Upper Limit on the Cosmological - Ray Background Yoshiyuki Inoue (Stanford) Kunihito Ioka (KEK) 1.
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Transcript of Upper Limit on the Cosmological - Ray Background Yoshiyuki Inoue (Stanford) Kunihito Ioka (KEK) 1.
![Page 1: Upper Limit on the Cosmological - Ray Background Yoshiyuki Inoue (Stanford) Kunihito Ioka (KEK) 1.](https://reader035.fdocuments.in/reader035/viewer/2022062421/56649d005503460f949d2f11/html5/thumbnails/1.jpg)
Upper Limit onthe
Cosmological g-Ray
BackgroundYoshiyuki Inoue (Stanford)
Kunihito Ioka (KEK)
1
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g-ray Sky
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g-ray Background
Sky map - Resolved point - Galactic diffuse (p0,Bremss,IC)- Solar & Local = Isotropic Extragalactic (inc. residual CR)
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History Discovered by SAS-2 satellite EGRET on CGRO LAT on Fermi
Fichtel+ 78
Streekumar+ 98
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LAT EGB Spectrum 2010
Spectrum can be fitted by power law: γ = 2.41 +/- 0.05Flux above 100 MeV: F100 = 1.03 +/- 0.17 x 10-5 cm-2 s-1 sr-1 (extrapolated)Foreground modeling uncertainty not included in error bands (~ 25%)Softer than EGRET measurement (Sreekumar et al. 98)No spectral features around a few GeV as seen in reanalysis of EGRET data (Strong+ 04)
Abdo+ 10
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©Ackermann
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Unresolved Blazars
Blazars dominate in LAT band Extrapolation of source count
of resolved LAT blazars allows estimate of their contribution
23%±5(sta)±12(sys) [100MeV-100GeV]
Abdo+ 10
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LAT EGB Spectrum 2011
Up to 580 GeVAckermann TeVPA11
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EBLStar Light +Dust Reemission⇒ IR-Opt. Bkg.geV gTeV→e+e-
Deplete TeV g
©Totani
★IR=Infra Red~0.01eV Opt=Optical~eV
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Gamma Ray HorizonCosmological Horizon
> TeV g Horizon
Coppi & Aharonian 97
Difficult to measureIR background
due to zodiacal light
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EBL Observations
We use conservative EBL
Black: Our EBL modelFilled: Integrated flux of galaxies (Min EBL)
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Cascade Emission Created e± scatter CMB via
inverse Compton ge~TeV/mec2~106
Eg,c~ge2 ECMB~GeV
Cooling time < Hubble time Absorbed energy ⇒ Cascade
emission
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Upper Limit
If cosmological sources produce the background,
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Upper Limit
The flux beforeabsorption shouldbe much higher
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Upper Limit
The absorbed fluxcascades to lowenergy horizontallyin this figure
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Upper Limit
Then some modelviolates the currentobservations
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Upper Limit
The current observationsalready limit the BG
cf. Coppi & Aharonian 97
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Primary Emission
Parameters: Gph, bevo, Eobs
Most known sources show positive evolution bevo>0
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Cascade Emission
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Calculation Iterative: 2nd, 3rd, … Cascades Not affected by magnetic field Scatter CMB dominantly Most absorption is local Cooling spectrum is not calculated
(only affect the low energy region)
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Cascade-limit Case
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Primary-limit CaseG~1.5 givesconserva.upper limit
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Negativeevolution,Low Emax
ease limits
HBL bevo=0Elliptical -0.86Cluster -1
bevo & Eobs
No know g-ray sources w/ bevo<0
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Different Spectrum
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With Known Sources
Violate the upper limit!
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With Different Model
Still Inconsistent?
Starburstmodel
uncertainty
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Possibilities Hard spectrum, Sub-TeV Emax &
bevo<0– No known g-ray sources, TeV HBL?,
LLGRB? New physics: Axion or LIV? Dark matter in local group? More <10GeV Sources? – Halo pulsars? Radio-quiet AGN?
Foreground?– Fermi bubble?
Our upper limit is useful forfuture: Fermi, CTA, CALETSee also Murase+ 12
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TeV HBLBlazar sequence
TeV selected high-frequency-peaked
BL Lac
Fossati+ 97, 98; Kubo+ 98; Donato+ 01; Kino & Takahara 04, Stawarz+ 07; many others
Abdo+ 09
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Low-Luminosity GRB?
Ahlers & Salvado 11
GRB most likely emit TeV gGRB energy generation rate ~ UHECR energy generation rate~ Low luminosity GRB energy generation rateLLGRB could negatively evolve due to metal Murase+ 06
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Fermi Bubble
Data subtraction reveals the gamma-ray bubbles
~1.66yr
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Thank You