252 research outputs found
SMA Imaging of the Maser Emission from the H30 Radio Recombination Line in MWC349A
We used the Submillimeter Array to map the angular distribution of the
H30 recombination line (231.9 GHz) in the circumstellar region of the
peculiar star MWC349A. The resolution was 1\farcs2, but because of high
signal-to-noise ratio we measured the positions of all maser components to
accuracies better than 0\farcs01, at a velocity resolution of . The
two strongest maser components (called high velocity components) at velocities
near -14 and are separated by 0\farcs048 \pm 0\farcs001 (60 AU)
along a position angle of 102 \pm 1\arcdeg. The distribution of maser
emission at velocities between and beyond these two strongest components were
also provided. The continuum emission lies at the center of the maser
distribution to within 10 mas. The masers appear to trace a nearly edge-on
rotating disk structure, reminiscent of the water masers in Keplerian rotation
in the nuclear accretion disk of the galaxy NGC4258. However, the maser
components in MWC349A do not follow a simple Keplerian kinematic prescription
with , but have a larger power law index. We explore the
possibility that the high velocity masers trace spiral density or shock waves.
We also emphasize caution in the interpretation of relative centroid maser
positions where the maser is not clearly resolved in position or velocity, and
we present simulations that illustrate the range of applicability of the
centroiding method.Comment: 23 pages with 9 figures (two of these figures are vertically aligned
as Figure 4) submitted to the Astrophysical Journa
Zooming towards the Event Horizon - mm-VLBI today and tomorrow
Global VLBI imaging at millimeter and sub-millimeter wavelength overcomes the
opacity barrier of synchrotron self-absorption in AGN and opens the direct view
into sub-pc scale regions not accessible before. Since AGN variability is more
pronounced at short millimeter wavelength, mm-VLBI can reveal structural
changes in very early stages after outbursts. When combined with observations
at longer wavelength, global 3mm and 1mm VLBI adds very detailed information.
This helps to determine fundamental physical properties at the jet base, and in
the vicinity of super-massive black holes at the center of AGN. Here we present
new results from multi-frequency mm-VLBI imaging of OJ287 during a major
outburst. We also report on a successful 1.3mm VLBI experiment with the APEX
telescope in Chile. This observation sets a new record in angular resolution.
It also opens the path towards future mm-VLBI with ALMA, which aims at the
mapping of the black hole event horizon in nearby galaxies, and the study of
the roots of jets in AGN.Comment: 6 pages, to appear in 11th European VLBI Network Symposium, ed. P.
Charlot et al., Bordeaux (France), October 9-12, 201
Resolving the inner jet structure of 1924-292 with the EVENT HORIZON TELESCOPE
We present the first 1.3 mm (230 GHz) very long baseline interferometry model
image of an AGN jet using closure phase techniques with a four-element array.
The model image of the quasar 1924-292 was obtained with four telescopes at
three observatories: the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in
Hawaii, the Arizona Radio Observatory's Submillimeter Telescope (SMT) in
Arizona, and two telescopes of the Combined Array for Research in
Millimeterwave Astronomy (CARMA) in California in April 2009. With the greatly
improved resolution compared with previous observations and robust closure
phase measurement, the inner jet structure of 1924-292 was spatially resolved.
The inner jet extends to the northwest along a position angle of at
a distance of 0.38\,mas from the tentatively identified core, in agreement with
the inner jet structure inferred from lower frequencies, and making a position
angle difference of with respect to the cm-jet. The size of
the compact core is 0.15\,pc with a brightness temperature of
\,K. Compared with those measured at lower frequencies, the
low brightness temperature may argue in favor of the decelerating jet model or
particle-cascade models. The successful measurement of closure phase paves the
way for imaging and time resolving Sgr A* and nearby AGN with the Event Horizon
Telescope.Comment: 6 pages, 4 figures, accepted for publication in ApJ
Project 8 Phase III Design Concept
We present a working concept for Phase III of the Project 8 experiment,
aiming to achieve a neutrino mass sensitivity of ( C.L.)
using a large volume of molecular tritium and a phased antenna array. The
detection system is discussed in detail.Comment: 3 pages, 3 figures, Proceedings of Neutrino 2016, XXVII International
Conference on Neutrino Physics and Astrophysics, 4-9 July 2016, London, U
Results from the Project 8 phase-1 cyclotron radiation emission spectroscopy detector
The Project 8 collaboration seeks to measure the absolute neutrino mass scale
by means of precision spectroscopy of the beta decay of tritium. Our technique,
cyclotron radiation emission spectroscopy, measures the frequency of the
radiation emitted by electrons produced by decays in an ambient magnetic field.
Because the cyclotron frequency is inversely proportional to the electron's
Lorentz factor, this is also a measurement of the electron's energy. In order
to demonstrate the viability of this technique, we have assembled and
successfully operated a prototype system, which uses a rectangular waveguide to
collect the cyclotron radiation from internal conversion electrons emitted from
a gaseous Kr source. Here we present the main design aspects of the
first phase prototype, which was operated during parts of 2014 and 2015. We
will also discuss the procedures used to analyze these data, along with the
features which have been observed and the performance achieved to date.Comment: 3 pages; 2 figures; Proceedings of Neutrino 2016, XXVII International
Conference on Neutrino Physics and Astrophysics, 4-9 July 2016, London, U
First 230 GHz VLBI Fringes on 3C 279 using the APEX Telescope
We report about a 230 GHz very long baseline interferometry (VLBI) fringe
finder observation of blazar 3C 279 with the APEX telescope in Chile, the
phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory
(ARO). We installed VLBI equipment and measured the APEX station position to 1
cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230
GHz VLBI track with baseline lengths of 2800 M to 7200 M and
a finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on all
baselines with SNRs of 12 to 55 in 420 s. The correlated flux density on the
longest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy.
Visibility data suggest an emission region <38 uas in size, and at least two
components, possibly polarized. We find a lower limit of the brightness
temperature of the inner jet region of about 10^10 K. Lastly, we find an upper
limit of 20% on the linear polarization fraction at a fringe spacing of ~38
uas. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 uas.
This allows one to resolve the last-photon ring around the Galactic Center
black hole event horizon, expected to be 40 uas in diameter, and probe radio
jet launching at unprecedented resolution, down to a few gravitational radii in
galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in
detail, follow-up observations with APEX and five other mm-VLBI stations have
been conducted (March 2013) and are being analyzed.Comment: accepted for publication in A&
1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-Variable Emission on Event Horizon Scales
Sagittarius A*, the ~4 x 10^6 solar mass black hole candidate at the Galactic
Center, can be studied on Schwarzschild radius scales with (sub)millimeter
wavelength Very Long Baseline Interferometry (VLBI). We report on 1.3 mm
wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on
Mauna Kea, the ARO/SMT on Mt. Graham in Arizona, and two telescopes of the
CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator
1924-292 were observed over three consecutive nights, and both sources were
clearly detected on all baselines. For the first time, we are able to extract
1.3 mm VLBI interferometer phase information on Sgr A* through measurement of
closure phase on the triangle of baselines. On the third night of observing,
the correlated flux density of Sgr A* on all VLBI baselines increased relative
to the first two nights, providing strong evidence for time-variable change on
scales of a few Schwarzschild radii. These results suggest that future VLBI
observations with greater sensitivity and additional baselines will play a
valuable role in determining the structure of emission near the event horizon
of Sgr A*.Comment: 8 pages, submitted to ApJ
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