New Limits On The Density Of The Extragalactic Background Light From The Spectra Of All Known TeV Blazars Daniel Mazin Max-Planck-Institut für Physik,

New Limits On The Density New Limits On The Density Of The Extragalactic Of The Extragalactic

Background Light From The Background Light From The Spectra Of All Known TeV Spectra Of All Known TeV

Blazars Blazars Daniel Mazin

Max-Planck-Institut für Physik, Munichand

Martin Raue (Hamburg University)

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich

What is EBL?What is EBL?

• Metagalactic Radiation Field (MRF=EBL for z=0) or evolving Extragalactic Background Light: 0.1-1000 m

• Cosmic Infrared Background (CIB) : 1-1000 m• Source contribution:

Stellar radiation dominant Gravitational (AGN, brown dwarfs, …) ~ 10% Exotic (decay of primordial particles) ~0% ?

• Difficulties: No unique spectral characteristics Strong foreground emissions


Spectral Energy Spectral Energy Distribution of the Distribution of the

EBLEBL

• Unique imprint of the history of the universe

• Test of star formation and galaxy evolution models

• Cosmological evolution models have to explain current EBL

• Opacity source of GeV-TeV photons

Redshifted stellar light Redshifted dust

light

Figure adapted from Dwek&Krennrich (2005)


EBL: current statusEBL: current status

• Robust lower limits provided by galaxy counts

• Upper limits from direct measurements

• Controversial excess measured in near infrared


Population III starsPopulation III stars

First stars, metallicity zero, z15 (20?) to z=7 (10?)

• Emitted a lot of UV light: reionization of the early Universe

How much background is due to these stars?• A lot:

Direct: Matsumoto et al. (IRTS satellite) Fluctuation analyses: Kashlinsky,

Salvaterra

• Almost nothing: Indirect constraints using TeV blazars


Attenuation of GeV-TeV Attenuation of GeV-TeV photonsphotons

• Direct measurements of the EBL in UV to IR are difficult (foregrounds)

• TeV photons are attenuated via pair production with UV to IR photons from the EBL

• Imprint of the EBL density and shape in the measured TeV spectra

e+

e-

ir

TeV

IACT

EBL


Previous problemsPrevious problems

• A: TeV crisis (pile-up at high energies)• B: Too hard spectra (spectral index < 1.5)

AB


Mrk 501 (z=0.034)Mrk 501 (z=0.034)

HEGRA results and interpretations


Other previous Other previous measured sourcesmeasured sources

HEGRA: it can be easier…

No need for exotic explanations!

unpublishe

d

Also others showed that there are EBL realizations, which give reasonable intrinsic TeV spectra (e.g. Dwek and Krennrich, Costamante et al.)


New StudyNew Study

• Provide limits on the EBL density, which do not rely on a predefined shape or model

• Treat all TeV blazars in a consistent way, using generic assumptions about the intrinsic spectrum and statistical evident exclusion criteria

• Use spectral data from all detected TeV blazars to Derive upper limits on the EBL from individual

spectra Combine these results to a single robust on

the EBL for a wide wavelength range

Aims:


New StudyNew Study

• Grid in the complete EBL range• Shapes constructed using not-interpolating splines

(superposition of smooth gauss-like base functions)• Thinnest EBL structure: Planck-like spectrum• Extremely sharp features (cut-offs) are not possible

to be modeled with this grid setup

Planck spectrum


Grid ScanGrid Scan

• Highest shape on the level of the existing upper limits

• Lowest shape on the level of the existing lower limits

• 8,064,000 shapes to test

Grid setup


TeV blazar sampleTeV blazar sample

• Select best statistics• Select hardest among similar• Select best coverage in energy


TeV blazar sampleTeV blazar sample

Scaled spectra of the used TeV blazars


Method, exclusion Method, exclusion criteriacriteria

• Likelihood ratio test to determine a “better” function

• Conservative error on spectral index : + + sys < max

Statistical tools:

• For each EBL shape and each TeV spectrum: Find a satisfactory analytical expression for the intrinsic spectrum

