High-energy activity of rotation-powered pulsars Bronis aw Rudak - PowerPoint PPT Presentation

High-energy activity of rotation-powered pulsars Bronis ł aw Rudak CAMK PAN POLNS18 26-28 March 2018

Pulsars Rotating, strongly magnetized neutron stars acting as unipolar inductors. Maximum potential drop (voltage): V max ≈ 6 × 10 12 (B/10 12 G) P -2 Volts. Realistic potential drops - much smaller, but high enough to accelerate particles to ultrarelativistic energies.

Pulsar detections: from radio to gamma rays ~ 2600 in radio 1+2(?) in mIR, 5 in nIR, ~10 in optical, 10 in nUV, 4 in fUV > 100 in X-rays (mostly Chandra and XMM Newton) 211 in gamma-rays ( Fermi LAT, AGILE) Detections by Cherenkov arrays: Crab pulsar: 25 GeV – 1.5 TeV (MAGIC,VERITAS) Vela pulsar : 20 – 120 GeV (H.E.S.S. II, mono), 3 TeV & 7 TeV (H.E.S.S. I, stereo) 3

Fermi LAT Pulsar Yield (Feb 2018) 211 public gamma-ray PSRs Young: 115 Millisecond: 96

Period – Period time derivative D.Smith+ 2017

Gamma-ray pseudo luminosity vs. Spin-down power (Abdo+ 2013)

Pulsar mul5wavelength spectra and pulsa5ons Non-thermal (magnetospheric) components Geminga Spectra - piecewise power law (w. Breakpoints) - [sub-]exponen5al at high-energy cutoff, or power-law tail (the Crab pulsar at ~1.5 TeV) Pulse profile morphology - sharp pulses, high pulsed frac5on, energy dependent Thermal components (in so5 X-rays only) Spectra - blackbody, strongly magne5zed atmosphere models (H, He or Fe) Pulse profile morphology - smooth pulsa5ons, low pulsed frac5on 7

Light Curve Classes Courtesy: C. Venter 1. γ -ray peak(s) lag main radio peak Ø Young pulsars & MSPs Ø “Class I” 2. γ -ray peaks aligned with radio peaks Ø Nearly exclusive to MSPs Ø “Class II” 3. γ -ray peak(s) lead main radio peak(s) Ø Exclusive to MSPs Ø “Class III” Venter et al. (2012); Abdo et al., (2013)

Examples of pulse profile morphology in radio and gamma (2nd Fermi LAT Pulsar Catalog, 2013 )

Examples of pulse profile morphology in radio and gamma (2nd Fermi LAT Pulsar Catalog, 2013 )

Mul5frequency profiles PSR B1821-24 in M28, P = 3 ms PSR B0531+21, P = 33 ms (”miniCrab” in X-rays) 73000 Soft gamma-rays (Comptel, 0.75 - 30 MeV) (e) Radio (Nancay telescope, 1.4 GHz) (a) 2 72000 Radio intensity (au) 71000 1.5 70000 Counts 69000 1 68000 67000 0.5 66000 65000 0 450 4.5 Gamma-rays (EGRET, >100 MeV) (f) Optical (SCam-3) (b) 400 4 Normalized count rate 350 3.5 300 3 Counts 250 2.5 200 2 1.5 150 100 1 0.5 50 0 0 4500 2000 X-rays (RXTE, 2 - 16 keV) (c) Gamma-rays (Fermi LAT, >100 MeV) (g) 4000 3500 1500 3000 Counts/s Counts 2500 1000 2000 1500 500 1000 500 0 0 186.5 VHE gamma-rays (MAGIC, >25 GeV) (h) Hard X-rays (INTEGRAL, 100 - 200 keV) (d) 1.61 186 ) ) 3 3 Counts (x10 185.5 Counts (x10 1.6 185 184.5 1.59 184 183.5 1.58 183 182.5 1.57 182 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Phase Phase Johnson+ 2013

PSR J2021+4026: First Variable Gamma-ray Pulsar • RQ pulsar • 20% decrease in flux > 100 MeV in 1 week • Simultaneous 4% increase in spin-down rate Ng+ 2016 12

PSR J2021+4026: First Variable Gamma-ray Pulsar Ng+ 2016 Before the glitch ader Change in magnetosphere structure? Modified beaming? 13

Phased-averaged spectral energy distribu5on Examples of Spectral Energy Distribu5ons (from X-rays to gamma rays) Kuiper+ 2017

TeV pulsed emission from the Crab pulsar detected by MAGIC Ansoldi+ 2015 ] -1 s -10 -2 10 [TeV cm -11 10 dEdAdt dN -12 10 2 E -13 10 Fermi-LAT P1 Fermi-LAT P2 -14 10 MAGIC P1 MAGIC P2 -15 10 -1 2 3 10 10 10 1 10 Energy [GeV]

