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, Munich and Martin Raue (Hamburg University)

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich What is EBL? Metagalactic Radiation Field (MRF=EBL for z=0) or evolving Extragalactic Background Light:  m Cosmic Infrared Background (CIB) :  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

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Spectral Energy Distribution of the EBL 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)

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich EBL: current status Robust lower limits provided by galaxy counts Upper limits from direct measurements Controversial excess measured in near infrared

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Population III stars First stars, metallicity zero, z  15 (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

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Attenuation of GeV-TeV photons 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+ e-e-  ir  TeV IACT EBL

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Absorption of the energy spectra of AGNs Attenuation coefficient Energy Measured flux is a function of  energy and a red shift z Not just a simple cut- off in spectra expected Fazio-Stecker relation: GeV-TeV energy with  =1 At 10 GeV: the universe is transparent

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Previous problems A: TeV crisis (pile-up at high energies) B: Too hard spectra (spectral index < 1.5) A B

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Mrk 501 (z=0.034) HEGRA results and interpretations

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Other previous measured sources HEGRA: it can be easier… No need for exotic explanations! unpublished Also others showed that there are EBL realizations, which give reasonable intrinsic TeV spectra (e.g. Dwek and Krennrich, Costamante et al.)

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

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

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Grid 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 blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich TeV blazar sample Select best statistics Select hardest among similar Select best coverage in energy

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich TeV blazar sample Scaled spectra of the used TeV blazars

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Method, exclusion criteria 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

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Fitting functions In order to allow for multi-zone (multi- component) emission, breaks in spectrum are allowed

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich 2 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 - 

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Individual results Close by and well measured: Mkn 421, Mkn 501; similar redshift but less statistics: 1ES , 1ES , and Mkn 180 Intermediate distance, wide energy range: H , PKS Distant sources, hard spectrum: 1ES , H , 1ES categories of AGN spectra:

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Prototype of close by source: Mkn shapes excluded out of Excluded area is small because certain types of EBL shapes allowed independent on the level

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Prototype of an inter-mediate source: H shapes excluded out of Excluded area is small because certain types of EBL shapes allowed independent on the level

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Prototype of a distant source: 1ES shapes excluded out of Excluded area is rather big; given the upper limit at 0.4  m, the NIR excess is excluded

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Combined results: realistic scan Upper limit is defined as an envelope of all allowed shapes

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Combined results: realistic scan Upper limit derived here H.E.S.S. upper limit

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Extreme Scan:  > 2/3 Limits are (as expected) less restrictive. Still a very high number of excluded shapes NIR excess at 1  m is still excluded

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Combined results: extreme scan extreme scan (  <2/3) realistic scan (  <1.5)

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

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Summary / 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/ Results can be interpreted in two ways: NIR excess not extragalactic and source counts resolved almost everything Blazar physics has to be reconsidered (improbable)

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

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Systematic check: resolution of the grid n16 is default. We tested n18 and n20. Up to 35% difference but 

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Systematic check: resolution of the grid n20 results in shapes which are not realistic (too many bumps )  treat as an extreme case

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Systematic check: energy shift by 15% Shift by 15% results in shifting the sensitivity range of the scan. Not a big effect.

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Katarzynski et al. Almost monoenergetic electron population (truncated power law spectrum?)

TeV blazars and Cosmic Background Radiation Daniel Mazin, MPI, Munich Conclusions / 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 TeV to obtain EBL limits in MIR and FIR (10-30  m)