Hard X-ray emission from Novae

Transcription

1 Hard X-ray emission from Novae Indrek Vurm (Columbia University) in collaboration with: Brian D. Metzger, Andrei M. Beloborodov (Columbia) Koji Mukai (NASA) Shocks and Particle Acceleration in Novae and Supernovae New York, 2016

2 Gamma-rays from classical novae L γ ~ erg s 1 L γ L opt ~ The Fermi-LAT collaboration (2014)

3 Gamma-rays from classical novae L γ ~ erg s 1 L γ L opt ~ The Fermi-LAT collaboration (2014) Inevitable link between gamma-rays and non-thermal X-rays

4 X-rays from shocks: thermal vs. non-thermal Thermal Free-free and line emission from shock-heated plasma V sh = 10 8 cm/s => T = 10 7 K => 1 kev Carries bulk of the power dissipated in radiative shocks Absorbed via bound-free by neutral material ahead of the shock (at early times), reprocessed to optical Sets an upper limit on the shock power for given optical luminosity Non-thermal (>10 kev) Bremsstrahlung and inverse Compton from relativistic electrons/pairs same leptons produce GeV Opacity: Thomson/Compton

5 Hard (>10 kev) X-ray observations V339 Del X-rays (NuSTAR, preliminary) (24 ksec, t+1 week) ν Fν (20 kev) < erg cm 2 s 1 (Mukai et al., in prep.) gamma-rays (Fermi/LAT) ν Fν (100 MeV) = erg cm 2 s 1 V5668 Sgr X-rays (preliminary) gamma-rays ν Fν (20 kev) < ν Fν (100 MeV) (52 ksec, t+2 weeks) ν Fν (20 kev) < erg cm 2 s 1 (Mukai et al., in prep.) ν Fν (100 MeV) = erg cm 2 s 1 ν Fν (20 kev) < ν Fν (100 MeV)

6 Leptonic de kin dlnε e Hadronic Metzger et al. (2015) Non-thermal acceleration spectrum (leptonic and hadronic): de kin dlnε p e.g. Blandford & Ostriker (1978); Park et al. (2015) Bulk of the energy above 1 GeV

7 Radiative processes: leptonic Inverse Compton Characteristic photon energy GeV: Hard X-rays: Bremsstrahlung: γ 10 4 γ ~ 10 2 E ph 4 3 γ 2 E opt Characteristic photon energy GeV: Hard X-rays: E ph m e c 2 γ γ ~ 10 3 γ ~ 10 2!? Coulomb losses!

8 Bremsstrahlung vs IC Critical parameter: χ = U opt m e c 2 n = L opt, n 9 R 14 IC and bremsstrahlung losses equal at: γ = 5α fs χ χ 5 Inverse Compton: Bremsstrahlung: =>

9 Radiative processes: hadronic Collisions between relativistic and thermal protons: Cooling time: Elastic: energy loss to thermal plasma Inelastic: pion production: pp π ±,π 0 γ,e ±,ν Photons: e± pairs: Kamae et al. 2006

10 Model: radiative shock Thermal and non-thermal plasma injected at the shock Downstream evolution Cooling/compression at constant total pressure p th + p nth,e + p nth,p + p B = const. Thermal processes line cooling, free-free emission kev radiation reprocessed to optical by neutral upstream Nonthermal processes relativistic bremsstrahlung inverse Compton Coulomb collisions elastic/inelastic proton-proton collisions synchrotron T 10 7 K T 10 4 K Absorbing neutral upstream v 10 8 cm/s Shock thermal X-rays Cooling layer Compressed layer hard X-rays, γ-rays Line cooling Radiative shock: t line < t dyn 1 week

11 Spectra Leptonic: Coulomb break Hadronic 50 kev GeV 50 kev GeV Parameters: n = cm L opt =10 38 erg/s R=10 14 cm Acceleration spectrum:

