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Gamma Rays from the Radio Galaxy M87

Gamma Rays from the Radio Galaxy M87. Outline. The uniqueness of M87 Overview and morphology Gamma-ray Observations Models for gamma-ray emission Leptonic Hadronic Production of UHECRs Observational distinctions between models. VHE Sky E>150 GeV. Mrk421. M87. H1426. Mrk501.

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Gamma Rays from the Radio Galaxy M87

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  1. Gamma Rays from the Radio Galaxy M87

  2. Outline • The uniqueness of M87 • Overview and morphology • Gamma-ray Observations • Models for gamma-ray emission • Leptonic • Hadronic • Production of UHECRs • Observational distinctions between models

  3. VHE Sky E>150 GeV Mrk421 M87 H1426 Mrk501 1ES1959 PSR1259 RXJ1713 CasA SNRG0.9 VelaJr TeV2032 GC Crab 1ES2344 MSH15-05 PKS2005 HessJ1303 PKS2155 Pulsar Nebula AGN adapted from R.A.Ong May 2005 SNR Other, UNID What’s so special about M87? • VHE Cherenkov Telescopes: 8 AGN, 7 blazars + M87 • Doppler boosting intensifies gamma-ray emission in blazars • What about M87? • Jet opening angle ~ 35° • Close • Low jet luminosity ~ 5 × 1044 erg s-1 less heating to surrounding gas, less  ray attenuation

  4. Chandra VLA (90 cm) HST 31” (~2.4 kpc) Owen, Eilek, & Kassim 2000 - Center of Virgo cluster - Distance ~ 16 Mpc - MBH = 3 × 109 M☼ Morphology 2 kpc jet Large-scale jets & radio halo

  5. Chandra VLA (90 cm) HST 2MASS R  4’ 31” (~2.4 kpc) Owen, Eilek, & Kassim 2000 - Center of Virgo cluster - Distance ~ 16 Mpc - MBH = 3 × 109 M☼ Morphology 2 kpc jet Large-scale jets & radio halo

  6. Morphology of central region nucleus (VLA, 15 GHz) (HST) (Chandra) (~390 pc)

  7. Summary of Gamma-ray Observations • Upper limits: • EGRET: F (> 100 MeV) < 2.2 × 10-8 cm-2 s-1 • Whipple 2001-03: F (>250 GeV) < 2.6 × 10-11 cm-2 s-1(Lebohec et al. 2001) • HEGRA 1998-99: F (>730 GeV) = 0.96 × 10-12 cm-2 s-1(Aharonian et al. 2003) • HESS 2003-04: • 211 ± 38 events • Energy threshold: 160 GeV • F (>730 GeV) ~ 0.2-0.5 × 10-12 cm-2 s-1 • 2005 data analysis underway, >6 detection

  8. 2003-04 HESS Observations HEGRA HESS Consistent with point source from nuclear region Beikicke et al. 2005

  9. 2003-04 HESS Observations HEGRA HESS Consistent with point source from nuclear region Evidence for variability Beilicke et al. 2005

  10. nucleus HST-1 Knot A What is the source of the TeV emission? • Variability: flux dropped by factor of ~3 between 1998/99 and 2003/04 • Knot A • ~80 pc × 55 pc (projected)  t ~ few hundred years • Variability timescale too short • HST-1 • Increase in X-ray flux by factor of ~3 in spring of 2004 • Increase by factor of ~50 between 1999 and 2004 (Harris et al. 2005) • No evidence for increase in TeV observations • Lack of coordinated variability  no TeV emission • Leptonic model for nuclear emission… Georganopoulos, Perlman, & Kazanas 2005

  11. Leptonic Model for Nuclear Emission • Homogeneous SSC model fails for HE emission • Decelerating flow model:  • sub-pc deceleration • from 0 = 20 to  = 5 over 3 × 1017 cm (0.1 pc) • Beaming is frequency-dependent • “Upstream Compton” scattering Decelerating flow Homogeneous SSC Georganopoulos, Perlman, & Kazanas 2005

  12. Synchrotron Proton Blazar (SPB) Model • Blob of material moving relativistically along jet axis • p & e- accelerated across shocks • Power-law distribution of protons in high B (~5-50 G) • p ~ 1010-11 > 108  pion production • Gamma-ray production from: • Proton-photon interactions: • 0  2 • ±  ± +  • ±  e± +  + e • e± cascades (2  e±  2 …) • ± &± synchrotron radiation • p synchrotron radiation • Low-energy hump from e- synchrotron Mücke et al. 2003

  13. LBL HBL Protheroe, Donea, & Reimer 2003 Reimer, Protheroe, & Donea 2004 SPB Model Results for M87 • Input spectra from average SEDs • Non-simultaneous data • HE flux contributors: • p synchrotron (dashed) • ± synchrotron (dashed triple-dot) • 0 cascade (dotted) • ± cascade (dashed-dotted) HBL model LBL model

  14. A Site for Cosmic Ray Acceleration • In proton models, ultra-high-energy cosmic ray protons are produced by: • Direct acceleration at termination shocks of jets • Decay of neutrons produced in jets or accretion shocks outside galaxy: pn • UHECRs (E > 1020 eV) attenuated by CMB (GZK cutoff) • At 3 × 1020 eV, MFP ~ 5 Mpc, energy loss distance ~ 20 Mpc • UHECR detections claimed with E > 1020 eV • M87 is close enough to produce them • Neutrons from M87 can account for observed flux “if the extragalactic magnetic field topology is favorable” (Protheroe, Donea, & Reimer 2003)

  15. HBL LBL Observational Distinctions between Models • Neutrino flux (difficult to detect!) • Independent measure of B • More simultaneous observations • Larger sample of -ray sources • Tighter model constraints • GLAST?

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