723 research outputs found
A compact spectroradiometer for solar simulator measurements
Compact spectral irradiance probe has been designed and built which uses wedge filter in conjunction with silicon cell and operational amplifier. Probe is used to monitor spectral energy distribution of solar simulators and other high intensity sources
The Quantasyn, an improved quantum detector
Quantasyn provides absolute measurement of radiation flux in the range 1000 A to 4500 A and into the vacuum ultraviolet. This radiation detector cimbines the high quantum efficiency and inherent linearity of the silicon solar cell with the constant quantum response of the fluorescent organic compound liumogen
Compact spectroradiometer
Development and characteristics of spectroradiometer with wedge filters to eliminate adverse effect of pinholes in filter
Chandra view of Kes 79: a nearly isothermal SNR with rich spatial structure
A 30 ks \chandra ACIS-I observation of Kes 79 reveals rich spatial
structures, including many filaments, three partial shells, a loop and a
``protrusion''. Most of them have corresponding radio features. Regardless of
the different results from two non-equilibrium ionization (NEI) codes,
temperatures of different parts of the remnant are all around 0.7 keV, which is
surprisingly constant for a remnant with such rich structure. If thermal
conduction is responsible for smoothing the temperature gradient, a lower limit
on the thermal conductivity of 1/10 of the Spitzer value can be derived.
Thus, thermal conduction may play an important role in the evolution of at
least some SNRs. No spectral signature of the ejecta is found, which suggests
the ejecta material has been well mixed with the ambient medium. From the
morphology and the spectral properties, we suggest the bright inner shell is a
wind-driven shell (WDS) overtaken by the blast wave (the outer shell) and
estimate the age of the remnant to be 6 kyr for the assumed dynamics.
Projection is also required to explain the complicated morphology of Kes 79.Comment: 12 pages, 6 figures (3 in color), ApJ, in press, April 20, 200
X-Ray Light Curves of Gamma-ray Bursts Detected with the All-Sky Monitor on RXTE
We present X-ray light curves (1.5-12 keV) for fifteen gamma-ray bursts
(GRBs) detected by the All-Sky Monitor on the Rossi X-ray Timing Explorer. We
compare these soft X-ray light curves with count rate histories obtained by the
high-energy (>12 keV) experiments BATSE, Konus-Wind, the BeppoSAX Gamma-Ray
Burst Monitor, and the burst monitor on Ulysses. We discuss these light curves
within the context of a simple relativistic fireball and synchrotron shock
paradigm, and we address the possibility of having observed the transition
between a GRB and its afterglow. The light curves show diverse morphologies,
with striking differences between energy bands. In several bursts, intervals of
significant emission are evident in the ASM energy range with little or no
corresponding emission apparent in the high-energy light curves. For example,
the final peak of GRB 970815 as recorded by the ASM is only detected in the
softest BATSE energy bands. We also study the duration of bursts as a function
of energy. Simple, singly-peaked bursts seem consistent with the E^{-0.5} power
law expected from an origin in synchrotron radiation, but durations of bursts
that exhibit complex temporal structure are not consistent with this
prediction. Bursts such as GRB 970828 that show many short spikes of emission
at high energies last significantly longer at low energies than the synchrotron
cooling law would predict.Comment: 15 pages with 20 figures and 2 tables. In emulateapj format. Accepted
by ApJ
Supernova Remnants in the Magellanic Clouds. V. The Complex Interior Structure of the N206 SNR
The N206 supernova remnant (SNR) in the Large Magellanic Cloud (LMC) has long
been considered a prototypical "mixed morphology" SNR. Recent observations,
however, have added a new twist to this familiar plot: an elongated,
radially-oriented radio feature seen in projection against the SNR face.
