Astronomical X‐ray sources provide opportunities for global remote sensing of the Earth’s atmosphere. We present a novel technique, complementary to other methods, that involves atmospheric ...occultation of celestial X‐ray sources to measure the neutral density of the upper mesosphere and lower thermosphere in the 70‐ to 150‐km region. These are the first such measurements in the 2‐ to 45‐keV (∼0.28–6.0 Å) passband, and the technique permits both dayside and nightside soundings. Measurements were made using the Unconventional Stellar Aspect (USA) experiment aboard the Advanced Research and Global Observation Satellite (ARGOS) and the Proportional Counter Array (PCA) on the Rossi X‐ray Timing Explorer (RXTE) satellite. The data are time‐tagged, energy‐resolved photon extinction curves which provide sufficient information to determine the altitude profile of the neutral atmosphere. An ensemble of observations of the Crab Nebula and Cygnus X‐2 were used to develop a “proof of concept” of this new technique, and results are presented for each source.
As requirements for satellite on-board processing throughput continue to increase, users of radiation tolerant electronics are driven to ever decreasing feature sizes. As device feature sizes drop ...below the current radiation hardened capabilities of 130 nm one should include more of the high-energy space environment in the analysis of the potential effects. The effects due to particle showers produced by very high-energy celestial gamma-rays and charged particles have been neglected to date because of their low numbers, but small feature size large area devices may have susceptibilities. Above an energy of 30 MeV, the primary photon interaction with matter is pair production. These particles in turn interact producing an electromagnetic shower. The result of such an interaction is that many charged particles will pass through the system at one time. The integrated flux is approximately 10 photons/cm 2 /day with each photon producing two or more charged daughter particles. Since the incident particles are photons they are not affected by the Earth's magnetic field and the integrated rate will be approximately the same for any orbit. An interaction anywhere on the space vehicle, primary structure, subsystem enclosures, or actual electronic parts will produce a shower that can affect any components downstream of it. There is a definite need to study this problem. The NASA gamma-ray large area space telescope, to be launched in the spring of 2008, will be the most sophisticated Gamma- ray telescope ever flown. GLAST is a pair conversion telescope which measures the direction and energy of the daughter products of the incident photon using a silicon strip tracker and CsI calorimeter. It will provide detailed information on both celestial and Earth albedo Gamma-rays as well as providing additional detail on the charged particle environment in low Earth orbit through its on-board and ground segment charged particle rejection capabilities.
The radiation hardness characteristics of nano-electromechanical single-walled carbon nanotube (SWNT) memory elements has been studied. The NRAM bits have been exposed to 100 krad, 1 Mrad and 10 Mrad ...of gamma-radiation. Initial test results indicate that NRAM is an extremely radiation hard memory.
Optimization of the energy resolution of Josephson tunnel junction X-ray detectors requires the minimization of event-to-event variation in the number of nonequilibrium quasiparticles that tunnel and ...are thereby detected for monochromatic input. This requires a detailed understanding of the determinants of the time scales for the degradation of the energy and expansion of the disturbed volume, of possible quasiparticle (QP) self-trapping and phonon bottlenecking, and of the impact of materials parameters such as grain size. Moreover, the signals of distributed detectors cannot be interpreted without a detailed model of the evolution of the spatial variation in QP density. These matters, and the extent to which the details of the QP tunneling pulse probes the energy degradation and expansion, are discussed. The expansion is modeled in two dimensions with Monte Carlo simulations of ballistic quasiparticle propagation between randomizing collisions and compared with published data for a distributed junction detector. Alternative explanations of the high quasiparticle loss rate and curvature seen in the published plots of the relative fraction of the QP detected by the two sensing junctions are offered.
Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 seconds is possibly the brightest well-isolated pulse observed to date. A fine time ...resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. But, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. We found it difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.
The Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources using the observations of the exceptionally bright ...gamma-ray burst (GRB) 130427A. We found that GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.
We present a linear diffusion model for the evolution of the double-peaked
outburst in the transient source XTEJ1118+480. The model treats the two
outbursts as episodic mass deposition at the outer ...radius of the disk followed
by evolution of disk structure according to a diffusion process. We demonstrate
that light curves with fast-rise, exponential decay profile are a general
consequence of the diffusion process. Deconvolution of the light curve proves
to be feasible and gives an input function specifying mass deposition at the
outer disk edge as well as the total mass of the disk, both as functions of
time. The derived evolution of total disk mass can be correlated with the
observed evolution of the ~0.1 Hz QPO in the source reported in Wood et al.
(2000).
We present a linear diffusion model for the evolution of the double-peaked outburst in the transient source XTEJ1118+480. The model treats the two outbursts as episodic mass deposition at the outer ...radius of the disk followed by evolution of disk structure according to a diffusion process. We demonstrate that light curves with fast-rise, exponential decay profile are a general consequence of the diffusion process. Deconvolution of the light curve proves to be feasible and gives an input function specifying mass deposition at the outer disk edge as well as the total mass of the disk, both as functions of time. The derived evolution of total disk mass can be correlated with the observed evolution of the ~0.1 Hz QPO in the source reported in Wood et al. (2000).
Astrophys.J.571:763-770,2002 This paper reports X-ray spectral observations of a relatively nearby z =
0.048 BL Lacertae (BL Lac) object 1ES1959+650, which is a potential TeV
emitter. The ...observations include 31 short pointings made by the Unconventional
Stellar Aspect (USA) Experiment on board the Advanced Research and Global
Observation Satellite (ARGOS), and 17 pointings by the PCA on board the Rossi
X-ray Timing Explorer (RXTE). Most of these observations were spaced by less
than 1 day. \es was detected by the ARGOS USA detector in the range 1-16 keV,
and by the PCA in the 2-16 keV range but at different times. During the closely
spaced RXTE observations beginning on 2000 July 28, an ending of one flare and
a start of another are visible, associated with spectral changes, where the
photon index Gamma ranges between ~ 1.4 and 1.7, and the spectrum is harder
when the source is brighter. This implies that 1ES1959 is an XBL-type blazar,
with the X-ray emission likely to originate via the synchrotron process. The
USA observations reveal another flare that peaked on 2000 November 14 and
doubled the flux within a few days, again associated with spectral changes of
the same form. The spectral variability correlated with the flux and timing
characteristics of this object that are similar to those of other nearby BL
Lacs, and suggest relativistic beaming with a Doppler factor delta > 1.6 and
magnetic fields of the order of a few mG. We also suggest that the steady
component of the X-ray emission -- present in this object as well as in other
XBLs -- may be due to the large-scale relativistic jet (such as measured by
Chandra in many radio-loud AGN), but pointing very closely to our line of
sight.
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