179 research outputs found
The memory space: Exploring future uses of Web 2.0 and mobile internet through design interventions.
The QuVis Quantum Mechanics Visualization project aims to address challenges
of quantum mechanics instruction through the development of interactive
simulations for the learning and teaching of quantum mechanics. In this
article, we describe evaluation of simulations focusing on two-level systems
developed as part of the Institute of Physics Quantum Physics resources.
Simulations are research-based and have been iteratively refined using student
feedback in individual observation sessions and in-class trials. We give
evidence that these simulations are helping students learn quantum mechanics
concepts at both the introductory and advanced undergraduate level, and that
students perceive simulations to be beneficial to their learning.Comment: 15 pages, 5 figures, 1 table; accepted for publication in the
American Journal of Physic
Interactive Simulations To Support Quantum Mechanics Instruction for Chemistry Students
Study of the photon flux from the night sky at La Palma and Namibia, in the wavelength region relevant for imaging atmospheric Cherenkov telescopes
The level of the night sky background light at La Palma and Namibia was
determined, with emphasis on the wavelength region and solid angle coverage
relevant for the operation of imaging atmospheric Cherenkov telescopes. The
dependence of the night sky background light both on celestial coordinates
(alt, az) and on galactic coordinates (b, l) was measured, with an angular
resolution of about 1 degr. Average light levels near the zenith are similar in
both locations -- 2.2 x 10^12 to 2.6 x 10^12 photons per sr s m^2 for 300 nm <
lambda < 650 nm. With increasing zenith angle the level of background light
increases at La Palma, whereas a constant level is measured in Namibia. Near
the center of the Milky Way, background light levels are increased by a factor
up to 4 and more. Also the level of light backscattered from the ground has
been studied.Comment: 21 Pages, 12 figures, Latex, Nucl. Instr. Meth., in pres
Laue diffraction lenses for astrophysics: From theory to experiments
Based on the laws of X-ray diffraction in crystals, Laue lenses offer a promising way to achieve the sensitivity and angular resolution leap required for the next generation of hard X-ray and gamma-ray telescopes. The present paper describes the instrumental responses of Laue diffraction lenses designed for nuclear astrophysics. Different possible geometries are discussed, as well as the corresponding spectral and imaging capabilities. These theoretical predictions are then compared with Monte-Carlo simulations and experimental results (ground and stratospheric observations from the CLAIRE project)
Simultaneous X-Ray and TeV Gamma-Ray Observations of the TeV Blazar Markarian 421 during February and May 2000
In this paper we present the results of simultaneous observations of the TeV
blazar Markarian 421 (Mrk 421) at X-ray and TeV Gamma-ray energies with the
Rossi X-Ray Timing Explorer (RXTE) and the stereoscopic Cherenkov Telescope
system of the HEGRA (High Energy Gamma Ray Astronomy) experiment, respectively.
The source was monitored from February 2nd to February 16th and from May 3rd to
May 8th, 2000. We discuss in detail the temporal and spectral properties of the
source. Remarkably, the TeV observations of February 7th/8th showed
statistically significant evidence for substantial TeV flux variability on 30
min time scale. We show the results of modeling the data with a time dependent
homogeneous Synchrotron Self-Compton (SSC) model. The X-ray and TeV gamma-ray
emission strengths and energy spectra together with the rapid flux variability
strongly suggest that the emission volume is approaching the observer with a
Doppler factor of 50 or higher. The different flux variability time scales
observed at X-rays and TeV Gamma-rays indicate that a more detailed analysis
will require inhomogeneous models with several emission zones.Comment: Accepted for Publication in ApJ, 21 Pages, 5 Figure
The Energy Spectrum of TeV Gamma-Rays from the Crab Nebula as measured by the HEGRA system of imaging air Cherenkov telescopes
The Crab Nebula has been observed by the HEGRA (High-Energy Gamma-Ray
Astronomy) stereoscopic system of imaging air Cherenkov telescopes (IACTs) for
a total of about 200 hrs during two observational campaigns: from September
1997 to March 1998 and from August 1998 to April 1999. The recent detailed
studies of system performance give an energy threshold and an energy resolution
for gamma-rays of 500 GeV and ~ 18%, respectively. The Crab energy spectrum was
measured with the HEGRA IACT system in a very broad energy range up to 20 TeV,
using observations at zenith angles up to 65 degrees. The Crab data can be
fitted in the energy range from 1 to 20 TeV by a simple power-law, which yields
dJg/dE = (2.79+/-0.02 +/- 0.5) 10^{-7} E^{-2.59 +/- 0.03 +/- 0.05}, ph m^{-2}
s^{-1} TeV^{-1} The Crab Nebula energy spectrum, as measured with the HEGRA
IACT system, agrees within 15% in the absolute scale and within 0.1 units in
the power law index with the latest measurements by the Whipple, CANGAROO and
CAT groups, consistent within the statistical and systematic errors quoted by
the experiments. The pure power-law spectrum of TeV gamma-rays from the Crab
Nebula constrains the physics parameters of the nebula environment as well as
the models of photon emission.Comment: to appear in ApJ, 29 pages, 6 figure
Rejection of the hypothesis that Markarian 501 TeV photons are pure Bose-Einstein condensates
The energy spectrum of the Blazar type galaxy Markarian 501 (Mrk 501) as
