The Milky Way in VHE γ-rays. Christopher van Eldik Max-Planck-Institut für Kernphysik Heidelberg

The Milky Way in VHE γ-rays Christopher van Eldik Max-Planck-Institut für Kernphysik Heidelberg

Discovery of Cosmic Radiation - ++ + - + - Victor Hess 1912 + conductivity of air increases with elevation

Spectrum power-law: F ~ E-2.7 no characteristic energy non-thermal radiation energy density 1 ev/cm3 Composition Protons 87% Helium 12% heavier nuclei 1% few electrons & gammas almost solar abundance Propagation stay 107 years in Galaxy have to sustain 3 1040 erg/s energy-dependent escape source spectra ~ E-2

Supernova Remnants... accelerators of Galactic Cosmic Rays? Energetics: ejected mass 10 solar masses velocity 5 108 cm/s total kinetic energy: E = 3 1043 J = 3 1050 erg 1 Galactic SN in 30 years total sustained flux: F = 3 1034 W = 3 1041 erg/s need 10% efficiency to sustain cosmic ray pool Astrophysics: blast waves shock the interstellar medium stochastic particle acceleration at shock front Cas A (Chandra)

Supernova Remnants... accelerators of Galactic Cosmic Rays?

... accelerators of Galactic Cosmic Rays? ns o t o Pr s? n o r ct e l e or RXJ 1713-3946, H.E.S.S. Collaboration Supernova Remnants...we see SNRs in VHE γ-rays!

Windows for Astronomy Energy Radio X-ray Infrared Soft Gamma VHE Gamma B. Giebels Optical

Detection Principle Gamma Ray Atmosphere Particle Shower

Detection Principle Gamma Ray Atmosphere 10 γ-rays / m² yr from the Crab nebula Particle Shower but > 50.000 m² detection area flux of > 1 γ-ray / min Cherenkov Light ~ 120 m

Detection Principle Gamma Ray Atmosphere Particle Shower Camera Cherenkov Light ~ 120 m

Detection Principle Atmosphere Particle Shower Camera Cherenkov Light ~ 120 m image intensity γ-ray energy Image form background reduction Image orientation γ-ray direction

Detection Principle Atmosphere Particle Shower Camera Cherenkov Light ~ 120 m stereo reconstruction improved direction background reduction low energy threshold

The Catalogue of VHE Sources Jim Hinton ICRC 2007

Cherenkov Telescopes World Map VERITAS 10/2006 MAGIC 08/2004 Cangaroo III 03/2004 H.E.S.S. 12/2003

The High Energy Stereoscopic System Khomas Highlands, Namibia

H.E.S.S. Details 4 telescopes 120 m spacing 107 m2 mirror surface each energy threshold ~100 GeV energy resolution < 15 % angular resolution ~0.1 pointing accuracy < 20'' sensitivity (5σ): 5% of Crab in 1 h 1% of Crab in 25 h HEGRA: 5% of Crab in 100 h 1000 h of observations / year during moonless nights MPI Kernphysik, Heidelberg Humboldt-Univ. zu Berlin Ruhr-Univ. Bochum Univ. Erlangen-Nürnberg Univ. Hamburg LSW Heidelberg Univ. Tübingen Ecole Polytechnique, Palaiseau APC Paris Univ. Paris VI-VII Paris Observatory, Meudon LAPP Annecy LAOG Grenoble LPTA Montpellier CEA Saclay CESR Toulouse Durham Univ. Univ. Leeds Dublin Inst. for Adv. Studies Polish Academy of Sciences, Warsaw Jagiellonian Univ., Cracow Charles Univ., Prague Yerewan Physics Inst. Univ. Adelaide North-West Univ., Potchefstroom Univ. of Namibia, Windhoek

The H.E.S.S. Cameras 960 pixels (0.16 per pixel) 5 field of view sensitive photomultipliers fast readout and trigger electronics

need short exposures......because Cherenkov flashes are short-lived! 1/10000 (100 µs) 1/100000 (10 µs) 1/1000000 (1 µs) 1/10000000 (100 ns) 1/100000000 (10 ns)

