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TeV blazars and their distance

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TeVblazarsand 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

- TeVblazarsand EBL
- Combined GeV+TeV spectra:
- TEST the max slope hypothesis
- Use it to set u.l. on the distance of unknown z sources
- Propose anempirical method to estimate blazarsz

- Update: new data

E. Prandini TeV blazars and their distance CRF2010, Hamburg

- Blazars:“radio loud” AGNs with the jet almost aligned to the line of sight of the observer

Simplified SED model of emitted spectrum of TeVblazars

log(energy density)

- The blazar emission isnon thermal and covers the entire e.m. spectrum
- It is composed by two bumps:
- Syncrotron emission
- High energy emission

eVkeVMeVGeVTeV

log(E)

Fermi

TeV

E. Prandini TeV blazars and their distance CRF2010, Hamburg

Hauser & Dwek (2001)

- 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 blazarshave unknown distance!

SED

log(energy density)

eVkeVMeVGeVTeV

log(E)

EBL: the EMITTED spectrum is deformed

E. Prandini TeV blazars and their distance CRF2010, Hamburg

EBLmodel

SED

log(energy density)

Hypotheses on the intrinsic spectrum

eVkeVMeVGeVTeV

log(E)

Blazar distance

E. Prandini TeV blazars and their distance CRF2010, Hamburg

- With Fermi + TeV spectral points the second bump is resolved!

Abdo et al. (2010)

Observed spectrum

De-absorbed spectrum

- Use the Fermi slope as limiting slopefor the TeV de-absorbed spectrum in order to set alimit on the source distance:z*

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

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!

Uncertain redshift

bisector

THIS TEST CONFIRMS THAT THE SLOPE MEASURED BY FERMI CAN BE USED AS A LIMIT ON THE VHE SLOPE FOR CONSTRAINING THE REDSHIFT

E. Prandini TeV blazars and their distance CRF2010, Hamburg

- Is there any relation among z* and z[true]?
- FollowingStecker & 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 ApJ709 L124

E. Prandini TeV blazars and their distance CRF2010, Hamburg

- We can use the fit to estimate the redshiftof a source (and not only a limit)
- Method:
- De-absorbTeV 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

E. Prandini TeV blazars and their distance CRF2010, Hamburg

Residuals distributionz[true]-z[rec]

- Sigma of the Gaussian fit: 0.05
- Uncertain redshiftsources are well outside the distribution...

E. PrandiniTeVblazars and their distance CRF2010, Hamburg

- Similar results with extreme EBL models:
- Low EBL: Kneinske & Dole 2010
- Mean EBL: Franceschini et al. 2008
- High EBL: Stecker et al. 2006

E. PrandiniTeVblazars and their distance CRF2010, Hamburg

- Combining Fermi and TeV spectra: themax hardness hypothesis is successfully testedon known redshiftsources LIMIT on z
- Moreover: we found a linear relation between the zlimit (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)

E. Prandini TeV blazars and their distance CRF2010, Hamburg

- Since last year:
- New Fermi catalogue (1 y)
- New TeV sources
- New EBL model (Dominguez et al. 2010)

E. Prandini TeV blazars and their distance CRF2010, Hamburg

E. Prandini TeV blazars and their distance CRF2010, Hamburg

Confirm previous results

- The two EBL models give very similar results

Prandini et al. , in prep.

Prandini et al. , in prep.

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

- 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.

E. PrandiniTeVblazars and their distance CRF2010, Hamburg

- The updated work basically confirms the results
- Fermi slope as limiting slope for TeVblazars
- Empirical law allows an estimate on blazars distance

- Increase statistics (new TeV sources)
- Use simultaneous Fermi - TeV data
- Extend the z range (CTA?)

Newly detected TeV extragalactic objects:

… & Outlook

Danke!

E. PrandiniTeVblazars and their distance CRF2010, Hamburg

Backup slides

E. Prandini TeV blazars and their distance CRF2010, Hamburg

45 sources (November 2010)

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

E. Prandini TeV blazars and their distance CRF2010, Hamburg

E. Prandini TeV blazars and their distance CRF2010, Hamburg

E. Prandini TeV blazars and their distance CRF2010, Hamburg

Stecker & Scully, 2010

E. Prandini TeV blazars and their distance CRF2010, Hamburg

Linear releation still fits well!

E. Prandini TeV blazars and their distance CRF2010, Hamburg

E. Prandini TeV blazars and their distance CRF2010, Hamburg

E. Prandini TeV blazars and their distance CRF2010, Hamburg