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

High-energy activity of rotation-powered pulsars

Bronisław Rudak CAMK PAN POLNS18 26-28 March 2018

Pulsars

Rotating, strongly magnetized neutron stars acting as unipolar inductors. Maximum potential drop (voltage): Vmax ≈ 6 × 1012 (B/1012 G) P-2 Volts. Realistic potential drops - much smaller, but high enough to accelerate particles to ultrarelativistic energies.

3

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)

211 public gamma-ray PSRs Fermi LAT Pulsar Yield (Feb 2018)

Young: 115 Millisecond: 96

Period – Period time derivative

D.Smith+ 2017

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

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Pulsar mul5wavelength spectra and pulsa5ons

Non-thermal (magnetospheric) components Spectra

• piecewise power law (w. Breakpoints)
• [sub-]exponen5al at high-energy cutoff,
• r 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

Geminga

• 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)

Light Curve Classes

Courtesy: C. Venter

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

Examples of pulse profile morphology in radio and gamma

(2nd Fermi LAT Pulsar Catalog, 2013)

PSR B1821-24 in M28, P = 3 ms PSR B0531+21, P = 33 ms (”miniCrab” in X-rays)

Johnson+ 2013

Mul5frequency profiles

Radio intensity (au)

0.5 1 1.5 2

Radio (Nancay telescope, 1.4 GHz) (a) Normalized count rate

0.5 1 1.5 2 2.5 3 3.5 4 4.5

Optical (SCam-3) (b) Counts/s

500 1000 1500 2000 2500 3000 3500 4000 4500

X-rays (RXTE, 2 - 16 keV) (c) Phase

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

)

3

Counts (x10

1.57 1.58 1.59 1.6 1.61

Hard X-rays (INTEGRAL, 100 - 200 keV) (d) Soft gamma-rays (Comptel, 0.75 - 30 MeV) (e) Counts

65000 66000 67000 68000 69000 70000 71000 72000 73000

Gamma-rays (EGRET, >100 MeV) (f) Counts

50 100 150 200 250 300 350 400 450

Gamma-rays (Fermi LAT, >100 MeV) (g) Counts

500 1000 1500 2000

Phase

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

VHE gamma-rays (MAGIC, >25 GeV) (h) )

3

Counts (x10

182 182.5 183 183.5 184 184.5 185 185.5 186 186.5

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Ng+ 2016

• RQ pulsar
• 20% decrease in flux > 100 MeV in 1 week
• Simultaneous 4% increase in spin-down rate

PSR J2021+4026: First Variable Gamma-ray Pulsar

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Ng+ 2016

Before the glitch ader

PSR J2021+4026: First Variable Gamma-ray Pulsar

Change in magnetosphere structure? Modified beaming?

Phased-averaged spectral energy distribu5on

Kuiper+ 2017

Examples of Spectral Energy Distribu5ons (from X-rays to gamma rays)

TeV pulsed emission from the Crab pulsar detected by MAGIC

Energy [GeV]

• 1

10 1 10

2

10

3

10

]

• 1

s

• 2

[TeV cm dEdAdt dN

2

E

• 15

10

• 14

10

• 13

10

• 12

10

• 11

10

• 10

10

Fermi-LAT P1 Fermi-LAT P2 MAGIC P1 MAGIC P2

Ansoldi+ 2015

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Spectral energy distribu5on of the Vela pulsar

VHE (?)

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P1 P2 P3 P4

VHE

The many faces of Vela – the ul5mate challenge for models

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)

A brief history of pulsar models in three stages

Where and how does the dissipation of the spin-down power take place?

• inside the magnetosphere?
• in the wind?
• in both?

Key questions in pulsar electrodynamics models Cartoons: B. Cerutti

fff

Is the pulsar magnetosphere filled with dense plasma? NO NO

• Vacuum

(Deutsch’55)

• Charge-

separated plasma

(GJ69, Michel’73)

YES YES

• Force-free
• ‘Pulsar

Equation’

• Aligned

(Contopoulos’99)

• Oblique

(Spitkovsky’06)

• Full MHD

(Komissarov’06, Tchekovskoy’13)

Modelling Assumptions Not Not Ever ery- wher here Local gaps

(Harding, Romani, Cheng, Hirotani+)

Dissipative Magnetospheres

(Li’12, Kalapotharakos,’13)

Courtesy: C. Venter

Courtesy: C. Venter

γ-ray LCs, phase-resolved spectroscopy, polarization will help to constrain B

Vacuum retarded dipole (VRD) (Deutsch 1955) No charges, no currents

Different Regimes

Non-ideal MHD magnetosphere (Kalapotharakos et al. 2012, Li et al. 2012) Charges, currents + acceleration! Force-free magnetosphere (Spitkovsky 2006) No particle acceleration

Filled with plasma

Different regimes

Courtesy: C. Venter

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.

3D magnetospheric accelerators (gaps)

Traditional magnetospheric accelerators

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 + δP_em/δ t . Assump5ons in FFE:

• the iner5al mass density of the plasma ignored ( << B2/8πc2)
• 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 .

• 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 at self-consistent electrodynamics, with global current closure.

*) Macroscopic conduc5vity – phenomenological, free parameter

Global electrodynamics with the plasma - II

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• 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.

Lyubarskii 1990, … , Cerus & Beloborodov 2016

Aligned rotator with a force-free magnetosphere

Uzdensky & Spitkovsky (2014)

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

Properties of Current Sheet

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

Current Sheet (“Ballerina Skirt”)

Credit: A Spitkovsky

Force-Free magnetosphere at 60o inclination Heliospheric Current Sheet (artist’s concept)

Crab and Vela in the current sheet model

Crab Vela

Mochol & Petri 2015

MeV-TeV emission from Crab in the current sheet model

Mochol 2017

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Philippov+ 2017

High-energy emission modeling with Par5cle-In-Cell simula5ons

Synchrotron emission by rela5vis5c par5cles due to magne5c reconnec5on close to Y-point and in the current sheet.

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)