Detecting Archived Radio Transients (1980-Present)
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This document summarizes a research project detecting radio transients from archival data collected by the Very Large Array radio telescope between 1980 and the present. The presentation outlines the background on radio transients and interferometry, the project description, and the role of automated data processing pipelines and non-interactive cleaning. The involvement of the presenter includes analyzing a field of interest around gamma ray burst GRB030329 to help develop improved automated detection and analysis techniques.
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Detecting Archived Radio Transients (1980-Present)
- 1. Detecting Archived Radio Transients (1980-Present) _________________________________________________________________________________ Presentation by - Jesse DePinto (UWM) Faculty Research Advisor- Dr. David Kaplan (UWM Research Team – Geoffery Bower (Berkeley) Andrew Bass(Cornell) and Shami Chatterjee (Corne
- 2. Presentation Outline • Background on radio transients, radio interferometry and the Very Large Array (VLA) • Project description • My role in the research
- 3. What are radio transients? • Radio transients are sources of radio emission that are not present in one observation …
- 4. What are radio transients? • Radio transients are sources of radio emission that are not present in one observation … • Then present in another
- 5. What causes radio transients? Explosions Propagation Effects Accretion and Magnetic Fields Image from Geoffery Bower
- 6. What causes radio transients? Explosions Propagation Effects Accretion and Magnetic Fields
- 7. What causes radio transients? Explosions Propagation Effects Accretion and Magnetic Fields Plot by Hyman
- 8. Which radio sources matter to us? • We’re looking for small sources
- 9. Which telescope do we use? Ex. 1: Compare resolution of 1.44 GHz for multiple telescopes. – 1.44 GHz= 20.8 cm – Resolution=lambda/diameter • Resolution Green Bank Telescope = 474 arcsec • Resolution Arecibo Telescope = 141 arcsec • Resolution VLA D-Configuration = 45 arcsec • Resolution VLA A-Configuration = 1 arcsec
- 10. Very Large Array (VLA) Image from NRAO
- 11. Interferometry Image from Wikipedia Image from Ray Nor
- 12. Project Objectives • Do it manually • Do it automatically • Do it better automatically
- 13. Pipeline Processes • Preparing the raw UV data • Calibrating phase and flux calibrators • Clean the image (eliminate sidelobes) • Detect and Measure • Create light curves
- 14. Pipeline Processes • Preparing the raw UV data • Calibrating phase and flux calibrators • Clean the image (eliminate sidelobes) • Detect and Measure • Create light curves
- 15. Pipeline Processes • Preparing the raw UV data • Calibrating phase and flux calibrators • Clean the image (eliminate sidelobes) • Detect and Measure • Create light curves
- 16. Pipeline Processes • Preparing the raw UV data • Calibrating phase and flux calibrators • Clean the image (eliminate sidelobes) • Detect and Measure • Create light curves
- 17. Pipeline Processes • Preparing the raw UV data • Calibrating phase and flux calibrators • Clean the image (eliminate sidelobes) • Detect and Measure • Create light curves Plot from Andrew Bass
- 18. My Involvement Field of Interest: GRB030329
- 19. Need For Cleaning Before Interactive Clean After Interactive Clean
- 23. Non-Interactive Cleaning Cell Size Number of (arcsec) Iterations 1.00 500 1.25 500 1.50 500 1.75 500 2.00 500 1.00 1000 1.25 1000 1.50 1000 1.75 1000 2.00 1000 1.00 1500 1.25 1500 1.50 1500 1.75 1500 2.00 1500
- 24. Future Plans • Detect transient radio sources in the archive • Multi-wavelength follow-up observations • Statistically describe astrophysical phenomena
Editor's Notes
- -More appropriately worded- sources with time-variable radio emissions
- -Gamma Ray Bursters, Radio Superovae, energetic, extreme physics, across the universe-Geoffrey Bower’s glance at an archived data field, showing faint transients. Could be RSNe or NS, etc…
- -Twinkling in the ISM (helps to study turbulence)-Maitia’s plot of Extreme scattering for PSR
- -Magnetars and pulsars. Matter falling on black hole or neutron star, then heating once it hits.-Hyman’s plot of galactic center transients, turns on and off (or just an unusually long period for a pulsar) accreting or flaring star, WD, Pulsar, etc… -In summary, radio transients are weird occurrences that we need to many sources to better statistically characterize
- -Since transients are usually explosive events, seen from far away (across universe), they appear tiny, and they must be tiny for our purposes, point sources -For the brightness in an image to change coherently, the source must be smaller than C*time scale of measurement (timescale of hours to weeks) -We are also looking at faint sources (yet to be detected), need sensitive telescope (large collecting area)-Specifically, we are looking at point sources, which are by definition unresolved, because the source is smaller than the beam size (resolution=lambda/baseline diameter)
- -Diameter= primary mirror or baseline diameter (multiple dishes/interferometer), R inverse prop to D-Green Bank = 100m-Arecibo = 305m -VLA D = 1000 m-VLA A = 36,000 m- best resolution for small sources -We need a telescope to makes actual detailed images with good resolution, probably an interferometer (VLA)
- -1980-present (over 30 years of archived data)-27 radio antennas in a Y-configuration, D=25m each-Radio interferometry telescope-Angular resolution is restricted by diameter-Interferometry- superposition and interferences of light, determines phase differences-Wavelengths between 1mm- 90cm-Configurations = (D) 600 m and (A) 36 km
- -Young’s Double Slit Experiment- Constructive Interference-Geometric path difference -Interferometer measures the coherence in electric field between 2 pairs of points (baselines)-Correlator- multiplies the voltages of each baseline pair (351 for 27 antennas) -Visibilities (raw UV data)- result of cross correlating from antennas. Complex= amplitude (real) and phase (imaginary)
- -Detect radio transient sources from the VLA archive, reduce the UV data to obtain flux values and images, create light curves then compare findings to known values-Develop an automated pipeline which can detect radio transients, reduce the UV data to obtain flux values and obtain images, and then produce light curves for them-Repeat with different fields, Make the pipeline smarter by testing a variety of observations-Goal is to automatically reduce VLA continuum data in any frequency band from the raw UV data, to save the tedium of reducing UV data sets
- -Raw UV (spatial frequencies) data refers to the complex visibility (amplitude and phase) -Imports VLA archive data set into Casa, list observations summary, flag autocorrelation data and RFI
- -Fluxscale takes flux calibrator and set basic flux scale -Gaincal takes UV data and fit to model -Applycal finds phase calib close to target, fit to model (should be a flat line, point source)-Plot shows vector average amplitude over Uvdistance (units of wavelength)
- -Because the Y-configuration of the VLA doesn’t completely sample the point spread function, there are artifacts present, or sidelobes (more on that later)
- -Detects sources using source extractor, (generally sources above 3*sigma) -Eventually obtain time-dependent flux and rms values for the point source
- -Light curves using multiple observations
- InfluentialGamma Ray Burster- actually, THE GRB that provided us with the necessary link between SNe and GRB-10-Apr-2011-VLA D- Configuration-Frequency 8.44 GHz
- -Clean side lobes by setting clean boxes, invert and deconvolve with algorithms
- 1.) Non-Interactive mode with no clean boxes2.) Non-Interactive mode with pre-defined clean boxes specified in advance3.) Interactive mode with clean box covering 1024x1024 (no clean boxes)4.) Interactive mode with pre-defined clean boxes set around source
- -After the pipeline is up and running…