1 / 23

Models for non-HBL VHE Gamma-Ray Blazars

0. Models for non-HBL VHE Gamma-Ray Blazars. Markus B öttcher Ohio University, Athens, OH, USA. “TeV Particle Astrophysics” SLAC, Menlo Park, CA, July 13 – 17, 2009. Motivation. Until a few years ago, all TeV blazars were high-frequency-peaked BLLac objects (HBLs).

baxter
Download Presentation

Models for non-HBL VHE Gamma-Ray Blazars

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 0 Models for non-HBL VHE Gamma-Ray Blazars Markus Böttcher Ohio University, Athens, OH, USA “TeV Particle Astrophysics” SLAC, Menlo Park, CA, July 13 – 17, 2009

  2. Motivation Until a few years ago, all TeV blazars were high-frequency-peaked BLLac objects (HBLs). Recently, the Intermediate BL Lac objects W Comae and 3C66A (VERITAS), the low-frequency-peaked BL Lac object (LBL) BL Lacertae, and even the FSRQ 3C279 (MAGIC) and were detected in TeV g-rays. Similar in physical parameters to other TeV blazars (HBLs)? (→ SSC dominated?) Or more similar to LBLs? (→ EC required?)

  3. 0 Leptonic Blazar Model Synchrotron emission Injection, acceleration of ultrarelativistic electrons Relativistic jet outflow with G ≈ 10 nFn g-q Qe (g,t) n Compton emission g1 g2 g Radiative cooling ↔ escape => nFn g-q or g-2 n Qe (g,t) g-(q+1) Seed photons: Synchrotron (within same region [SSC] or slower/faster earlier/later emission regions [decel. jet]), Accr. Disk, BLR, dust torus (EC) g1 gb g2 g gb: tcool(gb) = tesc gb g1 g2

  4. 0 Spectral modeling results along the Blazar Sequence: Leptonic Models High-frequency peaked BL Lac (HBL): Low magnetic fields (~ 0.1 G); High electron energies (up to TeV); Large bulk Lorentz factors (G > 10) The “classical” picture Synchrotron No dense circumnuclear material → No strong external photon field SSC

  5. 0 Spectral modeling results along the Blazar Sequence: Leptonic Models Radio Quasar (FSRQ) High magnetic fields (~ a few G); Lower electron energies (up to GeV); Lower bulk Lorentz factors (G ~ 10) External Compton Plenty of circumnuclear material → Strong external photon field Synchrotron

  6. The Quasar 3C279 on Feb. 23, 2006 0 nFn, g ~ 5x1013 Jy Hz nFn,sy ~ 1013 Jy Hz • Feb. 23: • High optical flux • Steep optical spectrum (a = 1.7 -> p = 4.4) • High X-ray flux • Soft X-ray spectrum nsy ~ 5x1013 Hz => esy ~ 4x10-7 ng ~ 1025 Hz => eg ~ 105 Accretion disk: LD ~ 2x1045 erg/s; eD ~ 10-5

  7. Parameter Estimates: SSC • Optical index a = 1.7 => p = 4.4 => cooling break (3.4 -> 4.4) would not produce a nFn peak => peak must be related to low-energy cutoff, gp = g1 • Separation of synchrotron and gamma-ray peak => gp = (eg/esy)1/2 ~ 1.6x105 • nsy = 4.2x106gp2 BG D/(1+z) Hz => BG D1 ~ 7x10-5

  8. Parameter Estimates: External Compton • External photons of es ~ 10-5 can be Thomson scattered up to eg ~ 105 => Accretion disk photons can be source photon field. • Location of gamma-ray peak => gp = (eg/[G2es])1/2 ~ 104G1-1 • nsy = 4.2x106gp2 BG D/(1+z) Hz => BG ~ 1.8x10-2G12 D1-1 • Relate synchrotron flux level to electron energy density, eB = u’B/u’e => eB ~ 10-8G17 R163 a) G ~ 15, B ~ 0.03 G, eB ~ 10-7 b) eB ~ 1, B ~ 0.25 G, G ~ 140 R16-3/7

  9. Attempted leptonic one-zone model fit, EC dominated X-rays severely underproduced! (Bӧttcher, Reimer & Marscher 2009)

  10. Alternative: Multi-zone leptonic model X-ray through gamma-ray spectrum reproduced by SSC; optical spectrum has to be produced in a different part of the jet. • Linj = 2.3*1049 erg/s • gmin = 104 • gmax = 106 • q = 2.3 • B = 0.2 G • G = D = 20 • RB = 6*1015 cm • u’B/u’e = 2.5*10-4 (Bӧttcher, Reimer & Marscher 2009) Requires far sub-equipartition magnetic fields!

