Investigating Emission Mechanisms by Mapping Pulsar Magnetospheres in 3D

Transcription

1 Investigating Emission Mechanisms by Mapping Pulsar Magnetospheres in 3D Candidacy Presentation, 22 Aug 2016 Sam McSweeney Supervisors: Ramesh Bhat Steven Tremblay Avinash Deshpande

2 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

3 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. ~ K) How to generate beamed, coherent radio emission?

4 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. ~ K) The Emission Mechanism Problem

5 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

6 Neutron stars predicted (Baade & Zwicky, 1934)

7 Two classes of models for stellar magnetic fields Vacuum Dipole Model vs Rotating Magnetosphere Model

8 Vacuum dipole models (Davis, 1947)

9 Rotating magnetosphere models (Alfven, 1942)

10 Neither can be strictly true On one hand, magnetosphere must exist

11 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

12 Early models: Gold (1969) (Gold, 1969)

13 Rotating Vector Model (Radhakrishnan & Cooke, 1969)

14 The 1968 discovery of sub-pulse drifting Telescope: Obs. freq: Obs. year: Rot. period: Arecibo MHz s Pulse Number PSR B Time (ms) (Drake & Craft, 1968)

15 Average profile

16 Sub-pulse drifting PSR J Telescope: Obs. freq: Obs. year: Rot. period: MWA 185 MHz s

17 Ruderman & Sutherland Curvature radiation Particle bunching Acceleration gaps Pair production Discrete emission regions ExB drift (Ruderman & Sutherland, 1975)

18 An emerging picture: The carousel model

19 An explosion of models Radiative process (curvature / linear accel. / plasma) Acceleration gaps ( inner / outer / slot ) Mechanism for coherence ( bunching / other plasma instability)

20 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

21 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?

22 Empirical models

23 Cone vs Core emission (Rankin et al., 1983)

24 Cartographic transform Assumptions: Emission structures rotate around magnetic axis at some (possibly variable) rate Viewing geometry

25 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

26 Cartographic transform PSR B Telescope: Obs. freq: Obs. year: Rot. period: Arecibo 430 MHz s (Deshpande & Rankin 1999, 2000)

27 Radius-to-frequency mapping Rotation phase (degrees) (Cordes et al., 1978) (Credit: Unknown)

28 Radius-to-frequency mapping (Smits et al., 2005)

29 Cartographic transform + radius-to-frequency mapping = 3D Lower frequency emission Higher frequency emission PULSAR SURFACE

30 Cartographic transform + radius-to-frequency mapping = 3D 117 MHz PSR B Telescope: Obs. freq: Obs. year: Rot. period: GBT MHz 2012(?) 1.29 s 330 MHz (Maan et al., 2013)

31 Cartographic transform + radius-to-frequency mapping = 3D MWA MHz GMRT MHz Parkes MHz PULSAR SURFACE

32 Cartographic transform + time = evolving emission regions PSR B Telescope: Obs. freq: Obs. year: Rot. period: Arecibo 430 MHz s

33 Case study: PSR J PSR J Telescope: Obs. freq: Obs. year: Rot. period: MWA 185 MHz s

34 P3 Terminology: P2, P3, driftbands Drift rate: P2 / P3 P2 P2 P3

35 Measuring drifting properties: Longitude-Resolved Fluctuation Spectrum FFT

36 Measuring drifting properties: 2D Fluctuation Spectrum FFT FFT

37 Multiple drift modes + Nulls Mode A Mode B Null (Mode C) Mode B

38 Multiple drift modes + Nulls ~ 40 minutes A BC?

39 Cartographic transform of J ? 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

40 Variable drift rate

41 Variable drift rate

42 Variable drift rate

43 Variable drift rate

44 Variable drift rate Mode A Mode B

45 Curved driftbands

46 Curved driftbands

47 Paper I almost ready...

48 Other pulsars to study

49 Other pulsars to study PSR J (EPN Pulsar Database) Regular drifter

50 Other pulsars to study PSR J Wide profiles Complex drifting characteristics PSR J (EPN Pulsar Database) J (Bhattacharyya et al., 2009)

51 Other pulsars to study PSR J (EPN Pulsar Database) 5 components in average profile Short duration nulls Unusual polarisation properties

52 Other pulsars to study PSR J components in average profile Only short nulls (NF ~ 20%) Unusual polarisation properties (EPN Pulsar Database) (Mitra & Rankin, 2007)

53 Data in the can! (Also Molonglo, whenever possible)

54 More LRFS