WANG

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Pulsar Nulling and Mode Changing

• WANG
• Urumqi Observatory, NAOC

Wang, Manchester, Johnston 2007, MNRAS, Vol.
377, 1383
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• Background Introduction
• Observations at Parkes
• Data analysis and results
• Discussion

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Background Introduction

• Pulsar flux density variation
• Stable intrinsic emission (Kaspi et al. 1992)
• Scintillation (Rickett, 1990)
• Mode changing (Ranking, 1986)
• Drifting (van Leeuwen et al. , 2002)
• Nulling (Biggs, 1992)

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Nulling

• Pulsar Nulling pulse emission ceases and
  recommences abruptly
• Nulling properties
• PSR B080974, B0818-13 Regular pulse drifting
  and sub pulse phase memory (Lyne et al. 1983
  van Leeuwen et al. 2002)
• PSR B0031-07, B194417 drifting pulse, no
  phase memory (Joshi et al. 2000 Wright et al.
  1986)
• PSR J17522359 emission decays into a null
  state gradually
• (Lewandowski et al. 2003)
• PSR B193124 7 days on, 30 days off(Kramer
  et al. 2006 Science, 312, 549), PSR J18320031
  and three more similar pulsars!

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PSR B193124Sometimes a pulsar

• 50 increase in d?/dt when
• ON!
• Timing can be well modelled
• when including this effect

the spin-down is faster when on!
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Nulling

• Questions
• Different type of pulsars?
• Nulling a sign of old pulsars beginning to die?
• Yes How and when pulsars die?
• No Young pulsars null?
• Ritchings 1976 nulling NF vs. pulsar age
• Biggs 1992 nulling vs. pulsar age, period,
  pulse
• width?
• Any hint for emission mechanism?

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• Choosing the nulling pulsars
• Using Parkes multi-beam survey data base
• (Manchester et al. 2001) 35min/obsFrequent
  nullers

Period distribution
DM distribution
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Distribution of selected nulling pulsars in
diagram Nulling not confined to old pulsars
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Observations Observed at Parkes, 2004
March June HOH Filterbank (576 MHz, 192
channels) 50cm Filterbank (64 MHz, 256
channels) 35 pulsars observed, 2 hours each
mostly 18 single pulse 8
integration 10-30 sec 9 integration
60 sec
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Nullers
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Nulls and mode change
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Null? Need more observations
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Central component burst
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Null 18
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Profile of PSR B1326-6700

• Single pulse
• Trailing component nulls
• Interval 2-10 (200-1000 pulses)
• Two main components cease for 1min
• The fourth component appears
• Frequent short intervals during B mode

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• On 10-30 min
• NF 1.6
• Short burst within a null
• Weak leading component

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Null Statistic
Threshold of nulls
Null Fraction NF Null length Null interval
Null durartion
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Solid line on-pulse Dotted line
off-pulse
Intensities normalized by the mean pulse
intensity for PSR J1049-5833. The dot-dashed line
is the on-pulse histogram after subtraction of
the null pulses.
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Discussion

• Parkes multibeam pulsar survey
• 35min, longer than most other large scale survey
• Easier to identify nulling pulsars whose off time
  more than several minutes, including RRATs
• 7 / 23 NFgt50
• 2 / 23 NFgt95
• Pulsars with low NF are more
• common than high NF pulsars

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• Large NF pulsars gt1Myr, some gt5Myr
• Nulling is related more to age than period
• PSR Name P(s) tc (Myr) NF
• 1820-0509 0.34 5.7
  67
• 052521 3.75 1.5
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• 1831-1223 2.86 8.3
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1. Pulsar period vs period derivative. 2.
Nulling pulsars circle 3. Circle area
proportional to the NF, with a lower bound of 5.
4. Pulsars in this work cross.
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Nulls vs. pulse profile

• There is no strong correlation of NF with profile
  morphology
• nulls seen in both narrow
  single-component multi-component profiles
• Nulls more common in multi-component profiles
  (?tc), consistent with the P-Pdot diagram
• Polarisation few data

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Discussion

• Do RRATs represent an extreme form of pulse
  nulling or are they an intrinsically different
  phenomenon?
• Giant pulses PK intense normal
  emission
• (Hankins et al 2003 Weltevrede et
  al. 2006)
• nulling and mode changing appear to be intimately
  related.
• Earlier work
• PSR B080974 emits in a different mode
  after nulls (va Leeuwen 2002)
• PSR B0826-34 weak emission with different
  profile in nulls (Esamdin 2005)
• PSR B230330 different nulling properties
  (Redman 2005)
• PSR B193124 change slow-down rate when
  null (Michael 2006)
• This work
• PSR J1701-3726 two modes are always
  separated by a null
• PSR J1703-4851 no nulls in weaker but
  common mode
• PSR J1326-6700 leading component trigger
  the null of trailing components
• PSR J1648-4458 1658-4306 weak emission
  rather than nulls

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Discussion

• Consider
• 1?Nulling Mode changing abruptly,occurring
  within one pulse period
• 2?Both nulling and mode changing are broad band
• 3?Null or weak emission in nulls
• 4?Increasing number of detections of weak
  emission, generally with a different pulse
  profile, in apparent null intervals
• These might suggest
• 1?Both nulling and mode changing result from
  large-scale and persistent changes in the
  magnetospheric current distribution.
• 2?Mode changes must be a manifestation of a
  redistribution of current flow in the
  magnetosphere, resulting in changes in the radio
  beam emission pattern and hence in the observed
  pulse profile.
• 3?Nulls may result from a cessation of (or at
  least a large reduction in) the current,but may
  also result from a current redistribution which
  leads to a beam pattern with little or no power
  in our direction.

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Discussion

• Tipping points a small perturbation lead to a
  sudden change to a different quasi-stable state
• The observations of pulsars imply changes in
  current flow which are quite drastic, completely
  changing the observed pulse profile and its
  polarisation and modulation characteristics, and
  in some cases making the pulsar unobservable.
• Change in accelerating potential or magnetic
  field configuration require
• drastic change, bistable, quasi-periodic,
  reversible
• If a small perturbation in current flow results
  in a change in the accelerating potential or
  magnetic field configuration which enhances the
  change, an instability could develop.

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• Thank you!