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The Highest Time-Resolution Measurements in Radio Astronomy: The Crab Pulsar Giant Pulses

The Highest Time-Resolution Measurements in Radio Astronomy: The Crab Pulsar Giant Pulses. Tim Hankins New Mexico Tech and NRAO, Socorro, NM Extreme Astrophysics in an Ever-Changing Universe 16-20 June, 2014. Acknowledgments. Jim Cordes Jared Crossley Tracey Delaney Jean Eilek

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The Highest Time-Resolution Measurements in Radio Astronomy: The Crab Pulsar Giant Pulses

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  1. The Highest Time-Resolution Measurements in Radio Astronomy: The Crab Pulsar Giant Pulses Tim Hankins New Mexico Tech and NRAO, Socorro, NM Extreme Astrophysics in an Ever-Changing Universe 16-20 June, 2014

  2. Acknowledgments Jim Cordes Jared Crossley Tracey Delaney Jean Eilek Glenn Jones Jeff Kern Mark McKinnon David Moffett Jim Sheckard Jim Weatherall Staffs of NRAO and NAIC Cornell University New Mexico Tech, NRAO New Mexico Tech, WV Wesleyan New Mexico Tech, NRAO Cal Tech, NRAO New Mexico Tech, NRAO New Mexico Tech, NRAO New Mexico Tech, Furman University New Mexico Tech New Mexico Tech, FAA

  3. Science objectives • What is the pulsar radio emission mechanism? • How does a relativistic magnetized pair plasma radiate at equivalent brightness temperatures of 1036 1042 K? • Can we understand Crab Nebula pulsar? Does the Crab fit the canonical pulsar model? Or is it unique?

  4. Summary Time resolution down to 0.2 nanoseconds achieved using a large-memory digital oscilloscope and coherent dedispersion

  5. Scientific Method: Form Hypothesis: Emission is a form Shot noise: Cordes, 1976 Make predictions: Shot noise cause: Collapsing solitons in turbulent plasma: Weatherall, 1998 Test by experiment: High-time resolution observations

  6. Collapsing soliton prediction I

  7. Prediction II

  8. How to get high time resolution: Coherent dedispersion required. Sample receiver voltage at Nyquist rate. Pass signal through a filter with the inverse dispersion characteristic of the Interstellar Medium. Use square-law detectors to obtain intensity. (Polarization slightly more complex.)

  9. Coherent dedispersion • Emitted signal: s(t)  S(w) • Dispersive ISM: H(w) = exp[ik(w)z]  h(t) • Received signal: s(t)*h(t)  S(w) H(w) • Dedispersion processing: S(w)H(w)•H(w)–1 s(t) • and 10,000 lines of code : Fourier Transform * : Convolution

  10. What Can You Do With It? Diagnostic for emission mechanism studies: Found nanostructure predicted by Weatherall Propagation studies: Precision DM determination Discoveries: Echoes of Crab “giant” pulses Crab Interpulse spectral bands

  11. Crab “Megapulse” at 9.25 GHz 2.2 Mega-Jansky pulse Duration: 0.4 nanoseconds 0.4 ns

  12. Not all pulses are so short Typical Main Pulse, 9 GHz 0 1 2 3 4 5 6 Time (Microseconds)

  13. Giant Pulse Widths

  14. Dispersion Measure Determination Methods: Time delay between two frequencies Must account for pulse shape change & Scattering broadening Split receiver passband Cross-correlate micro-, nanostructure Adjust dispersion removal filter to Maximize pulse intensity variance Minimize equivalent width

  15. Two-frequency Cross-correlation

  16. Split-band Cross-correlation

  17. Adjust Dispersion Measure  DM = 56.739780 DM = 56.739780 

  18. Adjust Dispersion Measure  DM = 56.735001  DM = 56.735001

  19. Modulation Spectra Main Pulses Interpulses 10-3 10-3 10-3

  20. Unexpected Discoveries Giant Pulse Echoes Dynamic Spectra: Interpulse Bands Main pulse DM ≠ Interpulse DM

  21. Giant pulse Echoes Echo 1435.1 MHz 1435.1 MHz 1435.1 MHz 1435.1 MHz Echo 4885.1 MHz 4885.1 MHz 4885.1 MHz

  22. Dynamic Spectra

  23. Intensity and spectrum of a Main pulse

  24. Intensity and spectrum of an Interpulse

  25. Main pulse:WidebandInterpulse:Banded

  26. Some definitions: Band Separation Band Width

  27. Interpulse band bandwidths

  28. Interpulse Band Frequencies At 30 GHz: Q ≈ Band Separation= 1.8 GHz = 36 Band Width 0.05 GHz Least-squares fit slope = Band Separation Band Separation = 0.058 Sky Freq

  29. Band Center Frequency Memory

  30. Main pulse/InterpulseDispersion

  31. Main pulseInterpulse

  32. Main Pulse Interpulse Dispersion corrected

  33. DM vs. Flux Interpulses Main pulses

  34. DM vs. Time Interpulses Main pulses −Jodrell Bank DM

  35. Summary Fast sampling: versatility in processing allows detailed emission studies. “The more you look, the more you see.” The Crab pulsar: Continues to “amaze and mystify”

  36. Future Dedispersion Processing: My old, 8-core Mac: 5 GHz data bandwidth: 4000x real time. (2 ms data in 8 seconds) [with lots of diagnostic overhead] Add n GPUs (Graphics Processor Units): Processing time reasonable. Moore’s Law:

  37. Coherent Dedispersion History: Bandwidth vs. Date

  38. Giant Main Pulses are WidebandFrom Glenn Jones at the GAVRT Telescope 3 4 5 6 7 8 9 10 Frequency (GHz) 5 10 15 20 25 30 5 15 25 Time (Microseconds)

  39. The End

  40. Giant pulse Echoes Echo 1435.1 MHz 20 40 60 Time (microseconds) 100 120 140

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