observing vela with xdm the first year
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Observing Vela With XDMThe First Year
Sarah BuchnerKAT Bursary conference – Dec 2009
Observing Vela with XDM 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
DMB
s3.8Smear3
GHzMHz
Observing Vela with XDM 13
Dedispersion
Observing Vela with XDM 14
Dedispersion and folding
DBE Dedisperse Fold Find TOA
BarycentreFind residuals
clock DM P
Std Profile
Pls position
Timestamp
Obs x,y,z
Observing Vela with XDM 15
Arrival Times (TOA)
53075.871601404853076.606809902953076.631509316253076.635258953453076.639008589753076.745305551253076.772805320553076.814437082853076.8440091993
Observing Vela with XDM 16
1st order - frequency
‘early’
‘late’
Observed - Predicted
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, 20090907.4847
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 / day100 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
DBE Dedisperse Fold Find TOA
correlate
Barycentre Find residuals
GPS rudidium DMPobs Std Profile
Timestamp
Pls RA/Dec
XDMAlt/Az
Linear pol
WOPT Find TOA
Gaussian
Barycentre Find residuals
Hart 26mEquatorialCircular
polarization
H maser
XDMx,y,z
Hartx,y,z
model
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
DBE Dedisperse Fold Find TOA
correlate
Barycentre Find residuals
DMPobs Std Profile
Timestamp
Pls RA/Dec
XDMAlt/Az
Linear pol
WOPT Find TOA
Gaussian
Barycentre Find residuals
Hart 26mEquatorialCircular
polarization
H maser
XDMx,y,z
Hartx,y,z
model
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
sunsetsunrise
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
Mark I timerDBE
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 51
meerKAT science case
• Please see Roy if you would like to be involved• Meeting planned in January
Observing Vela with XDM 52
Questions?
Answers?
Observing Vela with XDM 53
Observing Vela with XDM 54
Pointing Problems
Observing Vela with XDM 55
XDM prototype at HartRAO
Kitty
Observing Vela with XDM 56
KAT-7
Observing Vela with XDM 57
KAT -> meerKAT
Observing Vela with XDM 58
meerKAT
Observing Vela with XDM 59
Observing Vela with XDM 60
Neutron Stars and Pulsars
Observing Vela with XDM 61
Observing Vela with XDM
Observing Vela with XDM 62
• 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.
Pulsar Glitches
Observing Vela with XDM 63
Waiting for Vela to glitch
Observing Vela with XDM 64
Storm clouds over HartRAO
Observing Vela with XDM 65
• 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.
Pulsar Glitches
Observing Vela with XDM 66
Timing Vela with XDM
Observing Vela with XDM 67
Observing Vela with XDM 68
Observing Vela with XDM 69
KAT
• Glitch detection strategies• Regular observations needed• Find glitching pulsars• Pre-cursors?
Observing Vela with XDM 70
Vela Pulsar Glitches
Observing Vela with XDM 71
Predicting glitches
Observing Vela with XDM 72
Observing Vela with XDM 73
Observing Vela with XDM 74
Parallactic angle
Parallactic angle is the angle between the object’s hour circle and its vertical circle
www.mmto.org/MMTpapers/pdfs/itm/itm04-1.pdf
Observing Vela with XDM 75http://www.astro.caltech.edu/~mcs/CBI/pointing/
Observing Vela with XDM 76
Observing Vela with XDM 77
sunsetsunrise
Observing Vela with XDM 78
Observing Vela with XDM 79
Observing Vela with XDM 80
Observing Vela with XDM 81
Pulsars and Neutron Stars
• Very dense • Rapidly spinning• High magnetic field• Cosmic lighthouse