Fermi LAT Discovery of Gamma-rays from the Giant Radio Lobes of Centaurus A
Fermi-LAT Study of Cosmic-rays/Diffuse Gamma-rays and Implications on Particle Physics
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Transcript of Fermi-LAT Study of Cosmic-rays/Diffuse Gamma-rays and Implications on Particle Physics
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Fermi-LAT Study of Cosmic-rays/Diffuse Gamma-rays and
Implications on Particle Physics
Mar. 7, 2011 @ Kyoto Univ.Tsunefumi Mizuno (Hiroshima Univ.)On behalf of the Fermi-LAT collaboration
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Fermi 衛星による広がったガンマ線・宇宙線電子の観測と基礎物理への制限
2011 年 3 月 7 日 @ 京都大学基礎物理研究所
水野 恒史 ( 広島大学理学部 )On behalf of the Fermi-LAT collaboration
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OutlineIntroductionFermi LAT instrumentationGalactic Diffuse Gamma-raysBehind the diffuse gs: EGB and DM searchCosmic-ray Electrons
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Gamma-ray Sky
• GeV gamma-ray sky= Point sources + Diffuse Gamma-rays
Fermi-LAT 1 year all-sky map
>=80% of g-rays
3c454.3
Vela
Crab
Geminga
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What makes Diffuse g-rays?
• Diffuse Gamma-rays= Cosmic-rays x (ISM, ISRF)
Planck microwave map = ISM gas
InterStellar MediumInterStellar Radiation Field
Galactic plane
nearby gas in high latitude
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Gamma-ray Sky
• GeV gamma-ray sky~ Diffuse Gamma-rays = CRs x (ISM, ISRF)
Fermi-LAT 1 year all-sky map
phys. processes are well understood
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Why are they important?
• Diffuse Gamma-rays are– “probe” to study Galactic CRs and ISM– “foreground” to study exotic physics, e.g.,
• signal from dark matter (DM)• extragalactic g-ray background (EGB)
Fermi-LAT 1 year all-sky map
new source classes or DM signal
annihilation or decay
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Example: GeV Excess (EGRET Era)
• EGRET (1991-2000) reported excess emission when compared with a standard diffuse g-ray model– variety of explanations including DM signal
Hunter+97
G ~ 2.7(CR protons)
E2 x F
lux
0.1 1 10 GeV
excess
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Example: GeV Excess (Fermi Era)
• EGRET GeV excess not confirmed.• However, Fermi data allow us investigating
more subtle “anomalies” (and detailed study of CRs/ISM)
EGRETFermi-LAT
G ~ 2.7Abdo+09PRL 103, 251101
E2 x F
lux
0.1 1 10 GeV
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Fermi-LAT as Electron Detector
• Fermi-LAT reported a harder CR e- + e+ spectrum compared with a conventional model
Abdo+09PRL 102, 181101
Fermi Data (2009)
E3 x F
lux
10 100 1000 GeV
highest statistics:4.5 M events(6 months)
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Fermi-LAT as Electron Detector
• Fermi-LAT reported a harder CR e- + e+ spectrum compared with a conventional model– Lots of interpretations (astrophysical and exotic)
Fermi e- + e+ PAMELA e+ ratio
+DM?Nearby objects?=
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Fermi-LAT as Electron Detector
• Fermi-LAT reported a harder CR e- + e+ spectrum compared with a conventional model– Lots of interpretations (astrophysical and exotic)
2009 Jan. – 2010 Sep.
… and the paper is highly cited
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Fermi-LAT Instruments
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Fermi Launch• Launched on June 11, 2008• Science Operation on Aug 4,
2008• Orbit: 565 km, 26.5o (low BG)
Cape Canaveral Air Station @ Florida
5-yr mission(10-yr goal)
Fermi=LAT+GBM
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Fermi-LAT Collaboration
France
Italy
Japan
Sweden
US
• Hiroshima Univ.• Tokyo Tech• ISAS/JAXA• Waseda Univ.• Tokyo Univ.• Nagoya Univ.• Aoyama Gakuin Univ.
