Gamma-ray Blazars Present Status and Future Prospects

1. Gamma-ray BlazarsPresent Status and Future Prospects Deirdre Horan Harvard-Smithsonian Center for Astrophysics

2. Outline • Introduction • Detecting gamma-rays • The gamma-ray sky • Blazars • Different classes of blazar • The “Blazar Sequence” • Finding blazars • Search strategies • Some results

3. Gamma-Ray Energy Regimes “High Energy (HE)” “Very High Energy (VHE)” 1 MeV 10 MeV 100 MeV 1 GeV 10 GeV 100 GeV 1 TeV 10 TeV EGRET ~ 20 MeV – 30 GeV VERITAS, H.E.S.S., … ~50 GeV – 50 TeV Whipple ~ 300 GeV – 10 TeV LAT ~ 20 MeV – 300 GeV

4. Compton Gamma Ray Observatory • NASA “Great Observatory” • 1991-2000 • OSSE, COMPTEL, BATSE and EGRET

5. Detection Technique: EGRET Energy Range: 20 MeV – 30 GeV

6. VHE ground-based astronomy

7. VHE ground-based astronomy

8. Large Collection Area

9. The Early Days … Crimea Experiment 1960 - 1965

10. Whipple 10m Telescope Pioneered the IMAGING technique The Whipple 10m Telescope The 490-pixel Camera

11. Sample Events Camera Hadron

12. Sample Events Camera Gamma-ray

13. Gamma-ray Source Catalogs

14. 100 MeV Catalog after EGRET Hartman et al., 1999, ApJS, 123, 79

15. 100 MeV Catalog before EGRET

16. 100 MeV Catalog after EGRET Hartman et al., 1999, ApJS, 123, 79

17. 100 MeV Catalog after EGRET Hartman et al., 1999, ApJS, 123, 79 66 [27] Blazars Mostly Flat Spectrum Radio Quasars

18. TeV Sky Map 2005

19. TeV Sky Map 2005 19 Sources [13 confirmed]

20. TeV Sky Map 2005: Blazars Eight Blazars  All BL Lacertae Objects

21. Comparison of EGRET and Whipple Since VHE Instruments are not all-sky monitors  Need targets

22. Blazars (Buckley, Science, 1998)

23. Active Galactic Nuclei

24. Blazars (< 5% of all AGN) • Most powerful AGN known • Jet “points” toward us • Flat radio spectrum • Large amplitude variability • Optical polarization • Spectral energy distribution (Buckley et al, 1996, ApJ, 472, L9) (Biretta et al. Hubble Heritage Team (STScI/AURA) NASA) (Buckley et al, 1996, ApJ, 472, L9)

25. Spectral Energy Distribution • Synchrotron Self-Compton • External Compton • Proton-induced cascades • Proton synchrotron

26. Blazars Strong emission lines Non-existent or weak emission lines

27. Blazars FSRQs BL Lacs

28. Blazars FSRQs BL Lacs High Energy ~10 MeV to ~100 GeV Very High Energy ~300 GeV to ~10 TeV

29. Flat Spectrum Radio Quasars • Radio loud quasars • 5-10% of quasars • Broad emission lines • If have high degree of polarization (> 3%) • “Highly Polarized Quasars” (HPQ) • More luminous than BL Lacs • Larger redshifts

30. BL Lacertae Objects (BL Lacs) Almost complete lack of emission lines! Radio Surveys X-ray Surveys “RBLs” “XBLs” (Guetta et al., 2004, A&A, 421, 877)

31. BL Lacertae Objects (BL Lacs) Almost complete lack of emission lines! Radio Surveys X-ray Surveys “RBLs” “XBLs” Intrinsic differences  Not just orientation A more physical classification (Padovani & Giommi, 1995, ApJ, 444, 567) “Low-frequency peaked BL Lac” “High-frequency peaked BL Lac” LBL HBL

32. BL Lacs: Subclassification LBLs HBLs Giommi, Ansari & Micol, 1995, A&AS, 109, 267

33. Deeper Surveys RGB: ROSAT + Green Bank REX: NVSS + ROSAT Laurent-Muehleisen, 1999, ApJ, 525, 127; Caccianiga et al., 1999, ApJ, 513, 51

34. 26 The Blazar Sequence (Fossati et al., 1998; Krawczynski 2003)

35. Increased dominance of an external radiation field, total energy density and injected power as one progresses through the HBL->LBL->FSRQ. (Ghisellini 1998). There have also been suggestion that this could be an evolutionary scenario where there is a reduction of black hole accretion power with time (Boettcher and Dermer 2002). Cavaliere and D'Elia (2002) also consider the blazar sequence to be due to systematic changes in accretion rate. They also use this to explain the differences in evolution between FSRQsand BL Lacs. Georganopolous (2000) proposed that the observed distribution of properties could be due to a combination of orientation and intrinsic luminosity. Possible Explanations of Sequence

36. The Blazar Sequence 106 105 HBL 104 Гpeak LBL HPQ 103 LPQ 102 101 U, linj, lext, Lc / Ls

37. Searching for Blazars at Very High Energies

38. Blazar Program Outline • Discovery • Find more TeV emitters including other blazar classes • Study these (spectra, flux, blazar sequence, population studies)  Acquire more known TeV Emitters… • Study Known TeV Emitters • More accurate spectra on known the 5 TeV sources • Low State Spectra, e.g. Mrk501 • EBL • Variability Studies, e.g. Mrk421 …  Understand blazars better at TeV energies … • Modeling of Blazars • Multiwavelength studies very helpful … • Hadronic/Leptonic models • Broadband SED  Blazar Sequence?  Gain a greater understanding of the blazar class… • What about other classes of AGN?

39. The 6 Confirmed TeV Blazars

40. VERITAS

41. Search Strategies • Try to identify when blazar is in high emission state: • Monitor activity in other wavebands • Establish list of likely candidates based on broadband properties: • Study these in detail (and monitor in x-ray) • Monitor likely candidates on a regular basis with VHE telescope

42. Whipple Blazar Survey: Horan et al., 2004, ApJ 603, 51

43. Whipple Blazar Survey • 29 Objects observed • Mostly z<0.2 • 5 EGRET sources Horan et al., 2004, ApJ 603, 51

44. Whipple Blazar Survey

45. Whipple Blazar Survey • 29 Objects observed • Mostly z<0.2 • 5 EGRET sources • No detections • Upper limits on VHE emission • If we observed Markarian 501 in this mode … Horan et al., 2004, ApJ 603, 51

46. Markarian 501 Lightcurve (Quinn et al., 1999, ApJ, 518, 693)

47. 1ES 1959+650 (Holder et al. 2002)

48. 1ES 1959+650 6 TeV Flux [Crab] 4 2 0 10 keV Flux [keV-1 cm-2 s-1] 0.002 0 3-25 keV Photon Index 2.5 2.0 1.5 0 20 40 60 80 100 Date [MJD – 52400] (Krawczynski et al. 2003)

49. Correlated Lightcurves (Buckley 2004)

50. Monitor Blazars in other Wavebands All-Sky Monitor Burst Alert Telescope Large Area Telescope ~2 – 10 keV ~15 – 150 keV ~20 MeV – 300 GeV