2014-09_CTA_FermiDM.pptx

Fermi ガンマ線衛星による暗黒物質探査
2014年10月3日@東京大学柏キャンパス(高エネルギーガンマ線でみる極限宇宙2014)水野恒史(広島大学 宇宙科学センター)
On behalf of the Fermi-LATcollaboration
T. Mizuno et al.

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2014-09_CTA_FermiDM.pptx

Dark Matter Search withFermi Large Area
Telescope
Oct. 3, 2014@Kashiwa(The Extreme Universe viewedin very high-energy -rays)
T. Mizuno(Hiroshima Univ.)
On behalf of the Fermi-LATcollaboration
T. Mizuno et al.

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2014-09_CTA_FermiDM.pptx

Dark Matter (DM) Search with -rays• Gamma-rays may encrypt the DM signal
Gamma Ray Flux Particle Physics(measured by Fermi-LAT)(photons per annihilation)

DM Distribution(line-of-sight integral)

T. Mizuno et al.

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2014-09_CTA_FermiDM.pptx

Dark Matter (DM) Search with -rays• Gamma-rays may encrypt the DM signal
Gamma Ray Flux Particle Physics(measured by Fermi-LAT)(photons per annihilation)<v>~3x10-26 cm3 s-1
to reproduce the matter density(if DM is a thermal relic)(J-factor)
DM Distribution(line-of-sight integral)indirect search of a DM signal iscomplementary to direct detection(e.g., distribution of DM)
T. Mizuno et al.

NFW profile is usually assumed
2r 0 1  r 0 / a 0  r    0r 1  r / a 0 2
(0~0.3 GeV cm-3, a0~20 kpc,
r0=8.5 kpc for the MW)
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2014-09_CTA_FermiDM.pptx

Fermi Gamma-ray Space Telescope• Fermi = LAT + GBM• LAT = GeV Gamma-ray Space Telescope(20 MeV ~ >300 GeV; All-Sky Survey )2008.06 launch2008.08 Sci. Operation

3c454.3

Cape Canaveral,Florida

T. Mizuno et al.

1873 sources
Nolan+125 /30

2014-09_CTA_FermiDM.pptx

Fermi LAT•

Pair-conversion telescope (TKR+CAL+ACD)– good background rejection due to “clear” -ray signature– (also sensitive to CR electrons)•Tracker (TKR): pair conversion, tracking– angular resolution is dominated by multiple scattering below ~GeV•

Calorimeter (CAL):– use shower profile to compensate
for the leakage•

Anti-coincidence detector (ACD):

Si Tracker
70 m2, 228 m pitch
Atwood+09 ~0.9 million channels
(Japanese contribution)– efficiency>99.97%
Large Area
Telescope (LAT)

energy band: 20 MeV to >300 GeV
effective area: ~8000 cm2 (>1 GeV)
FOV: >2.4 srangular resolution: <1 deg (>1 GeV)
energy resolution: ~10% (@1 GeV)

T. Mizuno et al.

Anti-coincidence Detector
Segmented scintillator tiles

e+

GBM

eCsI Calorimeter8.6 radiation length

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2014-09_CTA_FermiDM.pptx

Gamma-ray Sky• GeV gamma-ray sky= Galactic Diffuse + astrophysical objects +unresolved sources + others

VelaVela
GalacticplaneGeminga
GemingaCrab3c454.3

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Fermi-LAT 4 year all-sky map

2014-09_CTA_FermiDM.pptx

DM Search Strategies with -rays (1)(Figure taken from Pieri+11)

Galactic Center:

Pros: Good statistics
Cons: confusion, diffuse BG
Satellites:
Pros: Low BG and good source id
Cons: low statistics

MW halo:

Pros: very good statistics
Cons: diffuse BG

Baltz+08

Spectral lines:

Pros: no astrophysical uncertainty(Smoking gun)
Cons: low statistics
Clusters:

T. Mizuno et al.

Extragalactic:

Pros: very good statistics
Cons: diffuse BG,astrophysical uncertainties

Pros: low BG and good source id
Cons: low statistics, astrophysicaluncertainties

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2014-09_CTA_FermiDM.pptx

DM Search Strategies with -rays (2)• In short, we search for DM signal in -rays by utilizing
their spatial and/or spectral signatures
Fermi-LAT data

Galactic Diffuse,Sources, isotropic(unresolved sources, BG)

DM signal(e.g., MW halo)?

