b. degrange icatpp, october 2010 1 recent results from h.e.s.s. bernard degrange, for the h.e.s.s....
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B. Degrange ICATPP, October 2010 1
Recent results from H.E.S.S.
Bernard Degrange, for the H.E.S.S. collaboration LLR, Ecole polytechnique & CNRS/IN2P3
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Since 2003, the H.E.S.S. array has been unveiling the southern TeV gamma-ray sky
Stereoscopic array of 4 atmospheric Cherenkov telescopes
Khomas Highlands (Namibia, 23°S, 15°E, 1800 m a.s.l.)
Large mirrors (13 m diameter dishes)
Fine grain cameras (960 pixels/camera), fast trigger electronics located in the camera, 5° field of view well adapted to extended sources
Energy threshold : from 120 GeV (zenith) to 700 GeV at 60° from zenith
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H.E.S.S. sensitiviy at zenith : 1% of the flux of the Crab nebula is detected in 25 hours with a 5σ significance for a point-like source.
Angular resolution Δθ ≈ 0.07° , always < 0.1°
Gamma-ray sources can be located with a precision of 1 arc min. or better
Advanced reconstruction methods have improved sensitivity (higher background rejection) and angular resolution
The present H.E.S.S. catalogue includes > 60 sources of TeV gamma-rays
M. de Naurois & L. Rolland
Astropart. Phys. 2009
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Galactic sources : new shell-type supernova remnants
Normal nearby galaxies : LMC and NGC 253
Active Galactic Nuclei : radio-galaxies and blazars
Towards HESS phase II and conclusion
Outline
A few recent H.E.S.S. results
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Inner Galaxy (2004) + extension (2005-2008) from ℓ = -85° (or 275°) to ℓ = +60° and |b|<3°
Survey is complete for fluxes > 0.09 Crab (+ deeper observations)Low diffuse flux (≠ Fermi/AGILE) → Individual sources appear clearlyMost of the revealed sources are mildly extended (D > 3 ' to 4 ')
G.C.
1. Galactic sources: new shell-type supernova remnants
Sun
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1.1 The remnant of a historical supernova : SN 1006
The explosion took place slightly above the Galactic Plane in a rather uniform medium and magnetic field, as attested by the morphology in two polar caps observed in X-rays (XMM-Newton, Rothenflug et al. 2004)
The morphology likely reflects the NE-SW orientation of the average magnetic field, suggesting that parallel shocks (i.e. B // shock normal) lead to efficient acceleration (Völk et al. 2003).
However, the ambient density of interstellar matter is low (≈ 0.05 cm-3) (Acero et al. 2007) and 130 hours of observations were necessary for H.E.S.S. to firmly detect the source A&A 516 (2010)A62
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H.E.S.S. results on SN 1006 : morphologyA&A 516 (2010)A62
White contours: constant X-ray intensity derived from XMM-Newton flux map and smoothed to the
H.E.S.S. point-spread function, enclosing 80%,60%,40%,20% of the X-ray emission
Radial profile (NE-SW)
Azimuthal profile
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Very low fluxes (< 1% Crab nebula) NE Φ(>1TeV) = (0.233 ± 0.043 ± 0.047) × 10-12 cm-2 s-1
SW Φ(>1TeV) = (0.155 ± 0.037 ± 0.031) × 10-12 cm-2 s-1
Power-law spectra from both lobes with similar indicesΓ = 2.35 ± 0.14 ± 0.2Γ = 2.29 ± 0.18 ± 0.2
H.E.S.S. results on SN 1006 : energy spectrum A&A 516 (2010)A62
E2 dΦ/dE dΦ/dE
Mixed leptonic/hadronic scenario
• Leptonic scenario: difficulty to reproduce the H.E.S.S spectrum.
• Hadronic scenario: too much energy in the protons to account for the H.E.S.S spectrum.