H.E.S.S. Trigger 4x single telescope pixel threshold trigger typical rates 500-800 Hz multiplicity-2 system trigger typical system rate 150-250 Hz system trigger provides efficient background reduction reduced energy threshold for a given dead time O(100 GeV) energy threshold! Funk et al. (2005)

Background Modeling - Ring Background - Off-Region: ring around On-Region Off-Events subtracted from On-Events - proper area factor - acceptance correction insensitive to linear gradients in background applicable all over the field of view (Sky Maps, morphology) not very well suited for spectra due to acceptance correction

Background Modeling - Reflected Region Background - Off-Region: ring of circular regions around observation position (same distance as On-Region) Observation position must be outside the On-Region no acceptance correction needed assuming radially symmetric acceptance insensitive to systematics of acceptance determination very well suited for spectra

H.E.S.S. Galactic Plane Scan -

H.E.S.S. Galactic Plane Scan including re-observations

Pulsar Wind Nebulae Classification from Aharonian, Buckley, Kifune and Sinnis (2008) H.E.S.S. Galactic Plane Scan including re-observations

Supernova Remnants Classification from Aharonian, Buckley, Kifune and Sinnis (2008) H.E.S.S. Galactic Plane Scan including re-observations

Binary Systems Classification from Aharonian, Buckley, Kifune and Sinnis (2008) H.E.S.S. Galactic Plane Scan including re-observations

Galactic Centre Classification from Aharonian, Buckley, Kifune and Sinnis (2008) H.E.S.S. Galactic Plane Scan including re-observations

Unidentified Sources Classification from Aharonian, Buckley, Kifune and Sinnis (2008) H.E.S.S. Galactic Plane Scan including re-observations

Source Population longitude distribution PhD S. Hoppe (2008) latitude distribution narrow band along Galactic Plane slightly offset following matter distribution

Source Population photon index PhD S. Hoppe (2008) flux distribution many sources close to detection limit gamma flux vs energy well described by power-laws narrow range of photon indexes common acceleration mechanism?

Scale-free Spectra d N E =ae energy gain E de dn = b N dt particle loss independent of E dn bn = de ae b / a N E =N0 E

Acceleration in Strong Shocks downstream 2 v 2 conservation laws for particle transport through the shock front upstream 1 v 1 = 2 v 2 Fmass v 1 1 2 2 P1 1 v 1 =P2 2 v 2 Fm o m 1 2 5 P1 1 2 5 P2 v 1 = v2 E 2 2 1 2 2 2 limit of strong shock (vs >> cs) ideal + monoatomic gas 1 v 2 = v 1 2 =4 1 4

Acceleration in Strong Shocks downstream v 2 =3 /4 v s upstream v 1 =0 vs assume isotropisation on both sides of the shock particles that cross shock from upstream collide head-on with downstream medium energy gain: E v 2 = cos E c

Acceleration in Strong Shocks downstream v 2 =0 upstream v 1 =3 /4 v s 1 /4 v s assume isotropisation on both sides of the shock particles that cross shock from upstream collide head-on with downstream medium energy gain: E v 2 = cos E c same argument holds shock crossing from downstream average over all pitch angles E 4 V vs = = E 3 c c

Acceleration in Strong Shocks after k cycles: vs E=E0, =1 c vs k N=N0 P, P=1 c k energy spectrum vs vs c c vs v s l n =l n 1 c c l np=l n 1 lnp 1 l n dn E de 1 1 =E P: probability to stay in accelerator 2 =E unique spectral index in right range modifications for weak shocks, relativistic shocks, feedback, synchrotron losses...

Radiation processes - electrons energy flux E2 F(E) e e B γ γ Inverse Compton radiation e B X radio infrared e γ Inverse Compton upscattering Synchrotron radiation visible X-ray VHE Gamma

Radiation processes - protons energy flux E2 F(E) π0 p gas Inelastic proton gas collisions radio infrared visible X-ray Inverse Compton VHE upscattering Gamma

Supernova Remnants

SNR RX J1713.7-3946 ASCA X-ray discovered 1996 in ROSAT all-sky survey 1 diameter distance: probably 1 kpc age: ~1000 years pure non-thermal X-ray continuum emission almost no radio emission possibly interacting with molecular clouds enhanced target density for pp collisions

SNR RX J1713.7-3946 H.E.S.S. 40 hours Aharonian et al. 2006 ASCA X-ray first resolved VHE image of an SNR excellent correlation with X-ray morphology common origin of X-rays and γ-rays?

