Scuola di Dottorato di Ricerca in Fisica Ciclo XXIII

1. TeV Observations of blazars and constraints on their redshifta detailed study of PG 1553+113 and PKS 1424+240 with MAGIC ScuoladiDottoratodiRicerca in Fisica Ciclo XXIII DirettoredellaScuola: Prof. Attilio Stella Supervisore: Prof. MosèMariotti Correlatore: Dott. FabrizioTavecchio Dottoranda: Elisa Prandini Padova, March 16th 2011

2. Outline • Introduction: VHE gamma ray astrophysics • The Physics case: gamma rays from Active Galactic Nuclei • MAGIC Observations • 5 years of PG 1553+113 data • The source PKS 1424+240 • Constraints on blazars distances • Limits on the redshifts • A new empirical method • Conclusions and Outlook

3. The Physics Case: VHE g-rays Very High Energy g-rays: E > 100 GeV [TeV regime]

4. The Physics Case: VHE g-rays • Propagate from cosmological distances: • From their interactions  cosmology • Ideal messengers of non thermal processes in the Universe • Neutrality Very High Energy g-rays: E > 100 GeV [TeV regime]

5. The VHE gamma-ray sky

6. The VHE gamma-ray sky: Extragalactic Component All but two sources are Active Galactic Nuclei!

7. Active Galactic Nuclei: the most powerful accelerators • Supermassiveblack holes (109 solar masses) • Are probably at the center of every galaxy • In some cases (radio loud AGNs) there are two narrow jets of particles • The emitted spectrum is a superposition of several components

8. Active Galactic Nuclei: the most powerful accelerators Supermassiveblack holes (109 solar masses) Are probably at the center of every galaxy In some cases (radio loud AGNs) there are two narrow jets of particles The emitted spectrum is a superposition of several components

9. Radio Loud AGNs: Unified Scheme The observed radiation depends on the viewing angle • Radio galaxies • Blazars • FSRQ • BL Lac Objects

10. Radio Loud AGNs: Unified Scheme The observed radiation depends on the viewing angle • Radio galaxies • Blazars • FSRQ • BL Lac Objects

11. The blazars Spectral Energy Distribution • non thermaland covers the entire e.m. spectrum • beaming effects • Two bumps structure: • Synchrotron emission • High energy emission • Leptonic models (Inverse Compton) • Hadronic models (p0 decay) Simplified SED nFn eVkeVMeVGeVTeV log(E)

12. The blazars SED: Mkn 421 a real example - Clear two bump structure - High variability

13. The study of VHE gamma rays from blazars: why? • A new unexplored regime! • Characterize the emitting region • Discriminate the emission models • Up to z~0.5: cosmology! Simplified SED nFn eVkeVMeVGeVTeV log(E)

14. The study of VHE gamma rays from blazars: why? • A new unexplored regime! • Characterize the emitting region • Discriminate the emission models • Up to z~0.5: cosmology! Simplified SED nFn eVkeVMeVGeVTeV log(E) HOW?

15. Detection technique: Imaging Atmospheric Cherenkov Telescopes VHE gamma ray Earth atmosphere Atmospheric shower (electromagnetic) ~ 1o ~ 10 km Cherenkov cone ~ 120 m

16. Detection technique: Imaging Atmospheric Cherenkov Telescopes VHE gamma ray Earth atmosphere Atmospheric shower (electromagnetic) ~ 1o ~ 10 km Cherenkov cone ~ 120 m

17. Images Background Signal [Gamma-like]

18. IACTs in the world MAGIC VERITAS H.E.S.S.

19. The MAGIC Telescopes ACQUISITION SYSTEM IPE IPE IPE NET CE STRUCTURE SIGNAL TRANSPORT CAMERA MIRRORS

20. The MAGIC Telescopes MAGIC II (2009) MAGIC I (2004) • Energy threshold 60 GeV • Energy Resolution ~20% • FOV 3.5o • Angular Resolution ~0.1o • Sensitivity (5 s in 50 hours) ~1% Crab Nebula flux (> 100 GeV)