measured by the High-Energy-Gamma-Ray Astronomy (HEGRA) air Cerenkov telescopes
extends beyond 16 TeV and constitutes the most energetic photons observed from
an extragalactic object. A fraction of the emitted spectrum is possibly
absorbed in interactions with low energy photons of the diffuse extragalactic
infrared radiation, which in turn offers the unique possibility to measure the
diffuse infrared radiation density by TeV spectroscopy. The upper limit on the
density of the extragalactic infrared radiation derived from the TeV
observations imposes constraints on models of galaxy formation and stellar
evolution. One of the recently published ideas to overcome severe absorption of
TeV photons is based upon the assumption that sources like Mrk 501 could
produce Bose-Einstein condensates of coherent photons. The condensates would
have a higher survival probability during the transport in the diffuse
radiation field and could mimic TeV air shower events. The powerful
stereoscopic technique of the HEGRA air Cerenkov telescopes allows to test this
hypothesis by reconstructing the penetration depths of TeV air shower events:
Air showers initiated by Bose-Einstein condensates are expected to reach the
maximum of the shower development in the atmosphere earlier than single photon
events. By comparing the energy-dependent penetration depths of TeV photons
from Mrk 501 with those from the TeV standard-candle Crab Nebula and simulated
air shower events, we can reject the hypothesis that TeV photons from Mrk 501
are pure Bose-Einstein condensates.Comment: 9 pages, 2 figures, published by ApJ Letters, revised version
(simulation results added
The TeV Energy Spectrum of Mkn 501 Measured with the Stereoscopic Telescope System of HEGRA during 1998 and 1999
During 1997, the BL Lac object Mkn 501 went into an extraordinary state of
high X-ray and TeV gamma-ray activity, lasting more than 6 months. In this
paper we report on the TeV emission characteristics of the source in the
subsequent years of 1998 and 1999 as measured with the Stereoscopic Cherenkov
Telescope System of HEGRA (La Palma, Canary Islands). Our observations reveal a
1998-1999 mean emission level at 1 TeV of 1/3 of the flux of the Crab Nebula, a
factor of 10 lower than during the year of 1997. A dataset of 122 observations
hours with the HEGRA telescope system makes it possible to assess for the first
time the Mkn 501 TeV energy spectrum for a mean flux level substantially below
that of the Crab Nebula with reasonable statistical accuracy. Excluding the
data of a strong flare, we find evidence that the 1998--1999 low-flux spectrum
is substantially softer (by 0.44+-0.1(stat) in spectral index) than the 1997
time averaged spectrum. The 500 GeV to 10 TeV energy spectrum can well be
described by a power law model with exponential cutoff: dN/dE ~ E^(-alpha)
exp(-E/E0) with alpha=2.31+-0.22(stat), and E0=5.1 (-2.3+7.8)(stat) TeV. Within
statistical accuracy, also a pure power law model gives an acceptable fit to
the data: dN/dE ~ E^(-Gamma) with Gamma=2.76+-0.08(stat). After presenting the
1998-1999 TeV characteristics of the source we discuss the implications of the
results.Comment: Accepted for publication in The Astrophysical Journal, Part 1, on
August 4th, 200
Recent Topics on Very High Energy Gamma-ray Astronomy
With the advent of imaging atmospheric Cherenkov telescopes in late 1980's,
ground-based observation of TeV gamma-rays came into reality after struggling
trials by pioneers for twenty years, and the number of gamma-ray sources
detected at TeV energies has increased to be over seventy now. In this review,
recent findings from ground-based very-high-energy gamma-ray observations are
summarized (as of 2008 March), and up-to-date problems in this research field
are presented.Comment: 6 pages, 4 figures, Proceedings of the International Workshop on
Advances in Cosmic Ray Science, March 17-19, 2008, Waseda University, Tokyo,
Japan; to be published in Journal of the Physical Society of Japan
(supplement
Correlated intense X-ray and TeV activity of Mrk~501 in 1998 June
We present exactly simultaneous X-ray and TeV monitoring with {\it RXTE} and
HEGRA of the TeV blazar Mrk 501 during 15 days in 1998 June. After an initial
period of very low flux at both wavelengths, the source underwent a remarkable
flare in the TeV and X-ray energy bands, lasting for about six days and with a
larger amplitude at TeV energies than in the X-ray band. At the peak of the TeV
flare, rapid TeV flux variability on sub-hour timescales is found. Large
spectral variations are observed at X-rays, with the 3--20 keV photon index of
a pure power law continuum flattening from to on a
timescale of 2--3 days. This implies that during the maximum of the TeV
activity, the synchrotron peak shifted to energies keV, a behavior
similar to that observed during the longer-lasting, more intense flare in 1997
April. The TeV spectrum during the flare is described by a power law with
photon index and an exponential cutoff at 4 TeV; an
indication for spectral softening during the flare decay is observed in the TeV
hardness ratios. Our results generally support a scenario where the TeV photons
are emitted via inverse Compton scattering of ambient seed photons by the same
electron population responsible for the synchrotron X-rays. The simultaneous
spectral energy distributions (SEDs) can be fit with a one-zone
synchrotron-self Compton model assuming a substantial increase of the magnetic
field and the electron energy by a factor of 3 and 10, respectively.Comment: Accepted for publication in ApJ, Part
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