Utilizing the high resolution and sensitivity available with the Hubble Space
Telescope, Chandra, and XMM-Newton, we have obtained optical emission-line
images and spatially resolved X-ray spectral maps for this intriguing SNR. Our
findings present the SNR itself as a remnant in the mid to late stages of its
evolution. X-ray emission associated with the radio "linear feature" strongly
suggests it to be a pulsar-wind nebula (PWN). A small X-ray knot is discovered
at the outer tip of this feature. The feature's elongated morphology and the
surrounding wedge-shaped X-ray enhancement strongly suggest a bow-shock PWN
structure.Comment: 41 pages including 7 figures, accepted for publication by the
Astrophysical Journa
Practical free-space quantum key distribution over 1 km
A working free-space quantum key distribution (QKD) system has been developed
and tested over an outdoor optical path of ~1 km at Los Alamos National
Laboratory under nighttime conditions. Results show that QKD can provide secure
real-time key distribution between parties who have a need to communicate
secretly. Finally, we examine the feasibility of surface to satellite QKD.Comment: 5 pages, 2 figures, 2 tables. Submitted to Physics Review Letters,
May 199
X-ray Spectroscopy of Candidate Ultracompact X-ray Binaries
We present high-resolution spectroscopy of the neutron star/low-mass X-ray
binaries (LMXBs) 4U 1850-087 and 4U 0513-40 as part of our continuing study of
known and candidate ultracompact binaries. The LMXB 4U 1850-087 is one of four
systems in which we had previously inferred an unusual Ne/O ratio in the
absorption along the line of sight, most likely from material local to the
binaries. However, our recent Chandra X-ray Observatory LETGS spectrum of 4U
1850-087 finds a Ne/O ratio by number of 0.22+/-0.05, smaller than previously
measured and consistent with the expected interstellar value. We propose that
variations in the Ne/O ratio due to source variability, as previously observed
in these sources, can explain the difference between the low- and
high-resolution spectral results for 4U 1850-087. Our XMM-Newton RGS
observation of 4U 0513-40 also shows no unusual abundance ratios in the
absorption along the line of sight. We also present spectral results from a
third candidate ultracompact binary, 4U 1822-000, whose spectrum is well fit by
an absorbed power-law + blackbody model with absorption consistent with the
expected interstellar value. Finally, we present the non-detection of a fourth
candidate ultracompact binary, 4U 1905+000, with an upper limit on the source
luminosity of < 1 x 10^{32} erg s^{-1}. Using archival data, we show that the
source has entered an extended quiescent state.Comment: 8 pages, 3 figures, accepted for publication to the Astrophysical
Journa
The first orbital solution for the massive colliding-wind binary HD93162 (=WR25)
Since the discovery, with the EINSTEIN satellite, of strong X-ray emission
associated with HD93162 (=WR25), this object has been predicted to be a
colliding-wind binary system. However, radial-velocity variations that would
prove the suspected binary nature have yet to be found. We spectroscopically
monitored this object to investigate its possible variability to address this
discordance. We compiled the largest available radial-velocity data set for
this star to look for variations that might be due to binary motion. We derived
radial velocities from spectroscopic data acquired mainly between 1994 and
2006, and searched these radial velocities for periodicities using different
numerical methods. For the first time, periodic radial-velocity variations are
detected. Our analysis definitively shows that the Wolf-Rayet star WR25 is an
eccentric binary system with a probable period of about 208 days.Comment: 7 pages, 4 figures, accepted by A+
Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE
We report on the discovery of hard spectral tails for energies above 10 keV
in the total and pulsed spectra of anomalous X-ray pulsars 1RXS J1708-4009, 4U
0142+61 and 1E 2259+586 using RXTE PCA (2-60 keV) and HEXTE (15-250 keV) data
and INTEGRAL IBIS ISGRI (20-300 keV) data. Improved spectral information on 1E
1841-045 is presented. The pulsed and total spectra measured above 10 keV have
power-law shapes and there is so far no significant evidence for spectral
breaks or bends up to ~150 keV. The pulsed spectra are exceptionally hard with
indices measured for 4 AXPs approximately in the range -1.0 -- 1.0. We also
reanalyzed archival CGRO COMPTEL (0.75-30 MeV) data to search for signatures
from our set of AXPs. No detections can be claimed, but the obtained
upper-limits in the MeV band indicate that for 1RXS J1708-4009, 4U 0142+61 and
1E 1841-045 strong breaks must occur somewhere between 150 and 750 keV.Comment: Accepted for publication in ApJ; 19 pages; 4 Tables; 15 Figures (6
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