Institute for Astrophysical Research (Boston University) Iván Agudo 1,2 with the collaboration of S. G. Jorstad 2, A. P. Marscher 2, V. M. Larionov 3,4, J. L. Gómez 1, A. Lähteenmäki 5, M. Gurwell 6, P. S. Smith 7, H. Wiesemeyer 8, C. Thum 9, J. Heidt 10 1 Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18080, Granada, Spain 2 Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA 3 Astronomical Institute, St. Petersburg State University, Universitetskij Pr. 28, Petrodvorets, St. Petersburg, Russia 4 Isaac Newton Institute of Chile, St. Petersburg Branch, St. Petersburg, Russia 5 Aalto University Metsähovi Radio Observatory, Metäahovintie 114, FIN Kylmälä, Finland 6 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA 7 Steward Observatory, University of Arizona, Tucson, AZ , USA 8 Instituto de Radio Astronomía Milimétrica, Avenida Divina Pastora, 7, Local 20, E Granada, Spain 9 Institut de Radio Astronomie Millimétrique, 300 Rue de la Piscine, St. Martin d’H`eres, France 10 ZAH, Landessternwarte Heidelberg, Königstuhl, Heidelberg, Germany Instituto de Astrofísica de Andalucía (CSIC) Location of the γ -ray flaring emission in the jet of OJ287 >14pc from the SMBH

Outline of the talk Introduction New data Results Discussion Conclusions AO Introduction The problem of locating the gamma ray emission site in blazars Our method The new observational data Results 7 mm Jet Structure and Kinematics Flares in the C1 Jet Region at 1 mm and 7 mm γ-ray Flares Variability of Linear Polarization Low Probability of Chance Coincidences Discussion Summary of observational results γ–ray emission consistent with SSC model Proposed model for the multi spectral-range emission Conclusions The new case of BL Lac object AO Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona,

Introduction The information that γ-ray obs. provide depends on where γ-ray emission originates. We employ the technique used by Marscher et al. (2010) and Jorstad et al. (2010) : combination of ultra-high angular-resolution VLBI (∼0.15 mas) to monitor changes of innermost jet regions With dense monitoring at all other available spectral ranges (including polarization if possible) to look for correlations across spectral bands (and hence locate the emitting regions relative to those resolved with VLBI) Marscher et al. (2010) We add Monte Carlo simulations to check for the statistical significance of correlations Dense time sampled Fermi-LAT light curves are a key ingredient to this kind of work. Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

The new observational data >24 monthly VLBA 43 GHz pol. Images 0.15 mas resolution 2008 to 2010 From BU Blazar monitoring I, p & χ curves from: 7mm VLBA strong features 3mm IRAM 30m Tel. (from 2008) Optical measurements from several telescopes (& Villforth et al. 2010) Fermi-LAT data from mid 2008 (5 day bins) SWIFT-XRT data from 2008 Optical data from several telescopes SMA (1 & 0.8 mm)light curves from mm light curve from the Metsahovi radio observatory Light curves from the brighter VLBI jet features (C0=the Core & C1) Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

7 mm Jet Structure and Kinematics We model the 7mm brightness distribution with a small number of circular Gaussian components. Our model fits include a bright quasi-stationary feature (C1) ∼0.2 mas from the innermost jet region (C0= the core). C0 C1 The identification of C0 as the innermost jet feature (i.e. the Core) is justified by: the decreasing intensity westward of C1, and the detection after mid 2010 of superluminal motion of features M1 and M2 with speeds of 10.8c ± 1.3c and 6.7c±1.4c, and M3, which crossed C1 in 2010 October (preliminary speed of 10 c). OJ287 VLBA 43GHz total intensity images Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

7 mm Jet Structure and Kinematics We model the 7mm brightness distribution with a small number of circular Gaussian components. Our model fits include a bright quasi-stationary feature (C1) ∼0.2 mas from the innermost jet region (C0= the core). The identification of C0 as the innermost jet feature (i.e. the Core) is justified by: the decreasing intensity westward of C1, and the detection after mid 2010 of superluminal motion of features M1 and M2 with speeds of 10.8c ± 1.3c and 6.7c±1.4c, and M3, which crossed C1 in 2010 October (preliminary speed of 10 c). OJ287 VLBA 43GHz total intensity images C0 C1 Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

