202 research outputs found
TeV Cherenkov Events as Bose-Einstein Gamma Condensations
The recent detection of gamma radiation from Mkn 501 at energies as high as
25 TeV suggests stringent upper bounds on the diffuse, far infrared,
extragalactic radiation density. The production of electron-positron pairs
through photon-photon collisions would prevent gamma photons of substantially
higher energies from reaching us across distances of order 100 Mpc. However,
coherently arriving TeV or sub-TeV gammas - Bose-Einstein condensations of
photons at these energies - could mimic the Cherenkov shower signatures of
extremely energetic gammas. To better understand such events, we describe their
observational traits and discuss how they might be generated.Comment: 12 pages, 2 figures, accepted for publication in Ap.J.(Lett.
A practical multi-spectrum Hadamard Transform Spectrometer
A Hadamard Transform Spectrometer (HTS) which simultaneously obtains fifteen infrared spectra, each having 255 spectral elements was constructed. Spectra are obtained essentially in real time through use of a minicomputer with 8K words of memory and a CRT display. This permits operation of the instrument in the field
High resolution 10 mu spectrometry at different planetary latitudes. A practical Hadamard transform spectrometer for astronomical application
Infrared observations at different latitudes were studied in order to obtain spectra in the 10 micrometers region to understand differences in chemical composition or physical structure of the optical features. In order to receive such spectra of a rotating planet, simultaneous observations at different latitudes were made. A Hadamard transform spectrometer with 15 entrance slits was used to obtain 15 simultaneous spectra, at a resolution of 0.01 micrometers. The spectral band covered contained 255 spectral elements
A Spitzer Unbiased Ultradeep Spectroscopic Survey
We carried out an unbiased, spectroscopic survey using the low-resolution
module of the infrared spectrograph (IRS) on board Spitzer targeting two 2.6
square arcminute regions in the GOODS-North field. IRS was used in spectral
mapping mode with 5 hours of effective integration time per pixel. One region
was covered between 14 and 21 microns and the other between 20 and 35 microns.
We extracted spectra for 45 sources. About 84% of the sources have reported
detections by GOODS at 24 microns, with a median F_nu(24um) ~ 100 uJy. All but
one source are detected in all four IRAC bands, 3.6 to 8 microns. We use a new
cross-correlation technique to measure redshifts and estimate IRS spectral
types; this was successful for ~60% of the spectra. Fourteen sources show
significant PAH emission, four mostly SiO absorption, eight present mixed
spectral signatures (low PAH and/or SiO) and two show a single line in
emission. For the remaining 17, no spectral features were detected. Redshifts
range from z ~ 0.2 to z ~ 2.2, with a median of 1. IR Luminosities are roughly
estimated from 24 microns flux densities, and have median values of 2.2 x
10^{11} L_{\odot} and 7.5 x 10^{11} L_{\odot} at z ~ 1 and z ~ 2 respectively.
This sample has fewer AGN than previous faint samples observed with IRS, which
we attribute to the fainter luminosities reached here.Comment: Published in Ap
van der Kruit to Spitzer: A New Look at the FIR-Radio Correlation
We present an initial look at the far infrared-radio correlation within the
star-forming disks of four nearby, nearly face-on galaxies (NGC~2403, NGC~3031,
NGC~5194, and NGC~6946). Using {\it Spitzer} MIPS imaging and WSRT radio
continuum data, we are able to probe variations in the logarithmic
70~m/22~cm () flux density ratios across each disk at sub-kpc
scales. We find general trends of decreasing with declining surface
brightness and with increasing radius. We also find that the dispersion in
within galaxies is comparable to what is measured {\it globally} among
galaxies at around 0.2 dex. We have also performed preliminary phenomenological
modeling of cosmic ray electron (CR) diffusion using an image-smearing
technique, and find that smoothing the infrared maps improves their correlation
with the radio maps. The best fit smoothing kernels for the two less active
star-forming galaxies (NGC~2403 and NGC~3031) have much larger scale-lengths
than that of the more active star-forming galaxies (NGC~5194 and NGC~6946).
This difference may be due to the relative deficit of recent CR
injection into the interstellar medium (ISM) for the galaxies having largely
quiescent disks.Comment: 6 pages, 3 figures, To appear in the proceedings of the "Island
Universes: Structure and Evolution of Disk Galaxies" conference held in
Terschelling, Netherlands, July 2005, ed. R. de Jong (Springer: Dordrecht
Effects of CPT and Lorentz Invariance Violation on Pulsar Kicks
The breakdown of Lorentz's and CPT invariance, as described by the Extension
of the Standard Model, gives rise to a modification of the dispersion relation
of particles. Consequences of such a modification are reviewed in the framework
of pulsar kicks induced by neutrino oscillations (active-sterile conversion). A
peculiar feature of the modified energy-momentum relations is the occurrence of
terms of the form \delta {\bbox \Pi}\cdot {\bf {\hat p}}, where \delta
{\bbox \Pi} accounts for the difference of spatial components of flavor
depending coefficients which lead to the departure of the Lorentz symmetry, and
, being the neutrino momentum. Owing to the
relative orientation of with respect to \delta {\bbox \Pi}, the
{\it coupling} \delta {\bbox \Pi}\cdot {\bf {\hat p}} may induce the
mechanism to generate the observed pulsar velocities. Topics related to the
velocity distribution of pulsars are also discussed.Comment: 10 pages, 1 figur
The Structure of Winds in AGB Stars
Most dusty winds are described by a set of similarity functions of a single
independent variable that can be chosen as the overall optical depth at visual.
The self-similarity implies general scaling relations among the system
parameters, in agreement with observations. Dust drift through the gas has a
major impact on the structure of most winds.Comment: To appear in proc. of "Workshop on Mass-Losing Pulsating Stars and
their Circumstellar Matter", Sendai, Japan (May 2002
The Warm Molecular Gas Around the Cloverleaf Quasar
We present the first broadband lambda = 1 mm spectrum toward the z=2.56
Cloverleaf Quasar, obtained with Z-Spec, a 1-mm grating spectrograph on the
10.4-meter Caltech Submillimeter Observatory. The 190-305 GHz observation band
corresponds to rest-frame 272 to 444 microns, and we measure the dust continuum
as well as all four transitions of carbon monoxide (CO) lying in this range.
The power-law dust emission, F_nu = 14 mJy (nu/240GHz)^3.9 is consistent with
the published continuum measurements. The CO J=6->5, J=8->7, and J=9->8
measurements are the first, and now provide the highest-J CO information in
this source. Our measured CO intensities are very close to the
previously-published interferometric measurements of J=7->6, and we use all
available transitions and our 13CO upper limits to constrain the physical
conditions in the Cloverleaf molecular gas disk. We find a large mass
(2-50x10^9 Msun) of highly-excited gas with thermal pressure nT > 10^6 Kcm^-3.
The ratio of the total CO cooling to the far-IR dust emission exceeds that in
the local dusty galaxies, and we investigate the potential heating sources for
this bulk of warm molecular gas. We conclude that both UV photons and X-rays
likely contribute, and discuss implications for a top-heavy stellar initial
mass function arising in the X-ray-irradiated starburst. Finally we present
tentative identifications of other species in the spectrum, including a
possible detection of the H20 2_0,2->1_1,1 transition at lambda_rest = 303
microns.Comment: ApJ in press, 12 pages in emulateAp
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