  11. Hadronic Model Fits (Bӧttcher, Reimer & Marscher 2009) • Optical and g-ray spectral index can be decoupled • X-rays filled in by electromagnetic cascades • However: Requires very large jet luminosities, Lj ~ 1049 erg/s

  12. W Comae • Detected by VERITAS in March 2008 (big flare on March 14) • One-zone SSC model requires extreme parameters: • Linj = 2.8*1045 erg/s • gmin = 450 • gmax = 4.5*105 • q = 2.2 • B = 0.007 G • G = D = 30 • RB = 1017 cm Acciari et al. (2008) LB/Le = 5.7*10-2 Wide peak separation and low X-ray flux require unusually low magnetic field!

  13. W Comae • Much more natural parameters for EC model • For Compton scattering in Thomson regime, external photons must have E ~ (mec2)2/EVHE ~ 0.1 – 1 eV => IR • Linj = 2*1044 erg/s • gmin = 700 • gmax = 105 • q = 2.3 • RB = 1.8*1015 cm • B = 0.25 G • -> Equipartition! • G = D = 30 Dtvar ~ 35 min. allowed with external IR photon field (Acciari et al. 2008)

  14. W Comae Major VHE g-ray flare detected by VERITAS in June 2008. Similar modeling conclusions to March 2008: High flux state on MJD 54624 • SSC fit: • B= 0.24 G • LB/Le = 2.3*10-3 • EC fit: • B = 0.35 G • LB/Le = 0.32 (Acciari et al. 2009, in prep.)

  15. 3C66A Major VHE g-ray flare detected by VERITAS in October 2008 Pure SSC fit requires far sub-equipartition magnetic field: • B = 0.1 G • LB/Le = 8.0*10-3 • G = D = 30 • RB = 3*1016 cm • => dtvar,min = 13 hr

  16. 3C66A Fit with external IR radiation field (next = 1.5*1014 Hz) yields more natural parameters: • B = 0.3 G • LB/Le = 0.1 • G = D = 30 • RB = 2*1016 cm • => dtvar,min = 8.9 hr

  17. 0 Summary The MAGIC detection of 3C279 poses severe problems for leptonic models. Hadronic models provide a viable alternative, but require a very large jet power. Recent VHE gamma-ray detections of inermediate- and low-frequency peaked BL Lac objects extends the TeV blazar source list towards new classes of blazars. IBLs appear to require source parameters truly intermediate between HBLs and LBLs: In leptonic models, a non-negligible contribution from external Compton on an external IR radiation field yields more natural parameters than a pure SSC interpretation.

  18. 0 Blazar Classification Intermediate objects: Low-frequency peaked BL Lacs (LBLs): Peak frequencies at IR/Optical and GeV gamma-rays Intermediate overall luminosity Sometimes g-ray dominated (Hartman et al. 2000) Quasars: Low-frequency component from radio to optical/UV High-frequency component from X-rays to g-rays, often dominating total power Peak frequencies lower than in BL Lac objects High-frequency peaked BL Lacs (HBLs): Low-frequency component from radio to UV/X-rays, often dominating the total power High-frequency component from hard X-rays to high-energy gamma-rays (Boettcher & Reimer 2004)

  19. Constraints from Observations Estimates from the SED: nFn (C) / nFn (sy) ~ u’rad / u’B → Estimate u’rad nFn (C) nsy = 3.4*106 (B/G) (D/(1+z)) gp2Hz → Estimate peak of electron spectrum, gp nFn (sy) Fn ~ n-a If g-rays are from SSC: nC/nsy = gp2 If g-rays are from EC (BLR or IR): nC ~ G2eextgp2 From synchrotron spectral index a: nsy nC Electron sp. Index p = 2a + 1

  20. Constraints from Observations If g-rays are Compton emission in Thomson regime: u’sy SSC LD nFn (C) u’disk ≈ EC(disk) 4pr2G2c LD tBLRG2 u’BLR ≈ nFn (sy) EC(BLR) u’rad = 4prBLR2c u’IR ≈ G2 uIR EC(IR) EC(jet) u’jet ≈ Grel2u’jet ’ = in the co-moving frame of the emission region nFn (C) / nFn (sy) ~ (dE/dt)T / (dE/dt)sy = u’rad / u’B

  21. W Comae Low-flux state around MJD 54626 is poorly constrained because of lack of g-ray detections Low-flux state on MJD 54626 • SSC fit: • B= 1.0 G • LB/Le = 0.40 • (can easily be ruled out by any g-ray-detection!) • EC fit: • B = 0.35 G • LB/Le = 0.35

  22. W Comae Intermediate state around MJD 54631.5 (XMM-Newton ToO) ; also poorly constrained g-ray spectrum Intermediate-flux state on MJD 54631.5 • SSC fit: • B= 0.7 G • LB/Le = 0.10 • EC fit: • B = 0.45 G • LB/Le = 0.78

More Related