Investigating Emission Mechanisms by Mapping Pulsar Magnetospheres in 3D Candidacy Presentation, 22 Aug 2016 Sam McSweeney Supervisors: Ramesh Bhat Steven Tremblay Avinash Deshpande
Trying to figure out HOW pulsars emit by figuring out WHERE they emit Candidacy Presentation, 22 Aug 2016 Sam McSweeney Supervisors: Ramesh Bhat Steven Tremblay Avinash Deshpande
Recap on what is known Pulsars = NS (...neutron stars, not Nissans) Spin rates: O(ms) < P < O(s) They spin down Strong magnetic fields (~1012 G) Radiation is beamed Radiation is coherent (brightness temp. ~1020-1025 K) How to generate beamed, coherent radio emission?
Recap on what is known Pulsars = NS (...neutron stars, not Nissans) Spin rates: O(ms) < P < O(s) They spin down Strong magnetic fields (~1012 G) Radiation is beamed Radiation is coherent (brightness temp. ~1020-1025 K) The Emission Mechanism Problem
Other Motivations Detecting nhz gravitational waves using pulsar timing arrays Constraining the nuclear Equation of State Pulsar glitches: windows into pulsar interiors GR tests: Exotic systems (NS-NS, NS-BH, triples) Probing the Interstellar Medium The Emission Mechanism Problem
Neutron stars predicted (Baade & Zwicky, 1934)
Two classes of models for stellar magnetic fields Vacuum Dipole Model vs Rotating Magnetosphere Model
Vacuum dipole models (Davis, 1947)
Rotating magnetosphere models (Alfven, 1942)
Neither can be strictly true On one hand, magnetosphere must exist
Neither can be strictly true On one hand, magnetosphere must exist On the other hand, corotation must fail before the light cylinder radius 2π rlc = P1c P1 = rotation period c = speed of light
Early models: Gold (1969) (Gold, 1969)
Rotating Vector Model (Radhakrishnan & Cooke, 1969)
The 1968 discovery of sub-pulse drifting Telescope: Obs. freq: Obs. year: Rot. period: Arecibo 428.5 MHz 1968 1.34 s Pulse Number PSR B1919+21 Time (ms) (Drake & Craft, 1968)
Average profile
Sub-pulse drifting PSR J0034-0721 Telescope: Obs. freq: Obs. year: Rot. period: MWA 185 MHz 2016 0.943 s
Ruderman & Sutherland Curvature radiation Particle bunching Acceleration gaps Pair production Discrete emission regions ExB drift (Ruderman & Sutherland, 1975)
An emerging picture: The carousel model
An explosion of models Radiative process (curvature / linear accel. / plasma) Acceleration gaps ( inner / outer / slot ) Mechanism for coherence ( bunching / other plasma instability)
An explosion of models Radiative process (curvature / linear accel. / plasma) + Acceleration gaps ( inner / outer / slot ) + Mechanism for coherence ( bunching / other plasma instability) = Prediction of location and dynamics of emission regions
Emission mechanism questions What is the magnetosphere plasma made of? How is the magnetosphere replenished? How are the charged particles accelerated? How important are multipole components? Where exactly does the emission take place?
Empirical models
Cone vs Core emission (Rankin et al., 1983)
Cartographic transform Assumptions: Emission structures rotate around magnetic axis at some (possibly variable) rate Viewing geometry http://www.aanda.org/articles/aa/full/2007/14/aa6550-06/img188.gif
Cartographic transform Assumptions: Emission structures rotate around magnetic axis at some (possibly variable) rate Viewing geometry Convert from pulse stack coords to magnetic coords (k,φ) (R,Θ) Pulse number Rotation phase Magnetic colatitude Magnetic azimuth
Cartographic transform PSR B0943+10 Telescope: Obs. freq: Obs. year: Rot. period: Arecibo 430 MHz 1992 1.10 s (Deshpande & Rankin 1999, 2000)
Radius-to-frequency mapping Rotation phase (degrees) (Cordes et al., 1978) (Credit: Unknown)
Radius-to-frequency mapping (Smits et al., 2005)
Cartographic transform + radius-to-frequency mapping = 3D Lower frequency emission Higher frequency emission PULSAR SURFACE
Cartographic transform + radius-to-frequency mapping = 3D 117 MHz PSR B0809+74 Telescope: Obs. freq: Obs. year: Rot. period: GBT 117-330 MHz 2012(?) 1.29 s 330 MHz (Maan et al., 2013)
Cartographic transform + radius-to-frequency mapping = 3D MWA 170-200 MHz GMRT 593-627 MHz Parkes 1254-1510 MHz PULSAR SURFACE
Cartographic transform + time = evolving emission regions PSR B0943+10 Telescope: Obs. freq: Obs. year: Rot. period: Arecibo 430 MHz 1992 1.10 s http://www.rri.res.in/~desh/gif/movie_new430.gif
Case study: PSR J0034-0721 PSR J0034-0721 Telescope: Obs. freq: Obs. year: Rot. period: MWA 185 MHz 2016 0.943 s
P3 Terminology: P2, P3, driftbands Drift rate: P2 / P3 P2 P2 P3
Measuring drifting properties: Longitude-Resolved Fluctuation Spectrum FFT
Measuring drifting properties: 2D Fluctuation Spectrum FFT FFT
Multiple drift modes + Nulls Mode A Mode B Null (Mode C) Mode B
Multiple drift modes + Nulls ~ 40 minutes A BC?
Cartographic transform of J0034-0721? u a c e b t l u c Dif if r d se Null t o n t rate t n a t cons
Variable drift rate
Variable drift rate
Variable drift rate
Variable drift rate
Variable drift rate Mode A Mode B
Curved driftbands
Curved driftbands
Paper I almost ready...
Other pulsars to study
Other pulsars to study PSR J1946+1805 (EPN Pulsar Database) Regular drifter
Other pulsars to study PSR J0820-4114 Wide profiles Complex drifting characteristics PSR J0828-3417 (EPN Pulsar Database) J0820-4114 (Bhattacharyya et al., 2009)
Other pulsars to study PSR J1900-2600 (EPN Pulsar Database) 5 components in average profile Short duration nulls Unusual polarisation properties
Other pulsars to study PSR J1900-2600 5 components in average profile Only short nulls (NF ~ 20%) Unusual polarisation properties (EPN Pulsar Database) (Mitra & Rankin, 2007)
Data in the can! http://www.abc.net.au/news/image/4401760-3x2-940x627.jpg http://gmrt.ncra.tifr.res.in/gmrt_hpage/images/gmrt_dish/gmrt2.gif http://www.atnf.csiro.au/research/pulsar/parkesdish.jpg (Also Molonglo, whenever possible)
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