Probing Cosmic Hadron Colliders with hard X-ray detectors of ASTRO-H

Transcription

1 Probing Cosmic Hadron Colliders with hard X-ray detectors of ASTRO-H F.A. Aharonian, DIAS (Dublin) & MPIK (Heidelberg) ASTRO-H SWG Meeting, ISAS, Tokyo, Feb 25-26, 2009

2 X-rays - tracers of high energy electrons electronic component of hot (10 7 to 10 9 K) thermal plasmas IC X-rays - nonthermal relativistic but still (typically) modest ( e : 10 1 to 10 3 ) energy electrons synchrotron X-rays - multi-tev electrons ( e >10 6 )

3 TeV, PeV, EeV- gamma rays and neutrinos: carriers of information about hadronic colliders TeV -rays: effectively produced/detected, but difficult to identify the hadronic origin PeV/EeV -rays: (i) difficult to detect (limited detection areas) (ii) fragile (absorption in radiation and B-fields) TeV/PeV/EeV neutrinos: difficult to detect

4 transparency of the Universe for gamma-rays P. Coppi&FA 1997 mean free path of gamma-rays from ev to ev less than 1 Mpc

5 hard X-rays - hadronic messengers? the idea: synchrotron radiation of secondary electrons produced at interactions of protons with ambient gas or radiation fields (1) p p ( ) =>, K,, (2), K, =>,, e, μ (3) e B => X (1) p => e+ e- (2) e B => X why hard X-rays? radiation often peaks in the hard X-ray band not many competing production mechanisms no absorption in radiation and magnetic fields good sensitivity/good spectrometry/good morphology

6 two examples probing shock acceleration of protons in (1) young SNRs and (2) in galaxy clusters

7 SNRs - sources of CRs up to >10 15 ev? Cosmic Rays from 10 9 to ev up to ev (knee) - Galactic SNRs: E max ~ v shock Z x B x R shock for a standard SNR: E p,max ~ 100 TeV solution? amplification of B-field by CRs ev to ev: a few special sources? Reacceleration? above ev (ankle) - Extragalactic SNRs? Knee Ankle ev particles? : two options top-down (non- acceleration) origin or Extreme Accelerators T. Gaisser

8 SNRs the most probable factories of GCRs? straightforward proof: detection and identification of gamma-rays, neutrinos and hard X-rays from p-p interactions (as products of decays of secondary neutral and charged pions) objective: (i) to probe the content of nucleonic component of CRs in SNRs at d < 10kpc at the level erg, and (ii) to demonstrate that at least in some SNRs particles are accelerated to ev realization: sensitivity of detectors - down to erg/cm 2 s crucial energy domains: : up to 100+ TeV : TeV X: kev

9 Visibility of SNRs in high energy gamma-rays for CR spectrum with =2 F (>E)=10-11 A (E/1TeV) -1 ph/cm 2 s 0 decay (A=1) Inverse Compton A=(W cr /10 50 erg)(n/1cm -3 )(d/1kpc) o Crab 1 o sensitivity 1000 yr old SNRs (in Sedov phase) Detectability? compromise between angle (r/d) and flux F (1/d 2 ) typically A: : 0.1 o - 1 o TeV -rays detectable if A > 0.1 if electron o component spectrum >> dominates 10 TeV if A > synchrotron 0.1 (S x /10 μj)(b/10 X-rays μg and ) -2 IC TeV s nucleonic main component target photon of CRs field - visible 2.7 K: through F,IC /F x,sinch TeV =0.1 (and (B/10μG) GeV) gamma-rays -2!

10 RXJ > 30 TeV -rays and shell type morphology: acceleration of protons and/or electrons in the shell to energies (well) exceeding 100 TeV very good correlation with X-rays 2 1 almost constant photon index! for 0 -meson decay gamma-rays:

11 origin of gamma-rays the key issue: identification of -ray emission mechanisms: 0 or IC? 0 hadronic origin of gamma-ray derivation of the energy spectrum and the total energy Wp (with an uncertainty related to the uncertainty in n/d 2 ) IC leptonic origin of gamma-rays model-independent derivation of the spatial and spectral distributions of electrons and, in combination with X-ray data - model independent map of the B-field

12 leptonic model - IC on 2.7 K argument in favor of IC origin of -rays: existence of multi-tev electrons from synchrotron radiation nice spatial correlation with X-rays argument against hadronic models IC origin? very small B-field, B < 10 μg, and very large E max > 100 TeV two assumptions hardly can co-exists within standard DSA models; bad spectral fit below a few TeV IC origin of -rays implies that we see distribution of electrons => nice correlation of electron distribution with synchrotron X-ray distribution => homogeneous magnetic field, but distinct spatial variation of electrons

13 in the regime of Bohm diffusion and under assumpton of dominance of synchrotron cooling the spectra of electrons and synchrotron radiation can be calculated with god accuracy: the energy spectrum of electrons at the shock front *) E 0 almost coincides with the value derived from t acc = t synch the spectrum of synchrotron radiation at the shock front Synchrotron cutoff energy approximately 10 times h 0! observations of X-rays above 10 kev are needed to compare with model-predictions V.Zirakashvili & FA 2007