SNR RX J1713.7-3946... energy spectrum H.E.S.S. 67 hours 2 E Aharonian et al. 2007 proof of particle acceleration to at least 100 TeV electron scenario (Eγ > 30 TeV) Ee 2 0 E TeV 1 0 0 TeV 3.3 E proton scenario (Eγ > 30 TeV) Ep E /0.15 2 0 0 TeV approaching CR knee energies Is RX J1713 an accelerator of cosmic rays?

SNR RX J1713.7-3946... leptonic scenario E 3 e E 2 e...can in principle explain VHE emission by electrons, but...

Large Magnetic Fields in RX J1713?

Large Magnetic Fields in RX J1713? fast synchrotron cooling large magnetic field O(100 μg) less electrons needed to sustain X-ray flux not enough to power VHE flux Uchiyama et al. 2007 Chandra X-rays

SNR RX J1713.7-3946... hadronic scenario E 3 e non-linear shock modification Berezhko + Völk (2006) E 2 e large magnetic field O(120 μg) IC component insignificant

Old SNRs & cloud interaction W28 @ 2-3 kpc age: 35-150 kyr electrons hard to accelerate molecular clouds as target for cosmic rays W28 Radio/IR image Brogan et al. 2006 20/90 cm VLA MSX 8 micron

Old SNRs & cloud interaction W28 @ 2-3 kpc age: 35-150 kyr electrons hard to accelerate molecular clouds as target for cosmic rays Aharonian et al. 2008 W28 Radio/IR image Brogan et al. 2006 20/90 cm VLA MSX 8 micron

Old SNRs & cloud interaction W28 @ 2-3 kpc age: 35-150 kyr electrons hard to accelerate molecular clouds as target for cosmic rays Aharonian et al. 2008 NANTEN CO 10-20 km/s Radio/IR image Brogan et al. 2006 20/90 cm VLA MSX 8 micron

Pulsar Wind Nebulae

Pulsars Rapidly rotating magnetised neutron stars ms to s period pulsed emission in radio/optical electron acceleration due to rotating magnetic field pulsar winds termination shock in the ISM pulsar wind nebula shock acceleration

Crab Pulsar HST/Chandra pulsar inside the Crab Nebula (SN 1054) distance 1.9 kpc pulsar diameter 30 km discovered in radio 1949 later seen in X-rays and gamma-rays P=3 3 m s

Typical VHE Pulsar Wind Nebulae found in vicinity of brightest pulsars need O(1%) of spin-down power to power VHE source VHE emission is extended O(10 pc) emission often offset from pulsar kink during supernova? inhomogeneous medium?

HESS J1825-137 synchrotron cooling of electrons H.E.S.S. H.E.S.S. PSR J1826-1334 > 2.5 TeV 1 1.5 TeV < 1 TeV Aharonian et al (2006)

Binary Systems H.E.S.S. LS 5039 - a microquasar? massive object in 3.9 day orbit around luminous star radio emission from bipolar jet LS 5039

LS 5039...the first periodic VHE signal Aharonian et al (2006) H.E.S.S. Optical: 3.9060 days VHE: 3.908 days

LS 5039...the first periodic VHE signal folded using optical period data repeated for 2 cycles Aharonian et al (2006) at least partially an absorption process, but...