Flares in the C1 Jet Region at 1 mm and 7 mm C0 and C1 typically dominate the 7 mm flux, i.e. they governed the millimeter-wave evolution, of OJ287. Indeed, the two most prominent 1mm flares ever reported in OJ287 (A mm and B mm ) took place in C1, (indicated by correspondence of 7mm light curve of C1 with those at mm-λλ). From the angle of the jet axis to the line of sight in OJ287 (1.9°–4.1°; Jorstad et al. 2005; Pushkarev et al ), and the mean projected separation of C1 from C0 at the time of start of A mm and B mm (0.23±0.01 mas), we locate C1 > 14 pc downstream of C0 (=the core). OJ287 total flux light curves Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

Flares in the C1 Jet Region at 1 mm and 7 mm C0 and C1 typically dominate the 7 mm flux, i.e. they governed the millimeter-wave evolution, of OJ287. Indeed, the two most prominent 1mm flares ever reported in OJ287 (A mm and B mm ) took place in C1, (indicated by correspondence of 7mm light curve of C1 with those at mm-λλ). From the angle of the jet axis to the line of sight in OJ287 (1.9°–4.1°; Jorstad et al. 2005; Pushkarev et al ), and the mean projected separation of C1 from C0 at the time of start of A mm and B mm (0.23±0.01 mas), we locate C1 > 14 pc downstream of C0 (=the core). The actual distance between OJ287’s BH and C1 must be even greater if C0 lies downstream of the acceleration and collimation zone of the jet ( Jorstad et al. 2007; Marscher et al. 2008, 2010 ). OJ287 total flux light curves © A. P. Marscher C0=Core C1 Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

γ -ray Flares The two most pronounced γ-ray flares (A γ and B γ ) take place during the initial rising phases of A mm and B mm. Conforms with pattern found in the 1990s by Lähteenmäki & Valtaoja (2003). The discrete correlation function (DCF; Edelson & Krolik 1988 ) between the γ-ray and 1mm light curve shows a prominent peak at a time lag ∼ − 80 days. OJ287 total flux light curves OJ287 γ-1mm discrete correlation function Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

γ -ray Flares The two most pronounced γ-ray flares (A γ and B γ ) take place during the initial rising phases of A mm and B mm. Conforms with pattern found in the 1990s by Lähteenmäki & Valtaoja (2003). The discrete correlation function (DCF; Edelson & Krolik 1988 ) between the γ-ray and 1mm light curve shows a prominent peak at a time lag ∼ − 80 days. OJ287 total flux light curves OJ287 γ-1mm discrete correlation function Our Monte Carlo simulations of stochastic variability confirm, at 99.7% confidence, the correlation between B γ and B mm, the most luminous γ-ray and 1 mm flares in our data. Correlation of γ-ray and 8 mm light curves is of similarly high significance. Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

γ -ray Flares The two most pronounced γ-ray flares (A γ and B γ ) take place during the initial rising phases of A mm and B mm. Conforms with pattern found in the 1990s by Lähteenmäki & Valtaoja (2003). The discrete correlation function (DCF; Edelson & Krolik 1988 ) between the γ-ray and 1mm light curve shows a prominent peak at a time lag ∼ − 80 days. Our Monte Carlo simulations of stochastic variability confirm, at 99.7% confidence, the correlation between B γ and B mm, the most luminous γ-ray and 1 mm flares in our data. OJ287 total flux light curves OJ287 γ-1mm discrete correlation function Correlation of γ-ray and 8 mm light curves is of similarly high significance. Probability that two random γ-ray flares occur during the rising phase of two mm flares is only 3%, i.e., events A mm and B mm are associated with A γ and B γ, respectively, at 97.0% confidence The optical light curves show two sharp flux increases at essentially zero time lag from A γ and B γ. Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

p C0 never exceeds 10%, but C1 shows the two largest peaks in p ever observed in OJ287 at 7 mm, p C1 ≈ 14% on 2008 Nov., and p C1 ≈ 22% on 2009 Oct. The first maximum in p C1 follows the peak of A γ by one month, while the second more pronounced p C1 peak is already in progress when the γ-ray flux of flare B γ peaks. Variability of Linear Polarization The coincidence of the brightest γ-ray outburst, and highest polarization fraction in C1 as strong evidence that the C1 jet feature >14 pc from the central engine is the site of the variable γ-ray emission. Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

p C0 never exceeds 10%, but C1 shows the two largest peaks in p ever observed in OJ287 at 7 mm, p C1 ≈ 14% on 2008 Nov., and p C1 ≈ 22% on 2009 Oct. The first maximum in p C1 follows the peak of A γ by one month, while the second more pronounced p C1 peak is already in progress when the γ-ray flux of flare B γ peaks. Variability of Linear Polarization The coincidence of the brightest γ-ray outburst, and highest polarization fraction in C1 as strong evidence that the C1 jet feature >14 pc from the central engine is the site of the variable γ-ray emission. p opt peaks (at ≈35%) at essentially the same time as p C1 at 7 mm during flare B γ. p opt ≈ 35%, requires a well-ordered magnetic field. χ opt & χ mm ≈ 160 ◦ –170 ◦ (essentially the position angle of the jet) Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