• Mixed scenario: satisfactory
But no scenario can be really excluded
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1.2 A new shell-type supernova remnant: the formerly unidentified source HESS J1731-347
Discovered in the H.E.S.S. galactic plane survey as an unidentified source (Aharonian et al. 2008)Tian et al. 2008 find a faint shell-like structure in radio (ATCA & Parkes) and in X-rays (ROSAT) coincident with the H.E.S.S. source (G353.6-0.7) 0.4° diameter, age estimated to 27 kyrDeeper X-ray observations (Acero et al. ICRC 2009) with Suzaku, XMM and Chandra → interaction with a molecular cloud in foreground → distance > 3.2 kpcH.E.S.S. deeper observations (60 hr) detect a new shell (22 σ) in very-high-energy gamma-rays; flux ~ 9% Crab
Aharonian et al. 2008
Tian et al. 2008
F. Acero et al.,
COSPAR 2010
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HESS J1731-347 : a 5th shell detected at very high energies, the first whose discovery was based on
gamma-ray observations
The radial profile clearly suggests a shell (filled sphere excluded at 3.9σ)Distance estimated to be > 3.2 kpc :
X-ray show a strong gradient (SE-NW) of absorption → molecular cloud in foreground12CO survey data (CfA) can explain the absorption column density obtained from X-rays by a distance of 3.2 kpc
At such a distance, the luminosity of the source (> 1.07 × 1034 erg s-1) is greater than that of RX J1713-3946Source B could be due to cosmic ray interactions in a nearby molecular cloud.
Acero et al. COSPAR 2010
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2. Nearby normal galaxies The Large Magellanic Cloud
(D=50kpc) The starburst galaxy NGC 253
(2.6 Mpc<D<3.9 Mpc)
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2.1 A young pulsar-wind nebula, N157B, in the Large
Magellanic Cloud (50 kpc)
47 hours of good-quality data revealed the young (≈5000 years) pulsar-wind nebula N157B (15 σ) at the border of the star-forming region 30 Doradus
The source is point-like and well separated from SN1987A.
This nebula, observed in radio and X-rays (Chandra), is powered by pulsar PSR J0537-6910, which has the highest spin-down luminosity 4.8 × 1038 erg s-1
Gamma-ray energy flux (1-10 TeV) = 1.4 × 10-12 erg cm-2 s-1. from N157B ~2% Crab
Upper limit on the energy flux from SN1987A (>1 TeV) : < 5 × 10-13 erg cm-2 s-1 (99%CL) is a factor of ~2 above the values predicted by Berezhko & Ksenofontov 2006.
N. Komin et al. COSPAR 2010
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Bubbles created by many stellar explosions and stellar winds may coalesce, thus creating a super-bubble whose shock wave can accelerate particles over a longer period than that of an isolated supernova → particle acceleration up to > PeV ?
Superbubbles are difficult to observe in the Milky Way, due to their wide angular extension.
Solution : observe a nearby galaxy with a boosted formation rate of massive stars → increased rate of supernovae: starburst galaxy.
H.E.S.S. detected NGC 253: 5.2 σ in 119h of observation. Flux (>220 GeV) ≈ 0.3% that of the Crab nebula is concentrated in the nucleus
Density of protons (E>1.3 TeV) in the 100 central parsecs = 1400 × that in the central region of the Milky Way.
2.2 The starburst galaxy NGC 253
Science 326 (2009) 1080
2.6 Mpc<D<3.9 Mpc
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To date, H.E.S.S. has detected 15 AGN All these sources are radio-loud AGN (~5% of all AGN) ; the radio emision is due to the relativistic jets ejected from the central region.All AGN from the H.E.S.S. catalogue but 2 belong to the “blazar” class, whose characteristics result from an observation effect: jets are emitted at small angle with respect to the line of sight.The 2 exceptions are radio-galaxies:
M87 (HEGRA, H.E.S.S., MAGIC, VERITAS) variability on day-scale confirmed → size of emission region <0.15 pc Flux ≈ 1% to 5% that of the Crab nebula → flare 10% Crab in 2008Centaurus A (H.E.S.S.) : Flux ≈ 0.8% that of the Crab nebula
3. Active Galactic Nuclei (AGN)
Courtesy of C.M. Urry and P. Padovani
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Two radio-galaxies: emission region compatible with radio core
GalaxyDistance
(Mpc)
Angle (jet-l.o.s.)
