TeV observations of the Galactic Centre & Starburst Galaxies · 2014. 7. 30. · Starburst galaxies...
Transcript of TeV observations of the Galactic Centre & Starburst Galaxies · 2014. 7. 30. · Starburst galaxies...
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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
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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
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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 )
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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
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STACEE
MILAGRO
TIBETARGO-YBJ
PACT
GRAPES
TACTIC
VERITAS
MAGIC
HESS CANGAROO
TIBETMILAGROSTACEE
TACTIC
VHE γ-ray world
HAWC
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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
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Galactic Centre – The HESS View
2 point like sources (G 0,9+0,1 & Sgr A* ?)
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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
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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)
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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?
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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?
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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
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The Central Source
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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
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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)
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Variability
No long-variability detected so far (1995 - 2006)
No periodicity, no QPOs detected
Disfavor emission linked with the central black hole
HESS
Whipple
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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
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SED
HE
SS
. Col
l (20
09)
Variable
non-
vari
able
non-variable
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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)
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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
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Counterparts - Dark Matter Search for halo around the Galactic Center to exclude diffuse emission + central
source
Complicated background
regions
See dedicated talks on friday
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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.
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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)
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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)
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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
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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
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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
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First Events
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Sgr A* with HESS-II
Very Preliminary
Only 3 hours of data
Calibration still in development
Commissioning data
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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
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Thank you
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backup
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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
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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
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Flares @ TeV?
No change in spectrum / flux
See Poster by Karl Kosack
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Counterparts - Dark Matter
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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)