21. Outline • Introduction: VHE gamma ray astrophysics • The Physics case: gamma rays from Active Galactic Nuclei • MAGIC Observations of AGNs • 5 years of PG 1553+113 data • The source PKS 1424+240 • Constraints on blazars distances • Limits on the redshifts • A new empirical method • Conclusions and Outlook

22. The blazarsPG 1553+113 &PKS 1424+240 • Is a new detectedTeV emitter • Observed by MAGIC since 2006, detected in 2009 • My analysis: 2009 (M1) and 2010 (stereo) data analysis • Is a well known TeV emitter • Observed by MAGIC since 2005 • My analysis: from 2007 to 2009 (only M1) Both sources have unknown/uncertain distance (redshift)

23. The blazarsPG 1553+113 &PKS 1424+240 • Is a well known TeV emitter • Observed by MAGIC since 2005 • My analysis: from 2007 to 2009 (only M1) • Is a new detectedTeV emitter • Observed by MAGIC since 2006, detected in 2009 • My analysis: 2009 (M1) and 2010 (stereo) data analysis Both sources have unknown/uncertain distance (redshift)

24. The blazarsPG 1553+113 &PKS 1424+240 • Is a well known TeV emitter • Observed by MAGIC since 2005 • My analysis: from 2007 to 2009 (only M1) • Is a new detectedTeV emitter • Observed by MAGIC since 2006, detected in 2009 • My analysis: 2009 (M1) and 2010 (stereo) data analysis Both sources have uncertain/unknown distance (redshift)

25. The Distance PKS 1424+240 • Largely uncertain: • z > 0.06 [PG, Falomo & Scarpa 1995] • z > 0.67 [HST, Sbarufatti et al. 2005] Falomo & Scarpa 1995 PG 1553+113 Treves et al. 2007 z > 0.09 [VLT no lines, Sbarufatti et al. 2006a] z > 0.78 [HST, Sbarufatti et al. 2006b] z > 0.25 [HST, new method for gal. magnitude, Treves et al. 2007] 0.4 < z < 0.58 [ISM-IGM lines, Danforth et al. 2010] z < 0.58 [TeV, Mazin & Goebel 2007, E.P. et al. 2009]

26. PG 1553+113: data analysis and results • Signal Search • Spectral Analysis • Time Analysis • Multiwavelength View of the Source • Spectral Energy Distribution (SED)

27. PG 1553+113: data analysis and results The MAGIC Collaboration Submitted to ApJ 2007 2008 A clear signal every year 2007 (11.5 hrs) : 5.8 s 2008 (8.7 hrs) : 8.1 s 2009 (8.5 hrs) : 4.2 s 2009 Signal Search

28. PG 1553+113: data analysis and results The MAGIC Collaboration Submitted to ApJ Differential energy spectrum dN/dE = F0 (E/E0)-G (Crab Nebula G~2.5) Signal Search Spectral Analysiss

29. PG 1553+113: data analysis and results The MAGIC Collaboration Submitted to ApJ • One of the best followed TeV sources • Yearly variations (4%- 11% Crab flux) • No clear intra-year variations Signal Search Spectral Analysis Time Analysis

30. Multiwavelength PG 1553+113 The MAGIC Collaboration Submitted to ApJ

31. PG 1553+113: data analysis and results • Signal Search • Spectral Analysis • Time Analysis • Multiwavelength View of the Source • Spectral Energy Distribution (SED)

32. Spectral Energy Distribution • Model Parameters • B = 0.5 G • R ~1016 cm • - Lr= 6 x 1044 erg/s • Assumption: z=0.4 All the results are in agreement with the leptonic model! The MAGIC Collaboration Submitted to ApJ