+=DM signal (e.g., line)?

Good understanding of Galactic diffuse
emission and the instrument is crucial

T. Mizuno et al.

(Figure taken from Abdo+10)

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2014-09_CTA_FermiDM.pptx

DM Search Strategies with -rays(Figure taken from Pieri+11)

Galactic Center:

Pros: Good statistics
Cons: confusion, diffuse BG
Satellites:
Pros: Low BG and good source id
Cons: low statistics

MW halo:

Pros: very good statistics
Cons: diffuse BG

Baltz+08

Spectral lines:

Pros: no astrophysical uncertainty(Smoking gun)
Cons: low statistics
Clusters:

T. Mizuno et al.

Extragalactic:

Pros: very good statistics
Cons: diffuse BG,
astrophysical uncertainties

Pros: low BG and good source id
Cons: low statistics, astrophysicaluncertainties

10 /302014-09_CTA_FermiDM.pptx[1] Search for a Galactic DM Substructure••

In the standard cosmological model, structures form frombottom up. Numerical simulations predict that the MW should
be surrounded by smaller structures.
Optically observed Dwarf Spheroidal (dSph) galaxies are themost attractive candidate subhalo objects– relatively nearby– known position and mass (stellar velocity dispersion)– very high M/L ratio (>=100 Msun/Lsun)– low astrophysical gamma-ray backgroundM/L ratio(Wilkinson+06)

Ursa Minor(Credit:Mischa Schirmer)
T. Mizuno et al.

1xMsun/Lsun
11 /30Fermi-LAT Study of dSphs•

2014-09_CTA_FermiDM.pptx

No significant -ray emission if found to be coincident with anyof the 25 known dSphs

Ackermann+14(CA: Cohen-Tanugi, Conrad, Drlica-Wagner, Llena Garde and Mozaiotta)
T. Mizuno et al.

12 /30Fermi-LAT Study of dSphs•

2014-09_CTA_FermiDM.pptx

No significant -ray emission if found to be coincident with anyof the 25 known dSphs

Ackermann+14(CA: Cohen-Tanugi, Conrad, Drlica-Wagner, Llena Garde and Mozaiotta)
T. Mizuno et al.

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J-Factors of dSphs••

18 dSphs with kinematically determined J-factors
15 “nonoverlaping” dSphs used for a combined analysis()(T. Mizuno et al.

) ()A.Drlica-Wagner DPF 201314 /30Combined Limits by 15 dSphs•••

4 years of data, 500 MeV500 GeV
J-factor uncertainties
accounted for
Expected sensitivity
calculated from the data:– choose 25 blank-sky
locations as a control
sample (high Galactic
lat. (|b|>30deg), >1deg
from 2FGL)– combined analysis on
300 randomly selected
sets of blank fields

T. Mizuno et al.

2014-09_CTA_FermiDM.pptx

Ackermann+14(CA: Cohen-Tanugi, Conrad, Drlica-Wagner, LlenaGarde, Mazziotta)

Ackermann+11, PRL 107, 241302(CA: Cohen-Tanugi, Conrad, Garde)

MWIMP>=10 GeV to satisfy <v>=3x10-26 cm3 s-1
Largest excess (TS=8.7) for 25 GeV WIMP to bb(global p-value ~ 0.08 or 1.4)15 /302014-09_CTA_FermiDM.pptx

Synergy with Cherenkov Telescopes (1)•Although not so constraining (yet), ground Cherenkov Telescopes
gave limits complementary to Fermi-LAT results

Ackermann+14
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Synergy with Cherenkov Telescopes (2)•••Although not so constraining (yet), ground Cherenkov Telescopes gavelimits complementary to Fermi-LAT results
CTA is able to exclude (or detect) WIMP of M>=300 GeV
With a factor of 3 improvement of the Fermi-LAT (more exposure,improved response, more dSphs), WIMP mass of 10 GeV ~ >1 TeV will becovered with sensitivity at <v>~3x10-26 cm3 s-1

Ackermann+14
T. Mizuno et al.

