A Fan Beam Model for Radio Pulsars Hongguang Wang （王洪光） Center for Astrophysics, Guangzhou University 广州大学天体物理中心 Fast Pulsar Symposium 4

1.Radio beam models 2. Observational tests 3. Application

Radio pulse profile & Pol., emission mechanism, 1967 Searching 1967 Optical pulsar 1969 X-ray pulsar 1969 Scintillation 1969 Gamma-ray pulsar 1972 Glitch 1971 Binary pulsar 1974 Quark star 1969 Pulsar & Galactic B field 1969 Pulsar wind 1972 Pulsar timing & gravitational wave 1979 SGR & AXP 1980s Pulsar navigation 1980s …

Hollow cone (1970) 1. Empirical models for radio emission beam ?

Double cones + core Patchy beam (Rankin 1983 … 2015, 11 papers) (Lyne & Manchester 1988)

Han & Manchester 2001 Efforts of observation test

Why cone? Assumption: narrow band emission Inverse Compton scattering Qiao 1988 Qiao & Lin 1998 Xu et la Liu et al Wang et al Lee et al Lv et al …… Physical Models Curvature radiation Gil et al. 1990, 2004 Wang P.F. et al. 2012, , 2015 ……

Cordes 1979 ; Buschauer & Benford 1980; Barnard & Arons 1986; Michel 1987; Melrose 1996  Luminosity, frequency dependence of double profiles, polarization can be alternatively explained by wideband models. What if wideband? Michel’s fan beam model Michel 1987, ApJ Dyks et al’s model Dyks et al. 2012

LOS Polar Cap flux tube Rotation Axis Neutron Star Pulse Profile sub-beam Our work: flux tubes + wideband emission => fan beam Wang et al. 2014, ApJ Chen & Wang 2014, ApJS

Polar Cap Neutron Star Model Pulse Profile

Fan beam Conal beamPatchy beam 2. Observational tests    Pulse width fan beam conal beam Prediction

Test 1 pulse width - impact angle relationship Fan beam conal beam Need larger samples! Wang et al ApJ

Test 2 2-D beam structure of precessional pulsars J Manchester et al ApJ Parkes Desvignes et al IAUS 291 Arecibo, GBT, WSBK J

PSR J B Lomiashvili and Lyutikov 2014 MNRAS GBT PSR B Clifton & Weisberg 2008 ApJ Arecibo

Test 3 Impact angle – pulsar distance Wang et al ApJ Pulsars in the Magellanic Clouds have narrower pulse widths (Manchester et al. 2006, Ridley et al. 2013) LMC SMC  LOS W10: ~ 20deg (21 psrs in LMC), ~15deg (5 psrs in SMC)

The conal beam model is widely used in population studies of pulsars, e.g. globular cluster, gamma-ray pulsars, and in the studies on the detection capability of pulsars for SKA, FAST. The fan beam model can be used instead. (1) Population studies 3. Application

Pulse width – impact angle relationship

Intensity-radius relationship

(2) Pulse morphology Difference between normal pulsars and MSPs Simple profile of young pulsars Weak components: partial cone, precursor & post-cursor, off-pulse emission Frequency dependence of pulse profiles Physical meaning of pulse components Pulse width-period relationship

New results from a census of frequency dependence of pulse width for 150 normal radio pulsars Chen & Wang 2014 ApJS Data set: 150 pulsars with multi-frequency profiles selected from the EPN 81 pulsars (54%) with apparently decreasing trend

40 pulsars (27%) with slight variation

29 pulsars (19%) with apparently increasing trend

Future work Further observational test - Binary pulsars - Larger samples Applications - Pulse profile interpretation - Population study (FAST, SKA) - Polarization and propagation effects in pulsar magnetosphere

Open question: what causes different kinds of spectral distribution across the emission region?

(1-1) Interpretation for frequency dependence of pulse profiles Komesaroff 1970, Cordes 1978 high freq. cone low freq cone Steep Flat spectrum Steep Chen et al. 2007, Chen & Wang 2014

(1-2) New interpretation for pulse components

(3) Propagation effects and polarizations Previous studies of propagation effects usually assume uniform plasma density distribution. Plasma in and between flux tubes is not uniform. Challenging!

Evolution of polarization New results of J ( ) Profile evolution

The beam structure depends on particle flow Density distribution of particles above the polar cap 2-D beam structure for the B2 particle distribution

Modeled profiles for different impact angles

Precessional Binary Pulsars (Kramer et al review) All the monitoring are between 400MHz and 1400MHz. High frequency beam structure is unknown S1400(mJy) 1.6/ >

Non-RFM Phase-dependent spectrum Wang et al ACTA, Chen & Wang 2014 ApJS