LS 5039...spectral variations 1. 8 E Aharonian et al (2006) E 2.5 absorption predicted mainly for low energies different acceleration due to dynamic change of environment

The Centre of the Milky Way

The Centre of the Milky Way H.E.S.S. (55 hours) H.E.S.S. J1745-290 point-like < 1.2' (95% CL) 38 sigma (55h) G 0.9+0.1 Aharonian et al. (2006)

The Centre of the Milky Way H.E.S.S. 2004 (55 hours) H.E.S.S. J1745-290 point-like < 1.2' (95% CL) 38 sigma (55h) G 0.9+0.1 Diffuse emission 15 sigma (55h) Aharonian et al. (2006)

Diffuse Emission... enhanced cosmic ray density Not just passive illumination - enhanced flux for > 1 TeV - photon index ~2.3 Similar index as HESS 1745-290 - everywhere in the region Many sources of electrons? - strong cooling: expect compact sources - should be strong X-ray emitters but not observed

Diffuse Emission... molecular cloud association Lack of γ-rays for l > 1 Injection of protons at GC Assume k = ~3 kpc2 Myr-1 for TeV protons injection 104 years ago Fits age of Sgr A East

G0.9+0.1 HESS J1745-290 Sgr A* VLA 300'' SNR Sgr A East? Chandra SMBH Sgr A* or DM annihilation? 10'' PWN G359.95-0.04?

Position of HESS J1745-290... Sgr A East effectively ruled out Best Fit HESS J1745-290 (Aharonian et al. 2004) Best Fit HESS J1745-290 (van Eldik et al. 2007) - preliminary- Sgr A East Sgr A* VLA 90cm image van Eldik et al., Proc. ICRC 2007 0.04 deg

HESS J1745-290... a Pulsar Wind Nebula? Best Fit HESS J1745-290 Best Fit HESS J1745-290 - preliminary - Sgr A* 0.01 deg van Eldik et al., Proc. ICRC 2007 G 395.95-0.04

HESS J1745-290... not much room for Dark Matter Aharonian et al (2006) NFW Dark Matter: r d N F v de 2 dl m2 DM 1 H.E.S.S. PSF radial source profile fits NFW DM at first glance, but...

HESS J1745-290... not much room for Dark Matter Aharonian et al (2006) diffuse emission subtracted d N F v de 2 dl m2 DM NFW Dark Matter: r 1 H.E.S.S. PSF radial source profile fits NFW DM at first glance, but...... point-like after subtraction of diffuse emission DM density stronger peaked than r-1.2 (99% CL)

HESS J1745-290... not much room for Dark Matter energy spectrum: straight powerlaw exponential cutoff: EC > 9 TeV @ 95% CL curved annihilation spectra + uncomfortably large masses in MSSM 10% DM contribution not ruled out derived limits on <σv> not very constraining neutralino (14 TeV) (5TeV) (10TeV) Aharonian et al. 2006

Evolutions MAGIC-II - 2nd 17 m telescope almost finished - first stereoscopy in the ~50 GeV region - substantial sensitivity improvement expected

Evolutions MAGIC-II - 2nd 17 m telescope almost finished - first stereoscopy in the ~50 GeV region - substantial sensitivity improvement expected HESS-II - a 28 m telescope in the centre of HESS phase 1 - push down to ~20 GeV - completion 2009 gain experience with future arrays ﾴ

The Future: CTA Concept an IACT array observatory an order of magnitude more sensitive than HESS: 1 mcrab wide energy coverage: O(10) GeV - O(100) TeV possibly sites in the south and north Consortium largely European HESS + MAGIC + many others 15 countries currently involved Currently in design phase Prototype construction in 2-3 years High priority in European road maps: Jim Hinton (Gamma 2008)

Angular Resolution Jim Hinton (Gamma 2008) German Hermann 6 deg0.2 FoV angular resolution: deg (> (~ 50 GeV) Expecting / hoping for : O(1000) sources (galactic + extragalactic)

Angular Resolution Jim Hinton (Gamma 2008) German Hermann 6 deg0.05 FoV angular resolution: 0.2 deg deg(~(>50 1 TeV) GeV) Expecting / hoping for : O(1000) sources (galactic + extragalactic)

Summary VHE γ-ray instruments reach critical sensitivity to do real astronomy Close to having solved the problem of cosmic ray origin Expect to see 10x more sources with CTA VHE γ-ray astronomy enters a golden era

A few Ads... C. van Eldik W. Hofmann Physik Journal 01/2008 or visit www.hess-experiment.eu www.cta-observatory.org