Hi John, I am checking with our australian colleagues, it should not be there. I can’t remember now if we ever discussed this. This is also a very small array of course (16 antennas) so it has some features that won’t be present for larger stations.
Eloy. > On 7 Oct 2015, at 16:32, Jonathan Pober <[email protected]> wrote: > > Thanks, Eloy. The feature at 100 MHz in the Y polarization is definitely the > most prominent. Maybe it's related to FM? The X polarization also has > smaller features around the gap at ~130 MHz, possibly also related to > flagging, and a discontinuity at ~180 MHz. I was postulating the that latter > might be due to different 30.72 MHz chunks being observed on different > nights. The explanation for the overall larger values at higher frequencies > seems totally plausible. > > On Wed, Oct 7, 2015 at 7:50 AM, Eloy de Lera Acedo <[email protected] > <mailto:[email protected]>> wrote: > Hi John, > > Do you mean the feature at 100 MHz? That one is not predicted by the modeling > and indeed it is very strange because it does not show up in the other > polarisation. We will check with our Australian colleagues, see what they > think. That should not be there. > > The reason why the A/T measurements give larger values than the model can be > related to this: > "For Hydra A, our model predicts the flux density at 300 MHz to be ∼1/3 that > at 74 MHz. However, detailed measurements specifically targeting Hydra A at > 74 and 330 MHz [35] show that the flux density of the compact central region > reduces less steeply with frequency, and would be only ∼1/2 that at 74 MHz. > Unlike the surrounding diffuse emission, the compact central region is not > spatially filtered at the higher frequencies, thus our modelled "known" flux > density causes an underestimate of the actual flux density, resulting in a > higher than actual A/T . In future processing of measurement, we expect > significant convergence as the models of calibrator sources are improved for > the MWA and other wide-band low-frequency telescopes." > > Regarding A/T, in this paper (Fig. 15) you have our best estimates for A/T > calculation for SKA before re-baselining (before halving the number of > elements). > > http://rd.springer.com/article/10.1007/s10686-015-9439-0 > <http://rd.springer.com/article/10.1007/s10686-015-9439-0> > > Cheers, > Eloy. > >> On 7 Oct 2015, at 15:31, Jonathan Pober <[email protected] >> <mailto:[email protected]>> wrote: >> >> I'm not used to thinking about A/T this early in the morning, but are >> Figures 14 and 15 what we've always wanted to see from the SKA? Measured >> (and simulated) frequency responses? >> >> http://arxiv.org/abs/1510.01515 <http://arxiv.org/abs/1510.01515> >> >> (There seems to be a prevalance of 15's here, which numerology.com >> <http://numerology.com/> tells me corresponds to "Loving, forgiving, >> tolerant" -- for those of you perhaps looking for guidance in your relation >> to the SKA.) >> >> In Figure 14 there are a few sharp features beyond what the model predicts. >> I need to read the paper in more detail to figure out exactly what the >> measurement is. Those could be due to sidelobes from other sources >> affecting their spatial filter, although they are using the full 128 tiles >> of the MWA for cross correlation, so the PSF should be good. They're also >> stitching together the band from several 30.72 MHz chunks, so those could be >> artifacts at band edges. >> >> Maybe Eloy and/or Nima have some thoughts on these results? Very nice to >> see this work taking place and moving ahead. >> >> Cheers, >> >> Jonnie > > -- > Dr. Eloy de Lera Acedo > > Senior Research Associate > Astrophysics Group > Cavendish Laboratory > University of Cambridge > JJ Thomson Avenue > Cambridge CB3 0HE > > Teaching Associate and Bye-Fellow > Downing College > Regent Street > Cambridge CB2 1DQ > > Telephone: (+44) (0)1223 (3)37365 > Fax: (+44) (0)1223 337563 <tel:%28%2B44%29%20%280%291223%20337563> > Email: [email protected] <mailto:[email protected]> > Webpage: http://eloydeleraacedo.weebly.com > <http://eloydeleraacedo.weebly.com/> > -- Dr. Eloy de Lera Acedo Senior Research Associate Astrophysics Group Cavendish Laboratory University of Cambridge JJ Thomson Avenue Cambridge CB3 0HE Teaching Associate and Bye-Fellow Downing College Regent Street Cambridge CB2 1DQ Telephone: (+44) (0)1223 (3)37365 Fax: (+44) (0)1223 337563 Email: [email protected] Webpage: http://eloydeleraacedo.weebly.com <http://eloydeleraacedo.weebly.com/>
