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Observing Vela With XDM The First Year

Observing Vela With XDM The First Year. Sarah Buchner KAT Bursary conference – Dec 2009. Summary. Pulsar timing Timing Vela pulsar Looking for glitches – sudden spin-ups For last year I have observed Vela pulsar with XDM for 15 hours per day. Outline. Introduction

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Observing Vela With XDM The First Year

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  1. Observing Vela With XDMThe First Year Sarah Buchner KAT Bursary conference – Dec 2009

  2. Summary • Pulsar timing • Timing Vela pulsar • Looking for glitches – sudden spin-ups • For last year I have observed Vela pulsar with XDM for 15 hours per day. Observing Vela with XDM

  3. Outline • Introduction • What is a pulsar glitch? • Motivation for XDM observations • Pulsar Timing 101 • Early results • Challenges! • Conclusion Observing Vela with XDM

  4. Observing Pulsars Observing Vela with XDM

  5. Pulsars as clocks • Massive flywheel -> very good clock • Can unambiguously number pulses • Model rotation and compare observed arrival of pulse with predicted arrival Observing Vela with XDM

  6. Pulsar Glitches • Very good clock but … • Sudden increase in frequency or “spin-up” • Frequency increases by few parts per million • In energy terms • earthquake of 17 on Richter scale • surface of the earth moves by 15 m. Observing Vela with XDM

  7. HartRAO Glitch observations Observing Vela with XDM

  8. Questions • How fast does the crust spin-up? • What is the recovery? • Interior of neutron star Observing Vela with XDM

  9. XDM Glitch observations • Hart 26m bearing failure • Observe Vela while above the horizon (15 hours / day) • Why? • First prize: Catch a glitch “in the act” • Second Prize: Parameterize the recovery • Free gift: • Pulsar timing provides exacting test of polarization and timing of XDM. • Soak test – continous observing Observing Vela with XDM

  10. XDM: First light Observing Vela with XDM

  11. Effect of ISM • Observe over wide-bandwidth to increase sensitivity • BUT Observing Vela with XDM

  12. Dispersive Smearing Observing Vela with XDM

  13. Dedispersion Observing Vela with XDM

  14. Dedispersion and folding Std Profile Dedisperse Fold Find TOA DBE DM P clock Timestamp Find residuals Barycentre Obs x,y,z Pls position Observing Vela with XDM

  15. Arrival Times (TOA) • 53075.8716014048 • 53076.6068099029 • 53076.6315093162 • 53076.6352589534 • 53076.6390085897 • 53076.7453055512 • 53076.7728053205 • 53076.8144370828 • 53076.8440091993 Observing Vela with XDM

  16. 1st order - frequency Observed - Predicted ‘early’ ‘late’ Observing Vela with XDM

  17. 2nd order Observing Vela with XDM

  18. 2nd order Observing Vela with XDM

  19. Residuals 32.04 us Observing Vela with XDM

  20. 12 m @ Parkes 50.66 us Hobbs et al, 2009 0907.4847 Observing Vela with XDM

  21. Residuals 32.04 us Observing Vela with XDM

  22. AsideWhat does a glitch look like? Observing Vela with XDM

  23. 1000 days of Vela Observing Vela with XDM

  24. Challenges Observing Vela with XDM

  25. 1000 days of Vela Observing Vela with XDM

  26. Offset relative to 26m transit Observing Vela with XDM

  27. Residuals 32.04 us Observing Vela with XDM

  28. Slopes Observing Vela with XDM

  29. Observing Vela with XDM

  30. Diurnal Slopes 100 us / day Observing Vela with XDM

  31. No slopes in 26m data!! • We do not see similar slopes in the HartRAO 26m data • What causes the slopes? • What causes the offset? • What is the difference between the two systems? • Does the ‘problem’ lies in the signal or our system? • Or in the wetware? Observing Vela with XDM

  32. HartRAO vs XDM XDM Alt/Az Linear pol DBE Dedisperse Find TOA correlate Find residuals Fold Barycentre GPS rudidium DM XDM x,y,z Pls RA/Dec Std Profile Timestamp Pobs model Hart x,y,z H maser Hart 26m Equatorial Circular polarization WOPT Find TOA Gaussian Find residuals Barycentre Observing Vela with XDM

  33. Clocks • DBE • GPS disciplined rubidium • HartRAO Timer • Hart hydrogen maser • Feed 5MHz and 1 pps from H-maser into DBE • Both systems now run off of the same clock Observing Vela with XDM

  34. Position offset • Part of the formation of residuals involves transformation from observatory reference frame to solar system barycentre • Need to know position of observatory • Is this correct? • 100 us per day is 30 km light travel • Can rule out • Incorrect observatory position • Distortion of antenna • Cable expansion Observing Vela with XDM

  35. HartRAO vs XDM XDM Alt/Az Linear pol DBE Dedisperse Find TOA correlate Find residuals Fold Barycentre DM XDM x,y,z Pls RA/Dec Std Profile Timestamp Pobs model H maser Hart x,y,z Hart 26m Equatorial Circular polarization WOPT Find TOA Gaussian Find residuals Barycentre Observing Vela with XDM

  36. DBE or signal? • Mix RF from XDM down to IF of 160 MHz and feed a 8 MHz band into Mark I timer. • Now the same signal is being fed into both timers • Mark 1 timer narrow bandwidth & only one channel Observing Vela with XDM

  37. DBE or signal • Same slope • Problem lies in signal • Polarisation issue!! Observing Vela with XDM

  38. Polarization • XDM is alt-az mount with linear feeds • Hart 26m is equatorial with circular feeds Observing Vela with XDM

  39. Effect of mount sunrise sunset Polarization axes seem to shift in sky relative to feed Observing Vela with XDM

  40. Parallactic angle • XDM compensates by rotating the feed in order to keep the polarization axis constant • Is this being done correctly? • How would this effect the residuals? Observing Vela with XDM

  41. Parallactic angle • Feed rotation and parallactic angle Observing Vela with XDM

  42. Pulse shape changes Observing Vela with XDM

  43. WARNING!! • Sensitive KAT engineers should close their eyes Observing Vela with XDM

  44. Experimental RA Observing Vela with XDM

  45. Circular polarization Convert from linear to circular using a hybrid Observing Vela with XDM

  46. Results DBE Mark I timer Observing Vela with XDM

  47. Conclusion There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know. Donald Rumsfeld Observing Vela with XDM

  48. Conclusion • There are two effects • Polarization effect – corrected with circular polarization • Timing problem in the DBE • We now obtained slope free residuals from XDM • Using circular polarization, narrow BW, Mark I timer Observing Vela with XDM

  49. Concluding remarks • Pulsars are amazing! • Pulsar timing provides stringent testing • Timing • polarization • Highly recommend that pulsar timing forms part of single dish commisioning for KAT-7. • meerKAT will be great pulsar instrument – galactic centre • Pulsar observing is more than plugging a timer into data spigot • Capacity building of pulsar timing community • First South African observations using multi channel pulsar timer with dedispersion • Steep learning curve • International community Observing Vela with XDM

  50. Thanks • meerKAT team especially Adriaan Pens-Hough • George Nicolson Observing Vela with XDM

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