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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2

3

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1

2

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10

30252015105 E [GeV]

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10

53

2

fiducial K04

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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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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?