~400 members
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Large Area Telescope
• Pair-conversion type g-ray telescope
• ACD: plastic scintillatorsBG rejection
• Calorimeter: CsI scintillatorsEnergy measurement
• Tracker: Si-strip detectorsdirection measurement
20 MeV- 300 GeV
segmented tiles =>prevent self-veto
hodoscopic crystals =>shower profile
~200 um pitch =>high precision tracking
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Large Area Telescope
• Pair-conversion type g-ray telescope
• Tracker: Si-strip detectorsdirection measurement
Key-element of LAT, developed by HPK and Hiroshima Univ.
Low-noise (~2.5nA/cm2)High-quality (dead strip: <0.01%)~106 channels in total
SSD
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Performance of the LAT
• Large FOV (2.4 sr)• Large Aeff (>=8000 cm2 in 1-100 GeV)• Good PSF (0.6 deg@ 1GeV)
EGRET 3rd Catalog271 sources
Fermi-LAT 1st year catalog1451 sources
Atwood+09
sensitivity to point sources
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Science, December 2009
• Fermi is recognized as one of the top science breakthroughs
Science Breakthroughs of 2009
Discovery of 16 new pulsars
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GeV Gamma-ray Sky by LAT
• and provides us with high-quality data!– g-ray sources, diffuse g-rays and more
Fermi-LAT 1 year all-sky map
>100 publicationsas of Feb. 2011
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Diffuse g-rays as probe of CRs and
ISM
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GeV “Non” Excess
• Fermi does not confirm EGRET GeV excess
EGRETFermi-LAT
Abdo+09, PRL 103, 251101(CA: Johannesson, Porter, Strong)
local (<= 1 kpc from the sun)Diffuse Gamma-rays
E2 x F
lux
0.1 1 10 GeV
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GeV “Non” Excess
• Fermi does not confirm EGRET GeV excess
EGRETFermi-LAT
Abdo+09(CA: Johannesson, Porter, Strong)
Instead, data is compatible with a standard model
E2 x F
lux
0.1 1 10 GeV
Gamma = CR x (ISM, ISRF)
G ~ 2.7
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Diffuse gs in the Outer Galaxy
• Any unexpected in diffuse gs?– Yes. New information on CRs and ISM
The outer Galaxy (from outside)
sun
II quad III quad
L=90deg
L=180deg
L=270deg
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Diffuse gs in the Outer Galaxy
• Any unexpected in diffuse gs?– Yes. New information on CRs and ISM
Abdo+10, ApJ 710, 133Ackermann+11, ApJ 726, 81
The outer Galaxy (from the Fermi-LAT)
anticenterGC
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ISM not visible by Standard Tracers
• Fermi revealed ISM gas not traced by radio surveys
Ackermann+11, ApJ 726, 81(CA: Grenier, Mizuno, Tibaldo)
Residual when fitted by N(HI)+CO
excess gammas= residual gas
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ISM not visible by Standard Tracers
• Fermi revealed ISM gas not traced by radio surveys– confirming an earlier claim based on EGRET study
(Grenier+05)
Ackermann+11, ApJ 726, 81(CA: Grenier, Mizuno, Tibaldo)
Residual when fitted by N(HI)+CO Residual gas inferred by dust
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More CRs than Expected
• Fermi detected more gs (more CRs) than a prediction based on SNR distribution and standard CR halo
Gam
ma-
ray
inte
nsity
Distance from GC (kpc)
Ackermann+11ApJ 726, 81(CA: Grenier, Mizuno, Tibaldo)
Sun
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More CRs than Expected
• Fermi detected more gs (more CRs) than a prediction based on SNR distribution and standard CR halo– More CR sources or larger CR halo
Gam
ma-
ray
inte
nsity
Distance from GC (kpc)
Ackermann+11ApJ 726, 81(CA: Grenier, Mizuno, Tibaldo)
Sun
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Remarks on Diffuse gs
• g-rays = CR x (ISM, ISRF)• “dark gas” is confirmed (more ISM gas)• More CRs than expected in outer Galaxy
• Improvement of diffuse g-ray modelBasis to search for anomalies
(in spectral and spatial distribution)
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Behind Diffuse g-rays: Study of EGB and DM
search
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Extragalactic Gamma-ray Background
• “Cosmic” Extragalactic Gamma-ray Background (EGB) has been known since 1970s
GeV background(EGRET)
CXB(resolved into AGNs)
Sreekumar+98
E2 x F
lux
keV MeV GeV
G ~ 2.1
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Why is EGB Important?