Black hole mass (solar masses)
Photon index Detection
M87 16.7 30° (6.0±0.5) × 109 2.62±0.35 (2004) 2.22±0.15 (2005)
HEGRA,HESS, VERITAS,
MAGIC
Centaurus A 3.7 15°-80° (5.5±3) × 107 2.7±0.5±0.2 HESS
M87 Multi-wavelength campaign 2008 H.E.S.S./MAGIC//VERITAS + VLBA (43 GHz)
+Chandra: Science 325 (2009) 444 emission likely due to core
innermost resolved knot HST1 in jet excluded (low state of HST1 in X-rays during largest
γ-ray flare in Feb. 2008 (10% Crab))
Chandra
Cen A: 5 σ in 115 h of observation Flux (E>250GeV) ~ 0.8% Crab
Cen A: ApJ 695(2009)L40
E2 dΦ/dE
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Blazars are characterized by a two-bump broad band spectrum: e.g. Optical (ATOM)-X-ray (Swift, RXTE)-Fermi LAT-H.E.S.S.
on the blazar PKS 2155-304 (z=0.117) in a low state in 2008
Blazars detected by Cherenkov arrays are mostly « High-frequency-peaked BL Lac objects» or HBLSimultaneous multi-wavelength campaign on PKS2155-304 in 2008 reveals a typical HBL spectrum:
synchrotron bump peaks in UV/X,γ-ray bump peaks in the 100 GeV range
August 25 to September 6, 2008
ApJ 696 (2009) L150
E2 dΦ/dE
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GalaxyRedshift
zBlazar class
Flux (%Crab)
Photon index Γ
Variability
Mkn 421 0.030 HBL ~ 300 2.1±0.1 < hour
AP Librae 0.049 LBL ~ 2
PKS 0548-322 0.069 HBL 1.4 2.86±0.34
PKS 2005-389 0.071 HBL 2.8 4.0±0.4 ~ month
RGB J0152+017 0.080 HBL 2.0 2.95±0.36 ~ month
PKS 2155-304 0.116 HBL 15 to 1500 3.53±0.06 ~ 3 min.
1ES 0229+200 0.139 HBL 1.8 2.50±0.19
H 2356-309 0.165 HBL 2.3 3.09±0.24 ~ month
1ES 1101-232 0.186 HBL 2.3 2.94±0.20 ~ year
1ES 0347-121 0.188 HBL 2.0 3.10±0.23 ~ year
PKS 0447-439 0.205 HBL 1.0 4.47±0.37
1ES 0414+009 0.287 HBL 1.0 3.53±0.39
PG 1553+113 >0.25 HBL 3.4 4.5±0.3
Blazars detected
by H.E.S.S., as of 2010
Recent detections
are in boldface
characters
Blazars not
detected by Fermi-LAT are in purple
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Blazar variability: the case of PKS 2155-304
PKS 2155-304: most of the time, flux ~ 15% Crab (“quiescent” regime)In July 2006, flaring regime during 4 nights with extreme (minute scale) variability ApJ 664 (2007) L71
1st night MJD53944
Light curve (monthly averages) 2005-2007arXiv:1005.3702
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PKS 2155-304 variability (arXiv:1005.3702)
Flux distribution (2005-2007) excluding the flaring period (left histogram) is well reproduced by a lognormal law.Flux distribution including the flaring period (right histogram) can be described by the superposition of two lognormal lawsLognormal behaviour in the flaring period confirmed by strong correlations (ρ > 0.80) between excess r.m.s. of flux in small time bins (measurement errors subtracted) and flux.
