805 research outputs found
Detection of Radio Emission from the Hyperactive L Dwarf 2MASS J13153094-2649513AB
We report the detection of radio emission from the unusually active L5e + T7
binary 2MASS J13153094-2649513AB made with the Australian Telescope Compact
Array. Observations at 5.5 GHz reveal an unresolved source with a continuum
flux of 370+/-50 microJy, corresponding to a radio luminosity of L_rad = nuL_nu
= (9+/-3)x10^23 erg/s and log10(L_rad/L_bol) = -5.44+/-0.22. No detection is
made at 9.0 GHz to a 5 sigma limit of 290 microJy, consistent with a power law
spectrum S_nu ~ nu^-a with a > 0.5. The emission is quiescent, with no evidence
of variability or bursts over 3 hr of observation, and no measurable
polarization (V/I < 34%). 2MASS J1315-2649AB is one of the most radio-luminous
ultracool dwarfs detected in quiescent emission to date, comparable in strength
to other cool sources detected in outburst. Its detection indicates no decline
in radio flux through the mid-L dwarfs. It is unique among L dwarfs in having
strong and persistent Halpha and radio emission, indicating the coexistence of
a cool, neutral photosphere (low electron density) and a highly active
chromosphere (high electron density and active heating). These traits, coupled
with the system's mature age and substellar secondary, makes 2MASS J1315-2649AB
an important test for proposed radio emission mechanisms in ultracool dwarfs.Comment: 5 pages, 4 figures, accepted for publication in ApJ Letter
An Analysis of the Environment and Gas Content of Luminous Infrared Galaxies
Luminous and ultraluminous infrared galaxies (U/LIRGs) represent a population among the most extreme in our universe, emitting an extraordinary amount of energy at infrared wavelengths from dust heated by prolific star formation and/or an active galactic nucleus (AGN). We present three investigations of U/LIRGs to better understand their global environment, their interstellar medium properties, and their nuclear region where molecular gas feeds a starburst or AGN. To study the global environment, we compute the spatial cluster-galaxy amplitude, Bgc, for 76 z 1 Jy), and at moderately high elevation (> 45°). We map Arp 193 in 12CO(2-1) with CARMA, achieving 0.18'' x 0.12'' (~65 pc) resolution, and demonstrating an improvement with C-PACS. We compute a molecular gas mass of 2 x 109 Msun and find ~20% of the total mass is in the form of molecular gas out to a radius of 750 pc. In the inner 150 pc of the nucleus, N(H2) > 1025 cm-2
The Intermediate Mass Black Hole Candidate in the Center of NGC 404: New Evidence from Radio Continuum Observations
We present the results of deep, high-resolution, 5 GHz Expanded Very Large
Array (EVLA) observations of the nearby, dwarf lenticular galaxy and
intermediate mass black hole candidate (M ~4.5 x 10^5 M_sun), NGC 404. For the
first time, radio emission at frequencies above 1.4 GHz has been detected in
this galaxy. We found a modestly resolved source in the NGC 404 nucleus with a
total radio luminosity of 7.6 +/- 0.7 x 10^17 W/Hz at 5 GHz and a spectral
index from 5 to 7.45 GHz of alpha = -0.88 +/- 0.30. NGC 404 is only the third
central intermediate mass black hole candidate detected in the radio regime
with subarcsecond resolution. The position of the radio source is consistent
with the optical center of the galaxy and the location of a known, hard X-ray
point source (Lx ~1.2 x 10^37 erg/s). The faint radio and X-ray emission could
conceivably be produced by an X-ray binary, star formation, a supernova remnant
or a low-luminosity AGN powered by an intermediate mass black hole. In light of
our new EVLA observations, we find that the most likely scenario is an
accreting intermediate mass black hole, with other explanations incompatible
with the observed X-ray and/or radio luminosities or statistically unlikely.Comment: Accepted for publication to Ap
A VLA Study of High-redshift GRBs I - Multi-wavelength Observations and Modeling of GRB 140311A
We present the first results from a recently concluded study of GRBs at
with the Karl G. Jansky Very Large Array (VLA). Spanning to
GHz and 7 epochs from 1.5 to 82.3 d, our observations of GRB 140311A are
the most detailed joint radio and millimeter observations of a GRB afterglow at
to date. In conjunction with optical/near-IR and X-ray data, the
observations can be understood in the framework of radiation from a single
blast wave shock with energy erg
expanding into a constant density environment with density, . The X-ray and radio observations require a jet break at d, yielding an opening angle of and a beaming-corrected blast wave kinetic energy of
erg. The results from our radio follow-up
and multi-wavelength modeling lend credence to the hypothesis that detected
high-redshift GRBs may be more tightly beamed than events at lower redshift. We
do not find compelling evidence for reverse shock emission, which may be
related to fast cooling driven by the moderately high circumburst density.Comment: 16 pages, 13 figures, submitted to Ap
Friedlander-Keller ray expansions and scalar wave reflection at canonically-perturbed boundaries
This paper concerns the reflection of high-frequency, monochromatic linear waves of wavenumber k (>>1) from smooth boundaries which are O (k-1/2) perturbations away from either a specified near-planar boundary or else from a given smooth, two-dimensional curve of general O(1) curvature. For each class of perturbed boundary, we will consider separately plane and cylindrical wave incidence, with general amplitude profiles of each type of incident field.
This interfacial perturbation scaling is canonical in the sense that a ray approach requires a modification to the standard WKBJ 'ray ansatz' which, in turn, leads to a leading-order amplitude (or 'transport') equation which includes an extra term absent in a standard application of the geometrical theory of diffraction ('GTD'). This extra term is unique to this scaling, and the afore-mentioned modification that is required is an application of a generalised type of ray expansion first posed by F G Friedlander and J B Keller [1]
Analytical study of an exclusive genetic switch
The nonequilibrium stationary state of an exclusive genetic switch is
considered. The model comprises two competing species and a single binding site
which, when bound to by a protein of one species, causes the other species to
be repressed. The model may be thought of as a minimal model of the power
struggle between two competing parties. Exact solutions are given for the
limits of vanishing binding/unbinding rates and infinite binding/unbinding
rates. A mean field theory is introduced which is exact in the limit of
vanishing binding/unbinding rates. The mean field theory and numerical
simulations reveal that generically bistability occurs and the system is in a
symmetry broken state. An exact perturbative solution which in principle allows
the nonequilibrium stationary state to be computed is also developed and
computed to first and second order.Comment: 28 pages, 6 figure
On the local existence of maximal slicings in spherically symmetric spacetimes
In this talk we show that any spherically symmetric spacetime admits locally
a maximal spacelike slicing. The above condition is reduced to solve a
decoupled system of first order quasi-linear partial differential equations.
The solution may be accomplished analytical or numerically. We provide a
general procedure to construct such maximal slicings.Comment: 4 pages. Accepted for publication in Journal of Physics: Conference
Series, Proceedings of the Spanish Relativity Meeting ERE200
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