In the name of science

Science experiments, as in life, are plagued by uncertainties.  As sarah showed last week, a particularly pernicious one is the response of the  telescope across the image. Things tend to get dimmer towards the edges, but without some very well known source in that area, its difficult to correct.  Most telescopes get around this problem by physically scanning across a known source, tracing out the response function.  Our new low frequency telescopes (MWA,PAPER) are fixed to the ground, we do not have the option of moving the telescope. So its time to get creative.  We can use satellites, known astronomical radio sources, or we can even fly a known transmitter over the telescope.

So, I hope this explains this picture here.

Danny flying the Octocopter. Next, we’ll be attaching a calibration antenna.

The Octocopter is on loan from our colleagues at Curtin University. (Here’s a great video they made with it.) We’ll be attaching a calibration source and flying grid pattern over the telescope.  Today we just attached a go pro camera.  Here’s the footage

The sound of PAPER

Today I needed a distraction so I transcoded some PAPER data into sound. It sounds really weird!

Creatures of the Night

Low frequency radio astronomers do it at night.

I was re-reading my post from last month and I realized something.  For years, astronomers using radio telescopes have been accustomed to observing, day or night, rain or shine. Of course there are always exceptions, but as a rule, if your desired source was up during the day, this did not present any particular difficulty because the giant dishes could focus away from the sun. Those were the days!

Now, as we push the boundaries with wider fields of view, like the MWA which looks at almost a third of the sky at a time, we find that we can must limit out observing to times when the sun is set, effectively cutting the telescope time in half!  In fact, as we continue to build sensitivity we might be further restricted to times during the night when the ionosphere has settled down and the “seeing” is good enough.

Ironically this all happened because we got rid of the steerable dish, that last vestige of similarity to traditional optical telescopes,in favor of dipole antennas that see the entire sky at once.

Here be dragons

Greetings readers.  My name is Danny Jacobs. I’m a postdoc working for Judd Bowman here in the SESE Low Frequency Cosmology (LoCo) lab. My job is to help commission the Murchison Widefield Array (MWA) in Australia and the Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa.  I visit the telescopes to help with construction and the rest of the time I try to make sense of the data. Someday I want to make an image of the ultra-distant hydrogen between the first galaxies. This is my first post here on ASU Explorers.

A handy guide to the radio sky hanging in my office. Dragons locations drawn in red.

Last month I was imaging the sky with PAPER and I made an amazing discovery… or so I thought.  Within a few months a dim, unremarkable supernova remnant had become brighter than the Crab Nebula, one of the brightest radio sources in the sky.  I had discovered the Sun! Again!

The radio sky is a big invisible place and its easy to lose track of whats going on. Disgusted with myself, I took a break from imaging and put together a map of the sky. There it is to the right, hanging on my office wall. (pdf) It has the brightest few sources, the galaxy, and the seasonal position of the Sun. I also made a supplemental map showing the footprint of my telescopes on the sky. (pdf) The footprints are so large, its easy to forget what will be visible.