Implications of VHE Emission in Gamma-Ray AGN Amir Levinson, Tel Aviv University

Outline Constraints on source parameters from VHE  -ray obs. Rapid TeV flares  D>>1 ? Inconsistent with SL motion and unification. Stationary radio features in blazars are common (Jorstad et al. 2001). Reasons? Radiative deceleration of Γ>>1 shells, and rapid TeV variability. Size and location of emission region ? HST1 in M87 and TeV blazars. Collimation and dissipation in recollimation shocks. TeV emission from BH magnetosphere? Constraints on production of VHE neutrinos in jets from  -ray observations. GLAST can be exploited to identify best candidates for upcoming km^3 detectors.

Opacity sources (  and photo-π) MQ blazar  Target photons: synchrotron and /or external  Electromagnetic: synchrotron, IC, pair production  Hadronic: photopion production, nuclear collisions

Challenges Estimates of black hole mass from M -  relation: Mrk Mrk 501 -

relevant to powerful blazars (e.g., 3C279)  -spheric radius versus energy GLAST external synchrotron (Levinson 2006) relevant to TeV blazrs Pair production opacity

 if dissipation occurs over a wide range of radii then flares should propagate from low to high  -ray energies (Blandford/Levinson 95).  250 sec delay between γ at >1.2 TeV and γ at TeV was reported for Mrk 501 (Albert etal. 07). Corresponds to  r=  2 ct delay  (  /30) 2 cm Will be constrained by GLAST in powerful blazars and MQs r(cm) r0r MQ Powerful blazar Implications for variability in opaque sources

r0r0 Constraints on Doppler factor from variability (measured or computed) (measured) (unknown) (measured)

Consistent with estimates based on fits of SED to SSC model Assuming that or more generally that the synchrotron emission originates from the same region emitting TeV rays implies a lower limit on Doppler factor of emitting fluid:

Other requirements Synchrotron cooling Cooling time: SSC in Poynting dominated blob (Begelman et al. 2008): opacity cooling No momentum loss → Why radio jet much slower? PKS 2155 IC cooling: ERC: Jet decelerates? Photon breading ? Next talk

Large Γ really necessary ? If they are then why pattern  are much smaller than fluid  ? What is the origin of rapid TeV flares ?

Radiative deceleration and Rapid TeV flares  Fluid shells accelerated to Γ 0 where dissipation occurs. Radiative drag then leads to deceleration over a short length scale (Georgapoulos/Kazanas 03).  Dissipated energy is converted to TeV photons – no missing energy.  Minimum power of VLBI jet in Mrk 421, Mrk 501 is ~ erg/s, consistent with this model.  What are the conditions required for effective deceleration and sufficiently small pp opacity that will allow TeV photons to escape? Γ 0 >>1  Γ  ~ 4 VLBI jet (Levinson 2007)

Radiative friction We solved fluid equations: - If q sufficiently small (  2 is best) and   (Γ 0  max ) ~ a few, then.. a background luminosity of about erg/s is sufficient to decelerate a fluid shell from  0 >>1 to   ~ a few, but still be transparent enough to allow TeV photons to escape the system. Energy distribution of emitting electrons:

Emission region located at a large radius?   opacity may decrease with radius. Large Doppler factor may not be required if r em >>  r.  Large Γ are still required if synchrotron emission originates from the same region emitting the TeV photons (can be constrained by variability of IR emission) but!! only a fraction (  r/R) 2 of jet energy can be tapped for  -ray production. May be difficult to explain large amplitude flares! Is there a way to channel the bulk energy into a small region?

M87- HST1  Source of violent activity. Deprojected distance of ~ 120 pc (  =30 deg)  Resolved in X-rays. Variability implies  r ~ 0.02  D pc.  Radio: stationary with substructure moving at SL speed  M87 has been detected at TeV, with  r ~  D pc. Related to HST1 ? From Cheung et al. 2006

Can HST1 knot be the site of TeV emission? See also Sikora et al for 3C454.3 May be an important dissipation channel also in blazars, MQs, and GRBs

Collimation of a jet by pressure and inertia of an ambient medium Bromberg + Levinson 2007 (see also simulations by Alloy et al.) Shocked layer unshocked flow Confining medium Internal shocks at reflection point

Effect of cooling (preliminary results) Internal shocks at reflection point

Cold jet

Confinement by a supersonic wind Outer shock Inner shock

TeV from black hole ? Particle acceleration in vacuum gap of a Kerr BH. Proposed originally by Boldt/Gosh ‘99 to explain UHECRs from dormant AGNs Implies efficient curvature emission at TeV energies; detectable by current TeV telescopes (Levinson ‘00) Application to M87 (Neronov/Aharonian ‘07)

Vacuum gap But! Vacuum breakdown will quench emission. Expected if luminosity of ambient emission exceeds roughly Potential drop along B field lines Gap potential is restored intermittently ?

Hadronic processes Inelastic nuclear collisions Photopion production

p + n  p + p +  -   - +   e - + e +  +  p + n  n + n +  +   + +   e + + e +  +  p + n  p + n +  0   +  Inelastic nuclear collisions in AGNs, Microquasars (except perhaps for HMXBs where stellar wind may contribute) May be important in GRBs

p +    + + n   + +   e + + e +  +  p +    0 + p   +  Photo-  production π - sphere ext sync dissipation radius

Relations between photo-  production and  γ pair-production  Same target photons for both processes.

Opacity ratio (target: synchrotron photons)    GeV  GeV  TeV  TeV Mrk 421 (blazar) (MQ)

Regions of significant photo-  opacity are opaque to emission of VHE gamma rays. Highly variable VHE  -ray sources, in particular TeV blazars are not good candidates for km 3 neutrino detectors. In regions of high photo-  opacity,  - rays produced through π 0 decay will be quickly degraded to GeV energies (in blazars and lower in MQs). Correlation between GeV and neutrino emissions is expected. (Also temporal changes in the  -ray spectrum in the GLAST band during intense neutrino emission.) Consequences

Neutrino yields (in a km 3 detector)  TeV BLLac: < 0.03 event per year for Mrk 421, 501 during intense flares  MQ: a few events from a powerful flare like the 1994 event seen in GRS 1915  Blazars: ~ 1 event per year at Z~1 for the most powerful sources (e.g, 3c279). May be constrained further by GLAST.  GRBs: a few events from a nearby source or cumulative detection

Summary Large Doppler factors are implied by  -ray obs. in blazars. Seem to differ considerably from pattern speed. Location of emission region may far from the BH, as HST1 in M87. Suggests that collimation may be an important dissipation channel. Also in GRBs? Can this account for rapid variability at relatively large radii? Extreme flares in TeV blazars may be produced by radiative deceleration of fast fluid shells on small scales? Consistent with the small superluminal speeds on VLBA scales and minimum jet power estimates. Forthcoming obs. of VHE emission can be used to identify potential neutrino sources

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