Spectral energy distribu5on of the Vela pulsar VHE (?) 16

The many faces of Vela – the ul5mate challenge for models P1 P2 P4 P3 VHE 17

A brief history of pulsar models in three stages Stage 1 The vacuum magne5c dipole model passé, but some features s/ll in use Stage 2 The co-rota5ng magnetosphere models in low-density, charge-separa5on limit Stage 3 Towards Global Electrodynamics, microscopic conduc5vity (PIC simula5ons)

Key questions in pulsar electrodynamics models Where and how does the dissipation of the spin-down power take place? - inside the magnetosphere? - in the wind? - in both? Cartoons: B. Cerutti

Modelling Assumptions Courtesy: C. Venter Is the pulsar magnetosphere filled with dense plasma? NO NO Not Not YES YES Ever ery- fff • Force-free wher here • Vacuum • ‘Pulsar (Deutsch’55) Equation’ • Charge- • Aligned separated Local (Contopoulos’99) plasma gaps • Oblique Dissipative (GJ69, (Spitkovsky’06) (Harding, Magnetospheres Michel’73) Romani, • Full MHD (Li’12, Cheng, (Komissarov’06, Kalapotharakos,’13) Hirotani+) Tchekovskoy’13)

Different Regimes Different regimes Courtesy: C. Venter Vacuum retarded dipole (VRD) Force-free magnetosphere (Deutsch 1955) (Spitkovsky 2006) No charges, no currents No particle acceleration Courtesy: C. Venter Non-ideal MHD magnetosphere (Kalapotharakos et al. 2012, Li et al. 2012) Charges, currents + acceleration! Filled with plasma γ -ray LCs, phase-resolved spectroscopy, polarization will help to constrain B

3D magnetospheric accelerators (gaps) Traditional magnetospheric accelerators To be solved simultaneously in the magnetosphere: - non-vacuum Poisson equa5on, - Boltzmann equa5on for pairs, - radia5ve transfer Boundary condi5ons assumed ad hoc. Global current closure not addressed. Cartoon by K. Hirotani

Global electrodynamics with the plasma - I Star9ng point: force-free electrodynamics (FFE) models The electromagne5c force per unit volume f _em = σ E + J x B + δ P _em/δ t . Assump5ons in FFE: - the iner5al mass density of the plasma ignored ( << B 2 /8πc 2 ) - the momentum density of EM ignored The force-free condi5on becomes f _em = σ E + J x B /c = 0 but it cannot hold everywhere .

Global electrodynamics with the plasma - II 1. Force-free (FF) magnetospheres and winds: - no dissipa5on inside but dissipa5on *) outside the magnetosphere 2. Dissipa5ve magnetospheres and winds: - MHD with macroscopic conduc5vity *) , - Microscopic level: Par5cle-In-Cell ( PIC ) simula9ons - include pair crea5on and accelera5on, Aim a t self-consistent electrodynamics, with global current closure. *) Macroscopic conduc5vity – phenomenological, free parameter

Aligned rotator with a force-free magnetosphere Lyubarskii 1990, … , Cerus & Beloborodov 2016 - dense (n > n_GJ) plasma ouplow, - split monopole magne5c field at r >> R_LC - current sheet forms. Strong non-thermal emission can be produced in the CS and in the separatrix sheets inside the light cylinder. 25

Properties of Current Sheet • Magnetic reconnection? • Plasmoids? • Dissipation? • Internal thermal pressure / thickness? Uzdensky & Spitkovsky (2014) Cf. Arka & Dubus (2013), deVore et al. (2014), Mochol & Pétri (2015), etc.

Oblique rotator –> Current Sheet becomes corrugated; striped wind forms 27

Current Sheet (“Ballerina Skirt”) Force-Free magnetosphere at 60 o inclination Heliospheric Current Sheet (artist’s concept) Credit: A Spitkovsky

Crab and Vela in the current sheet model Mochol & Petri 2015 Crab Vela

MeV-TeV emission from Crab in the current sheet model Mochol 2017

High-energy emission modeling with Par5cle-In-Cell simula5ons Philippov+ 2017 Synchrotron emission by rela5vis5c par5cles due to magne5c reconnec5on close to Y-point and in the current sheet . 31

Conclusions • Recent developments in pulsar magnetosphere models largely driven by HE & VHE observations • Theoretical developments: - Dissipative magnetospheres (MHD) - Particle approaches (PIC) - Role of GR - Polarization • Observational developments: - Pulsed VHE emission - Gamma-ray pulsar ‘glitch’ - Spider binaries - Spectral sequence - Distributed blind

Puzzling high-energy pulsa5ons of the energe5c radio-quiet gamma-ray pulsar J1813-1246 Marelli+ 2014 > 100 MeV Fermi LAT (black) 0.3 – 10 keV XMM Newton (blue)

Puzzling high-energy pulsa5ons of the energe5c radio-quiet gamma-ray pulsar J1813-1246 Marelli+ 2014

Gamma-ray pulsar posi5ons (Abdo+ 2013)

Gamma-ray pulsar posi5ons (Abdo+ 2013)