Collaborators Peking University Guojun Qiao, Renxin Xu, Jiguang Lu, Kejia Lee Qian Xuesen Laboratory of Space Technology Yuanjie Du China West Normal University Xiongwei Liu The Capability of FAST in Studying Radio Emission Mechanisms of Pulsars Hongguang Wang （王洪光） Center for Astrophysics, Guangzhou University （广州大学）

Outline 1. Current problems on pulsar radio emission 2. What can FAST do 3. Summary

Curvature radiation ? Problems - emission mechanism Electrons / positrons Radio emission (Ruderman & Sutherland 1975, Gil et al. 1990, Wang P.F. et al …)

Inverse Compton scattering ? Electrons / positrons Radio emission Low freq. EM waves Problems - emission mechanism (Qiao1988, Qiao & Lin 1998 …)

Plasma instabilities ? Instabilities induced EM emission Plasma Problems - emission mechanism (Zheleznyakov & Shaposhnikov 1979, Melrose 1981, Kazbegi et al. 1987, Luo & Melrose 1994 … )

Conal beam ? Emission cones Ring-like cross section of plasma flow Problems – radio beam structure Assumption: narrow band emission (single-frequency emission is generated at a given altitude ) (Rankin 1983 … 2015, 11 papers)

Scattered Plasma Patchy beam ? Problems - radio beam structure Randomly bright patches in the emission window (Lyne & Manchester 1988)

Bright stripes originated from flux tubes Plasma flow along flux tubes Fan beam ? Problems - radio beam structure Assumption: broadband emission (multifrequency emission is generated at a given altitude ) (Michel 1987, Dyks et al. 2010, Wang et al …)

Problems - physics of dynamical phenomena — Subpulse drifting ~100 psrs, E×B drift of plasma, plasma instability? — Mode changing ~100 psrs, unknown — Nulling ~200 psrs, various electrodynamic processes — Giant pulse ~10 psrs, coherent emission, plasma instabilities?

FAST’s Specification

Total intensity profiles

Single pulse Number of the single-pulse candidates versus signal-to-noise ratio required for a single pulse detection.

Fan beam Conal beamPatchy beam Impact angle    Pulse width fan beam conal beam Prediction Empirical beam models have different predictions Wang et al Rankin 1983Lyne & Manchester 1988 Dyks et al. 2010, 2012, 2015 Michel 1987

Statistical test Fan beam conal beam Wang et al ApJ Need more samples!

Deeper polarization observation for better constrains on viewing geometry   Rotating Vector Model (Radhakrishnan & Cooke 1969)

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

Fan beam Conal beam Wang et al Gangadhara & Gupta 2001 Search for weak components in averaged pulse profiles Kramer et al Yan et al. 2011Dai et al. 2015

Multifrequency profile evolution for a large sample ~50% ~20% Chen & Wang 2014 ApJS (150 pulsars) Curvature radiation and most plasma emission models: RFM type Freq. increases RFMAnti-RFM Inverse Compton scattering model: RFM & anti-RFM types

Mode switching Observation strategy Survey Timing Multi-station simultaneous observation Ultra broadband receiver Detecting more mode switching pulsars Revealing broadband properties - Spectral behavior - Multifrequency single pulse energy distribution - Frequency dependent polarization

Subpulse drifting 2006 WSRT survey (Weltevrede et al. 2006) 68 drifters identified from106 high S/N candidates more likely old pulsars P3, and the drift direction, are not significantly correlated with the pulsar age and the surface magnetic field strength. Could not rule out different emission models Comparison between FAST and WSRT For S/N>130 Telescope candidates detected drifter WSRT FAST 771 ～ 200 ？

Nulling Biased by selection effect? For PSRs with Edot < 2E30 erg/s & S/N=9 FAST 13 / 16 Arecibo 7 / 11 Parkes 1 / 37

Suggested observational programs in different phases of FAST (a)MF stands for multiple frequency observation. (b) IM - observing mode of total intensity; PM – observing mode of polarization.

Summary FAST is expected to expand the high S/N samples by a factor of ~3. FAST is hopeful to overcome bias for mean pulse and single pulse observations Large sample statistics will be helpful for testing emission models