• The EGB may encrypt the signature of the most powerful processes in astrophysics
Blazars contribute 20-100% of the EGB
Star forming galaxies
Particles accelerated in Intergalactic shocks
4% A
tom
s
Annihilation of Cosmological Dark Matter
Markevitch+05
Point sources
or diffuse
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The Fermi EGB
• Fermi data + improved diffuse model– new EGB spectrum in 0.2-100 GeV
• carefully examine systematic uncertainty
Abdo+10, PRL 104, 101101
+
+
=
LAT sky
gal. diffuse
point sources
Instrumenta
l BG
+”EGB”0.1 1 GeV 10 100
G ~ 2.4
Single PL, softer than EGRET result
(CA: Ackermann, Porter, Sellerholm)
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Blazar Contribution
• Blazars account for a minimum of 16+-2%– Even if we extrapolate and integrate logN-logS
to zero, contribution is still <40%
logN-logS:Most of un-associated sources are likely to be blazars
0.1 1 GeV 10 100
flatter in F<=6x10-
8
Fermi EGB vs. source contribution
Abdo+10, ApJ 720, 435(CA: Ajello, Tramacere)
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Blazar Contribution
• Blazars account for a maximum of 40% of EGB– g-ray “Fog” by Mysterious Dragons– star-forming galaxies, normal AGNs or truly diffuse?
0.1 1 GeV 10 100
Fermi EGB vs. source contribution
Abdo+10, ApJ 720, 435(CA: Ajello, Tramacere)
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Limits on DM Annihilation
• Limits on DM by imposing the EGB is not violated
0.1 1 10 100 GeV
1.2 TeV m+m-
1.2x10-23 cm3/s200 GeV bb 5x10-25 cm3/s
180 GeV gg2.5x10-26 cm3/s
Abdo+10, JCAP 4, 14(CA: Conrad, Gustafsson, Sellerholm, Zaharijas)
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Limits on DM Annihilation
• Limits on DM by imposing the EGB is not violated
10-22
10-25
<sv> (cm3/s)
100 1000GeVWIMP mass
w/o astrophysical sources
w/ astrophysical sources
Abdo+10, JCAP 4, 14(CA: Conrad, Gustafsson, Sellerholm, Zaharijas)
m+/m-
FermiPAMELA
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Limits on DM Annihilation
• Limits on DM by imposing the EGB is not violated– already excluded some models, e.g., m+/m- channel favored
by PAMELA/Fermi e-/e+
10-22
10-25
<sv> (cm3/s)
100 1000GeVWIMP mass
w/o astrophysical sources
w/ astrophysical sources
Abdo+10, JCAP 4, 14(CA: Conrad, Gustafsson, Sellerholm, Zaharijas)
m+/m-
Fermi fit
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Other Constraints on DM
Abdo+10, ApJ 712, 147(CA: Cohen-Tanugi, Farnier, Nuss, Profumo, Jeltema)
• Dwarf Spheroidal Galaxies are DM dominated– small BG (gas, star-forming activity)
dwarfs
m+/m- ULwith CMB IC
Diffusion coeff.
