Multi-frequency study of the TeV blazar Markarian 421 with VLBA observations taken during 2011

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1 Multi-frequency study of the TeV blazar Markarian 421 with VLBA observations taken during 2011 Presented by: Rocco Lico M.Giroletti, M.Orienti, G.Giovannini, Y.Y.Kovalev, A.Marscher, S.Jorstad, T.P. Krichbaum, M.A. Perez-Torres, K.V. Sokolovsky, G.Piner, W.Cotton, P.G.Edwards, L.Fuhrmann, M.Kino, D.Paneque East Asia To Italy: Nearly Global VLBI CNR Research Area, Bologna, October 2012 INAF Istituto di Radioastronomia

2 Mrk421 is a near BL Lac object (z = 0.031) P 1.4GHz ~ Watt/Hz D core ~ mas (~1-2x10 17 cm) Markarian 421 Abdo et al. (2011) HBL (High-frequency peaked BL Lac). Giroletti et al. (2006) It shows a jet structure oriented in North-West direction, starting from the core and extending for several tens of mas. Detected by EGRET. It is a bright Fermi source. It is the first extragalactic object revealed in TeV band

3 Data set The source was observed once per month, throughout the entire 2011, for a total of 12 epochs at 15 e 24 GHz. Main Goals To make a detailed structural and physical analysis of the source on parsec scale: proper motion analysis, Doppler factor, flux density variations, spectral index. Multifrequency campaign VLBA (Very Long Baseline Array) This study is part of an ambitious multifrequency campaign, with observations in: sub-mm (SMA), optical/ir (GASP), UV/X-ray (Swift, RXTE, MAXI), and γ rays (Fermi-LAT, MA- GIC, VERITAS). Extension of Abdo et al. project (2011).

4 Maps 15GHz 24GHz It shows a jet structure well defined and well-collimated emerging from a compact nuclear region. The jet is oriented in North-West direction (PA ~ -35 ), and it extends over an angular distance of about 4.5 mas (for z= it corresponds to about 2.67 pc). The flux density of nuclear region at 15 GHz is ~ 350 mjy, and it gradually decreases along the jet away. The angular resolution at 15 GHz is ~0.92mas x 0.54mas, while at 24 GHz is ~0.58mas x 0.35mas.

5 Distance from the core (mas) Distance from the core (mas) 15GHz /11/10 07/01/11 26/02/11 17/04/11 06/06/11 26/07/11 14/09/11 03/11/11 23/12/11 11/02/12 24GHz Structural analysis: modelfit Observation date 18/11/10 07/01/11 26/02/11 17/04/11 06/06/11 26/07/11 14/09/11 03/11/11 23/12/11 11/02/12 Data points occupy particular places in this plane, and this seems consistent with the identification of individual components. The identification is confirmed from flux density variation analysis. The components cover an area of ~5mas (the closest to the core is at ~0.43 mas, the most distant is at ~4.6 mas). Observation date All components appear essentially stationary

6 Proper motion analisys core distance (mas) /11/10 07/01/11 26/02/11 17/04/11 06/06/11 26/07/11 14/09/11 03/11/11 23/12/11 11/02/12 Data di osservazione CI CII CIII Linear fit to the position versus time component by component. Apparent speed Component β app CI 0.3 ± 0.2 Dicore distance (mas) /11/10 07/01/11 26/02/11 17/04/11 06/06/11 26/07/11 14/09/11 03/11/11 23/12/11 11/02/12 Observation date CIVa CIVb CII 0.2 ± 0.2 CIII 0.1 ± 0.1 CIVa 0.0 ± 0.2 CIVb 0.0 ± 0.1 NOT observed significant proper motions CAVEAT: the modelfit with Gaussian components is a mathematycal representation, it may not exactly describe the real physical status of the jet!

7 Proper motion analisys K. Niinuma, M. Kino, S. Koyama, A. Doi Soon after the burst: positional fluctuation for C1 (blue diamonds) seems to be larger than the last four epochs. Model fitted image of Mrk 421 in Feb 9 th Observation frequency: 22 GHz

8 Flux Density (Jy) Light curves Observation date (MJD) Mrk 421 Green: total flux density Red: core flux density Blue: total flux core flux Core dominated source 1.3 Normalized light curves Green: Mrk 421 total flux density Blue: J total flux density Stot/Smean Observation date (MJD)

9 Brightness Temperature ν is the observed frequency (15 GHz), and z is the redshift (0.031). d L is the luminosity distance in meters. ΔS max is the difference between the maximum and the minimum value for the core flux density. τ is the variability time (~90 days). a and b represent the full widths at half maximum of the major and minor axes respectively of the component measured in mas. These values for T B do not require any significant beaming

10 θ and β limits from jet-counterjet brightness ratio B J ~24.4 mjy/beam (measured at 15 GHz on a component at ~1 mas from the core). B cj ~0.17 mjy/beam (value provided by the map noise). We obtain: R > and βcosθ > 0.80 Assuming that the pattern velocities are representative of the bulk velocity By varying θ we obtain lower limits for β and also for β app. θ β β app The previous values obtained for β app are compatible with θ~4.8 and β~0.81, which yield δ=3.0 β Relativistic radio jet with marginal effects of beaming θ

11 Interpretative framework δ HE = δradio RULED OUT Combining high Doppler factor implied by the high-energy observations with stationary components from radio observations, then very small viewing angles are obtained (θ<1 ). But such small viewing angles imply unreasonable number of parent objects (Piner & Edwards 2005) δ HE δ Radio DOPPLER FACTOR CRISIS Deceleration. Spine/Layer Model. Fast inner spine, surrounded by a slower layer Supported by limb brightened structure (Piner & Edwards 2005).

12 Conclusions and results There is a velocity structure in this jet, with: 2 < θ < 5 β radio ~ 0.83 and δ Radio ~ 3 β HE ~ 0.99 and δ HE ~ 15 For the core, assuming θ~4.8 and β~0.99, we obtain δ= For α~0.36 and P c oss ~ 6.8 x Watt/Hz P c intr ~ 5.04 x Watt/Hz Unification Model for BL Lac objects with FRI type radiogalaxies.

13 Summary Relativistic radio jet with marginal effects of beaming, that already at about 0.6 pc of projected distance from the core shows absence of proper motions, low flux density variability and steep spectral index. Radio images show us the outer surface (layer). Radiative losses are important. 43 GHz data available. Future prospects We intend to combine our dataset with those of other works (e.g. Piner & Edwards 2005 or the MOJAVE survey, Lister et al. 2009) to increase the temporal coverage of the observations and obtain even tighter constraints over a longer time frame. Comparison with other wavelenghts. Nature of the radiating particles. Connection between the radio and γ-ray emission. The location of the emitting regions. Origin of the flux variability.

14 Breaking news

15 Thanks for your attention.