The (Horse) Fly’s Eye A Search for Highly Energetic Radio Pulses from Extragalactic Sources Crab Pulsar: Giant Pulse Detection (sigma = 15.75) 240 1501 using the Allen Telescope Array 1483 200 1465 CASPER Workshop II 08.04.08 1448 160 Uncalibrated Power Frequency (MHz) 1430 Griffin Foster, Andrew Siemion, Peter McMahon 120 1412 1395 80 1377 fitted dm = 56.78 1359 40 1342 6 13 19 25 31 38 44 Time (ms) Geoff Bower, Jim Cordes, Griffin Foster, Joeri van Leeuwen, William Mallard, Peter McMahon, Andrew Siemion, Mark Wagner, Dan Werthimer
Motivation Exciting Results From Lorimer et al. • Lorimer, et. al., “A Bright Millisecond Radio Burst of Extragalatic Origin.” Science , 318 , 2007. ‣ Announced September 2007 ‣ Single pulse at L-band ‣ 30 Jy, saturated digitizer in one beam ‣ Located 3° from the SMC ‣ DM = 375 pc/cm 3 implies D ~ 1Gpc Parkes Multibeam Pointing During Lorimer Detection Frequency vs. Time Waterfall for Lorimer Detection
The Fly’s Eye: The Search for HERPES ‣ Highly Energetic Radio Pulses for Extragalactic Sources ‣ Goal: Build a set of 44 independent spectrometers for the ATA and use them to search for HERPES over a large portion of the sky. Timeline ‣ November 19, 2007 - Dan Werthimer and Geoff Bower have lunch to discuss a suggestion made by Jim Cordes to perform a transient search using the ATA. ‣ November 20, 2007 - Dan Werthimer tasks a group of mostly undergraduate students at the Center for Astronomy Signal Processing and Electronics Research (CASPER) to begin building a transient instrument. ‣ December 22, 2007 - Fly’s Eye Team installs Fly’s Eye at ATA. ‣ February, March 2008 - Conducted 500 hours of weekend observations. ‣ April - August... 2008 - Data analysis underway
The Allen Telescope Array ‣ Located in Hat Creek, CA (~5 hours from Berkeley) ‣ 42 x 6 m dishes, 0.5-11 GHz usable band ‣ 4 independent tunable IFs ‣ First light was less then a year ago, October 2007 (Galaxy M31) Text Advantages ‣ Newly commissioned, so there is plenty of observing time available ‣ Each antenna has a wide beam, ~2° FWHM (at L band) ‣ With independent, tunable IFs commensal observing is very easy
iBOB Spectrometer Using standard CASPER libraries and the pocket correlator design the 4 input spectrometer used in Fly’s Eye was completed in 3 weeks.
The Instrument 44 independent spectrometers - constructed using a system of eleven iBOB/iADC quad spectrometers Built using open-source CASPER hardware and software libraries in about one month. Sky Coverage: 22 - 42 beams 100-200 square degrees Spectrometer Specifications (each): 208 MHz bandwidth, at 1430 MHz 128 spectral channels 0.625 mS readout Distributions: Spatial, DM, Power, Pulse Width Fly’s Eye Rack at ATA
Instrument Diagnostics PSR B0329+54 Detection PSR B0329+54 (36 beams summed, 15 minutes folded) PSR B0329+54 detected in 41/44 signal paths. PSR B0329+54 Detections in all 44 Beams (15 minutes folded)
Control and Monitoring After initial instrument setup at the ATA all observations were done remotely
Observation Diagnostics ibob-g47 ibob-g48 50 50 ‣ All observations were done via 40 40 AA 30 30 scripts on a control machine BB 20 20 CC and recorded to a data server 10 10 DD 0 0 (via gulp) 32 32 64 96 128 64 96 128 ‣ For every hour of observations ibob-g44 ibob-g45 ibob-g46 58 minutes were used in the 50 50 50 40 40 40 horseshoe pattern, 1 minutes 30 30 30 20 20 20 was used for recording 10 10 10 diagnostic data to assure data 0 0 0 32 32 32 64 96 128 64 96 128 64 96 128 quality, note the 21 cm line. ibob-g41 ibob-g42 ibob-g43 ‣ Packet loss statistics and 50 50 50 40 40 40 spectra from diagnostic runs 30 30 30 were uploaded to a web server 20 20 20 10 10 10 0 0 0 32 32 32 64 96 128 64 96 128 64 96 128 ibob-g38 ibob-g39 ibob-g40 50 50 50 40 40 40 30 30 30 20 20 20 10 10 10 0 0 0 32 64 96 128 32 64 96 128 32 64 96 128
Observations Drift scan Fly’s Eye observations were conducted in campaign mode on weekends between February and April 2008. Initial plan was for “fly’s eye” sky patch observing, eventually transformed to “horseshoe” constant declination strip. Total observing time thus far is approximately 480 hours. Both North and South pointing observations were performed, primarily North due to kinder RFI environment. Total dataset is approximately 17 terabytes. Fly’s Eye Beam Pointing Diagram
