Gamma Rays from the Gamma Rays from the Radio Galaxy M87Radio Galaxy M87

OutlineOutline

• The uniqueness of M87The uniqueness of M87

• Overview and morphologyOverview and morphology

• Gamma-ray ObservationsGamma-ray Observations

• Models for gamma-ray emissionModels for gamma-ray emission– Leptonic Leptonic – HadronicHadronic– Production of UHECRsProduction of UHECRs

• Observational distinctions between modelsObservational distinctions between models

• VHE Cherenkov Telescopes: 8 AGN, 7 blazars + M87VHE Cherenkov Telescopes: 8 AGN, 7 blazars + M87

• Doppler boosting intensifies gamma-ray emission in Doppler boosting intensifies gamma-ray emission in blazarsblazars

• What about M87?What about M87?– Jet opening angle ~ 35Jet opening angle ~ 35°°

– CloseClose– Low jet luminosity ~ 5 Low jet luminosity ~ 5 × 10× 104444 erg s erg s-1-1 less heating to less heating to

surrounding gas, less surrounding gas, less ray attenuation ray attenuation

What’s so special about M87?What’s so special about M87?Mrk421 H1426

Mrk5011ES1959

1ES2344

PKS2155

CasARXJ1713

CrabTeV2032

M87

PKS2005

PSR1259

VelaJr

MSH15-05

SNRG0.9

HessJ1303

GC

adapted fromR.A.Ong

May 2005

Pulsar Nebula

SNR

AGN

Other, UNID

VHE SkyE>150 GeV

2 kpc jetChandra

31” (~2.4 kpc)

HST

MorphologyMorphology

Large-scale jets & radio halo

Owen, Eilek, & Kassim 2000

VLA (90 cm)

- Center of Virgo cluster - Distance ~ 16 Mpc- MBH = 3 × 109 M☼

2 kpc jetChandra

31” (~2.4 kpc)

HST

MorphologyMorphology

Large-scale jets & radio halo

Owen, Eilek, & Kassim 2000

VLA (90 cm)

- Center of Virgo cluster - Distance ~ 16 Mpc- MBH = 3 × 109 M☼

R 4’

2MASS

Morphology of central regionMorphology of central region

(~390 pc)

(VLA,15 GHz)

(HST)

(Chandra)

nucleus

Summary of Gamma-ray Summary of Gamma-ray ObservationsObservations

• Upper limits:Upper limits:– EGRET: EGRET: FF (> 100 MeV) < 2.2 (> 100 MeV) < 2.2 × 10× 10-8-8 cm cm-2-2 s s-1-1

– Whipple 2001-03: Whipple 2001-03: F F (>250 GeV) < 2.6 × 10(>250 GeV) < 2.6 × 10-11-11 cm cm--

22 s s-1-1 (Lebohec (Lebohec et al.et al. 2001) 2001)

• HEGRA 1998-99: HEGRA 1998-99: F F (>730 GeV) = 0.96 × 10(>730 GeV) = 0.96 × 10-12-12 cm cm-2-2 ss-1-1 (Aharonian (Aharonian et al.et al. 2003) 2003)

• HESS 2003-04:HESS 2003-04:– 211 ± 38 events211 ± 38 events– Energy threshold: 160 GeVEnergy threshold: 160 GeV– F F (>730 GeV) ~ 0.2-0.5 × 10(>730 GeV) ~ 0.2-0.5 × 10-12-12 cm cm-2-2 s s-1-1

– 2005 data analysis underway, >62005 data analysis underway, >6 detection detection

2003-04 HESS Observations2003-04 HESS Observations

HEGRA

HESS

Consistent with point source from nuclear region

Beikicke et al. 2005

2003-04 HESS Observations2003-04 HESS Observations

HEGRA

HESS

Consistent with point source from nuclear region

Evidence for variabilityBeilicke et al. 2005

What is the source of the TeV What is the source of the TeV emission?emission?