33. Spectral Energy Distribution • Model Parameters • B = 0.5 G • R ~1016 cm • - Lr= 6 x 1044 erg/s • Assumption: z=0.4 All the results are in agreement with the leptonic model! The MAGIC Collaboration Submitted to ApJ

34. PKS 1424+240: data analysis and results • Signal Search • Spectral Analysis • Time Analysis • Spectral Energy Distribution (SED)

35. PKS 1424+240: data analysis and results 2009 • Signal Search • - 2009 (13 hrs): 4.2 s DISCOVERY of the source at TeV (together with VERITAS)! • 2010 (16.6 hrs): 5.75 s • past MAGIC observations: no signal --ATel #2098-- 2010 (stereoscopic data)

36. PKS 1424+240: data analysis and results Individual years specra Mean spectrum The MAGIC Collaboration Paper in preparation • Signal Search • Spectral Analysis

37. The MAGIC Collaboration Paper in preparation PKS 1424+240: data analysis and results • Signal Search • Spectral Analysis • Time Analysis • Results: • Monthly variations in 2009 • Year variations •  the source is highly variable (typical of BL Lacs)

38. PKS 1424+240: data analysis and results • Signal Search • Spectral Analysis • Time Analysis • Spectral Energy Distribution (SED) distance of the source?

39. Outline • Introduction: VHE gamma ray astrophysics • The Physics case: gamma rays from Active Galactic Nuclei • MAGIC Observations of AGNs • 5 years of PG 1553+113 data • The source PKS 1424+240 • Constraints on blazars distances • Limits on the redshifts • A new empirical method • Conclusions and Outlook

40. VHE photons absorption by the Extragalactic Background Light x x x VHE photon + diffuse light  electron-positron pairs production VHEEBLe+e- Absorption: dF/dEobs= (dF/dEem) e-t

41. VHE photons absorption by the Extragalactic Background Light EBL SED Hauser and Dwek (2001) VHE photon + diffuse light  electron-positron pairs production VHEEBLe+e-

42. VHE photons absorption by the Extragalactic Background Light Dominguez et al. (2011) VHE photon + diffuse light  electron-positron pairs production VHEEBLe+e- Large uncertainties!

43. Absorption: dF/dEobs= (dF/dEem) e-t g-gopacity Our range of observations z= 1 z= 0.5 z= 0.3 z= 0.1 z= 0.03 z= 0.01 z= 0.003 EBL Model Franceschini et al. (2008)

44. Absorption: dF/dEobs= (dF/dEem) e-t g-gopacity Strong suppression z= 1 z= 0.5 z= 0.3 z= 0.1 z= 0.03 z= 0.01 z= 0.003 EBL Model Franceschini et al. (2008)

45. EBL absorption effect EBL model: Franceschini et al. (2008)

46. The effect of EBL on blazars spectra SED nFn eVkeVMeVGeVTeV log(E) EBL: the EMITTED spectrum is deformed The absorption is related to the distance of the source

47. Constraints from the absorption EBL model SED nFn Hypotheses on the intrinsic spectrum eVkeVMeVGeVTeV log(E) Blazar distance

48. Constraints from the absorption EBL model SED nFn Hypotheses on the intrinsic spectrum eVkeVMeVGeVTeV log(E) Blazar distance My work

49. EP, BonnoliG.,MaraschiL.,Mariotti M. & Tavecchio F., MNRAS 405,2010,L76 Constraints on blazars distances • We propose to use the lower energy slope as limiting slopefor the TeV de-absorbed spectrum in order to set a limit on the source distance Abdo et al. (2010)

50. EP, BonnoliG.,MaraschiL.,Mariotti M. & Tavecchio F., MNRAS 405,2010,L76 Constraints on blazars distances • We propose to use the lower energy slope as limiting slopefor the TeV de-absorbed spectrum in order to set a limit on the source distance Below 100 GeV: Fermi/LAT measure (launched in 2008) Abdo et al. (2010)