Instrument Diagnostics Giant Pulses From PSR B0531+21 The Crab pulsar has be well studied, and is know to produce giant pulses. The pulsar was observed for one hour, during which close to a dozen detectable pulses were detected (in summed data), the brightest of which was distinguishable in approximately half of single dish observations. Crab Pulsar: Giant Pulse Detection (sigma = 15.75) 240 1501 1483 200 1465 1448 160 Uncalibrated Power Frequency (MHz) 1430 120 1412 1395 80 1377 fitted dm = 56.78 1359 40 1342 6 13 19 25 31 38 44 Time (ms) Giant Pulse from PSR B0531+21 (single beam) Giant Pulses from PSR B0531+21 (35 beams)
Data Analysis ‣ DM search range: 50-2000 pc/cm 3 (with Raw gulp Error Analysis / Dropped IF Seperation Datafile Packet Correction (filterbank) decimation, non-integer spacing) .... IF 0 IF 1 IF 2 IF 43 IF SUM ‣ Computing grids used: RFI Rejection freq. and time 5 (Berkeley Wireless .... .... domains Research Center, UC Equalization / .... .... Normalization Berkeley EECS, DOE NERSC) De-dispersion De-dispersion De-dispersion De-dispersion .... DM 0 DM 1 DM 2 DM 1000 (dedisperse) (dedisperse) (dedisperse) (dedisperse) .... .... .... ‣ Total cores (peak): Frequency Compute RMS / Log Candidate Collapse Threshold Pulses (seek) (dedisperse) ~200 (Itanium64, Xeon, Sparc, Opteron) Decimate Disk Storage (seek) (MySQL Database) Fly’s Eye Data Analysis Pipeline ‣ Total throughput (peak): ~200 Mbits/second
The RFI Challenge Types of RFI: ‣ Wideband, short time period ‣ Narrowband, continuous(radio, airplanes, satellites) ‣ Narrowband, short time period(RADAR, more airplanes) ‣ Special cases(broken satellites?) Solutions: ‣ Pre data analysis: ‣ normalization and equalization of spectra, remove abnormal spectra(wideband RFI) ‣ time collapse and compute variance, similar to kurtosis methods(narrowband, short time) ‣ Post data analysis: ‣ flag times with a wide range on DM events ‣ Special cases for low(<50 DM) and high(>1800 DM) events ‣ RADAR Current Challenges: ‣ Narrowband, short time period RFI ‣ Equalization/Normalization methods
The RFI Challenge: Military Radar ARSR-4 Air Route Surveillance Radar ‣ Radar transmits on ~12s timescales ‣ With a low duty cycle the radar is hard to remove using variance RFI removal ‣ In northern California there are 2 nearby sites (Rainbow Ridge, Mill Valley) ‣ The stations operate out of phase with each other and at different frequencies false high DM detections ‣ Brute force solution: ignore these channels
Interesting RFI: Broken Satellites From our first pass script we found ~80 interesting events, one event in particular looked like something we had never seen before, it was too narrow band to be wide band RFI and it was centered around 1420 MHz. (Aliens?!?!?!) Then we zoomed in on the data... After zooming in on the event we determined it was not terrestrial RFI or Aliens, but based on the angular speed of the object it is probably a low orbit satellite(transmitting around 1420 MHz!).
Producing Results MySQL Server ‣ After data analysis the data is stored to a MySQL server where our graphing pipeline retrieves data. ‣ Using Python we do RFI flagging and generate a series of plots which can be viewed from a web interface Post RFI Rejection ‣ The next step of the web interface is to include user interaction to tag plots with i.e. interesting/bad rfi/ nothing... ‣ To view an interesting portion of the Corrected Plots Raw Plots Decimated Waterfalls data we retrieve the raw data from the tape backup, and generate a large waterfall plot of all the data for a time period (the large files sizes of Web Interface our data causes this step to take ~10 minutes to generate). Request Plots Full Waterfalls User Tag Events
Example Preliminary Results 480 hours of observations, 44 spectrometers, 10 minute sets, 9 plot types over a million plots! Result Browser Example Time vs. Sigma Plot Example Time vs. DM Plot
New and Future Analysis ‣ We have the plot, now we need the eyes! Using our first pass scripts we can find the interesting events in the best data but there is much more to be looked at. ‣ Reprocess! - Improve RFI rejection and implement new pulse search algorithms (underway) ‣ Improve SNR in some of the data by summing polarizations ‣ Include a measurement of the kurtosis to remove intermittent narrowband RFI ‣ Try different equalization techniques ‣ Improve speed of analysis
Assessment of Significance Region allowed by existing experiments Parameter space explored by Fly’s Eye I (Spring 2008) Parameter space potentially explored by a one-year commensal Fly’s Eye Experiment Parameter Space for Radio Transient Detection
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