Numerical Simulations of FRI jets

1. Numerical Simulations of FRI jets Manel Perucho Pla Max-Planck-Institut für Radioastronomie and J.M. Martí (Universitat de València)

2. Introduction: Laing & Bridle 2002a,b • Assumptions • Axisymmetric, time-stationary, relativistic jet • Symmetric jet/counterjet system • Parameterized distributions of velocity, magnetic field and synchrotron emissivity. • Comparison with VLA total intensity and polarization data allows to fix parameterizations. • Dynamical model based on conservation laws. • External gas density and pressure distributions are taken from Hardcastle et al. (2002) • Pressure equilibrium with the external medium assumed in the outermost studied region. • Results: • Jet axial structure: inner, flaring and outer regions • Spine velocity decreases (from 0.9 to 0.25 c) due to entrainment in the flaring region • Transversal structure: spine + shear layer • Jet dynamics: • The jet is overpressured at the inlet: expansion and acceleration. • Recollimation occurs when the jet becomes underpressured (wrt ambient). • Entrainment: peak in the entrainment rate at the recollimation site (stellar mass loss?); outwards the jet is slowly entrained and decelerated.

3. rm = 7.8 kpc Evolution of FRI jets: setup Perucho & Martí 2007, MNRAS Axisymmetric simulation of a purely leptonic jet with Lj ~ 1044 erg/s. • Jet injected according to Laing & Bridle (2002a,b) model at 500 pc from the core • ambient medium conditions from Hardcastle et al. 2002 Physical domain: 18 kpc x 6 kpc [Resolution: 8 cells/Rj (axial) x 16 cells/Rj (radial)]

4. Evolution of FRI jets: picture at 7 106 years Perucho & Martí 2007, MNRAS Last snapshot (T = 7 106 yrs ~ 10 % lifetime of 3C31) shocked ambient shocked ambient cavity/cocoon beam bow shock bow shock

5. ~ constant Evolution of FRI jets: dynamics Perucho & Martí 2007, MNRAS Extended B&C model: a ~ -0.1, b ~ -1 Ps t-1 t -1.3 Rs Nc b vbs Nc a Pc rc Cocoon evolution: Tc for negligible pollution with ambient particles (Nc b ~ 20 - 200 Nc a), andassuming self-similar transversal expansion

6. Evolution of FRI jets: dynamics in the beam Perucho & Martí 2007, MNRAS pressure density Mach number recollimation shock and jet expansion Simulation adiabatic expansion jet disruption and mass load L&B model As in Laing & Bridle’s model, the evolution is governed by adiabatic expansion of the jet, recollimation, oscillations around pressure equilibrium, mass entrainment and deceleration. However, in the simulation there are more shocks and all the entrainment is due to a destabilization of the jet as a result of those shocks. jet deceleration

7. Evolution of FRI jets: some thoughts Perucho & Martí 2007, MNRAS • Strong vs mild shock • Hardcastle et al. 2002 found X-ray emission from the flaring region of the northern jet, where the jet decollimates and shows brighter radio emission. • this is the region which we identify with the post-recollimation shock region, where particles could gain enough energy to emit in the X-ray • this fact favors the presence of a strong shock, as seen in the simulation jet disruption and mass load • Comparison with L&B • Simulations confirm the FRI paradigm qualitatively, but • jet flare occurs in a series of shocks • the presence of the cocoon is crucial: the jet is not interacting directly with the ambient, but with the cocoon. • comparison wth L&B model is difficult as the jet has not reached a steady state • The simulated jet is very young if compared to 3C31, but • how does it compare to younger FRI jets like CenA or NGC3801? jet deceleration

8. Comparison with young FRI’s Perucho & Martí 2007, MNRAS • Mach number of the bow shock by the end of the simulation M ~ 2.5, consistent with X-ray observations by Kraft et al. 2003 (Cen A) and Croston et al. 2007 (NGC3081): • M ~ 3 - 8 for the bow shock of those sources with ages ~ 106 yrs (NGC3801). Pressure, number density and Temperature in the shocked ambient gas (shell) and the ambient medium of the galactic gasare comparable too. jet disruption and mass load • The high temperature in the shell compared to observations could be due to: • Initial jet power of the simulated jet is 1044 erg/s (cf. 3 1042 erg/s in NGC 3801, Croston et al. 2007). • Lack of thermal cooling in the simulation. • The ambient medium in 3C 31 is modelled as hotter (107 K) and denser (104 m-3) than those in NGC3801 or Cen A (106 K, 103 m-3). • X-ray observing energies in those sources are low for these temperatures. jet deceleration

9. Thermal emission from young FRI’s t  106 yrs (LS  3 kpc) Tsh  109 K  100 keV ne,sh  6 x 10-2 cm-3 Vsh  1065 cm3 3C31 – NGC3801: DL  50 Mpc νSV  10-12 erg cm-2 s-1 L(100 keV)  8 1040 erg s-1 CenA: DL  3 Mpc νSV  10-10 erg cm-2 s-1 The evolution of the luminosity with time is as predicted by Kino et al. (2007):  t-1 t  7 106 yrs(LS  16 kpc) Tsh  109 K  100 keV ne,sh  6 x 10-3 cm-3 Vsh  1067 cm3 3C31 – NGC3801: DL  50 Mpc νSV  10-13 erg cm-2 s-1 L(100 keV)  1040 erg s-1 CenA: DL  3 Mpc νSV  10-11 erg cm-2 s-1 jet disruption and mass load Croston et al. 2007 NGC3801 (t  2 x 106 yrs) νSV  6 – 7 x 10-15 erg cm-2 s-1 LX 1039 erg s-1 (0.4-2 keV) Kraft et al. 2003 Cen A (t  ?) νSV  10-12 erg cm-2 s-1 LX 1039 erg s-1 (0.1-10 keV) • Siemiginowska et al. (2008) have found X-ray luminosities (0.5-10 keV) in GPS sources within 1042 - 1046 erg/s. • Suggested to be related to the accretion power. • A significant fraction of this flux could come from thermal emission if the sources are very young (t ≤ 103 yrs), depending also on their power (FRI’s or FRII’s). Our pre/post-diction is that young (t<107 yrs) FRI sources present bow-shocks in general and these should be observable in X-rays to gamma-rays, depending on the jet power. jet deceleration

10. FRI jets: next steps RATPENAT • Long term simulations (up to 100 kpc). • Supercomputation. • RATPENAT: a 3D RHD code parallelised for the use of supercomputers. • The parallelisation of the numerical grid has been performed in the direction of propagation of the flow. • Physics. • Relativistic EoS. • Mass load from stars. • Bremsstrahlung cooling. ...(couple of years)... • Magnetic fields.