280 research outputs found
Investigating the source of Planck-detected AME: high resolution observations at 15 GHz
The Planck 28.5 GHz maps were searched for potential Anomalous Microwave
Emission (AME) regions on the scale of or smaller, and several
new regions of interest were selected. Ancillary data at both lower and higher
frequencies were used to construct spectral energy distributions (SEDs), which
seem to confirm an excess consistent with spinning dust models. Here we present
higher resolution observations of two of these new regions with the Arcminute
Microkelvin Imager Small Array (AMI SA) between 14 and 18 GHz to test for the
presence of a compact (10 arcmin or smaller) component. For
AME-G107.1+5.2, dominated by the {\sc Hii} region S140, we find evidence for
the characteristic rising spectrum associated with the either the spinning dust
mechanism for AME or an ultra/hyper-compact \textsc{Hii} region across the AMI
frequency band, however for AME-G173.6+2.8 we find no evidence for AME on
scales of arcmin.Comment: 13 pages, 8 figures, 4 tables. Submitted to Advances in Astronomy AME
Special Issu
Using cm observations to constrain the abundance of very small dust grains in Galactic cold cores
In this analysis, we illustrate how the relatively new emission mechanism, known as spinning dust, can be used to characterize dust grains in the interstellar medium. We demonstrate this by using spinning dust emission observations to constrain the abundance of very small dust grains (a âČ 10 nm) in a sample of Galactic cold cores. Using the physical properties of the cores in our sample as inputs to a spinning dust model, we predict the expected level of emission at a wavelength of 1 cm for four different very small dust grain abundances, which we constrain by comparing to 1 cm CARMA observations. For all of our cores, we find a depletion of very small grains, which we suggest is due to the process of grain growth. This work represents the first time that spinning dust emission has been used to constrain the physical properties of interstellar dust grains
A detailed radio study of the energetic, nearby, and puzzling GRB 171010A
We present the results of an intensive multi-epoch radio frequency campaign
on the energetic and nearby GRB 171010A with the Karl G. Janksy Very Large
Array and Arcminute Microkelvin Imager Large Array. We began observing GRB
171010A a day after its initial detection, and were able to monitor the
temporal and spectral evolution of the source over the following weeks. The
spectra and their evolution are compared to the canonical theories for
broadband GRB afterglows, with which we find a general agreement. There are,
however, a number of features that are challenging to explain with a simple
forward shock model, and we discuss possible reasons for these discrepancies.
This includes the consideration of the existence of a reverse shock component,
potential microphysical parameter evolution and the effect of scintillation
Using Spinning Dust Emission To Constrain The Abundance Of Very Small Dust Grains In Dense Cores
We present the first analysis of using spinning dust emission as a method to characterise the properties of very small interstellar dust grains in dense cores
Rapid radio flaring during an anomalous outburst of SS Cyg
The connection between accretion and jet production in accreting white dwarf binary systems, especially dwarf novae, is not well understood. Radio wavelengths provide key insights into the mechanisms responsible for accelerating electrons, including jets and outflows. Here, we present densely sampled radio coverage, obtained with the Arcminute MicroKelvin Imager Large Array, of the dwarf nova SS Cyg during its 2016 February anomalous outburst. The outburst displayed a slower rise (3 dmag-1) in the optical than typical ones and lasted for more than three weeks. Rapid radio flaring on time-scales <1 h was seen throughout the outburst. The most intriguing behaviour in the radio was towards the end of the outburst where a fast, luminous ('giant'), flare peaking at ~20 mJy and lasting for 15 min was observed. This is the first time that such a flare has been observed in SS Cyg and insufficient coverage could explain its non-detection in previous outbursts. These data, together with past radio observations, are consistent with synchrotron emission from plasma ejection events as being the origin of the radio flares. However, the production of the giant flare during the declining accretion rate phase remains unexplained within the standard accretion-jet framework and appears to be markedly different to similar patterns of behaviour in X-ray binaries
AMI-LA Observations of the SuperCLASS Super-cluster
We present a deep survey of the SuperCLASS super-cluster - a region of sky
known to contain five Abell clusters at redshift - performed using
the Arcminute Microkelvin Imager (AMI) Large Array (LA) at 15.5GHz. Our
survey covers an area of approximately 0.9 square degrees. We achieve a nominal
sensitivity of Jy beam toward the field centre, finding 80
sources above a threshold. We derive the radio colour-colour
distribution for sources common to three surveys that cover the field and
identify three sources with strongly curved spectra - a high-frequency-peaked
source and two GHz-peaked-spectrum sources. The differential source count (i)
agrees well with previous deep radio source count, (ii) exhibits no evidence of
an emerging population of star-forming galaxies, down to a limit of 0.24mJy,
and (iii) disagrees with some models of the 15GHz source population.