CTA, MW halo,100 hr(taken from Doro+ 13)

17 /302014-09_CTA_FermiDM.pptx[2] Extragalactic Gamma-ray Background (EGB)(taken from M. Ackermann’s talk)T. Mizuno et al.

dedicated event class to obtain “clean” -rays
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Origin of EGB/IGRB•

The EGB may encrypt the signature of the most powerfulprocesses in astrophysics
Star forming galaxies, etc.
(taken from M. Ackermann’s talk)

Blazars contribute20-100% of theEGB
Particles acceleratedin Intergalactic shocks

Annihilation ofCosmological Dark
MatterTotal EGB = Isotropic Gamma-Ray BackgroundMarkevitch+0 (IGRB)+resolved sources
5 to IGRB
Possible Cosmological WIMP contribution
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Systematic Uncertainty from Galactic Diffuse•Galactic Diffuse dominates -ray sky, hence is the most significant
source of uncertainty for EGB/IGRB
Three Diffuse models are considered to gauge uncertainty•– ModelA: similar to a model in Ackermann+12 (baseline model)– ModelB: add population of electron-only sources near GC (better match to IC)– ModelC: non-uniform CR diffusion rate (better reproduce flat emissivity)
Variation of diffuse model parameters (e.g., halo size) also considered•(Model B – Model A) / Model A(Model C – Model A) / Model A

Preliminary (just accepted)(Fermi-LAT Collaboration, Ackermann, Bechtol)
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The Fermi EGB/IGRB•

Updated LAT measurement of IGRB
– 200 MeV-100 GeV (Abdo+10) -> 100 MeV – 820 MeV•

Significant high-energy cutoff feature in IGRB
– Consistent with simple source population attenuated by EBL••

Roughly half of total EGB intensity above 100 GeV now resolved intoindividual sources
Then, how about constraints on DM?
Preliminary(just accepted)

T. Mizuno et al.

(Fermi-LAT Collaboration, Ackermann, Bechtol)

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Contribution of Cosmological WIMP•

Flux from cosmological WIMP annihilation

Flux multiplier(clumpiness of DM)•

WIMP-induced spectrum

Clumpiness of DM is the main source of uncertainty. Two
independent and complementary approaches to compute (z)Preliminary• Use Halo Model as a Benchmark
model (Sánchez-Conde and Prada 14, Prada+12)• Use non-linear matter power spectrum
to gauge uncertainty (Sefusatti+14)(Fermi-LAT Collaboration,Franckowiak, Gustafsson, Sánchez-Conde, Zaharijas)

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22 /30Limits on Cosmological DM (1)••2014-09_CTA_FermiDM.pptx

Two types of “extreme” limits (they bracket the true limit)– Conservative, no assumed astrophysical contributions to IGRB
– Optimistic, 100% of the IGRB assumed to be of astrophysical origin
Galactic substructure taken into account (based on our Halo Model) toderive limits on cosmological WIMP

Preliminary

T. Mizuno et al.

Preliminary(Fermi-LAT Collaboration,Franckowiak, Gustafsson, Sánchez-Conde, Zaharijas)

23 /30Limits on Cosmological DM (2)••2014-09_CTA_FermiDM.pptx

Two types of “extreme” limits (conservative and optimistic)
Min/Max Galactic substructure considered to gauge uncertainty

Preliminary

Preliminary(Fermi-LAT Collaboration,Franckowiak, Gustafsson, Sánchez-Conde, Zaharijas)••

Strongest Fermi-LAT limits in the >-5 TeV range
Good sensitivity to WIMPs in 10-100 GeV range – potentially offer
a possibility to check the signal detected elsewhere

T. Mizuno et al.

24 /302014-09_CTA_FermiDM.pptx[3] Narrow Feature at ~130 GeV••

Several groups showed evidence for a narrow spectral featureat ~ 130 GeV near the Galactic Center (GC)
(E.g., Weniger+12) Over 4, S/N>30%, up to ~60% in optimized
region of interest

Weniger+12

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Improve the Model of Energy Dispersion••••

Use full MC to get Fermi-LAT energy dispersion
Previously modeled line with a triple Gaussians (1D PDF)
Updated analysis add a 2nd dimension to line model PE(probability that measured energy is close to the true value)
Including PE improves line sensitivity by ~15%

Ackermann+12(CA: Bloom, Edomonds, Essig)

T. Mizuno et al.

Ackermann+13(CA: Albert, Bloom, Charles, Winer)

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Evolution of line-like Feature near 133 GeV•••1) 1D PDF, unreprocessed data (public data)– 4.5 (local) 1D fit at 130 GeV
2) 1D PDF, reprocessed data (better energy calibration)– 4.1 (local) at 133 GeV
3) 2D PDF, reprocessed data
– 3.3 (local) at 133 GeV (Energy dispersion in data is narrower
than expected when PE is taken into account)– <2 global
4 year data, look in r=3deg from GC(1)

Ackermann+13
T. Mizuno et al.