12 X-ray to gamma-ray ratio: leptonic Hard X-ray to gamma-ray ratio Gamma-ray to optical ratio (observed) ε nth =10 2 L 30 kev L 1 GeV Metzger et al. (2015)

13 X-ray to gamma-ray ratio: leptonic Hard X-ray to gamma-ray ratio Gamma-ray to optical ratio (observed) ε nth =10 2 L 30 kev L 1 GeV Metzger et al. (2015)

14 X-ray to gamma-ray ratio: leptonic Hard X-ray to gamma-ray ratio ε nth =10 2 L 30 kev L 1 GeV L opt =10 38 erg s 1

15 X-ray to gamma-ray ratio: hadronic Hard X-ray to gamma-ray ratio ε p =10 1 L 30 kev L 1 GeV L opt =10 38 erg s 1

16 Nova V339 Del: leptonic NuSTAR + Fermi/LAT L X L γ νf ν (20 kev) νf ν (100 MeV) < Density: n cm 3 ε nth =10 2

17 Nova V339 Del: leptonic NuSTAR + Fermi/LAT L X L γ νf ν (20 kev) νf ν (100 MeV) < Density: n cm 3 ε nth =10 2

18 Nova V339 Del: hadronic NuSTAR + Fermi/LAT L X L γ νf ν (20keV) νf ν (100MeV) < ε p =10 1

19 Nova V339 Del: hadronic NuSTAR + Fermi/LAT L X L γ νf ν (20keV) νf ν (100MeV) < ε p =10 1

20 Nova V5668 Sgr Leptonic NuSTAR + Fermi/LAT νf ν (20 kev) νf ν (100 MeV) < Hadronic ε nth =10 2 ε p =10 1

21 Nova V5668 Sgr Leptonic NuSTAR + Fermi/LAT νf ν (20 kev) νf ν (100 MeV) < Hadronic ε nth =10 2 ε p =10 1

22 Nova V5668 Sgr Leptonic NuSTAR + Fermi/LAT νf ν (20 kev) νf ν (100 MeV) < Hadronic ε nth =10 2 ε p =10 1

23 Prospects for NuSTAR Fermi/LAT NuSTAR Harrison et al. (2013) LAT fluxes The Fermi-LAT collaboration (2014) νf ν ~ erg cm 2 s 1 V5668 Sgr νf ν (20 kev) < erg cm 2 s 1 (52 ksec)

24 Summary Hard X-ray emission inevitably accompanies GeV gamma-rays Radiative mechanism: bremsstrahlung or IC (less likely) Spectral index α 1 (νf ν ν) X-ray to gamma-ray ratio in radiative shocks >10-4: independent diagnostic of outflow properties low observed values can rule out leptonic models

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26 Thermal/nonthermal cooling Shocks are radiative at t ~ 1 week Thermal cooling fastest => X- and v sh 10 8 cm/s T 10 7 K IC gamma-rays from compressed layer Hard X-rays γ = Bremsstrahlung or IC? Coul. brems Critical parameter: thermal χ = U opt m e c 2 n = L opt,38 2 n 9 R 14 Parameters: L opt =10 38 erg s 1 R=10 14 cm v sh =10 8 cm s 1

27 Thermal/nonthermal cooling Shocks are radiative at t ~ 1 week Thermal cooling fastest => X- and v sh 10 8 cm/s T 10 7 K IC gamma-rays from compressed layer Hard X-rays γ = Bremsstrahlung or IC? Coul. brems Critical parameter: thermal χ = U opt m e c 2 n = L opt,38 2 n 9 R 14 Parameters: L opt =10 38 erg s 1 R=10 14 cm v sh =10 8 cm s 1

28 Coulomb cooling Coulomb losses dominate at Coulomb: Bremsstrahlung: Significant suppression of bremsstrahlung/ic X-rays

29 Postshock evolution Leptonic Hadronic

30 Spectra: leptonic

31 Cooling: thermal plasma Radiative shock

32 Cooling: non-thermal plasma