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Strong correlation between flux fluctuations (« excess flux r.m.s. ») and mean flux during the flaring period The flaring state can be described by a stationary random lognormal process → suggests a multiplicative process ...... similar to what is observed in X-rays for X-ray binaries and for Seyfert galaxies. A disk-jet connection ?There is no evidence of cutoff at the highest frequencies (minute.-1) allowed by the sensitivity of H.E.S.S. (doubling timescales on the order of a few minutes)The Fourier spectrum between 10-4 and 10-2 Hz in the flaring regime is well described by a power law of frequency P(ν) = K/να with α = 2.06±0.21 i.e. a red noise spectrum
PKS 2155-304 variability is well described as a red noise (arXiv:1005.3702, A&A accepted)
20 min. light curve segments
80 min. segments
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4. Prospects: towards H.E.S.S. II
H.E.S.S. II: a very large telescope (28 m diameter) in the centre of the present array (2012) + camera comprising 2048 pixels30 GeV threshold with the very large telescope80 GeV threshold with the very large telescope + one of the other 4Sensitivity × 2 for E>200 GeV Take advantage of the complementarity of satellites and ground-based instruments for observing variable sources (AGN) or transient events (gamma-ray bursts)
Satellites (large field of view) give the alert in case of a flare Ground-based detectors (large effective area) can measure the light curve with a high temporal resolution e.g. minute-sale variations.
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Backup slides
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Galactic sources: the identification problem
Supernova Remnants (SNR)Shell-type: γ-ray morphology coincide with radio/X-ray shell:
Shell-type + Molecular cloud: γ-ray emission from contact region between shell and molecular cloud + 1720 MHz OH masers (shock wave in cloud)
Pulsar Wind Nebula (PWN): presence of a pulsar surrounded by an X-ray nebula, γ-ray nebula may be significantly more extended than X-ray nebula
Binary systems: presently 2 High-Mass X-ray Binaries: PSR 1259-63, LS 5039 and one likely candidate HESS J0632+057
Point-like
Modulated emission
Unidentified sourcesSeveral plausible associations (i.e. Galactic Centre)
Stellar winds in star formation regions (OB associations)
No counterparts at other wavelengths: ancient PWN ?
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Resolved shell-type supernova remnants
Supernova remnants (SNR’s) are suspected to be the main accelerators of galactic cosmic-rays up to the knee
Diffusive shock acceleration
10% of the mechanical energy of supernovae can account for the injection of CR’s in the Galaxy.
Thin filaments seen in non-thermal (synchrotron) X-rays prove that electrons are accelerated up to 100 TeV and indicate the shock position
H.E.S.S. provided resolved images of several young shell-type SNR’s
RX J1713-3946 RX J0852.0-4622 RCW 86
A&A 464 (2007) 235 ApJ 661 (2007) 236 ApJ 692 (2009) 1500
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Supernova remnants interacting with molecular clouds :
the case of W28 A&A 481 (2008) 401
An old (> 35 kyr) supernova remnantRadio shell (white circle)Only the part of the shell coincident with a molecular cloud is detected in gamma-rays :
Only low-energy electrons (emitting in the radio range) remain in most parts of the shellHigh-energy particles are concentrated in the molecular cloud
The interaction between the remnant and the cloud is traced by 1720 MHz OH masers Hadronic scenario is likely : H.E.S.S. and Fermi (arXiv:1005.447) spectra in continuityOverdensity factors of cosmic rays within the clouds (with respect to average density in the Galaxy) of the order on 10 to 20
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Supernova remnants interacting with molecular clouds ? New candidates in complex regions ... but ...
