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Consecutive bright pulses in the Vela pulsar

Jim Palfreyman
Research Masters, University of Tasmania Supervisors: Dr Aidan Hotan & Professor John Dickey
Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Data Collection
· Been observing individual pulses since late 2007 · 64 MHz bandwidth · Phase coherent de-dispersion using 16 frequency channels using dspsr and psrchive · Time resolution of 10.9 us · 300 hours of observations covering over 107 pulses · Also did 100 hours over 10 consecutive days with no instrument changes
Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Bright pulses
· Giant is accepted in the literature as 10 times the mean flux density of the integrated pulse · Vela typically doesn't have Giants · Has giant micro pulses (Johnston et al 2001) but a FWHM of under 500 us. · We define "bright" as 5 times the mean flux density of the integrated pulse · On average Vela emits a bright pulse once every 180 rotations.
Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Consecutive Bright Pulses
· By accident a few years ago I found a few instances of 2 bright pulses in a row · Hence a long journey to find more · Was showing a US student one day what a pulsar looked like · Grabbed a random file and showed him this:

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Found this:

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Can it be something else?
· Local interference?
· All these bright pulses lead the normal pulse and have a similar micro structure. Dispersion similar to the integrated pulse. Interference is extremely obvious when it occurs. Many smaller consecutive events have also been observed

· Interstellar Scintillation?
· Cordes and Lazio, 2002 predict broadening of 1.2 us, bandwidth>30 kHz and a time scale of 30 sec.

· Random chance?

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Random Chance?
p n m q probability of bright pulse occurring number of bright pulses in a row number of pulses observed expected number of n bright pulses in a row q=2(1-p)pn+(m-n-1)(1-p)2pn q~=mpn
Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010

(for m>>n)
(for large m and low p)


For our 100 hours of observations we got (with p=0.0055 and m~=4 000 000): Consecutive Pulses (n) 2 3 4 5 6 Approximate Expected (q) 122 0.68 3.8x10-3 20x10-6 116x10-9

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


For our 100 hours of observations we got (with p=0.0055 and m~=4 000 000): Consecutive Pulses (n) 2 3 4 5 6 Approximate Expected (q) 122 0.68 3.8x10-3 20x10-6 116x10-9 Number Actually Observed 693 42 3 2 1

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Kontorovich (2009)

Emission is caused by the internal vacuum gap being a cavity resonator ­ and is relatively constant Magnetosphere acts as a "cloud" and blocks emission most of the time A "hole" lets through a bright pulse

Emission here is at full brightness of the largest bright pulse Standard pulse is energy "radiating through a waveguide near the magnetic axis or through a slot on the border of the open field lines"
Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


The Glitch
· Vela glitched on Jul 31.802 UT · A few hours after I finished an observation! · Fractional change in rotation frequency of 1.94 x 10-6

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Did the glitch change anything?

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Caveats
· This is one four hour data set · This needs to be checked more · This is a quick and dirty to get the theorists thinking (and possibly excited)

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


For 4 hours of observations: Consecutive Pulses (n) 1 2 3 4 Pre-glitch

896 28 2 0

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


For 4 hours of observations: Consecutive Pulses (n) 1 2 3 4 Pre-glitch Post-glitch

896 28 2 0

1508 120 7 3

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


The answer appears, quite possibly, maybe, to be:

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


The answer appears, quite possibly, maybe, to be:

Yes.

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


To my new theorist friends:

Why?

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


References
Cordes, J. M., & Lazio, T. J. W. 2002, "NE2001. I. A New Model for the Galactic Distribution of Free Electrons and its Fluctuations"; arXiv:astro-ph/0207156 Edwards, R. T., & Stappers, B. W. 2002, A&A 393, 733-748 Hotan, A. W., van Straten, W., & Manchester, R. N. 2004, PASA 21 (2004) 302-309 Johnston, S., van Straten, W., Kramer, M., & Bailes, M. 2001, ApJ, 549:L101-L104 Karastergiou, A., & Johnston, S. 2007, MNRAS 380, 1678-1684 Kontorovich, V., M., 2009, Proceedings of The 8th International Conference on Physics of Neutron Stars in Saint-Petersburg, 2008, arXiv:0911.3272v2 Lyne A. G., & Manchester, R. N. 1988, MNRAS, 234, 477 All photographs copyright © Jim Palfreyman and cannot be used without permission.

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010


Questions

Jim Palfreyman, University of Tasmania, Orange Pulsar Conference, 28-9-2010