Summary of observational results Two kinds of events in the mm range are related at high confidence to the to reported γ-ray outbursts (A γ and B γ ).: (1) The early rising phases of the two most luminous 1mm flares ever detected in OJ287 (A mm and B mm ) (2) The two sharp increases to unprecedented levels of linear polarization (∼14% and ∼22%) in bright jet feature C1 > 14 pc from the central engine. The exceptionally high polarization of C1 during γ-ray flare B γ provides extremely strong evidence that the event occurred in C1. Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

γ –ray emission consistent with SSC model In general, the γ-ray IC emission may arise from either the SSC process or IC scattering of optical-IR radiation from an external photon field. An SSC model is possible given the low ratio of γ-ray to synchrotron luminosity (≈2) in OJ287. However, emission from the dusty torus has not been detected thus far in BL Lac objects such as OJ287, and other standard EC photon fields (BLR and accretion disk) are also too weak for BL Lac objects. We thus favor the SSC mechanism. Proposed model for the multi spectral-range emission Scenario where optical and γ-ray flares are produced in C1 (standing conical shock beyond the 7mm core) by particle acceleration in a moving blob when it crosses a standing shock. Cawthorne (2006) shows that, in this case, the side of the conical shock nearest to the line of sight can be highly polarized with χ parallel to the jet axis. The remainder of the conical shock, farther from the line of sight, has much lower polarization. Because of light-travel delays, we first see the blob penetrate the near side, and therefore observe a major increase in polarization. As the outburst develops, more of the emission comes from the low- polarization far side, which decreases p while the millimeter-wave flux density continues to increase (observed pattern). Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

The mm and optical flares start at essentially the same time as the magnetic field and electron energies near the leading edge of the blob become amplified as they pass the standing shock front. The mm outburst continues as the relatively low-energy electrons fill the shocked region. The optical and γ-ray emission, produced by higher energy electrons that cannot travel far before suffering radiative energy losses, is confined closer to the shock front where particles are accelerated. If synchrotron losses were the sole factor, the optical and γ-ray flux would reach a plateau once the shocked blob plasma fills the entire layer behind the shock, declining only when the upstream side of the blob passes the shock front. However, if SSC emission dominates, the radiative losses will increase as synchrotron photons from the flare reach electrons that scatter them to high energies. This happens until the moment when there are not enough energetic electrons to continue the optical flare on, when the quenching of the optical and γ-ray flares occur. Proposed model for the multi spectral-range emission Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

Conclusions Agudo et al. (2011a, ApJL,726, L13 ) In contrast to other models assuming γ-ray emission to come from <<1pc from the central AGN engine, γ–ray flaring emission has been located >14pc from the BH in the jet of BL Lac object OJ287 This result is absolutely model independent. It comes directly from the analysis of observational data Multi spectral range behavior of γ–ray flares in OJ287 is difficult to reproduce in the EC(dust, BLR, disc) model. We favor the SSC mechanism. Similar concl. were obtained from quasars PKS (Marscher et al. 2010) and 3C454.3 (Jorstad et al. 2010) Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011, ApJL,726, L13 ) Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Introduction New data Results Discussion Conclusions AO

Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Agudo et al. (2011b, ApJL,735, L10 ) The case of BL Lac object AO Introduction New data Results Discussion Conclusions AO γ, X, optical, & mm peak contemporaneously Soon after, the strongest mm VLBI ejection ever seen in AO Optical linear polarization fraction ≥35% during the γ-ray flare 7mm linear polarization fraction of new emission feature (Qs) ≥15%

Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, The case of BL Lac object AO Introduction New data Results Discussion Conclusions AO

Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, Location of the γ-ray flaring emission in the jet of OJ287 >14pc from the SMBH. Iván Agudo, IAA-CSIC, Barcelona, AO : Agudo et al. (2011b, ApJL,735, L10 ) Introduction New data Results Discussion Conclusions AO In contrast to other models assuming γ-ray emission to come from <<1pc from the central AGN engine, γ–ray flaring emission has been located >14pc from the BH in the jet of BL Lac object OJ287 & AO This result is absolutely model independent. It comes directly from the analysis of observational data γ–ray flares are difficult to reproduce in the EC(dust, BLR, disc) models. We favor the SSC mechanism. Conclusions OJ287: Agudo et al. (2011a, ApJL,726, L13 )