Observing Vela With XDM
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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. Observing Vela with XDM 2 Outline • Introduction – What is a pulsar glitch? – Motivation for XDM observations • Pulsar Timing 101 • Early results • Challenges! • Conclusion Observing Vela with XDM 3 Observing Pulsars Observing Vela with XDM 4 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 5 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 6 HartRAO Glitch observations Observing Vela with XDM 7 Questions • How fast does the crust spin-up? • What is the recovery? – Interior of neutron star Observing Vela with XDM 8 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 9 XDM: First light Observing Vela with XDM 10 Effect of ISM • Observe over wide-bandwidth to increase sensitivity • BUT Observing Vela with XDM 11 Dispersive Smearing 3 B Smear 8Observing .3s Vela with XDM DM MHz GHz 12 Dedispersion Observing Vela with XDM 13 Dedispersion and folding Std Profile DBE Dedisperse clock DM Fold P Find residuals Observing Vela with XDM Find TOA Timestamp Barycentre Pls position Obs x,y,z 14 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 15 1st order - frequency Observed - Predicted ‘early’ ‘late’ Observing Vela with XDM 16 2nd order Observing Vela with XDM 17 2nd order Observing Vela with XDM 18 Residuals 32.04 us Observing Vela with XDM 19 12 m @ Parkes 50.66 us Observing Vela with XDM Hobbs et al, 2009 0907.4847 20 Residuals 32.04 us Observing Vela with XDM 21 Aside What does a glitch look like? Observing Vela with XDM 22 1000 days of Vela Observing Vela with XDM 23 Challenges Observing Vela with XDM 24 1000 days of Vela Observing Vela with XDM 25 Offset relative to 26m transit Observing Vela with XDM 26 Residuals 32.04 us Observing Vela with XDM 27 Slopes Observing Vela with XDM 28 Observing Vela with XDM 29 Diurnal Slopes 100 us / day Observing Vela with XDM 30 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 31 HartRAO vs XDM XDM Alt/Az Linear pol DBE Dedisperse Fold Find TOA Find residuals Barycentre correlate GPS rudidium DM H maser Hart 26m Equatorial Circular polarizatio n WOPT XDM Pls x,y,z Pobs Std Profile RA/Dec Timestamp Hart x,y,z Find TOA Barycentre model Find residuals Gaussian Observing Vela with XDM 32 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 33 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 34 HartRAO vs XDM XDM Alt/Az Linear pol DBE Dedisperse Fold Find TOA Find residuals Barycentre correlate DM H maser Hart 26m Equatorial Circular polarizatio n WOPT XDM Pls x,y,z Pobs Std Profile RA/Dec Timestamp Hart x,y,z Find TOA Barycentre model Find residuals Gaussian Observing Vela with XDM 35 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 36 DBE or signal • Same slope • Problem lies in signal • Polarisation issue!! Observing Vela with XDM 37 Polarization • XDM is alt-az mount with linear feeds • Hart 26m is equatorial with circular feeds Observing Vela with XDM 38 Effect of mount sunrise sunset Polarization axes seem to shift in sky relative to feed Observing Vela with XDM 39 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 40 Parallactic angle • Feed rotation and parallactic angle Observing Vela with XDM 41 Pulse shape changes Observing Vela with XDM 42 WARNING!! • Sensitive KAT engineers should close their eyes Observing Vela with XDM 43 Experimental RA Observing Vela with XDM 44 Circular polarization Convert from linear to circular using a hybrid Observing Vela with XDM 45 Results DBE Mark I timer Observing Vela with XDM 46 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 47 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 48 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 49 Thanks • meerKAT team especially Adriaan Pens-Hough • George Nicolson Observing Vela with XDM 50 meerKAT science case • Please see Roy if you would like to be involved • Meeting planned in January Observing Vela with XDM 51 Questions? Answers? Observing Vela with XDM 52 Observing Vela with XDM 53 Pointing Problems Observing Vela with XDM 54 XDM prototype at HartRAO Kitty Observing Vela with XDM 55 KAT-7 Observing Vela with XDM 56 KAT -> meerKAT Observing Vela with XDM 57 meerKAT Observing Vela with XDM 58 Observing Vela with XDM 59 Neutron Stars and Pulsars Observing Vela with XDM 60 Observing Vela with XDM Observing Vela with XDM 61 Pulsar Glitches • Sudden increase in frequency or “spin-up” • Frequency increases by few parts per million • In energy terms equivalent to earthquake of 17 on Richter scale in which the surface of the earth moves by 15 m. Observing Vela with XDM 62 Waiting for Vela to glitch Observing Vela with XDM 63 Storm clouds over HartRAO Observing Vela with XDM 64 Pulsar Glitches • Sudden increase in frequency or “spin-up” • Frequency increases by few parts per million • In energy terms equivalent to earthquake of 17 on Richter scale in which the surface of the earth moves by 15 m. Observing Vela with XDM 65 Timing Vela with XDM Observing Vela with XDM 66 Observing Vela with XDM 67 Observing Vela with XDM 68 KAT • Glitch detection strategies • Regular observations needed • Find glitching pulsars • Pre-cursors? Observing Vela with XDM 69 Vela Pulsar Glitches Observing Vela with XDM 70 Predicting glitches Observing Vela with XDM 71 Observing Vela with XDM 72 Observing Vela with XDM 73 Parallactic angle Parallactic angle is the angle between the object’s hour circle and its vertical circle Observing Vela with XDM www.mmto.org/MMTpapers/pdfs/itm/itm04-1.pdf 74 Observing Vela with XDM http://www.astro.caltech.edu/~mcs/CBI/pointing/ 75 Observing Vela with XDM 76 sunset sunrise Observing Vela with XDM 77 Observing Vela with XDM 78 Observing Vela with XDM 79 Observing Vela with XDM 80 Pulsars and Neutron Stars • • • • Very dense Rapidly spinning High magnetic field Cosmic lighthouse Observing Vela with XDM 81