CTB 37A / G348.5+0.1 / HESS 1714-3857
• Hadronic scenario : interaction with molecular clouds (OH masers)
• But X-ray non-thermal emission (Chandra) → plausible Pulsar Wind Nebula
W51C / G49.2-0.7 / HESS J1923+141
• Molecular cloud W51B associated with a star-forming region : interaction supported by the presence of OH masers
• But ASCA and Chandra have detected a Pulsar Wind Nebula CXO J192318.5+143035 Koo et al. 2005
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Pulsar-Wind NebulaeSome supernova remnants include a pulsar whose strong wind termination shock accelerates particles and thus powers a nebula at the back of the ejecta → synchrotron (radio to X-rays) + inverse Compton = steady signal in very-high-energy γ-rays ≠. periodic signal from the pulsar magnetosphere (as detected by Fermi-LAT at E<10-20 GeV)Some pulsar-wind nebulae are extended (≠ Crab Nebula, unresolved by Cherenkov telescopes), sometimes more than the corresponding X-ray nebula (in older objects). Sometimes, the nebula is displaced with respect to the pulsar (HESS J1825-137, Vela X)In old and extended pulsar-wind nebulae, the γ-ray spectrum steepens away from the pulsar (case of HESS J1825-137) where electrons are « older »
Courtesy of P. Slane
Vela X
HESS J1825-137 Spectral index vs; distance from pulsar
A&A 460 (2006) 365HESS J1825-137
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Unidentified sources : ancient pulsar wind nebulae ?
Most of galactic sources detected by H.E.S.S. are pulsar-wind nebulae
Some unidentified sources are likely to be ancient pulsar-wind nebulae (de Jager et al. arXiv:0906.2644)
Magnetic field decreases with time. A weak field → almost no more synchrotron losses → source undetectable in radio or X-rays
Inverse Compton losses dominate → very-high-energy gamma-rays
An unidentified source (HESS J1708-443) in the vicinity of PSR B1706-44 and of the supernova remnant candidate G343.1-2.3 (radio arc)
Region A (pulsar) : no signal found
Region B (circle centered on the radio arc, encompassing the whole radio structure) → 7σ signal (17% of the Crab nebula flux) with a hard spectrum Γ = 2.0 ± 0.1 stat ± 0.2sys
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Unidentified sources :Star-forming regions and OB associations ?
Young clusters of massive stars (OB associations) : O and B stars (M>8Msol) are those which end as supernovae → in this environment, particle acceleration may be due to strong stellar winds (presence of Wolf-Rayet stars) Westerlund 2 revisited with 45.5 hours of good quality data
HESS J 1023-575 now detected at 16σ, but Fermi-LAT discovery of the coincident young pulsar PSR J 1022-5746 gives more weight to the interpretation of the source as a pulsar-wind nebula. Intrinsic extension 0.18°±0.02°.Another H.E.S.S. source (SW of the former one) appears clearly wen the energy threshold is increased: HESS J 1026-582 (7σ). Intrinsic extension 0.14°±0.03°. Spectrum harder than that of the first source : Γ = 1.94 ± 0.20stat ± 0.20sys
Westerlund 1, the largest stellar cluster of our Galaxy (6 × 104 solar masses) : with 34 hours of good quality data, H.E.S.S. detects a very extended γ-ray source (~2°) at 17 σ
Westerlund 2
Westerlund 1
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NGC 253: Fermi-LAT vs. H.E.S.S.
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Centaurus A: Fermi-LAT vs H.E.S.S.