14 Elctron and synch. rad. spectra at shock front synch. rad. e downstream -functional approx. upstream =4, B 1 = B 2 electrons downstream Sy IC on 2.7 MBR Thompson! upstream upstream V.Zirakashvili, FA 2006

15 recent broad-band measurements of Suzaku energy spectrum of synchrotron radiation of electrons in the framework of DSA (Zirakashvili&FA 2007) h 0 =0.55 kev Uciyama et al strong support for acceleration in Bohm diffusion regime ( ~ 1) - from postion of synchrotron cutoff given that the shock speed v < 4000 km/s (Chandra) 1. electron spectrum derived from Suzaku data 2. DSA prediction (Zirakashvili&FA07) 3. standard E -3 exp(-e/e 0 ) type elec. spectrum Tanaka et al derived electron spectrum allows model-independent calculations of IC spectrum!

16 IC calculations based on Suzaku data 1. Solid - total 2. IC on IC on FIR 4. IR on optical Standard ISM radiation fields B=14μG density of Optical field: 140 ev/cm3 second electron component with a cutoff at 10 TeV or should adopt that the source is >10 4 years old

17 hadronic origin of TeV gamma-rays acceleration spectrum with power-law the same, except for index =2; B=200 μg, age: 1000 years =1.7 Wp=2.7 x (n/1cm -3 ) -1 erg Wp=1.6 x (n/1cm -3 ) -1 erg We=3.1 x erg We=6.0 x erg

18 challenges for hadronic models: strong X-TeV correlaton in fact this is more natural for hadronic rather than leptonic models - this could an indication that electrons and protons are accelerated relatively weak radio emission different than in other SNRs, but why not, i.e. because of very hard acceleration spectra lack of thermal X-ray emission because of (i) very low density plasma n or (ii) low electron temperature T e? gas density n cannot be much less than 1 cm -3 because of available energy budget we do not (yet) know the mechanism(s) of electron heating in supernova remnants; Coulomb exchange is not sufficient for heating; most likely this happens through plasma waves. As long as the mechanism is not understood one cannot use the lack of thermal emission as an argument against hadronic model

19 Variability of X-rays on year timescales - witnessing particle acceleration in real time flux increase - particle acceleration flux decrease - synchrotron cooling * ) both require B-field of order 1 mg in hot spots and, most likely, 100μG outside Uchiyama et al supporting the idea of amplification of B-field by in nonlinear shocks through non-resonant streaming instability of charged energetic particles (T. Bell) * ) explanation by variation of B-field does t work as demonstrated for Cas A (Uciyama&FA, 2008)

20 pp o good spectral fits pp ± μ,e reliable predictions protons: dn/de: E - exp[-(e/ecut) ] -rays/neutrinos dn/de: E - exp[-(e/e 0 ) ] = +, = 0.1, = /2, E 0 = Ecut/20 Wp(>1 TeV) = 0.5x10 50 (n/1cm -3 ) -1 (d/1kpc) 2 Kel ner et al. 2006

21 SNRs as Cosmic PeVatrons? 3 channels of information about cosmic PeVatrons: TeV gamma-rays TeV μ-neutrinos kev hard X-rays sensitivities? better than erg/cm 2 s -rays: difficult, but possible with future 10km 2 area multi-tev IACT arrays neutrinos: difficult, but KM3NeT should be able to see (marginal) signals from SNRs RX and Vela Jr prompt synchrotron X-rays: a very promising channel

22 Probing PeV protons with X-rays SNRs shocks can accelerate CRs to <100 TeV (e.g. Cesarsky&Lagage 1984) unless magnetic field significantly exceeds 10 μg Recent theoretical developments: applification of the B-field up to >100 μg is possible through plasma waves generated by CRs (Bell and Lucek 2000) >10 15 ev protons >10 14 ev gamma-rays and electrons prompt synchrotron X-rays cooling time: t( ) = 1.5 ( /1keV) -1/2 (B/1mG) -3/2 yr << t SNR energy range: typically between 1 and 100 kev with the ratio Lx/L larger than 20% (for E -2 type spectra) hadronic hard X-rays and (multi)tev -rays similar morphologies!

23 hadronic X-rays versus synchrotron radiation of primary electrons: electron injection spectrum Q e (E e )=Q o E e exp[(-e e /E e,o ) ] spectrum of synchrotron radiation of cooled electrons ( /2+1) exp[(- / o ) ] = / +2; =1 =0.5, =1/5 synchrotron spectrum of primary electrons: =2/(2+2)=1/2 : characteristic synchrotron frequency proportional BE 0 2 ( prop. to B 3 ) * for Eo =1 PeV, B=1 mg X-ray emission extends well beyond 10 kev while the cutoff energy in the synchrotron spectrum from directly accelerated electrons is expected around 1 kev simultaneous measurements of 0 -decay -rays and associated synchrotron radiation provide unambiguous estimate of B-field in the acceleration region!

