Crab observations: polarisation and RFI from aircraft
Presentation for the LOFAR status
meeting, Dwingeloo/Bonn, 23 March 2011
O. Wucknitz [1]
- Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
Abstract
This presentation consists of two parts. The first is about linear polarisation of the crab pulsar at frequencies 115-145 MHz. I find about 1 % polarisation with a rotation measure of about -45 rad/m2. The level seems to be strongly frequency-dependent in a non-monotonical way. In the past, levels of up to 50 % have been observed, which means that the polarisation must be highly variable.
I disentangle polarisation leakage terms from the intrinsic signal by applying rotation measure synthesis.
In the second part I describe RFI signals I found in the same observations. These are strong, short, wide-band spikes (<1sec) with consistent delays. Using the delays from several baselines, I can determine the position of the source and find that it is something moving with about 800 km/h at an altitude of about 10 km, i.e. an aircraft.
What is currently not understood is which system onboard the aircraft causes these spikes. They extend from at least 115 MHz up to 141 MHz, which is beyond the airband. It does not seem to be a common system. During this 12-h obvservation, only one such sources is detected.
There is additional information available on the LOFAR LBG wiki about the polarisation and about the aircraft RFI.
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PDF file (1.6 MB, last change 23 Mar 2011)
22 pages, suitable for presentation with acroread. This
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PDF file (1.3 MB, last change 23 Mar 2011)
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Script last modified on 7 Sep 2010
Last change to this data base entry on 23 Mar 2011