• Variability: flux dropped by factor of ~3 between Variability: flux dropped by factor of ~3 between 1998/99 and 2003/041998/99 and 2003/04

• Knot AKnot A– ~80 pc ~80 pc × 55 pc (projected) × 55 pc (projected) t ~ few hundred yearst ~ few hundred years– Variability timescale too shortVariability timescale too short

• HST-1HST-1– Increase in X-ray flux by factor of ~3 in spring of 2004Increase in X-ray flux by factor of ~3 in spring of 2004– Increase by factor of ~50 between 1999 and 2004 Increase by factor of ~50 between 1999 and 2004 (Harris (Harris

et alet al. 2005). 2005)

– No evidence for increase in TeV observationsNo evidence for increase in TeV observations– Lack of coordinated variability Lack of coordinated variability no TeV emission no TeV emission

• Leptonic model for nuclear emission…Leptonic model for nuclear emission…

Georganopoulos, Perlman, & Kazanas 2005

HST-1 Knot Anucleus

Leptonic Model for Nuclear Leptonic Model for Nuclear EmissionEmission

• Homogeneous SSC model fails for HE emissionHomogeneous SSC model fails for HE emission

• Decelerating flow model: Decelerating flow model: – sub-pc decelerationsub-pc deceleration

– from from 00 = 20 to = 20 to = 5 over 3 = 5 over 3 × 10× 101717 cm (0.1 pc) cm (0.1 pc)

– Beaming is frequency-dependentBeaming is frequency-dependent– ““Upstream Compton” scatteringUpstream Compton” scattering

Georganopoulos, Perlman, & Kazanas 2005

Homogeneous SSC

Decelerating flow

Synchrotron Proton Blazar (SPB) Synchrotron Proton Blazar (SPB) ModelModel

• Blob of material moving relativistically along jet axisBlob of material moving relativistically along jet axis• p & ep & e-- accelerated across shocks accelerated across shocks• Power-law distribution of protons in high B (~5-50 Power-law distribution of protons in high B (~5-50

G)G) pp ~ 10 ~ 1010-1110-11 > 10 > 1088 pion production pion production• Gamma-ray production from:Gamma-ray production from:

– Proton-photon interactions:Proton-photon interactions: 00 2 2 ±± ±± + +

– ±± e e±± + + + + ee

– ee±± cascades (2 cascades (2 e e±± 2 2 …) …)– ±± & & ±± synchrotron radiation synchrotron radiation– p synchrotron radiationp synchrotron radiation

• Low-energy hump from eLow-energy hump from e-- synchrotron synchrotronMücke et al. 2003

SPB Model Results for M87SPB Model Results for M87

HBL model LBL model

LBL

HBL

• Input spectra from average SEDsInput spectra from average SEDs• Non-simultaneous dataNon-simultaneous data• HE flux contributors:HE flux contributors:

– p synchrotron (dashed)p synchrotron (dashed)– ±± synchrotron (dashed triple-dot) synchrotron (dashed triple-dot)– 00 cascade (dotted) cascade (dotted)– ±± cascade (dashed-dotted) cascade (dashed-dotted)

Protheroe, Donea, & Reimer 2003Reimer, Protheroe, & Donea 2004

A Site for Cosmic Ray AccelerationA Site for Cosmic Ray Acceleration

• In proton models, ultra-high-energy cosmic ray In proton models, ultra-high-energy cosmic ray protons are produced by:protons are produced by:– Direct acceleration at termination shocks of jetsDirect acceleration at termination shocks of jets– Decay of neutrons produced in jets or accretion shocks Decay of neutrons produced in jets or accretion shocks

outside galaxy: poutside galaxy: pnn

• UHECRs (E > 10UHECRs (E > 102020 eV) attenuated by CMB (GZK cutoff) eV) attenuated by CMB (GZK cutoff)– At 3 At 3 × 10× 102020 eV, MFP ~ 5 Mpc, energy loss distance ~ 20 eV, MFP ~ 5 Mpc, energy loss distance ~ 20

MpcMpc

• UHECR detections claimed with E > UHECR detections claimed with E > 10102020 eV eV

• M87 is close enough to produce themM87 is close enough to produce them• Neutrons from M87 can account for observed flux “if Neutrons from M87 can account for observed flux “if

the extragalactic magnetic field topology is favorable” the extragalactic magnetic field topology is favorable” (Protheroe, Donea, & Reimer 2003)(Protheroe, Donea, & Reimer 2003)

Observational Distinctions between Observational Distinctions between ModelsModels

• Neutrino flux (difficult to detect!)Neutrino flux (difficult to detect!)

• Independent measure of BIndependent measure of B

• More simultaneous observationsMore simultaneous observations

• Larger sample of Larger sample of -ray sources-ray sources– Tighter model constraintsTighter model constraints– GLAST?GLAST?

HBL

LBL