Pulsar Nulling survey with GMRT Results on J17382330

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Pulsar Nulling survey with GMRTResults on
J1738-2330

• Vishal Gajjar (NCRA)?
• Bhal Chandra Joshi (NCRA)?
• Michael Kramer (JBO)

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Pulsar Toy Model
www.pulsar.ca.astro.it
www.outreach.atnf.csiro.au
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Pulsar Nulling in time series
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Background

• Backer D. C. in 1970 reported nulling in 4
  pulsars, which are B083406,B113316,B123725 and
  B192910.
• People have tried to correlate many pulsar
  parameter with the Nulling Fraction (NF) in later
  years.
• Ritching R.T., 1976, MNRAS
• Rankin J. M. , 1986, ApJ
• Biggs J. D., 1992, ApJ
• Vivekanand M., 1995, MNRAS
• Wang N, et al., 2007, MNRAS
• Although no strong correlation exist of any
  pulsar parameter with NF, a weak correlations
  exist with pulsar period and integrated profile
  class.
• Long period pulsar has large NF
• Core emission profile pulsar has small NF and
  conal emission profile pulsar has large NF

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Project and Observation

• 20 pulsars plus few control pulsars were observed
  with GMRT at 325 MHz as a part of on going survey
• Observation were carried out on 9th 10th and 22nd
  of Nov 2008
• Total time spent on each source is around 1.5 hrs
  
• 17 antennae in phased array is similar to 185m
  single dish
• Sensitivity of 2.5 mJy to detect single pulses
  with nearly 1 sec of period

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B080974 Nulling pulsar
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On pulse energy fluctuation
Off pulse energy fluctuation
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Energy histogram b080974
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Estimated nulling fraction for b080974 is around
1 (Lyne A. G., and Ashworth M. 1983, MNRAS)?
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B111250 Nulling pulsar
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Energy histogram b111250
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Estimated nulling fraction is around 60
(Ritching R. T., 1976 MNRAS)?
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Parameters comparison for J1738-2330

• J1738-2330 was discovered in 2006 from parks
  multibeam survey data (Lorimer D. R., 2006
  MNRAS)?
• Observations of j1738-2330 was carried out on
  22nd of Nov 2008
• Total time spent on source was around 2 hr

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Pulsar j1738-2330 16 pulses integrated Nulling
is clear and seems to be periodic
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Energy histogram j1738-2330
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Profile with the null and non null pulses
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Discussion

• To check for low level emission, all null pulses
  has been added
• The average power level of integrated profile
  with bursts pulses is 94 times higher than the
  power level during the null phase
• So even if there is a weak emission during null
  phase its nearly 100 times lower than the average
  emission

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Conclusion and future work

• The upper limit on nulling fraction of j1738-2330
  is around 90. The reason behind the nulling
  could be one of the following.
• The cessation of pair production in RS model
• The refraction of the emission beam
• Precession in rotating axis
• Rotation of extinguish sub beam in overall beam
• Periodic nulling is very clear which is quite a
  unique case
• Multifrequency observation will provide more
  information on nulling in case of j1738-2330

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Thank you