gamma-ray absorption by cosmic radiation fields
DESCRIPTION
blazar. GRB. Gamma-ray absorption by cosmic radiation fields. Susumu Inoue (Kyoto University). with (more than) a little help from my friends. Fermi. z~60-6. CTA. outline. 1. probe of high-z UV background. SI, R. Salvaterra, T. R. Choudhury, A. Ferrara, - PowerPoint PPT PresentationTRANSCRIPT
blazar
Gamma-ray absorption by cosmic radiation fields
GRB
Fermi
z~60-6
CTA
Susumu Inoue (Kyoto University)with (more than) a little help from my friends
outline
1. probe of high-z UV background
2. probe of Lorentz invariance violation
SI, R. Salvaterra, T. R. Choudhury, A. Ferrara,B. Ciardi, R. Schneider, MNRAS in press (arXiv:0906.2495)
Y. Inoue, M. Kobayashi, T. Totani, SI et al., work in prep.
effect in Galactic sources?
diffuse extragalactic background radiation at z=0
EBL=extragalacticbackgroundlight
gamma-ray absorption:probe of diffuse radiation fields
+ → e+ + e-
threshold condition: E (1-cos )>2 me2c4
E
e.g. TeV + 1eV (IR) 100 GeV + 10 eV (UV)
peak ,, =4 me2c4
pair productioncross section
CM energy
probe of local IRB throughgamma absorption in TeV blazars
Costamante et al 03
1.
probing local IR background with gamma-ray absorption
Aharonian+ 06 Nat.HESS observations of TeV blazars @z=0.165, 0.186
no strong Pop III• strongly disfavors NIR peak• close to lower limits from galaxy counts
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E(=
1)
EBL constraints at z=0.536
Albert+ 08 Sci.
close to lower limits from galaxy counts (little missing light)if “normal” blazar spectra >1.5
MAGIC observation80-500 GeV3C279 @z=0.536
EBL constraints at z=4.35 Abdo+ 09, Sci. 323, 1688
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Fermi/LAT detection of GRB 080916C up to 13 GeV without cutoff
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slides from T. R. Choudhury
cosmic reionization epoch
early? late? two-epoch?When?
mini-QSOs?What?
So what?suppression ofdwarf galaxyformation
How? topology?
Pop III? Pop II?
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Madau 07
dark matter decay?
z>6 current observational frontier
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slides from T. R. Choudhury
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high-z UV radiation field (“background”)crucial for understanding early universe
but direct detection impossible!
• reionizes the IGM (feedback on later galaxy formation)• dissociates H2 molecules (feedback on later star formation)• Ly pumping (determines HI hyperfine 21cm level population)
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model of cosmic reionizationChoudhury & Ferrara 05, 06, Choudhury 09
semi-analytical model with Pop III+II stars+QSOs, radiative+chemical feedback
WMAP3xHI
SFR
HUDF
Ly
Ly
LLS
photoion
TIGM
parameters *II, *III, esc, 0IGM
consistent with large set of high-z observations: WMAP, xHI, HUDF NIR counts, etc.
