Pulse Nulling and Subpulse Drifting Properties in Pulsars Zhigang, Wen Xinjiang Astronomical Observatory, CAS wenzhigang@xao.ac.cn 2014.07

Lighthouse model of radio pulsar!

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.

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

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

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).

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

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

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)

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

Comparison of nulling behaviour in pulsars with similar large NF J1738-2330 J1752+2359 Gajjar, et al., 2013

PSR J1727-2739 Integrated Pulse Profile Bursts Nulls Nulls Nulls

PSR J1727-2739 Burst Null Large NF (64%) pulsar

Connections between nulling and mode changing Wang et al., 2007 Burst Null PSR B0826-34 Esamdin, 2005

PSR J1741-0840 Effelsberg 1.5 GHz GMRT 610 MHz 15

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

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. 2012; Lorimer et al. 2012). Correlated changes in the spin down rate with the profile mode-changes (Lyne et al. 2010). 17

Durations of burst and null states of PSR J1727-2739 18

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

Bhattacharyya et al. 2010 B0818-41 Li et al., 2012 J1502-5653 Young et al., 2012 B0823+26

Pulse intensity modulation of PSR J1727-2739 21 Gradual relaxation Switch suddenly

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).

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

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 B0943+10, 20 sparks rotating around the magnetic axis at a uniform speed (Deshpande & Rankin 1999). PSR B0809+74, P3 changes after it goes through a null (Van Leeuwen et al. 2002). PSR B0031-07, 3 distinct drift modes, 13, 7, 4 P1, OPM.

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

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

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

PSR B0031-07 Smits et al., 2007 Mode A Emission Null Mode A (17.8%) NF: 1-61.8%=38.2% Mode B (80.1%) Mode C (2.1%)

Mode changing of subpulse drifting Pulse width variations

Resistive Magnetosphere The differential rotation of plasma Li et al., 2012 For PSR J1727-2739, 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.

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 B0031-07

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