1. Pulse Nulling and Subpulse Drifting Properties in Pulsars
Zhigang, Wen
Xinjiang Astronomical Observatory, CAS

2. Lighthouse model of radio pulsar!

3. Emission in individual pulses
Emission shows remarkable variability
Investigated in about 10% known pulsars.
Types of variability:
Pulse to pulse intensity fluctuations (giant/strong pulses, pulse nulling)
Changes in pulse phase (subpulse drifting)
Changes in pulse shapes (profile mode changing)
High time resolution structure of pulses (microstructure)
Changes in polarization angle (polarization mode changes)
Associated timescales: vary over order of magnitude.

4. Outline Pulsar Nulling Subpulse Drifting
Interaction between pulsar nulling and subpulse drifting
Revealing the potential radio emission mechanism

5. Absence of pulses: Pulsar Nulling
Bursts
Bursts
Bursts
Nulls
Nulls
Intensity fluctuation

6. Chronicles of nulling phenomenon
First discovered in four pulsars by Backer in 1970, almost 200 nulling pulsars have been found so far.
Nulling fraction (NF) was introduce to quantify nulling behavior and to investigate correlation with different pulsar parameters (Ritchings 1976).
Ritchings (1976) also suggested that pulsars die with increasing fraction of nulling in them.
Various attempts were made to correlate NF with different pulsar parameters but no strong correlation was found (Rankin 1986, Biggs 1992, Wang et al. 2007).
Pulsars with similar NF appear to show different nulling pattern (Vishal, 2012).

7. Pulsar Nulling NF ranging from less than 0.1% to larger than 95%.
Wang, et al., 2007

8. Pulsar Nulling
No strong correlation of NF with profile morphology, characteristic age, period, radio luminosity…
Wang, et al., 2007
Biggs, 1992
Biggs, 1992

9. Nulling Mechanisms
Cessation of sparking (Sturrock 1971; Kramer et al. 2006)
Continuous supply of particle (Filippenko and Radhkrishnan 1982)
Switching between CR/ICS (Zhang et al. 1997)
Surface composition changes (Bartel et al. 1982)
Magnetic field instabilities (Geppert et al. 2003)
Partial screen gap (Gil et al. 2003)
Reversal of the emission beam (Dyks 2005)
Orbital companions (Cordes and Shannon 2008)
Missing line-of-sight (Herfindal and Rankin 2007; 2008)
Time dependent pair cascade (Timokhin 2010)

10. Comparison of nulling behaviour in pulsars with similar samll NF
Gajjar, et al., 2012
Pulsars with similar and small NF exhibit different nulling behaviour.

11. Comparison of nulling behaviour in pulsars with similar large NFJ J
Gajjar, et al., 2013

12. PSR J
Integrated Pulse Profile
Bursts
Nulls
Nulls
Nulls

13. PSR J
Burst
Null
Large NF (64%) pulsar

14. Connections between nulling and mode changing
Wang et al., 2007
Burst
Null
PSR B
Esamdin, 2005

15. PSR J
Effelsberg
1.5 GHz
GMRT
610 MHz 15

16. Effelsberg
1.5 GHz
610 MHz
GMRT
NF~19%
NF~20%
Burst
Burst
Null
Null 16

17. Global state switching
Different spin-down rates have been reported during the On-Off states for the intermittent pulsars (Kramer et al. 2006; Camilo et al ; Lorimer et al. 2012).
Correlated changes in the spin down rate with the profile mode-changes (Lyne et al. 2010). 17

18. Durations of burst and null states of PSR J1727-273918

19. Intermittent Pulsar PSR B1931+24 with NF of (30d/35d) 85%
Off State
On State
(Kramer et al. 2006; Young N. 2013)
Pulsars with similar and large NF exhibit different nulling behaviour

20. Bhattacharyya et al B
Li et al., 2012 J
Young et al., 2012 B

21. Pulse intensity modulation of PSR J1727-273921
Gradual relaxation
Switch suddenly

22. Subpulse Drifting
Subpulses: one or more peaks in individual pulses, much narrower than the average pulse profile and the brightness, width, position and number of these subpulses often vary from pulse to pulse.
Subpulse drifting: rotating carousel model (RS75).

23. Rotating Carousel Model
Four parameters to describe drift of subpulses:
P1: Pulsar period
P2: the interval between successive subpulses within the same pulse, in units of degrees.
P3: the spacing at the same pulse phase, between the drift bands, the vertical spacing. In units of P1.
Delta phi: the subpulse drift rate, the fraction of pulse period over which a subpulse drifts

24. Chronicles of the drifting subpulses
First discovered in 1968 (Drake & Craft 1968).
68 subpulse drifting pulsars were detected in 187 pulsars survey (Edwards and Stappers, 2006 ).
For PSR B , 20 sparks rotating around the magnetic axis at a uniform speed (Deshpande & Rankin 1999).
PSR B , P3 changes after it goes through a null (Van Leeuwen et al. 2002).
PSR B , 3 distinct drift modes, 13, 7, 4 P1, OPM.

25. PSR J1727-2739 (LRF spectrum) Weak modulation Strong modulation
Mode A: 0.1 c/P1
Mode B: 0.2 c/P1

26. PSR J1727-2739 Rapid switching without nulls separated.
Some transitions between different drifting modes after it goes through a null state.
Rapid switching without nulls separated.
Mode A
Irregular drifting
Mode B

27. Mode B is stronger than mode A which is in turn stronger than mode C.
Same width.
Mode B is stronger than mode A which is in turn stronger than mode C.
For modes A and B, the leading and trailing components have the same intensity. While the leading is stronger than the trailing for mode C.
The P2 of drift mode A is larger than that in drift mode B by a factor of 18.5%.
The mode B drifts faster than mode A.
Combining the subpulse width, separation between subpulses, we could derive the number of subbeams on the rotating carousel. 27

28. PSR B
Smits et al., 2007
Mode A
Emission
Null
Mode A (17.8%)
NF: %=38.2%
Mode B
(80.1%)
Mode C
(2.1%)

29. Mode changing of subpulse drifting
Pulse width variations

30. Resistive Magnetosphere
The differential rotation of plasma
Li et al., 2012
For PSR J , the mode B has a faster observed E X B drift and stronger emission, which may be resulted from larger conductivity. However, same as the transitions between nulling and burst states, the trigger mechanism for variations of conductivity is still unclear.

31. A is more narrow than B at 4.85 GHz.
2 components
Right component at 328 MHz corresponds to single component at 4.85 GHz. The first component in the A-profile at 328 MHz disappears towards higher frequency.
Mode A
A is more narrow than B at 4.85 GHz.
A & C (equal intensity) are weaker than B at 328 MHz.
Mode B
90 deg jump
90 deg jump
All
90 deg jump
90 deg jump
PSR B

32. Thank you for your attention!