[evlatests] Zeeman problem?

[Steven T. Myers]

Interesting. The noise should go down with integration time, are there longer 
observations that show this?  E.g. 8 hours should be a factor 4 lower 
fluctuations if due to noise...

On Tue, 20 Sep 2011, Barry Clark wrote:

> We've been thinking for a while about looking to see whether the
> Zeeman problem occurs with the phased array.  So I thought I'd
> try a thought experiment to see how a perfect instrument would
> behave.  To simplify further I made the thought experiment a
> filter bank, rather than a correlation spectrometer, which
> obviously must give the same result.  Looking at the output of
> this receiver, the system receiver noise is, in SEFD terms, about
> 12 Jy, the antenna SEFD divided by the number of antennas.
>
> So, in the center frequency channel, the maser line _really_
> dominates the system, by a factor of 25 or so.  That being the
> case, the RMS on the channel will be the maser flux divided by
> the square root of BT.  For B = 2 kHz, T = 25m (roughtly the
> July 12 setup), the expected rms on the central channel is
> 300 Jy / sqrt(2000 * 1500) = 170 mJy.
>
> In the end channels, off the line, the power is about 25 times lower,
> so the rms will be also, about 7 mJy.
>
> It seems to me that this is not incompatible with what Emanuel
> sees in his reduction of the Zeeman observation.  The peak excursion
> on his Zeeman pattern is 290 mJy, about 1.7 sigma. something not
> unexpected.  That is, what we see is about (within a factor of two,
> anyway) what we would expect with a perfectly functioning correlator.
>
> We may have a Zeeman problem, but I no longer regard the evidence
> for it as very convincing.
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