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Blazars detected at very high energies are mostly high-frequency-peaked BL Lac’s (HBL)
Blazars are characterized by a two-bump broad-band spectrum E2 dΦ/dE
Synchrotron bumpGamma-ray bump, generally attributed to inverse Compton scattering
Classification according to broad-band spectrumLow-frequency-peaked BL Lac’s (LBL) : synchrotron peak in IR/optical, gamma-ray bump peaks in the GeV range (Fermi-LAT)High-frequency-peaked BL Lac’s (HBL) : synchrotron peak in UV/X, γ-ray bump peaks in the 100 GeV range (Cherenkov telescopes)
3 new blazars detected in the GeV range by AGILE or Fermi-LAT recently detected by H.E.S.S., including one LBLOnly 2 blazars from the H.E.S.S.catalogue have not been detected in the GeV range (1ES 0229+200 and PKS 0548-322)
Fossati et al. 1998
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PKS 2155-304 flaring regime Light curves in 4 energy bands (4 nights, July 2006)
arXiv:1005.3702
Photon index vs. time
E>0.2 TeV
0.2 TeV<E<0.35 TeV
0.35 TeV<E<0.6 TeV
0.6 TeV<E
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PKS 2155-304 spectral variability (arXiv:1005.3702)
Photon index vs flux:
Dark points correspond to the flaring period
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No anomaly in the H.E.S.S. cosmic-ray electron spectrum
First ground-based measurement of cosmic-ray electron spectrum (0.34 TeV - 5 TeV)
Use data far from Galactic Plane and exclude the vicinity of known sources (small contribution of diffuse γ-rays)
Electron/hadron discrimination by machine-learning algorithm → variable ζ : electron peak for ζ =1, hadrons accumulate at low values of ζ
Requiring ζ >0.6 removes 98-99.5% of hadrons.
Hadron background for ζ >0.6 is determined on the basis of proton shower simulations A&A 508 (2009) 561
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Indirect search for Dark Matter (DM) γ-rays from DM annihilation
Galactic Centre : HESS J1745-290 but the spectrum is mainly due to an unidentified astrophysical source. (A&A 503 (2009) 817), either the central black hole Sgr A* (but see also A&A 492 (2008) 492) or the pulsar wind nebula G359.95-0.04
DM component cannot be greater than 10% of the source flux → upper limit on <σv> are of the order of 10-24-10-23 cm3s-1 (Phys.Rev.Lett 97 (2006)221102)
M87 centre of the Virgo supercluster: but the variability of the signal (HEGRA,H.E.S.S.,MAGIC) excludes DM as the main source
Nearby dwarf spheroidal galaxies are interesting targets:
High Mass/Luminosity ratio inferred from the radial velocity dispersion of stars
No warm or hot gas, little dust and no cosmic rays
dssrJwithJdE
dN
m
v
dE
dlos )]([)(
8
1 22
00 exp
E
EEI
dE
d
Γ=2.10±0.04sta±0.1sys
E0=15.7±3.4sta±2.5sys
Galactic Centre
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H.E.S.S. observation of Dwarf Spheroidal GalaxiesH.E.S.S. observed 3 Dwarf Spheroidal Galaxies (Sagittarius dSph, Carina dSph and Sculptor dSph) and the overdensity Canis Major, the possible remnant of a disrupted dwarf galaxy
No signals → Upper limits (95%) on flux for photon indices between 1.8 and 2.4DM profile models (NFW, core profile) + Particle physics models → Upper limits on <σv> (pMSSM→LSP, Kaluza-Klein →LKP)
Sagittarius dSph (Astropart. Phys. 29 (2008) 55 & 33 (2010) 274)Distance 24 kpc (behind the Galactic Bulge)Φ(E>250 GeV) < 3.6 ×10-12 cm-2 s-1
<σv> < 10-23 – 10-24 cm3 s-1
Sculptor dSph Distance 79 kpcΦ(E>320 GeV) < (3.7 to 4.1) ×10-12 cm-2 s-1
<σv> < 10-22 – 10-21 cm3 s-1
Carina dSphDistance 101 kpcΦ(E>320 GeV) < (1.6 to 2.0) ×10-12 cm-2 s-1
<σv> < 10-22 – 10-21 cm3 s-1
Canis Major overdensity (ApJ 691 (2009) 175)Distance 8 kpc<σv> < 10-22 – 10-21 cm3 s-1
Sculptor dSph, A.Charbonnier for
the H.E.S.S. collaboration., COSPAR 2010
Fermi limits for NFW