(CA: Albert, Bloom, Charles, Winer)(3)

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Search 133 GeV in Earth Limb Data•

Earth Limb is bright and well understood– s are from CR interaction with atmosphere– Can be used to study instrumental effects••

Need to cut on time when the LAT waspointing at the limb
Have made changes to increase our Limb
datasetγ ray

Cosmic ray– Pole-pointed observation each week (2012 Oct2013 Oct)
– Extended target of opportunity (tracing Limb
while target is occulted)• Excess is seen (likely due to dips in efficiency
below/above 130 GeV)
• Not at the level of GC (S/Nlimb~15% while
S/NGC=30-60%)
More data and study are needed to clarify the originof 133 GeV feature (physical or systematic)
Ackermann+13
T. Mizuno et al.

(CA: Albert, Bloom, Charles, Winer) 28 /30

Future Prospects: Pass 8•

2014-09_CTA_FermiDM.pptx

dSphs are promising targets for DM search. Sensitivity isexpected to be improved– more data, more dSphs, improved response••

Pass 8 is a comprehensive revision of the Fermi-LAT response
Impact on scientific analysis (including DM search)– increased energy range (new mass parameter space)– Increased effective area (flux sensitivity)

T. Mizuno et al.

29 /30Summary

2014-09_CTA_FermiDM.pptx

-ray observation is a powerful probe to investigate
the DM property• No significant detection of the signal yet•

– (130 GeV line not significant globally with reprocessed dataand new Edisp model. Significance has declined since 2012Spring)• Constraints on the nature of DM have been placed(dSphs, IGRB)•– start to reach thermal-relic cross section
Future improvement of Fermi-LAT study (more data/dSphs andimproved response) and CTA will cover WIMP mass of 10 GeV1 TeV with good sensitivity

Thank you for your Attention
T. Mizuno et al.

30 /30Reference•••••••••••••••

2014-09_CTA_FermiDM.pptx

Nolan et al. 2012, ApJS 199, 31Atwood et al. 2009, ApJ 687, 1071
Baltz et al. 2008, JCAP 7, 13
Abdo et al. 2010, PRL 104, 091302
Pieri et al. 2011, PRD 83, 023518
Wilkinson et al. 2006, Messenger 124, 28
Ackermann et al. 2014, PRD 89, 042001
Doro et al. 2013, Astroparticle Physics 43, 189
Abdo et al. 2010, PRL 104, 101101
Sánchez-Conde and Prada 2014, MNRAS 442, 2271
Prada et al. 2012, MNRAS 423, 3018
Sefusatti et al. 2014, MNRAS 441, 1861
Weniger et al. 2012, JCAP 8, 7Ackermann et al. 2012, PRD 86, 2012
Ackermann et al. 2013, PRD 88, 082002

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Backup Slides

T. Mizuno et al.

32 /302014-09_CTA_FermiDM.pptx

Fermi-LAT Collaboration
FranceItaly
Japan
SwedenUS

T. Mizuno et al.

• Hiroshima Univ.
• ISAS/JAXA• Tokyo Tech
• Waseda Univ.
• Kyoto Univ.
• Nagoya Univ.
• Aoyama Gakuin Univ.
• Ibaraki Univ.

PI: Peter Michelson (Stanford)~400 Scientific Members
Cooperation between NASA andDOE, with key international
contributions from France, Italy,
Japan and Sweden.
Project managed at SLAC.

33 /302014-09_CTA_FermiDM.pptx

Contribution of Star-forming Galaxies••

Use L-LIR scaling to estimate contribution
Star-forming galaxies account for 4-23% of the EGB (~60% at themaximum if we add Blazars and SFGs)

Ackermann+12, ApJ 755, 164(CA: Bechtol, Cillis, Funk,Torres)•Radio galaxies can account for ~25% (e.g., Inoue+11). Still someroom for other source type or truly diffuse emission.

