We demonstrate the phase locking of a 2.7 THz metal–metal waveguide quantum cascade laser (QCL) to an external microwave signal. The reference is the 15th harmonic, generated by a semiconductor superlattice nonlinear device, of a signal at 182 GHz, which itself is generated by a multiplier chain (×12) from a microwave synthesizer at ?15? GHz . Both laser and reference radiations are coupled into a bolometer mixer, resulting in a beat signal, which is fed into a phase-lock loop. The spectral analysis of the beat signal confirms that the QCL is phase locked. This result opens the possibility to extend heterodyne interferometers into the far-infrared range.
We report the discovery of two highly dispersed pulsars in the direction of the Galactic Centre made during a survey at 3.1 GHz with the Parkes radio telescope. Both PSRs J1745–2912 and J1746–2856 have an angular separation from the Galactic Centre of less than 0°.3 and dispersion measures in excess of 1100 cm-3 pc, placing them in the top 10 pulsars when ranked on this value. The frequency dependence of the scatter-broadening in PSR J1746–2856 is much shallower than expected from simple theory. We believe it likely that the pulsars are located between 150 and 500 pc from the Galactic Centre on the near side, and are part of an excess population of neutron stars associated with the Centre itself. A second survey made at 8.4 GHz did not detect any pulsars. This implies either that there are not many bright, long-period pulsars at the Galactic Centre or that the scattering is more severe at high frequencies than current models would suggest.
Millimetron is a Russian-led 12 m diameter submillimeter and far-infrared space observatory which is included in the Space Plan of the Russian Federation for launch around 2017. With its large collecting area and state-of-the-art receivers, it will enable unique science and allow at least one order of magnitude improvement with respect to the Herschel Space Observatory. Millimetron will be operated in two basic observing modes: as a single-dish observatory, and as an element of a ground-space very long baseline interferometry (VLBI) system. As single-dish, angular resolutions on the order of 3 to 12 arc sec will be achieved and spectral resolutions of up to a million employing heterodyne techniques. As VLBI antenna, the chosen elliptical orbit will provide extremely large VLBI baselines (beyond 300,000 km) resulting in micro-arc second angular resolution.
We describe the technological concept and the first-light results of a 1024-channel spectrometer based on field programmable gate array (FPGA) hardware. This spectrometer is the prototype for the seven beam L-band receiver to be installed at the Effelsberg 100-m telescope in autumn 2005. Using "of-the-shelf" hardware and software products, we designed and constructed an extremely flexible Fast-Fourier-Transform (FFT) spectrometer with unprecedented sensitivity and dynamic range, which can be considered prototypical for spectrometer development in future radio astronomy.
We discuss our recent discovery of the giant radio emission from the Crab pulsar at its high frequency components (HFCs) phases and show the polarization characteristic of these pulses. This leads us to a suggestion that there is no difference in the emission mechanism of the main pulse (MP), interpulse (IP) and HFCs. We briefly review the size distributions of the Crab giant radio pulses (GRPs) and discuss general characteristics of the GRP phenomenon in the Crab and other pulsars.
The Anomalous X‐ray Pulsar 4U 0142+61 is the only neutron star where it is believed that one of the long searched‐for ‘fallback’ disks has been detected in the mid‐IR by Wang et al. [1] using Spitzer. Such a disk originates from material falling back to the NS after the supernova. We search for cold circumstellar material in the 90 GHz continuum using the Plateau de Bure Interferometer. No millimeter flux is detected at the position of 4U 0142+61, the upper flux limit is 150 μJy corresponding to the 3σ noise rms level. The re‐processed Spitzer MIPS 24μm data presented previously by Wang et al. [2] show some indication of flux enhancement at the position of the neutron star, albeit below the 3σ statistical significance limit. At far infrared wavelengths the source flux densities are probably below the Herschel confusion limits.
We report the status of a search for pulsars in the Galactic Centre, using a completely revised and improved high-sensitivity doublehorn system at 4.85-GHz. We also present calculations about the success rate of periodicity searches for such a survey, showing that in contrast to conclusions in recent literature pulsars can be indeed detected at the chosen search frequency.
Superconducting heterodyne receiver has played a vital role in the high resolution spectroscopy applications for astronomy and atmospheric research up to 2THz. NbN hot electron bolometer (HEB) mixer, as the most sensitive mixer above 1.5THz, has been used in the Herschel space telescope for 1.4-1.9THz and has also shown an ultra-high sensitivity up to 5.3THz. Combined a HEB mixer with a novel THz quantum cascade laser (QCL) as local oscillator (LO), such an all solid-state heterodyne receiver provides the technology which can be used for any balloon-, air- and space-borne heterodyne instruments above 2THz. Here we report the first high-resolution heterodyne spectroscopy measurement using a gas cell and using such a HEB-QCL receiver. The receiver employs a 2.9THz metal-metal waveguide QCL as LO and a NbN HEB as a mixer. By using a gas cell filled with methanol (CH3OH) gas in combination with hot/cold blackbody loads as signal source, we successfully recorded the methanol emission line around 2.918THz. Spectral lines at different pressures and also different frequency of the QCL are studied.
