Observation-constrained pulsar magnetospheric models Yes, this one needs to be serviced too. It is glitching, Jarek Dyks nulling, and drifting badly! Nicolaus Copernicus Astronomical Center Polish Academy of Sciences Toruń Cartoon by T.Baranowski
Pulsar is a source of this:
Radio ‘theory’ (conventional wisdom) says: Expectation: Blue: radio Pink: gamma rays => + B = pairs For decades observed for 50 % of known gamma ray pulsars i.e. for Crab only The other known was Vela pulsar
Crab and few Plenty of objects R 0.4P 0.1P Fermi Obs.: 90 % of pulsars: gamma rays lag radio Kanbach et al. Dyks & Rudak 2003 gamma ray peak separation : 0.4 P - 0.5 P lag of leading peak (LP) wrt radio: 0.1 P
Origin of gamma-ray profiles OUTER MAGNETOSPHERIC EMISSION most likely OUTER GAP MODEL Romani, Yadigaroglu 1995, K.S. Cheng et al. 1985, Holloway 1976
Magnetosphere-wide emitting surface (current sheet, narrow accelerating gap). Relativistic charges moving and emitting tangentially to the surface => caustic effects OG (outer gap) TPC Dyks & Rudak 2003 slot gap TPC = two-pole caustic model TPC better than OG only for few pulsars. OG does not show up in PIC simulations (TPC preferred eg. in Bai & Spitkovsky 2010).
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 No force in CF Corotation (Lor. transf. to OF) B z tells you the density Sort of measured observationally in 2006 (Kramer et al.) null charge surface
‘Observation of’ the GJ density: INTERMITTENT PULSARS (Kramer, Lyne, et al... 2006, 2007) B1931+24 J1832+0029 ~2 times faster spin-down when the magnetosphere is filled in with charges => estimate of rho possible!
First ‘measurement’ of rho GJ (Kramer et al. 2006) dipolar el-mag radiation + wind (‘on’-phase) excess spin down is caused by wind observed 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 observed, B1931+24 Theory works! + order of magnitude agreement for J1832+0029
Formation of the outer gap. Holloway 1976 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 of null charge surface is repelled => outer gap is formed with huge accelerating electric field and high-energy emission (best model for high-energy profiles) 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
Below null charge surface (B z = 0) OG is screened by pair avalanche R = radio R R R R R Romani & Yadigaroglu 1995
Caustic – (optics) a surface tangent to rays that were reflected or refracted by another surface Pulsars have surfaces emitting tangentially to themselves But do not have the mirror
Caustic effects: coincidence of rays emitted at distant locations and moments Photon A retarded Photons from B aberrated red: curved B-field line => 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
Observer frame view: caustic effects strong in caustic regions i.e. regions where the curvature of electron trajectory in OF is minimal caustic region of minimum curvature Conditions for: - maximum photon pileup - minimum curvature of trajectory have identical solutions Dyks, Wright, Demorest 2010
Rotational asymmetry: non-inertial / caustic effects Electron paths in inertial observer frame Photon paths in pulsar frame D2013 DRD10 If r_em >> Rns => “dipole axis” is on the trailing side Dyks, Wright, Demorest 2010
Sightline passing near the pole => pol. planes rotate quickly (PA swing, RVM model) Sky-projected B-field lines sightline path pol. angle vs time
Center of PA curve lags the profile center Blaskiewicz, Cordes & Wassermann 1991; Dyks 2008; Krzeszowski et al. 2009 Delay-radius relation: PA lag = 4 r / R lc (rad) Independent of dipole tilt
High S/N phase-resolved linear polarisation Steepest PA gradient not at the dipole at “high” energies: Crab in optical axis phase (~30 degrees ahead of MP) Steepest gradient observed at MP Caustic peaks = depolarization + PA swings Pol. angle Pol. degree Pol. angle OPTIMA+NOT: Slowikowska, Kanbach, Kramer & Stefanescu 2009 Pol. degree Dyks, Rudak & Harding 2004
Pulsar polarization in radio : crazy! Reason: coherent addition of radiation in two orthogonal pol. modes (OPMs) maximum V/I at orthogonal pol. jumps Single mode emission + split into OPMs in birefringent medium + phase lag + coherent sum Dyks 2017 Phase lag does matter! Weisberg & Taylor 1992 Pulsars are waveplate devices Polarization is a propagation effect
More crazy: loops and bifurcations of pol. angle track, twin minima in L/I, large V/I Model works at different nu Mitra et al. 2016 Dyks 2017
Radio beam shape: radial system of fan beams Or nested cone delusion made by a spiral ? Dyks, Rudak & Demorest 2010 Navarro et al. Mitra et al Demorest
Beam mapping for precessing pulsars : J1906+0746 Predicted: Dyks, Rudak & Demorest 2010 Observed: J1141-6545 P orb = 4 hr, P prec = 165 yr, t obs = 4 yr Desvignes et al. 2012 Manchester et al. 2010
PSR J0737: Double pulsar A eclipse Burgay et al. Filled-closed-dipolar- magnetosphere model M. Lyutikov
Eclipsing magnetosphere: Lyutikov 2005 Plasma multiplicity ~ 10^6 Dipolar B works
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
Pulsar group at CAMK + main collaborators Prof. Bronek Rudak (the pulsar group founder, initiator, advisor, supervisor, master, etc...)
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