dwarfs
No detection
give constraints on some models, particularly m+/m- channel
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Remarks on EGB and DM search
• “New” EGB spectrum in 0.2-100 GeV– Blazars account for <40% of EGB
• room for star-forming galaxies, normal AGNs or truly diffuse
• No evidence for DM annihilation– Constraints on models, in particular m+/m- channel– Astrophysical source contribution is important
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Cosmic-Ray Electrons
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PAMELA Positron Excess
• Convincing evidence of e+ ratio excess in >10 GeV– 2ndary e+ should be softer than primary e-
Adriani+08
Sources of “Primary” e+ are required
0.1 1 GeV 10 100
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CRE by Fermi-LAT (2009)
• Fermi-LAT reported hard e- + e+ spectrum– Standard models with proper choice of params are able to
reproduce Fermi data alone, but not Fermi + PAMELA
Abod+09PRL 102, 181101(CA: Latronico, Moiseev)
Fermi Data (2009)
10 100 1000 GeV
6 months data4.5 M events
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e-/e+ probe nearby sources
• CR e-/e+ loose energy via synchrotron and IC, hence probe nearby sources
We are here
e+ sources
Our Galaxy
KEK 井岡氏のトラぺより借用
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CRE by Fermi-LAT (2010)
• CREs collected for 12 month (data is doubled)– Cross-check with events with long path in CAL (>=13X0)– LE extention using high latitude (low cutoff) data
• Noticeable deviation from a single PL
20 GeV
Fermi Data (2010)pre-Fermi model
Ackermann+10PRD 82, 092004(CA: Moiseev, Sgro)1 10 100 GeV 1000
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CRE by Fermi-LAT (2010)
• Noticeable deviation from a single PL– Additional e-/e+ sources (astrophysical or extocis) can
provide a good fit to Fermi CRE and PAMELA e+/(e- + e+)
Example ofan additional component
Anisotropy of arrival direction may reveal sources or give constraints
1 10 100 GeV 1000
Ackermann+10PRD 82, 092004(CA: Moiseev, Sgro)
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CRE AnisotropyNo-anisotropy map
Flight data sky map
Significance map
• Construct no anisotropy map from flight data– shuffling and direct integration
• Compare obtained map with data– search for anisotoropy
Ackermann+10PRD 82, 092003(CA: Mazziotta, Vasileiou)
No evidence of anisotropyin energies/angles investigated
Eth: 60-480 GeVAngular scale: 10-90 deg
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Limit on Sources
• No evidence of anisotropies– Upper limit for the dipole anisotropy: 0.5-5%
• Limit already comparable to the value expected for a single nearby source dominating HE spectrum– will improve as more data are collected
Monogem
Vela
FermiHESS
Monogem
Vela
CRE spectrum at Earth Dipole Anisotropy
Fermi (3s UL)
Ackermann+10PRD 82, 092003(CA: Mazziotta, Vasileiou)
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Summary
• Diffuse g-ray emission is a powerful probe for studying CRs and ISM
• Constraints on some DM models. Study of diffuse g-rays and g-ray object is important
• UL of CR anisotropy is close to what is expected for single nearby source
Thank you for your Attention
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Summary
• 広がったガンマ線は , 宇宙線と星間ガスを研究する強力な手段 .
• DM探査で意味のある上限値が得られている . 広がった g線 + g線天体の理解は , DM探査にも資する .
• 電子陽電子源スペクトル +等方性も , 意味のある上限に近いところまできている .
Thank you for your Attention
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Backup Slides
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GeV “Non” Excess
Proton (pi0)
Electron (bremss) Electron (inverse Compton)
Isotropic (EGB+BG)
Abdo+090.1 1 10 GeV
E2 x F
lux
• instead, data is compatible with a model based on directly-measured CRs– solid basis to explore g-ray sky
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More CRs than Expected
• Fermi detected more gs (= more CRs) than a prediction based on SNR distribution and standard CR halo.
LAT data vs.
standard model
Gam
ma-
ray
inte
nsity
Distance from GC (kpc)
Abdo+10, ApJ 710, 133(CA: Grenier, Tibaldo) Sun
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e-/e+ probe nearby sources
• They loose energy via synchrotron and IC– dE/dt = -bE2
– T= 1/(bE) = 2.5x105 yr/(E/TeV)• hence are not able to reach far from the source
– R = (2DT)0.5 = 0.4-0.8 kpc @ 1TeV
• High Energy CR e-/e+ can probe nearby sources
D~(1-4)x1029 cm2/s@TeV
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CRE by Fermi-LAT (2010)
• CREs collected for 12 month (data is doubled)– Cross-check with events with long path in CAL (>=13X0)– LE extention using high latitude (low cutoff) data
15.9 X0 avg.(1TeV shower peak @ 11 X0)
Consistent within their own systematics
@1TeVDE~14%DE~5%
100 GeV 1000