24 protons broad-band GeV-TeV-PeV s synch. hard X-rays broad-band emision initiated by pp interactiosn : Wp=10 50 erg, n=1cm -3

25 key observations to prove the hadronic origin of gamma-rays Gamma-ray flux below 10 GeV (very low if IC) - Fermi very low if IC gamma-rays to and beyond 100 TeV - ACT/AGIS UHE gamma-ray studies (arrays for detection multi-tev gamma-rays) Neutrinos - IceCube and KM3NeT detection of neutrinos hard X-rays produced by secondary electrons - ASTRO-H (NuSTAR, SIMBOL X) detection of X-rays from 10keV to 100 kev

26 -ray ~ 10 km shower S eff = 1m 2 at 1 GeV 5 nsec 100m S eff >3x104 m 2 at 1 TeV

27 km3 volume neutrino telescopes km3 volume detector A. Kappes effective area: 0.3m 2 at 1 TeV 10m 2 at 10 TeV => several events from a 1Crab source per 1year km3 volume scale detectors will provide first meaningful probes of SNRs Jacques Paul Observables The Violent Universe International Winter School 13 and 14 March 2007 Slide 28

28 synchrotron radiation of secondary electrons from interactions of protons with radiation photomeson processes: p => N +np E th =m c 2 (1+m /2m p )=145 MeV plus pair production: p => e + e - threshold: 2m e c 2 =1 MeV

29 distributions of photons and leptons: E=10 20 ev

30 Energy losses of EHE CRs in 2.7 K CMBR due to pair production and photomeson processes lifetime of protons in IGM 1 - pair production, 2 - photomeson a - interaction rate, b- inelasticity

31 electron spectra from interactions of protons with 2.7 CMBR

32 production of electrons in IGM spectrum of protons: power-law with an exponential cutoff with power-law index a=2 and cutoff E cut =ke*; E*= ev

33 gamma-radiation spectra of secondary electrons E*= ev

34 Acceleration of UHE Protons at Cluster Accretion Shocks and Related Non-thermal Emission Giulia Vannoni: PhD Thesis (2008, Heidelberg)

35 Galaxy Clusters and UHE-CR Hillas, 1984 ~2.7 ~ 3.1 ~ ev

36 Particle Acceleration in Clusters ingredients: Formation of (strong) accretion shock at the virial radius (Bertschinger, 1985; Kang et al., 1994) Magnetic field of order mg Shock velocity - few 1000 km/s Acceleration time ~ Hubble time shock acceleration of protons possible to UHE

37 Non-relativistic shock wave: bulk plasma Diffusive Shock Acceleration shock (Fermi, 1949; Axford et al., 1977; Krymsky, 1977; Bell, 1978; Blandford & Ostriker, 1978) u 1 u 2 M 1 = u 1 c s (Mach number) 0 x R= u 1 u 2 (compression ratio) non thermal particles Diffusive acceleration, strong (M>10) shocks: E 2 shoc k dn de _ E_2 f _p p _4 2 1 (steady state distribution function at the shock position) E 1 V=-(u1-u2)

38 pair production Proton Energy Losses Assumption: Spherical accretion shock. Interaction with the CMB can become the limiting mechanism (Norman et al., 1995; Kang et al., 1997). Pair production dominant energy loss channel for all realistic sets of parameters. pion production Time dependent calculation needed

39 f _x, p,t_ f _x,p,t u _ t x A Self-consistent Approach x_ f _x,p,t_ D _ p x 3 u x f _x, p,t 1 p p 2 (Vannoni et al., in press) p _p2 L _x,p_f _x,p,t = Q_x,p_ Numerical formulation kept general: loss term - protons or electrons - general form of the loss term L(x,p) - general form of the diffusion coefficient D(x,p) - time evolution Simplifying assumptions: Q_x, p_= Q 0 x p_ p 0 _ D_p_= D 0 p _ L_x, p_= L_p_ B 2 =_B 1 injection at the shock independent of x, Bohm: D 0 = c2 3eB, _= 1 independent of x =4, random magnetic field (amplification)

40 Proton Spectrum no steady state cutoff energy around 7 x ev Pair production energy losses shape proton spectrum around the cut-off: small bump, non-exponential cut-off G. Vannoni et al., in preparation

41 Production and Cooling of Secondary Electrons upstream downstream electrons rapidly cool via synchrotron and IC KN effect electrons production spectra IC off CMB B1=0.3 mg B2=1 mg G.Vannoni et al., in preparation

42 cooled electron spectra tacc=5 Gyr pure synchrotron cooling SY+IC in KN regime upstream upstream downstream downstream IC cooling in Klein-Nishina regime: Features in the cooled spectrum around the cut-off. Upstream and downstream level comparable, shift in the cut-off energy G. Vannoni et al., in preparation

43 Broadband SED Wp=10 62 erg in the case of non-liner shocks => 100% effective synchrotron source for d=100 Mpc f E =10-12 erg/cm2 s detectable by ASTRO-H Self-consistent calculation: broader and less steep cut-off than exponential Synchrotron: ~factor 10 enhancement downstream due to higher B; peak energy ~100 kev. Inverse Compton: same emission level up and downstream peak between 10 and 100 TeV but absorption will reduce dramatically the gamma-ray flux Vannoni et al., in preparation