This week, in conjunction with the Low Frequency meeting, the MWA 21 cm science team got together to have a data crunch. A good time was had by all except the data which was severely crunched and is now much reduced from its former self.

We set up shop in a conference room, generously loaned to us by the defense folks down on 4.

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And here we all are!

MWA 21 cm group, Tempe Busy Week, December 2014

MWA 21 cm group, Tempe Busy Week, December 2014

 

 

03. December 2014 · Write a comment · Categories: research · Tags:
ECHO team members Mason Denny and Marc Leatham perform test on a scale model testbed

ECHO team members Mason Denny and Marc Leatham perform tests on a scale model testbed

This semester I start work in earnest on a new project thats been simmering in the background, the External Calibrator for Hydrogen Observatories (ECHO) an experimental method to provide an airborne calibration source for wide-field radio arrays observing Hydrogen at cosmological distances. In particular, accurate maps of the primary beam (the response of the receiver dipoles as a function of position on the sky) have been found to be crucial at multiple stages analysis of data from PAPER/MWA/LOFAR etc but have historically been measured through indirect means such as the amplitude of satellites or radio galaxies passing overhead. ECHO aims to provide a direct measurement with a system where all parameters are under the experimenter’s control.

At this point we are designing and building our transmitter (don’t need much power for a radio telescope!) and selecting a new drone platform. We’ve hired a small team of undergraduates to take point.

ECHO team members Marc Leatham and Victoria Serrano give the quad-rotor a shakedown flight. The quad is acting as a scale model and training frame for a larger platform soon to come.

ECHO team members Marc Leatham and Victoria Serrano give the quad-rotor a shakedown flight. The quad is acting as a scale model and training frame for a larger platform soon to come.

ECHO Version 1 A bicolog 5007 mounted on a Mikrokopter 8.

ECHO Version 1 A bicolog 5007 mounted on a 8 rotor Mikrokopter. An upgrade to a newer pixhawk-based platform is planned for the spring.

 

 

 

 

 

 

 

 

 

 


This project is supported by National Science Foundation and the Bowman Low frequency Cosmology lab in the School for Earth and Space Exploration.

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Science_November_2014_cosmic_dawnCheck out this article in Science magazine on Epoch of Reionization observations that really hits some interesting points not often covered in the media like the origin story of the MWA and LOFAR and the race to make a detection. Intrepid reporter Daniel Clery extracted some great quotes from the various PIs but my favorite is from Saleem Zaroubi:

To do what we do, you have to be hopelessly optimistic, but also brutally realistic.

Truth.

ASU undergrad and AZ Space Grant intern Michael Busch has been stopping by my office this semester, helping me look at MWA cosmology data and learning about radio astronomy. Turns out he’s a Pillar of the Community! Among other things he’s a Residential Assistant, responsible for a passel of undergrads in the newly refurbished Manzanita dorm.  Last month he was nominated as a Excellent Student Leader by the res life folks and was asked to bring along his favorite faculty advisors (Judd and I, naturally) to the award Gala.  Here we are trying to look swank.  Well done Michael!

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At the 2014 Student Leadership Gala. Left to Right: Judd Bowman, Michael Busch, Danny Jacobs

Here is a composite image of the entire sky in radio frequencies. It shows data from Parkes, Jodrell Bank and Effelsburg (ie the “Haslam map“, technically for you astro nerds the Global Sky Model by Angelica de Oliviera Costa which includes some data from other observations) as well as point sources from the VLA in the north and Molonglo in the south. This version is suitable for a 10x20inch poster. Those stars aren’t stars! Each is a radio galaxy undergoing a cataclysmic event emanating from a central million solar mass black hole. The nearest, double-lobed Centaurus A, features prominently center right. The radio Milky Way, a vast assemblage of supernova remnants, stretches across the center.

The sky in the FM radio radio band. A composite from many different telescopes around the world.

The sky in the FM radio radio band. A composite from many different telescopes around the world

Check out this MWA image of the galactic plane from David Kaplan (UWM). The image of 150MHz radiation covers 80 degrees wide and has a resolution of about 5 arcminutes. At about 125million pixels its a bit large to digest, so I’ve uploaded it to Gigapan, where you can pan and zoom ala google maps. Most of the circular things are supernova remnants, the imprints of ancient supernova explosions impressed on the galaxies plasma and magnetic fields.

This is just a sneak preview of the imaging capability of this fully operational battle station.

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Low res thumbnail. Click image for full map at Gigapan.

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A tiny fraction of the full resolution image. Look at all the supernova remnants! Click image for full map at Gigapan.

 

 

A nice composite of Centaurus A (as imaged by PAPER) and the moon to scale. Almost ten times the size of the moon, it really is a remarkable sight. Or would be if we could only see in the radio. For more, see Stefan et al.

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Centaurus A, a nearby radio galaxy is remarkably close. imaged here by PAPER. The galactic plane stretches across the bottom. Image by: Chris Carilli, Irina Stefan, Composite by: Danny Jacobs.

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With the new PAPER data (‘x’s) and a refined fitting procedure we can accurately model the EoR band flux to better than 2%.

Paper Title: A Flux Scale for Southern Hemisphere 21cm EoR Experiments

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If you look at typical catalogs of sources in the southern hemisphere epoch of reionization band you soon realize why measurements often disagree by 20%.  Even the brightest sources one would use for calibration are uncertain.  As you can see from the plot to the right, most of the old data (dots) are pretty uncertain. This source (Pictor A) is one of the brightest in the southern sky and is often use to set the flux scale.  The flux scale standard everyone uses to compare measurements is based on Cygnus A, which is not really even visible in the south, isn’t even defined at 150MHz.

So thats why we took a bunch of PAPER data and measured a bright source (Pictor A) several thousand times. This let us get rid of a lot systematics to get a nice spectrum. Then we fit a spectrum to old and new data using newish fitting procedure that accounts for error bars and nicely estimates the fit uncertainty. Previous estimates put the model uncertainty at about 20% (that number again!) but using the new fitter on the old data we found that we could predict the flux at about the 5% level, folding in the new PAPER data the model precision went below 2%.  An order of magnitude improvement!  we also verified this method on a couple dozen other sources with good success. Below is a nice large PAPER image of the area we were looking at.

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A PAPER mosaic of the southern EoR band sky. Sources measured in this paper have ‘x’s, only two (orange dots) seemed to disagree with other measurements.

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Comparing PAPER and MWA fluxes to come up with a model relating the two. The blue dots are all equally possible to within 76%.

Title: The precision and accuracy of early Epoch of Reionization foreground models: comparing MWA and PAPER 32-antenna source catalogs

This paper compares the fluxes in the first PAPER and MWA catalogs.  These sources are the brightest foregrounds in front of the EoR HI emission.  Various estimates suggest that we have to subtract these guys to anywhere from 0.1 to 0.01%. Percent!! Also we need to know the flux precisely so we can calibrate our power spectrum.

These first catalogs turn out to be accurate to about 20%.  We also looked at sources that were measured twice by the MWA and found that they didn’t agree very well (20-50% or more) away from the center of the image.  This means that the primary beam model used to flatten the flux scale was off.  This is probably true for both experiments.

In the end we noted that though 20% is no where near where we need to be for precise EoR foreground subtraction or flux calibration, its not too shabby for two experimental arrays at first light!

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During this trip we moved another 32 antenna into the grid configuration. This array will be left running over the (southern) Summer until sometime in mid 2013. This should be enough data to make the most sensitive EoR measurement yet!

Also: I got to be co-pilot in an airplane!

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