tev observations of the galactic centre & starburst galaxies · 2014. 7. 30. · starburst...

Mathieu de Naurois IAU Symposium 303, Santa Fee, 2013 1

TeV observations of the Galactic TeV observations of the Galactic Centre & Starburst GalaxiesCentre & Starburst Galaxies

Mathieu de NauroisMathieu de NauroisLLR IN2P3-CNRS-Ecole PolytechniqueLLR IN2P3-CNRS-Ecole Polytechnique


Atmospheric Showers

Primary particle

electron positron

Bremsstrahlung

Pair creation

At TeV energies, fluxes are too low to allow space-based detection

Interaction of primary particle with a nucleus in the atmosphere(~ 10 km altitude)

Pair creation & bremsstrahlung processes redistribute the energy to a large number of particles

Hadron induced showers carry nuclear fragments, muons & neutrinos


Scintillatoror water

µ

Hadrondetector

Primary (γ,hadron)

AtmosphericShower

Primary (γ,hadron)

AtmosphericShower

Cherenkov Telescope

CherenkovEmission

TIBET

MILAGRO

HESS, VERITAS, MAGIC, CANGAROOSTACEE, CELESTE, SOLAR II, GRAAL

Observables and experimental techniques

( E > 10 GeV )


γCosmic rayElectromagnetic

shower

Cere

nkov

ligh

t

❑Key parameter : speed (< 10 ns)

muon candidat γhadron

❑Image shape used in discrimination

Atmospheric Cherenkov Telescopes Cherenkov light-pool ~ 120 m

Image the shower on a fast camera (ΔT ~ 2ns)

Large effective area (105 m2) even with modest reflector


STACEE

MILAGRO

TIBETARGO-YBJ

PACT

GRAPES

TACTIC

VERITAS

MAGIC

HESS CANGAROO

TIBETMILAGROSTACEE

TACTIC

VHE γ-ray world

HAWC


The Galactic Center RegionL

aRos

a et

al.

(200

0 )

Quite extreme region: energy density/pressure of ISM ~ 2 orders of magnitude larger than in the disk (~100

eV cm-3) GC giant molecular clouds: unusually dense (~ 104 cm-3), turbulent (velocity

dispersion > 15 km/s) and warm (a few 10 K)

Significant starburst activity (3 orders of magnitude larger than in the disk, ~ 2 M

⊙ yr-1 pc-2


Galactic Centre – The HESS View

2 point like sources (G 0,9+0,1 & Sgr A* ?)


Galactic Centre – VERITAS

Observations at large zenith angle

→ High threshold (2.5 TeV)

→ 18 σ in 46 h

Hint for diffuse emission correlated with that of HESS

Hard spectrum compatible with HESS


CS Lines (dense clouds)

Galactic Centre – Diffuse Emission

After removal of two point like sources: Diffuse emission associated with

molecular clouds Interaction of cosmic rays with ISM?

pp → π0 → γγ ?

CS contours from Tsuboi et al. (1999)


Diffuse emission spectrum

HESS Collaboration, 2005

Interaction of diffuse CR with target material cannot account for observed emission

→ Need local sources of high energy CR

Photon index similar to that of central source

→ Diffusion of CR's from the central source?

→ Or similar engines?


Longitude profile

Correlation with molecular clouds is not perfect: No emission at longitudes > 1°

Effect of propagation from central source? Injection started ~ 104 years ago

Or sources of CR's inside the clouds Link with starburst activity?


SFR regions: Sgr B2, Sgr B1, Sgr C (Kendrew 2012,2013, Law & Ysef-Zadeh, 2004,...) Immediate vicinity of Sgr A* (Yusef-Zadeh et al, 2013) (~ pc scale)

Correlate pretty well with TeV data. See talks on Friday (Fermi Bubbles)

SFR regions & TeV emission


The Central Source


Precision pointing

Dedicated observation with guiding CCD on stars

Best fit position coincident with Sgr A* (and PWN 359.95)

9'' error circle on position (68% containment, including systematics)

Sgr A East discarded

VLA 90cm image

H.E.S.S. Coll. (2010)

G359.95-0.04

Radio centroid


Intrinsic Spectrum Previously published spectrum was

contaminated by diffuse emission(20% contamination)

Cutoff @ 7 TeV, index ~ 2.1

Supports PWN scenario

Diffuse (0.1°-0.4°)

“Intrinsic” central source(< 0,1 ° core) Viana, Moulin, HESS Collab (ICRC 2013)


Variability

No long-variability detected so far (1995 - 2006)

No periodicity, no QPOs detected

Disfavor emission linked with the central black hole

HESS

Whipple


Flares @ TeV?

Extensive monitoring campaign (1 Ms XVP program, 18 instruments)

Significant coverage in 2012

TeV data during 3 flares + historical 2006 flare

No change in spectrum / flux

See Poster by Karl Kosack

Blind search for flares (hours → 100 days) also unsuccessful (HESS Collab, 2008)

Chandra LightcurveHESS

Flare


SED

HE

SS

. Col

l (20

09)

Variable

non-

vari

able

non-variable


HESS J1745-290: a pulsar wind nebula?

