observing vela with xdm the first year

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.


Outline

• Introduction– What is a pulsar glitch?– Motivation for XDM observations

• Pulsar Timing 101

• Early results

• Challenges!

• Conclusion


Observing Pulsars


Pulsars as clocks

• Massive flywheel -> very good clock• Can unambiguously number pulses• Model rotation and compare observed arrival of

pulse with predicted arrival


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.


HartRAO Glitch observations


Questions

• How fast does the crust spin-up?

• What is the recovery?– Interior of neutron star


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


XDM: First light


Effect of ISM

• Observe over wide-bandwidth to increase sensitivity

• BUT


Dispersive Smearing

DMB

s3.8Smear3

GHzMHz


Dedispersion


Dedispersion and folding

DBE Dedisperse Fold Find TOA

BarycentreFind residuals

clock DM P

Std Profile

Pls position

Timestamp

Obs x,y,z


Arrival Times (TOA)

53075.871601404853076.606809902953076.631509316253076.635258953453076.639008589753076.745305551253076.772805320553076.814437082853076.8440091993


1st order - frequency

‘early’

‘late’

Observed - Predicted


2nd order


Residuals

32.04 us


12 m @ Parkes

50.66 us

Hobbs et al, 20090907.4847


Residuals

32.04 us


AsideWhat does a glitch look like?


1000 days of Vela


Challenges


1000 days of Vela


Offset relative to 26m transit


Residuals

32.04 us


Slopes


Diurnal Slopes

100 us / day100 us / day


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?


HartRAO vs XDM


correlate

Barycentre Find residuals

GPS rudidium DMPobs Std Profile

Timestamp

Pls RA/Dec

XDMAlt/Az

Linear pol

WOPT Find TOA

Gaussian


Hart 26mEquatorialCircular

polarization

H maser

XDMx,y,z

Hartx,y,z

model


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


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


HartRAO vs XDM


correlate


DMPobs Std Profile

Timestamp

Pls RA/Dec

XDMAlt/Az

Linear pol

WOPT Find TOA

Gaussian


Hart 26mEquatorialCircular

polarization

H maser

XDMx,y,z

Hartx,y,z

model


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


DBE or signal

• Same slope

• Problem lies in signal

• Polarisation issue!!


Polarization

• XDM is alt-az mount with linear feeds

• Hart 26m is equatorial with circular feeds


Effect of mount

sunsetsunrise

Polarization axes seem to shift in sky relative to feed


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?


Parallactic angle

• Feed rotation and parallactic angle


Pulse shape changes


WARNING!!

• Sensitive KAT engineers should close their eyes


Experimental RA


Circular polarization

Convert from linear to circular using a hybrid


Results

Mark I timerDBE


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


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


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


Thanks

• meerKAT team especially Adriaan Pens-Hough• George Nicolson


meerKAT science case

• Please see Roy if you would like to be involved• Meeting planned in January


Questions?

Answers?


Pointing Problems


XDM prototype at HartRAO

Kitty


KAT-7


KAT -> meerKAT


meerKAT


Neutron Stars and Pulsars


Observing Vela with XDM


• 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


Waiting for Vela to glitch


Storm clouds over HartRAO


• 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


Timing Vela with XDM


KAT

• Glitch detection strategies• Regular observations needed• Find glitching pulsars• Pre-cursors?


Vela Pulsar Glitches


Predicting glitches


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/


sunsetsunrise


Pulsars and Neutron Stars

• Very dense • Rapidly spinning• High magnetic field• Cosmic lighthouse

observing vela with xdm the first year

Documents

usobserving vela

xdmobserving vela

zobserving vela

zmodelobserving vela

conclusionobserving

xdmdedispersionobserving

xdmchallengesobserving

predictedobserving vela