Search results for "Millimeter"
showing 10 items of 44 documents
Search for Large Extra Dimensions in theMonojet+E̸TChannel with the DØ Detector
2003
We present a search for large extra dimensions (ED) in p (p) over bar collisions at a center-of-mass energy of 1.8 TeV using data collected by the DO detector at the Fermilab Tevatron in 1994-1996. Data corresponding to 78.8+/-3.9 pb(-1) are examined for events with large missing transverse energy, one high-p(T) jet, and no isolated muons. There is no excess observed beyond expectation from the standard model, and we place lower limits on the fundamental Planck scale of 1.0 and 0.6 TeV for 2 and 7 ED, respectively.
Detection of the high z GRB 080913 and its implications on progenitors and energy extraction mechanisms*
2010
We present multiwavelength observations of one of the most distant gamma-ray bursts detected so far, GRB080913. Based on these observations, we consider whether it could be classified as a short-duration GRB and discuss the implications for the progenitor nature and energy extraction mechanisms. Methods. Multiwavelength X-ray, near IR and millimetre observations were made between 20.7 h and ∼16.8 days after the event. Results. Whereas a very faint afterglow was seen at the 3.5m CAHA telescope in the nIR, the X-ray afterglow was clearly detected in both Swift and XMM-Newton observations. An upper limit is reported in the mm range. We have modeled the data assuming a collimated θ0 3◦ blast wa…
All good things come in threes: the third image of the lensed quasar PKS1830-211
2020
Strong gravitational lensing distorts our view of sources at cosmological distances but brings invaluable constraints on the mass content of foreground objects and on the geometry and properties of the Universe. We report the detection of a third continuum source toward the strongly lensed quasar PKS1830-211 in ALMA multi-frequency observations of high dynamic range and high angular resolution. This third source is point-like and located slightly to the north of the diagonal joining the two main lensed images, A and B, 0.3 arcsec away from image B. It has a flux density that is ~140 times weaker than images A and B and a similar spectral index, compatible with synchrotron emission. We concl…
4C 39.25: Multi-epoch polarisation observations at 15, 22 and 43 GHz
1999
We present multi-epoch simultaneous 15, 22 and 43 GHz VLBA polarimetric radio observations of the quasar 4C 39.25 which provide further evidence for the ongoing interaction between components `a' and `b' through the monitoring of the total and polarised flux densities of both components, the proper motion of `b' and, more importantly, of the polarisation angle associated with components `a' and `b'. There are strong pieces of evidence indicating that the superluminal component `b' is “colliding” or “crossing” the region associated with the stationary component `a': (i) at millimeter wavelengths, the total flux density of 4C 39.25 has reached a maximum and is already beginning to decline; (i…
Rare isotopic species of hydrogen sulfide: the rotational spectrum of H236S
2014
The rotational spectrum of the 36 S-bearing isotopologue of hydrogen sulfide (H2S) has been investigated for the first time in the 167 GHz−1.6 THz frequency range, thus providing an accurate and reliable set of spectroscopic parameters. The experimental investigation was backed up by state-of-the-art quantum-chemical calculations, which also allowed us to demonstrate the incorrectness of the previously reported spectroscopic constants. The present results are of suitable accuracy to attempt the astrophysical detection of the isotopic species under consideration. Finally, reliable predictions for the spectroscopic constants of other rare isotopologues of H2S, namely the mono- and bi-deuterat…
Millimeter VLBI of NGC 1052: Dynamics
2016
The LINER galaxy NGC 1052 is an ideal target to study the innermost regions of active galactic nuclei (AGN), given its close distance of about 20 Mpc. The source was observed at 29 epochs from 2005 to 2009 with the Very Long Baseline Array (VLBA) at 43 GHz. Here, we present a kinematic study of its twin-jet system from a subset of 9 epochs at 43 GHz carried out in 2005 and 2006, finding a bright central feature as the dynamic center. The resulting mean velocities of β = v / c = 0 . 46 ± 0 . 08 and β = 0 . 69 ± 0 . 02 for the western and eastern jet, respectively, give hints towards higher velocities in the eastern jet.
The hyperfine structure in the rotational spectrum of water: Lamb-dip technique and quantum-chemical calculations
2009
Seven ortho rotational transitions have been recorded for the main isotopic species of water in the mil- limeter- and submillimeter-wave region using the Lamb-dip technique in order to resolve the hyperfine structure due to the hydrogens and to provide accurate hyperfine constants. The experimental determi- nation has been supplemented by high-level quantum-chemical calculations of the hyperfine parameters thereby focusing in particular on a systematic study of the basis-set convergence and on vibrational effects.
The rotational spectrum of trans-DCOOD: Lamb-dip measurements, THz spectroscopy and quantum-chemical calculations
2011
Abstract The rotational spectrum of the bi-deuterated isotopologue of trans-formic acid, trans-DCOOD, was recorded at sub-Doppler resolution in the millimeter- and sub-millimeter-wave region using the Lamb-dip technique. The hyperfine structure due to the deuterium nuclei could be resolved and accurate hyperfine constants were derived. The experimental determination of the deuterium quadrupole-coupling constants was supported by high-level quantum-chemical calculations at the coupled-cluster level using large atomic-orbital basis sets. The Lamb-dip measurements were also supplemented by THz Doppler-limited measurements in order to extend the predictive capability of the available spectrosco…
Probing the radio emission from air showers with polarization measurements
2014
The emission of radio waves from air showers has been attributed to the so-called geomagnetic emission process. At frequencies around 50 MHz this process leads to coherent radiation which can be observed with rather simple setups. The direction of the electric field induced by this emission process depends only on the local magnetic field vector and on the incoming direction of the air shower. We report on measurements of the electric field vector where, in addition to this geomagnetic component, another component has been observed which cannot be described by the geomagnetic emission process. The data provide strong evidence that the other electric field component is polarized radially wit…
High gain/bandwidth off-chip antenna loaded with metamaterial unit-cell impedance matching circuit for sub-terahertz near-field electronic systems
2022
An innovative of-chip antenna (OCA) is presented that exhibits high gain and efciency performance at the terahertz (THz) band and has a wide operational bandwidth. The proposed OCA is implemented on stacked silicon layers and consists of an open circuit meandering line. It is shown that by loading the antenna with an array of subwavelength circular dielectric slots and terminating it with a metamaterial unit cell, its impedance bandwidth is enhanced by a factor of two and its gain on average by about 4 dB. Unlike conventional antennas, where the energy is dissipated in a resistive load, the technique proposed here signifcantly reduces losses. The antenna is excited from underneath the anten…