Plausible candidate

Dense radiation field→ IC emission dominant

But cannot account for GeV emission

Aharonian + Hinton (2007)

10''

Sgr A*

G359.95

Wang et al. (2005)


Protons accelerated by central BH?

GeV emission too high in simple IC model, contradicts the PWN scenario

Model with energy dependent diffusion of protons from central BH Need flare + steady state injection since 10 years⁴

H.E.S.S.

Chernyakova et al. (2011)

Fermi-LATDiffusive regime, protons are confinedVariability ~ 10 000 years

Almost balistic, fast escapeVariability ~ 10 yr


Counterparts - Dark Matter Search for halo around the Galactic Center to exclude diffuse emission + central

source

Complicated background

regions

See dedicated talks on friday


Testing the SFR hypothesis?

Normal Galaxies:

SFR Rate ~ 1 M⊙ yr-1 kpc-2

B ~ 10 μG

Urad

~ 1 eV/cm-3

n ~ 1 cm-3

Starburst Galaxies:

SFR Rate ~ 100 M⊙ yr-1 kpc⁻2

B ~ 200 μG

Urad

~ 250 eV/cm-3

n ~ 500 cm-3

SFR can be triggered by instabilities or galaxy mergers.


High Energy Star-forming regions

Fermi detections: LMC SMC M82 (Seyfert) NGC 253 (Seyfert) NGC 4945 NGC 1068 M31

TeV detection M82 (Veritas) NGC 253 (HESS)


Starburst Galaxies - NGC 253 Point-like at the HESS resolution

Consistent with nucleus

Diffuse emission from whole galaxy excluded

Hard spectrum (Γ = 2,14 ± 0,18)

TeV Luminosity >> Gal Center( 2 1038 erg/s vs ~ 1035 erg/s)


M82

Core starburst region: SF rate ~10x Milky Way SN rate ~0.1/yr CR density ~100x Milky Way Gas density ~150 cm-3

TeV emission: Faint (0,9% of Crab Nebula) Spectral Index 2,6 ± 0,6 Even more luminous:

luminosity ~ 2 1039 erg/s


Starburst galaxies vs GC

Much Higher SFR

Similar spectra (2,2 ...), but much more luminous in TeV (10³ to 10 )⁴ Higher B fields, higher CR densities, ...

Point-like emission for HESS, VERITAS, Fermi. < Galaxy size Starburst region is ~ 200 pc

Starburst could be quasi calorimetric, Sgr A is NOT Explain low TeV luminosity of milky way

Bri

an L

acki

Coo

per

et a

l


H.E.S.S. II – a new Giant

New huge telescope 600 m2 mirror 3° FOV camera of 2048 pixels Improved electronics

(~300 Hz → 3 Khz readout)

Physics: Threshold down to ~ 20 GeV Improved resolution &

sensitivity when used with HESS-I

Inaugurated Sept. 2012

Taking regular data since ~ January 2013


First Events


Sgr A* with HESS-II

Very Preliminary

Only 3 hours of data

Calibration still in development

Commissioning data


Conclusions

Deep TeV observation of Galactic Centre reveals point like source and extended diffuse emission

Better angular resolution is needed

HESS-II is starting: On-going extensive observation campaign (G2 gas cloud infall) with HESS-II Will respond to any TOO Threshold currently ~ 50 GeV, possibly lower in the future

→ Very well suited to the study of the putative 130 line But a full understanding of our systematics will take some time

Starburst galaxies are TeV emitters, at the limit of current instruments despite larger luminosities


Thank you


backup


High Energy Stereoscopic System International consortium

Site: 23°16'' S, 16°30'' E, 1800 m asl, 100 km from Windhoek (Namibia) Good sky transparency, medium altitude & dry weather conditions Southern hemisphere, direct view on the galactic centre

MPI Kernphysik, HeidelbergHumboldt Univ. BerlinRuhr-Univ. BochumUniv. HamburgLandessternwarte HeidelbergEcole Polytechnique, PalaiseauAPC ParisLPNHE Univ. Paris VI-VIICEA SaclayCESR ToulouseLPTA MontpellierLAOG GrenobleLAPP AnecyCENBG BordeauxObservatoire de ParisDurham Univ.Dublin Inst. for Adv. StudiesCharles Univ., PragYerewan Physics Inst.North-West Univ., PotchefstroomUniv. of Namibia, WindhoekDESY, ZeuthenLinne University, SwedenLeicester University, UK


Relation with Star Formation

Galactic Center CMZ – Inner 100 pc

Actually γ-ray dim per unit SFR (Crocker et al.) 10% of what would be expected from FIR luminosity

Claim (Lacki, Crocker) GC star-formation drives a super-wind CR are advected away from Galactic

Centre region and do not penetrate in densest molecular clouds

Terminal shock far away: Fermi Bubbles Steady star formation rate since ~ Gyr.

Brian Lacki


Flares @ TeV?

No change in spectrum / flux

See Poster by Karl Kosack


Counterparts - Dark Matter


Dark Matter Limits for χχ→qq

Currently best limits for masses in the TeV regime, close to decoupling limit

See talks on friday

H.E.S.S. Coll. (2011)

tev observations of the galactic centre & starburst galaxies · 2014. 7. 30. · starburst...

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