reionizationbegins z~1590% z~8100% z~6
(WMAP5 OK)
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intergalactic radiation field (volume average)
“local’’ optical depthspectra
• realistic UV IRF -> opaque for Erest~10’s-100’s GeV at z<~10• sharp cutoff at Erest~18 GeV from HI absorption above Ly edge (reionizing radiation cannot be probed directly)
caveat: model only for 4<z<22, no Pop I/dust
10-23
10-22
10-21
10-20
10-19
10-18
2 3 4 5 6 71
2 3 4 5 6 710
2
[ ]eV
7103
234567104
23456
[ ]A
=4z6
810
12
14
16
18
20
10-5
10-4
10-3
10-2
10-1
100
101
102
101
2 4 6 8
102
2 4 6 8
103
2 4 6 8
104
Erest [GeV]
z=4
8
12
16
20
6
10
14
18
SI+ arXiv:0906.2945
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0.1
2
3
456
1
2
3
456
10
30252015105 E [GeV]
8
10
53
2
fiducial K04
6
1
45
20
significant optical depth >12 GeV at z~5, down to 6-8 GeV at z~8-10
absorption optical depth
(high UV)
low z modelKneiske+ 04(high stellar UV)see also e.g.Stecker+ 06Razzaque+ 09Gilmore+ 09
but not much effect z>~8 due to declining star formation, path length
~0.4@z=4.35, E=13.2GeV(GRB 080916C)
SI+ arXiv:0906.2495
1.0
0.8
0.6
0.4
0.2
30252015105 E [GeV]
6
8
5
1020 1
2345
fiducial K04
appreciable differences in attenuation between z~5-8 at several GeV→ unique, important info on evolution of UV IRF below Ly edge during cosmic reionization/first star formation
low z modelKneiske+ 04(high stellar UV)
absorption attenuation factor
FermiCTA, AGIS5@5
(high UV)
alternative models
differences not large, attenuation not sensitive to reionization history→ predictions reasonably robust?
1.0
0.8
0.6
0.4
0.2
30252015105 E [GeV]
6
8
5
1020 1
2345
fiducial no Pop III
K04
e.g. late reionization modelwith no Pop III stars
detectability
most luminous blazars (LGeV~1049 erg/s, e.g. 3C454.3)detectable @10GeV by Fermi out to z~7
blazars
GRBs
distinction between intrinsic cutoffsspectral variability: IRF cutoff t-indep. <-> intrinsic cutoff t-dep.
few such objects plausible Y. Inoue, SI, Totani+, in prep.
most luminous GRBs (LGeV~1054 erg/s, e.g. GRB 080916C)detectable @10GeV by Fermi out to z~7
out to higher z by future large arrays! CTA, AGIS, 5@5
statistical: similar cutoffs for similar z, decreasing trend with z
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cosmic star formation rate
CAUTION:data at z>6mostly lower limitsto cosmic SFR
large uncertainties in SFR at z>6models with low Pop II but high Pop III also possible?
Y. Inoue, Totani, SI et al.in prep.
cosmic star formation rate
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estimated from GRB rateKistler+ 09
optical depth: comparison
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Y. Inoue et al., in prep.
large differences inabsorption!-> distinguishablethrough CTA obs.
absorption: probe of Lorentz invariance violation?2.
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following Jacob & Piran 08, PRD 78, 124010
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Kifune 99, Aloisio+ 00, Protheroe & Meyer 00…
n=1 E*(TeV)0.1 111 2310 50100 110
c.f. n=2E*(=1)=0.9x1017 TeV
modified threshold
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Jacob & Piran 08
modified absorption feature
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Jacob & Piran 08
caveat: assume LIV affects only th
effect on blazar spectra
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Jacob & Piran 08
BUT- depends on EBL uncertainties- blazar spectra to >10 TeV unlikely?
CTA100 TeV observations!
effect on Galactic sources?
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Moskalenko+ 06
- Galactic 100 TeV sources likely (e.g. SNRs)- appreciable >10 TeV absorption in Galactic Center region- probe of >20 TeV LIV recovery
R,z,0,0,0
20,0,90
20,0,180
summary
crucial contribution to understanding early star/galaxy formation
detectable in high-L GRBs/blazars to z~<7 by Fermi possibly to higher z by CTA, AGIS, 5@5
probe of UV intergalactic radiation fields at high z based on a model of cosmic reionization significant >12 GeV at z~5, down to 6-8 GeV at z>~8 -> valuable info on evolution of UV IRF below Ly edge (constraints on Ly/H2 dissociating radiation) but not much effect above z~8
-ray absorption by cosmic radiation fields
BUT alternative models with different Pop II/III SFRs possible? -> distinguishable through GeV observations?
probe of Lorentz invariance violation? recovery of absorption feature above ~20 TeV effect in Galactic center sources promising?