T. Mizuno et al.

34 /30DM Signal Example

2014-09_CTA_FermiDM.pptx• Example of DM signal (for extragalactic gamma-raybackground)

1.2 TeV +1.2x10-23 cm3/s

180 GeV 
2.5x10-26 cm3/s
200 GeV bb
5x10-25 cm3/s

0.1

110

Abdo+10, JCAP 4, 14T. Mizuno et al.

100 GeV(CA: Conrad, Gustafsson, Sellerholm, Zaharijas)

35 /302014-09_CTA_FermiDM.pptx

Stacking Analysis with Old Response (Pass6)•Stacking analysis using 10 dSphs and 2 years data– conservative limit on DM cross section (no “boost factor”)

3x10-26 cm3 s-1
Ackermann+11, PRL 107, 241302(CA: Cohen-Tanugi, Conrad, Garde)

MWIMP>=20 GeV to satisfy <v>=3x10-26 cm3 s-1
Rule out models with generic cross section using -rays for the first time
T. Mizuno et al.

36 /302014-09_CTA_FermiDM.pptx

Stacking Analysis with New Response (Pass7)•Update analysis with Pass 7– take account of an improved understanding of the instrument• Use new response (P6->P7) and redo
the analysis• This leads to a statistical reshufflingof -ray-classified events (only ~50%events are common in two dataset
above 10 GeV)
• Two limits are statistically consistent3x10-26 cm3 s-1

dSphs still constrain generic cross section for MWIMP<=10 GeV
and will remain a prime target for DM search
T. Mizuno et al.

37 /302014-09_CTA_FermiDM.pptx

Evolution of line-like Feature near 135 GeV•

Since Spring 2012, the significance of the feature has declined
signal-likebackground-like

Weniger+13
T. Mizuno et al.

(http://fermi.gsfc.nasa.gov/ssc/proposals/alt_obs/white_papers_eval.html) 38 /30

[4] Milky Way DM Halo•

2014-09_CTA_FermiDM.pptx

Another recent and complementary DM search for MW halo
– Search for continuous emission from DM annihilation/decay inthe smooth MW halo

DM signal• Analyze bands 5deg off the plane decrease astrophysical BG
 mitigate uncertainty from innerslope of DM density profile• Two approaches:-may map 1) more conservative - assume allemission are from DM (noastrophysical BG)
 2) more accurate – fit DM sourceand astrophysical emission
simultaneously
Ackermann+12, ApJ 761, 91

T. Mizuno et al.

(CA: Conrad, Yang, Zaharijas, Cuoco)

39 /30DM Halo Search: Method I

2014-09_CTA_FermiDM.pptx• Assume all -rays are from DM and give upper limits– conservative, robust to uncertainty• Expected DM counts (nDM) compared to observedcounts (ndata) and 3 upper limit are set using (in atlease one energy bin)nDM  3 nDM  ndata

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40 /30DM Halo Search: Method II

2014-09_CTA_FermiDM.pptx

allow several parameters to vary
(e.g., CRE injection spectrum, CR halo size andCR source distribution

DM haloaT. Mizuno et al.

NFW and Isothermal
consider bb, +- and +(annihilation and decay)

41 /30DM Halo Search: Method II•

2014-09_CTA_FermiDM.pptx

Disentangle DM signal from foreground by utilizing spatial andspectral shapes (good diffuse model is important)

DM halo

IC (astrophysical)

Ackermann+12, ApJ 761, 91
T. Mizuno et al.

(CA: Conrad, Yang, Zaharijas, Cuoco)

42 /30Constraints on DM Model••2014-09_CTA_FermiDM.pptx

Modeling the astrophysical emission improves DM constraints
by a factor of ~5
w/ astrophysical BG, the limit constrains the thermal reliccross section for WIMP with mass > 30 GeV (comparable todSphs)

Ackermann+12, ApJ 761, 91
T. Mizuno et al.

(CA: Conrad, Yang, Zaharijas, Cuoco)

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Cosmic-ray Electrons/Positrons• e+/e- is not compatible with a standard scenario(2ndary production)– Additional e-/e+ sources (astrophysical or exotic) can provide agood fit to Fermi CRE and e+/(e- + e+)
Fermi-LAT e-+e+
PAMELA/Fermi/AMS2
e+/e-

Example ofan additional component

T. Mizuno et al.

Aguilar+13,
PRL 110, 141102

Ackermann+10
PRD 82, 092004

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