pulsar wind nebula. It is
generally inferred that the progenitor of N23 is a core-collapsed massive star.
Based on information from the best-fit power-law model, we suggest that the
source emission is most likely from a rotation-powered pulsar and/or a pulsar
wind nebula. It is generally inferred that the progenitor of N23 is a
core-collapsed massive star.Comment: 16 pages, 5 figures, 1 table, Accepted to Ap
The Effects of Diuretics on Intracellular Ca2+ Dynamics of Arteriole Smooth Muscles as Revealed by Laser Confocal Microscopy
The regulation of cytosolic Ca2+ homeostasis is essential for cells, including vascular smooth muscle cells. Arterial tone, which underlies the maintenance of peripheral resistance in the circulation, is a major contributor to the control of blood pressure. Diuretics may regulate intracellular Ca2+ concentration ([Ca2+]i) and have an effect on vascular tone. In order to investigate the influence of diuretics on peripheral resistance in circulation, we investigated the alteration of [Ca2+]i in testicular arterioles with respect to several categories of diuretics using real-time confocal laser scanning microscopy. In this study, hydrochlorothiazide (100 µM) and furosemide (100 µM) had no effect on the [Ca2+]i dynamics. However, when spironolactone (300 µM) was applied, the [Ca2+]i of smooth muscles increased. The response was considerably inhibited under either extracellular Ca2+-free conditions, the presence of Gd3+, or with a treatment of diltiazem. After the thapsigargin-induced depletion of internal Ca2+ store, the spironolactone-induced [Ca2+]i dynamics was slightly inhibited. Therefore, the spironolactone-induced dynamics of [Ca2+]i can be caused by either a Ca2+ influx from extracellular fluid or Ca2+ mobilization from internal Ca2+ store, with the former being dominant. As tetraethylammonium, an inhibitor of the K+ channel, slightly inhibited the spironolactone-induced [Ca2+]i dynamics, the K+ channel might play a minor role in those dynamics. Tetrodotoxin, a neurotoxic Na+ channel blocker, had no effect, therefore the spironolactone-induced dynamics is a direct effect to smooth muscles, rather than an indirect effect via vessel nerves
The scaling infrared DSE solution as a critical end-point for the family of decoupling ones
Both regular (the zero-momentum ghost dressing function not diverging), also
named decoupling, and critical (diverging), also named scaling, Yang-Mills
propagators solutions can be obtained by analyzing the low-momentum behaviour
of the ghost propagator Dyson-Schwinger equation (DSE) in Landau gauge. The
asymptotic expression obtained for the regular or decoupling ghost dressing
function up to the order fits pretty well the low-momentum
ghost propagator obtained through the numerical integration of the coupled
gluon and ghost DSE in the PT-BFM scheme. Furthermore, when the size of the
coupling renormalized at some scale approaches some critical value, the PT-BFM
results seems to tend to the the scaling solution as a limiting case.Comment: Presented in QCSHS09; Madrid (Spain), 30 Aug. 201
Wide band X-ray Imager (WXI) and Soft Gamma-ray Detector (SGD) for the NeXT Mission
The NeXT mission has been proposed to study high-energy non-thermal phenomena
in the universe. The high-energy response of the super mirror will enable us to
perform the first sensitive imaging observations up to 80 keV. The focal plane
detector, which combines a fully depleted X-ray CCD and a pixellated CdTe
detector, will provide spectra and images in the wide energy range from 0.5 keV
to 80 keV. In the soft gamma-ray band up to ~1 MeV, a narrow field-of-view
Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe
detector will provide precise spectra with much higher sensitivity than present
instruments. The continuum sensitivity will reach several times 10^(-8)
photons/s/keV/cm^(2) in the hard X-ray region and a few times10^(-7)
photons/s/keV/cm^(2) in the soft gamma-ray region.Comment: 12 pages, 13 figures, to be published in the SPIE proceedings 5488,
typo corrected in sec.
Prospect of Studying Hard X- and Gamma-Rays from Type Ia Supernovae
We perform multi-dimensional, time-dependent radiation transfer simulations for hard X-ray and γ -ray emissions,
following radioactive decays of 56Ni and 56Co, for two-dimensional delayed-detonation models of Type Ia
supernovae (SNe Ia). The synthetic spectra and light curves are compared with the sensitivities of current and
future observatories for an exposure time of 106 s. The non-detection of the γ -ray signal from SN 2011fe at
6.4 Mpc by SPI on board INTEGRAL places an upper limit on the mass of 56Ni of 1.0 M, independently from
observations in any other wavelengths. Signals from the newly formed radioactive species have not yet been
convincingly measured from any SN Ia, but future X-ray and γ -ray missions are expected to deepen the observable horizon to provide high energy emission data for a significant SN Ia sample. We predict that the hard X-ray detectors on board NuStar (launched in 2012) or ASTRO-H (scheduled for launch in 2014) will reach to SNe Ia at ∼15 Mpc, i.e., one SN every few years. Furthermore, according to the present results, the soft γ -ray detector
on board ASTRO-H will be able to detect the 158 keV line emission up to ∼25 Mpc, i.e., a few SNe Ia per year.
Proposed next-generation γ -ray missions, e.g., GRIPS, could reach to SNe Ia at ∼20–35 Mpc by MeV observations.
Those would provide new diagnostics and strong constraints on explosion models, detecting rather directly the main energy source of supernova light
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