However, our source count is in agreement with recent work that provides an
analytical correction to the source count from the SKADS Simulated Sky,
supporting the suggestion that this discrepancy is caused by an abundance of
flat-spectrum galaxy cores as-yet not included in source population models.Comment: 17 pages, 14 figures, 3 tables. Accepted for publication in MNRA
Determining the Physical Lens Parameters of the Binary Gravitational Microlensing Event MOA-2009-BLG-016
We report the result of the analysis of the light curve of the microlensing
event MOA-2009-BLG-016. The light curve is characterized by a short-duration
anomaly near the peak and an overall asymmetry. We find that the peak anomaly
is due to a binary companion to the primary lens and the asymmetry of the light
curve is explained by the parallax effect caused by the acceleration of the
observer over the course of the event due to the orbital motion of the Earth
around the Sun. In addition, we detect evidence for the effect of the finite
size of the source near the peak of the event, which allows us to measure the
angular Einstein radius of the lens system. The Einstein radius combined with
the microlens parallax allows us to determine the total mass of the lens and
the distance to the lens. We identify three distinct classes of degenerate
solutions for the binary lens parameters, where two are manifestations of the
previously identified degeneracies of close/wide binaries and positive/negative
impact parameters, while the third class is caused by the symmetric cycloid
shape of the caustic. We find that, for the best-fit solution, the estimated
mass of the lower-mass component of the binary is (0.04 +- 0.01) M_sun,
implying a brown-dwarf companion. However, there exists a solution that is
worse only by \Delta\chi^2 ~ 3 for which the mass of the secondary is above the
hydrogen-burning limit. Unfortunately, resolving these two degenerate solutions
will be difficult as the relative lens-source proper motions for both are
similar and small (~ 1 mas/yr) and thus the lens will remain blended with the
source for the next several decades.Comment: 7 pages, 2 tables, and 5 figure
A Low-Mass Planet with a Possible Sub-Stellar-Mass Host in Microlensing Event MOA-2007-BLG-192
We report the detection of an extrasolar planet of mass ratio q ~ 2 x 10^(-4)
in microlensing event MOA-2007-BLG-192. The best fit microlensing model shows
both the microlensing parallax and finite source effects, and these can be
combined to obtain the lens masses of M = 0.060 (+0.028 -0.021) M_sun for the
primary and m = 3.3 (+4.9 -1.6) M_earth for the planet. However, the
observational coverage of the planetary deviation is sparse and incomplete, and
the radius of the source was estimated without the benefit of a source star
color measurement. As a result, the 2-sigma limits on the mass ratio and finite
source measurements are weak. Nevertheless, the microlensing parallax signal
clearly favors a sub-stellar mass planetary host, and the measurement of finite
source effects in the light curve supports this conclusion. Adaptive optics
images taken with the Very Large Telescope (VLT) NACO instrument are consistent
with a lens star that is either a brown dwarf or a star at the bottom of the
main sequence. Follow-up VLT and/or Hubble Space Telescope (HST) observations
will either confirm that the primary is a brown dwarf or detect the low-mass
lens star and enable a precise determination of its mass. In either case, the
lens star, MOA-2007-BLG-192L, is the lowest mass primary known to have a
companion with a planetary mass ratio, and the planet, MOA-2007-BLG-192Lb, is
probably the lowest mass exoplanet found to date, aside from the lowest mass
pulsar planet.Comment: Accepted for publication in the Astrophysical Journal. Scheduled for
the Sept. 1, 2008 issu
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