SLIDE 1 Observation-constrained pulsar magnetospheric models Jarek Dyks Nicolaus Copernicus Astronomical Center
Polish Academy of Sciences Toruń
Cartoon by T.Baranowski
Yes, this one needs to be serviced too. It is glitching, nulling, and drifting badly!
SLIDE 2
Pulsar is a source of this:
SLIDE 3 => Expectation: Blue: radio Pink: gamma rays For decades observed for 50 %
- f known gamma ray pulsars
i.e. for Crab only The other known was Vela pulsar Radio ‘theory’ (conventional wisdom) says: + B = pairs
SLIDE 4 Fermi Obs.: 90 % of pulsars: gamma rays lag radio gamma ray peak separation: 0.4 P - 0.5 P lag of leading peak (LP) wrt radio: 0.1 P
Kanbach et al. Dyks & Rudak 2003
Crab and few Plenty of objects 0.4P
0.1P
R
SLIDE 5
OUTER MAGNETOSPHERIC EMISSION most likely OUTER GAP MODEL Romani, Yadigaroglu 1995, K.S. Cheng et al. 1985, Holloway 1976
Origin of gamma-ray profiles
SLIDE 6 Dyks & Rudak 2003
Magnetosphere-wide emitting surface (current sheet, narrow accelerating gap). Relativistic charges moving and emitting tangentially to the surface => caustic effects OG (outer gap) TPC slot gap TPC better than OG only for few pulsars. OG does not show up in PIC simulations (TPC preferred eg. in Bai & Spitkovsky 2010).
TPC = two-pole caustic model
SLIDE 7
Goldreich-Julian density (1969), Michel 1969 (dead magnetosphere density, equilibrium density, corotation density, no-force density) density for which: 1) electric force = 0 in pulsar frame (corotating frame, CF) 2) el-mag force in observer's frame (OF, non-rotating) produces uniform corotation of charges with the star Sort of measured observationally in 2006 (Kramer et al.) No force in CF Corotation (Lor. transf. to OF) Bz tells you the density null charge surface
SLIDE 8 ‘Observation of’ the GJ density: INTERMITTENT PULSARS (Kramer, Lyne, et al... 2006, 2007)
~2 times faster spin-down when the magnetosphere is filled in with charges => estimate of rho possible! B1931+24 J1832+0029
SLIDE 9 First ‘measurement’ of rhoGJ (Kramer et al. 2006)
+ order of magnitude agreement for J1832+0029
Theory works! dipolar el-mag radiation + wind (‘on’-phase) excess spin down is caused by wind the larger the torque – the larger spin down you must crank harder to produce stronger current current = charge velocity * conductor’s cross-section * charge density
SLIDE 10 Formation of the outer gap.
Outflow of “e-” through the light cylinder => missing negative charge (to have “no-force” situation) => missing “e-” acts like excess of “e+” => positive charge on the other side
- f null charge surface is repelled
=> outer gap is formed with huge accelerating electric field and high-energy emission (best model for high-energy profiles)
Holloway 1976
Screening by e+e- pairs (two photon pair production in weak B) => the gap is:
- extended outwards (towards the light cylinder)
- thin
- adjacent to the last open B-field lines
=> profiles dominated / strongly affected by caustic effects
SLIDE 11 R R Below null charge surface (Bz = 0) OG is screened by pair avalanche R R R = radio R
Romani & Yadigaroglu 1995
SLIDE 12
Pulsars have surfaces emitting tangentially to themselves But do not have the mirror Caustic – (optics) a surface tangent to rays that were reflected or refracted by another surface
SLIDE 13
Caustic effects: coincidence of rays emitted at distant locations and moments => caustic effects due to combined effect of aberration, retardation, and B-field curvature Unrelated photons pile up at the same phase in pulse profile Those photons may be polarised at different angles => depolarisation Photon A retarded Photons from B aberrated red: curved B-field line
SLIDE 14 caustic region
curvature Observer frame view: caustic effects strong in caustic regions i.e. regions where the curvature of electron trajectory in OF is minimal
Dyks, Wright, Demorest 2010
Conditions for: - maximum photon pileup
- minimum curvature of trajectory
have identical solutions
SLIDE 15 Rotational asymmetry: non-inertial / caustic effects
Electron paths in inertial observer frame Photon paths in pulsar frame
DRD10 D2013
Dyks, Wright, Demorest 2010
If r_em >> Rns => “dipole axis” is on the trailing side
SLIDE 16 Sky-projected B-field lines sightline path
Sightline passing near the pole => pol. planes rotate quickly (PA swing, RVM model)
SLIDE 17 Blaskiewicz, Cordes & Wassermann 1991; Dyks 2008; Krzeszowski et al. 2009
Center of PA curve lags the profile center
Delay-radius relation: PA lag = 4 r / Rlc (rad)
Independent of dipole tilt
SLIDE 18 High S/N phase-resolved linear polarisation at “high” energies: Crab in optical
OPTIMA+NOT: Slowikowska, Kanbach, Kramer & Stefanescu 2009
Steepest PA gradient not at the dipole axis phase (~30 degrees ahead of MP) Steepest gradient observed at MP
Dyks, Rudak & Harding 2004
Caustic peaks = depolarization + PA swings
SLIDE 19 Pulsar polarization in radio: crazy! maximum V/I at orthogonal pol. jumps Reason: coherent addition of radiation in two orthogonal pol. modes (OPMs)
Single mode emission + split into OPMs in birefringent medium + phase lag + coherent sum
Dyks 2017 Weisberg & Taylor 1992
Pulsars are waveplate devices Polarization is a propagation effect Phase lag does matter!
SLIDE 20 More crazy: loops and bifurcations of pol. angle track, twin minima in L/I, large V/I
Mitra et al. 2016 Dyks 2017
Model works at different nu
SLIDE 21 Dyks, Rudak & Demorest 2010
Radio beam shape: radial system of fan beams Or nested cone delusion made by a spiral?
Mitra et al Navarro et al. Demorest
SLIDE 22 Beam mapping for precessing pulsars: J1906+0746 Porb = 4 hr, Pprec = 165 yr, tobs = 4 yr Desvignes et al. 2012
Dyks, Rudak & Demorest 2010
Predicted: Observed: J1141-6545 Manchester et al. 2010
SLIDE 23 PSR J0737: Double pulsar A eclipse
Burgay et al.
Filled-closed-dipolar- magnetosphere model
SLIDE 24
Eclipsing magnetosphere:
Lyutikov 2005 Plasma multiplicity ~ 10^6 Dipolar B works
SLIDE 25
CONCLUSIONS Steady, slow progress (despite several questions remain) PC => OG (low r => high r) (gamma + radio profiles) rho_GJ correct! (intermittent psrs) Thin, spatially extended OG => caustic peaks (aberration + retardation + B-field geometry) Caustic peaks at minimum curvature => Pol. angle curve lag => tilt-independent method to estimate r + depolarization + steep pol. angle swings in “high energy” (optical) Radio pol.: V max at OPM jumps + PA loops, bifurcations, large V => radio pol. = coherent propagation effect (coherent addition of OPMs, birefringence) Radio beams not conal (radial fan beams, curved into spirals?) (from bif. components + rare beam maps) (fan beams can do RFM and core lag) Double pulsar eclipse confirms large plasma multiplicity and dipolar field geometry
SLIDE 26 Pulsar group at CAMK + main collaborators
(the pulsar group founder, initiator, advisor, supervisor, master, etc...)
