1. TeV blazars and their distance E. Prandini, Padova University & INFN G. Bonnoli, L. Maraschi, M. Mariotti and F. Tavecchio Cosmic Radiation Fields - Sources in the early Universe Hamburg 9-12 November 2010

2. Outline  TeV blazars and EBL  Combined GeV+TeV spectra:  TEST the max slope hypothesis  Use it to set u.l. on the distance of unknown z sources  Propose an empirical method to estimate blazars z  Update: new data E. Prandini TeV blazars and their distance CRF2010, Hamburg2

3. TeV Blazars Blazars: “radio loud” AGNs with the jet almost aligned to the line of sight of the observer FermiTeV The blazar emission is non thermal and covers the entire e.m. spectrum It is composed by two bumps: Syncrotron emission High energy emission E. Prandini TeV blazars and their distance CRF2010, Hamburg3

4. The effect of EBL on blazars spectra E. Prandini TeV blazars and their distance CRF2010, Hamburg  The blazar EMITTED spectrum is partially absorbed and deformed (at TeV instruments energy range)  The absorption is related to the DISTANCE of the source  BUT: some blazars have unknown distance! log(E) log(energy density) eV keV MeV GeV TeV SED 4 EBL: the EMITTED spectrum is deformed Hauser & Dwek (2001) Hauser & Dwek (2001)

5. Constraints from the absorption E. Prandini TeV blazars and their distance CRF2010, Hamburg5 log(E) log(energy density) eV keV MeV GeV TeV SED EBL model Hypotheses on the intrinsic spectrum Blazar distance

6. Constraint on the distance E. Prandini TeV blazars and their distance CRF2010, Hamburg With Fermi + TeV spectral points the second bump is resolved! Use the Fermi slope as limiting slope for the TeV de-absorbed spectrum in order to set a limit on the source distance: z* Observed spectrum De-absorbed spectrum 6 Abdo et al. (2010) Abdo et al. (2010)

7. The sample E. Prandini TeV blazars and their distance CRF2010, Hamburg Fermi TeV sources (from Abdo et al. 2009) + TeV spectra from last generation of Cherenkov Telescopes (Magic, Veritas, H.E.S.S.) 14 sources with well known redshift 2 sources of uncertain redshift (S5 0716+714 and 3C 66A) Spectral break 7

8. Results: z* VS z[true] E. Prandini TeV blazars and their distance CRF2010, Hamburg All the limits (z*) are above the bisector Open points: uncertain redshift: the only values below the bisector! THIS TEST CONFIRMS THAT THE SLOPE MEASURED BY FERMI CAN BE USED AS A LIMIT ON THE VHE SLOPE FOR CONSTRAINING THE REDSHIFT 8 bisector Uncertain redshift

9. A step further: from limit to estimate E. Prandini TeV blazars and their distance CRF2010, Hamburg Is there any relation among z* and z[true]? Following Stecker & Scully, 2010 (1): linear expression for the steepening of the observed TeV slope z* is also related to the steepening: LINEAR RELATION Linear fit: z* = A + B z[true] Ref (1): Stecker and Scully, 2010 ApJ 709 L124 9

10. Reconstructed redshift E. Prandini TeV blazars and their distance CRF2010, Hamburg We can use the fit to ESTIMATE THE REDSHIFT of a source (and not only a limit) Method:  De-absorb TeV data according to the Fermi spectral measure  Estimate z* (and obtain a LIMIT on the distance)  Invert the linear relation and estimate z[rec] z[rec] = (z* - A)/B 10

11. Test on known distance blazars E. Prandini TeV blazars and their distance CRF2010, Hamburg Residuals distribution z[true]-z[rec] Sigma of the Gaussian fit: 0.05 Uncertain redshift sources are well outside the distribution... 11

12. Comparison between different EBL Models Similar results with extreme EBL models: Low EBL: Kneinske & Dole 2010 Mean EBL: Franceschini et al. 2008 High EBL: Stecker et al. 2006 12E. Prandini TeV blazars and their distance CRF2010, Hamburg

13. Conclusions of the Preliminary study E. Prandini TeV blazars and their distance CRF2010, Hamburg Combining Fermi and TeV spectra: the max hardness hypothesis is successfully tested on known redshift sources  LIMIT on z Moreover: we found a linear relation between the z limit (z*) and the real redshift (z[true]), that can be inverted and used for the estimate of the unknown distance of blazars, z[rec]. The result is EBL model independent! According to our results, the “uncertain” z attributed to 3C66A and S5 0716+714 is largely overestimated or these sources are peculiar More details in: E. Prandini et al. “Constraining blazar distances with combined Fermi and TeV data: an empirical approach”, MNRAS 405, L76-L80 (2010) 13

14. Update E. Prandini TeV blazars and their distance CRF2010, Hamburg14  Since last year:  New Fermi catalogue (1 y)  New TeV sources  New EBL model (Dominguez et al. 2010)

15. The updated sample E. Prandini TeV blazars and their distance CRF2010, Hamburg15

16. Results: Franceschini & Dominguez models E. Prandini TeV blazars and their distance CRF2010, Hamburg16  The two EBL models give very similar results Prandini et al., in prep.

17. Application: the distance of PKS 1424+240 E. Prandini TeV blazars and their distance CRF2010, Hamburg  estimate on the distance of unknown redshift sources observed at both TeV and GeV ranges: PKS 1424+240 17 Deabsorbed spectrum of PKS 1424+240 (Fermi 1y catal., Franceschini et al. EBL model)  z* = 0.45 ± 0.15  z[rec] = 0.26 ± 0.06 Prandini et al., in prep.

18. Conclusions…  The updated work basically confirms the results  Fermi slope as limiting slope for TeV blazars  Empirical law allows an estimate on blazars distance  Increase statistics (new TeV sources)  Use simultaneous Fermi - TeV data  Extend the z range (CTA?) 18 … & Outlook Newly detected TeV extragalactic objects: E. Prandini TeV blazars and their distance CRF2010, Hamburg Danke!

19. E. Prandini TeV blazars and their distance CRF2010, Hamburg19 Backup slides

20. The TeV extragalactic sky E. Prandini TeV blazars and their distance CRF2010, Hamburg 45 sources (November 2010) 20

21. Assumptions E. Prandini TeV blazars and their distance CRF2010, Hamburg  Not simultaneous GeV-TeV observations  But slopes seem somehow less variable than the corresponding fluxes (es. 1ES 1218+304 Veritas Coll.)  Different TeV instruments, sensitivities and energy thresholds (systematics?)  IC peak position: could be different 21

22. Results: z* VS z[true] in LINEAR SCALE E. Prandini TeV blazars and their distance CRF2010, Hamburg22

23. Application: the distance of PKS 1424+240 E. Prandini TeV blazars and their distance CRF2010, Hamburg23

24. Steepening of blazars spectra E. Prandini TeV blazars and their distance CRF2010, Hamburg Stecker & Scully, 2010 24

25. Results: Linear Relation E. Prandini TeV blazars and their distance CRF2010, Hamburg25 Linear releation still fits well!

26. z*: updated values E. Prandini TeV blazars and their distance CRF2010, Hamburg26

27. z[rec] E. Prandini TeV blazars and their distance CRF2010, Hamburg27