• evaluate fit parameters: Fitted photon index is outside of allowed

range Or: significant pile-up at high energies


Fitting functionsFitting functions

In order to allow for multi-zone (multi-component) emission,

breaks in spectrum are allowed


2 Scans2 Scans

Realistic Scan: < 1.5 Extreme Scan: < 2/3

Based on classical shock acceleration, taking maximum electron spectral index =2

Based on extreme SSC assumptions that almost monoenergetic electrons (heavily truncated electron-spectrum) are responsible for the -emission

At least part of TeV blazar spectrum: dN/dE ~ E-


Individual resultsIndividual results

• Close by and well measured: Mkn 421, Mkn 501; similar redshift but less statistics: 1ES 1959+650, 1ES 2344+514, and Mkn 180

• Intermediate distance, wide energy range: H1426+428, PKS2155-304

• Distant sources, hard spectrum: 1ES1101-232, H2356-309, 1ES1218+304

3 categories of AGN spectra:


Prototype of close by Prototype of close by source: Mkn 501source: Mkn 501

• 7766674 shapes excluded out of 8064000

• Excluded area is small because certain types of EBL shapes allowed independent on the level


Prototype of an inter-Prototype of an inter-mediate source: mediate source:

H1426+428H1426+428


• Excluded area is small because certain types of EBL shapes allowed independent on the level


Prototype of a distant Prototype of a distant source: 1ES1101-232source: 1ES1101-232


• Excluded area is rather big; given the upper limit at 0.4m, the NIR excess is excluded


Combined results: Combined results: realistic scanrealistic scan

Upper limit is defined as an envelope of all allowed shapes


Combined results: Combined results: realistic scanrealistic scan

Upper limit derived here

H.E.S.S. upper limit


Extreme Scan: Extreme Scan: > 2/3 > 2/3

• Limits are (as expected) less restrictive. Still a very high number of excluded shapes

• NIR excess at 1m is still excluded


Combined results: Combined results: extreme scanextreme scan

extreme scan (<2/3)

realistic scan (<1.5)


Systematic effectsSystematic effects

• Grid setup. The minimum width of the EBL structures that can be resolved 30%

• Evolution of EBL 10% (at most)• Absolute Energy scale of TeV blazars

2-3%• Numerical uncertainties while fitting

1-2%

Overall error (quadratic sum) 35%


Summary / ConclusionsSummary / Conclusions

• Strong limits from Optical to far IR using individual sources• Much stronger limits after combining individual results• Derived upper limits are conservative and robust for

systematic effects (estimated to be 35 %)• Submitted to A&A, astro-ph/0701694

Results can be interpreted in two ways:• NIR excess not extragalactic and source

counts resolved almost everything• Blazar physics has to be reconsidered

(improbable)


BACKUPBACKUP


Systematic check: Systematic check: resolution of the gridresolution of the grid

n16 is default. We tested n18 and n20. Up to 35% difference but


Systematic check: Systematic check: resolution of the gridresolution of the grid

n20 results in shapes which are not realistic (too many bumps ) treat as an extreme case


Systematic check: Systematic check: energy shift by 15%energy shift by 15%

Shift by 15% results in shifting the sensitivity range of the scan. Not a big effect.


Katarzynski et al.Katarzynski et al.

• Almost monoenergetic electron population (truncated power law spectrum?)


Conclusions / OutlookConclusions / Outlook

• GeV-TeV spectra of extragalactic objects are a powerful tool to probe the EBL models

• Can constrain SED of EBL• Currently on the edge (EBL, which is

consistent with galaxy counts, requires steep rising blazar spectra).

• Need blazar spectra below and around 100 GeV to observe the intrinsic spectra

• Need blazar spectra up to 20-30 TeV to obtain EBL limits in MIR and FIR (10-30 m)

Documents

New Limits On The Density Of The Extragalactic Background Light From The Spectra Of All Known TeV Blazars Daniel Mazin Max-Planck-Institut für Physik,