The Impact of Frequency Standards on Coherence in VLBI at the Highest Frequencies
MetadataShow full item record
We have carried out full imaging simulation studies to explore the impact of frequency standards in millimeter and submillimeter very long baseline interferometry (VLBI), focusing on the coherence time and sensitivity. In particular, we compare the performance of the H-maser, traditionally used in VLBI, to that of ultra-stable cryocooled sapphire oscillators over a range of observing frequencies, weather conditions, and analysis strategies. Our simulations show that at the highest frequencies, the losses induced by H-maser instabilities are comparable to those from high-quality tropospheric conditions. We find significant benefits in replacing H-masers with cryocooled sapphire oscillator based frequency references in VLBI observations at frequencies above 175 GHz in sites which have the best weather conditions; at 350 GHz we estimate a 20%-40% increase in sensitivity over that obtained when the sites have H-masers, for coherence losses of 20%-10%, respectively. Maximum benefits are to be expected by using co-located Water Vapor Radiometers for atmospheric correction. In this case, we estimate a 60%-120% increase in sensitivity over the H-maser at 350 GHz.
Showing items related by title, author, creator and subject.
Voronkov, M.; Walsh, Andrew; Caswell, J.; Ellingsen, S.; Breen, S.; Longmore, S.; Purcell, C.; Urquhart, J. (2011)We report the first detection of a methanol maser in the 101–92 A- transition at 23.4 GHz,discovered during the H2O southern Galactic Plane Survey (HOPS) with the 22-m MopraRadio Telescope. In the region covered by HOPS, ...
Jordan, C.; Walsh, Andrew; Lowe, V.; Voronkov, M.; Ellingsen, S.; Breen, S.; Purcell, C.; Barnes, P.; Burton, M.; Cunningham, M.; Hill, T.; Jackson, J.; Longmore, S.; Peretto, N.; Urquhart, J. (2015)We present the first results from the MALT-45 (Millimetre Astronomer's Legacy Team-45 GHz) Galactic Plane survey. We have observed 5 square degrees (l = 330°–335°, b = ±0.°5) for spectral lines in the 7 mm band (42–44 and ...
Tingay, Steven; Phillips, C.J.; Amy, S.W.; Tzioumis, A.K.; Kettenis, M.; Boven, E.P.; Szomoru, A.; Paragi, Z.; van Langevelde, H.; Verkouter, H.; Phillips, I.; Cowie, A.; Tam, T.; Huisman, W. (2009)We present an image of the expanding shell of the remnant associated with supernova1987A at the highest resolution to date at radio wavelengths, 85 milliarcseconds, using the e-VLBI technique, from 2007 October. This is ...