20 research outputs found
MEMS-based Speckle Spectrometer
We describe a new concept for a MEMS-based active spatial filter for
astronomical spectroscopy. The goal of this device is to allow the use of a
diffraction-limited spectrometer on a seeing limited observation at improved
throughput over a comparable seeing-limited spectrometer, thus reducing the
size and cost of the spectrometer by a factor proportional to r0/D (For the
case of a 10 meter telescope this size reduction will be approximately a factor
of 25 to 50). We use a fiber-based integral field unit (IFU) that incorporates
an active MEMS mirror array to feed an astronomical spectrograph. A fast camera
is used in parallel to sense speckle images at a spatial resolution of lambda/D
and at a temporal frequency greater than that of atmospheric fluctuations. The
MEMS mirror-array is used as an active shutter to feed speckle images above a
preset intensity threshold to the spectrometer, thereby increasing the
signal-to-noise ratio (SNR) of the spectrogram. Preliminary calculations
suggests an SNR improvement of a factor of about 1.4. Computer simulations have
shown an SNR improvement of 1.1, but have not yet fully explored the parameter
space.Comment: 11 pages, 5 figures, presented at SPIE Astronomical Telescopes and
Instrumentation, 24 - 31 May 2006, Orlando, Florida US
Investigating Gamma-Ray Lines from Dark Matter with Future Observatories
We study the prospects for studying line features in gamma-ray spectra with
upcoming gamma-ray experiments, such as HESS-II, the Cherenkov Telescope Array
(CTA), and the GAMMA-400 satellite. As an example we use the narrow feature at
130 GeV seen in public data from the Fermi-LAT satellite. We found that all
three experiments should be able to confidently confirm or rule out the
presence of this 130 GeV feature. If it is real, it should be confirmed with a
confidence level higher than 5 sigma. Assuming it to be a spectral signature of
dark matter origin, GAMMA-400, thanks to a projected energy resolution of about
1.5% at 100 GeV, should also be able to resolve both the \gamma\gamma-line and
a corresponding Z\gamma- or H\gamma-feature, if the corresponding branching
ratio is comparable to that into two photons. It will also allow to distinguish
between a gamma-ray line and the similar feature resulting from internal
bremsstrahlung photons.Comment: 12 pages, 6 figures, 1 tabl
Contributions of dark matter annihilation within ultracompact minihalos to the 21 cm background signal
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Dark Matter Signatures in the Anisotropic Radio Sky.
We calculate intensity and angular power spectrum of the cosmological
background of synchrotron emission from cold dark matter annihilations into
electron positron pairs. We compare this background with intensity and
anisotropy of astrophysical and cosmological radio backgrounds, such as from
normal galaxies, radio-galaxies, galaxy cluster accretion shocks, the cosmic
microwave background and with Galactic foregrounds. Under modest assumptions
for the dark matter clustering we find that around 2 GHz average intensity and
fluctuations of the radio background at sub-degree scales allows to probe dark
matter masses >100 GeV and annihilation cross sections not far from the natural
values ~ 3 x 10^(-26) cm^3/s required to reproduce the correct relic
density of thermal dark matter. The angular power spectrum of the signal from
dark matter annihilation tends to be flatter than that from astrophysical radio
backgrounds. Furthermore, radio source counts have comparable constraining
power. Such signatures are interesting especially for future radio detectors
such as SKA.Comment: 30 papes, jcap preprint format, 11 figures; final version, very minor
change