Heterodyne gas cell measurements at 2.9 THz using a quantum cascade laser as local oscillator
(2010)
We report on the setup and initial discoveries of the Northern High Time Resolution Universe survey for pulsars and fast transients, the first major pulsar survey conducted with the 100-m Effelsberg radio telescope and the first in 20 years to observe the whole northern sky at high radio frequencies. Using a newly developed 7-beam receiver system combined with a state-of-the-art polyphase filterbank, we record an effective bandwidth of 240 MHz in 410 channels centred on 1.36 GHz with a time resolution of 54 μs. Such fine time and frequency resolution increases our sensitivity to millisecond pulsars and fast transients, especially deep inside the Galaxy, where previous surveys have been limited due to intrachannel dispersive smearing. To optimize observing time, the survey is split into three integration regimes dependent on Galactic latitude, with 1500, 180 and 90-s integrations for latitude ranges |b| < 3 ∘.5, |b| < 15° and |b| > 15°, respectively. The survey has so far resulted in the discovery of 15 radio pulsars, including a pulsar with a characteristic age of ∼18 kyr, PSR J2004+3429, and a highly eccentric, binary millisecond pulsar, PSR J1946+3417. All newly discovered pulsars are timed using the 76-m Lovell radio telescope at the Jodrell Bank Observatory and the Effelsberg radio telescope. We present timing solutions for all newly discovered pulsars and discuss potential supernova remnant associations for PSR J2004+3429.
Context. Current generation millimeter wavelength detectors suffer from scaling limits imposed by complex cryogenic readout electronics. These instruments typically employ multiplexing ratios well below a hundred. To achieve multiplexing ratios greater than a thousand, it is imperative to investigate technologies that intrinsically incorporate strong multiplexing. One possible solution is the kinetic inductance detector (KID). To assess the potential of this nascent technology, a prototype instrument optimized for the 2 mm atmospheric window was constructed. Known as the Néel IRAM KID Array (NIKA), it has recently been tested at the Institute for Millimetric Radio Astronomy (IRAM) 30-m telescope at Pico Veleta, Spain.
Aims. There were four principle research objectives: to determine the practicality of developing a giant array instrument based on KIDs, to measure current in-situ pixel sensitivities, to identify limiting noise sources, and to image both calibration and scientifically-relevant astronomical sources.
Methods. The detectors consisted of arrays of high-quality superconducting resonators electromagnetically coupled to a transmission line and operated at ~100 mK. The impedance of the resonators was modulated by incident radiation; two separate arrays were tested to evaluate the efficiency of two unique optical-coupling strategies. The first array consisted of lumped element kinetic inductance detectors (LEKIDs), which have a fully planar design properly shaped to enable direct absorbtion. The second array consisted of antenna-coupled KIDs with individual sapphire microlenses aligned with planar slot antennas. Both detectors utilized a single transmission line along with suitable room-temperature digital electronics for continuous readout.
Results. NIKA was successfully tested in October 2009, performing in line with expectations. The measurement resulted in the imaging of a number of sources, including planets, quasars, and galaxies. The images for Mars, radio star MWC349, quasar 3C345, and galaxy M?87 are presented. From these results, the optical NEP was calculated to be around 1 × 10-15 W/Hz1/2. A factor of 10 improvement is expected to be readily feasible by improvements in the detector materials and reduction of performance-degrading spurious radiation.
A terahertz (THz) heterodynespectrometer is demonstrated based on a quantum cascade laser(QCL) as a local oscillator (LO) and an NbN hot electron bolometer as a mixer, and it is used to measure high-resolution molecular spectral lines of methanol (CH 3 OH) between 2.913–2.918 THz. The spectral lines are taken from a gas cell containing methanol gas and using a single-mode QCL at 2.9156 THz as an LO, which is operated in the free running mode. By increasing the pressure of the gas, line broadening and saturation are observed. The measuredspectra showed good agreement with a theoretical model.
We report on submillimetre bolometer observations of the isolated neutron star RX J1856.5−3754 using the Large Apex Bolometer Camera bolometer array on the Atacama Pathfinder Experiment telescope. No cold dust continuum emission peak at the position of RX J1856.5−3754 was detected. The 3σ flux density upper limit of 5 mJy translates into a cold dust mass limit of a few earth masses. We use the new submillimetre limit, together with a previously obtained H-band limit, to constrain the presence of a gaseous, circumpulsar disc. Adopting a simple irradiated disc model, we obtain a mass accretion limit of Graphic and a maximum outer disc radius of ∼1014 cm. By examining the projected proper motion of RX J1856.5−3754, we speculate about a possible encounter of the neutron star with a dense fragment of the CrA molecular cloud a few thousand years ago.
During recent years different types of millimetre-wave and terahertz-scanners have been developed, as well radar-based as passive radiometers. Mainly body scanners were in the focus of research. Although luggage and parcels are sufficiently inspected using X-ray techniques, the use of millimetre wave technology also for this application offers some advantages. Among them are easy deployment at any place, due to compact geometry, possible miniaturization of sensors and stand-off operation without any radiation hazard. Also the better contrast of dielectric material including explosives are of considerable advantage, not to neglect, that scanning is possible while the owner keeps the luggage in his hands. This allows tracking a piece of luggage together with its owner without losing their mutual relation. To allow a fast scanning, an array solution is investigated using state-of the art devices at the 80-GHz band.
