POLARIMETRIC TOMOGRAPHY OF BLAZAR JETS

Transcription

1 OF BLAZAR JETS PKS Ulisses Barres de Almeida Centro Brasileiro de Pesquisas Fisicas Fabrizio Tavecchio (INAF)

2 TABLE OF CONTENTS INTRODUCTION POLARIMETRIC TOMOGRAPHY CASE STUDY: APPLICATION TO PKS 2155 RESULTS OF THE METHOD FUTURE STEPS A POPULATION STUDY

3 INTRODUCTION Using polarimetry to approach SED fits Photometric data in multi-band campaigns gives info on the MWL correlations and thus on the emission processes, sizes (variability), and relative sites of radiation emission HESS Collab, A&A 2009

4 INTRODUCTION Using polarimetry to approach SED fits With radio polarisation data some groups are trying to map the precise location of the sites of e.g., VHE emission in jets. 3C 279 MAGIC Collab. HEPRO IV - Barcelona

5 INTRODUCTION Using polarimetry to approach SED fits The complexity of the emerging MWL variability and correlations gives a wealth of new info to understand blazars, but poses also challenges to understand them MAGIC Collab. HEPRO IV - Barcelona

6 INTRODUCTION Using polarimetry to approach SED fits 3C 279 The complexity of the emerging MWL variability and correlations gives a wealth of new info to understand blazars, but poses also challenges to understand them Changing correlation behaviour over different campaigns and also in sequential flares in a same (relatively short-term) campaign. MAGIC Collab. HEPRO IV - Barcelona

7 INTRODUCTION Using polarimetry to approach SED fits 3C 279 The complexity of the emerging MWL variability and correlations gives a wealth of new info to understand blazars, but poses also challenges to understand them Changing correlation behaviour over different campaigns and also in sequential flares in a same (relatively short-term) campaign. ORPHAN FLARES! MAGIC Collab. HEPRO IV - Barcelona

8 INTRODUCTION Using polarimetry to approach SED fits Complexity in behaviour complexity in structure How many emitting regions working at the same time? What are their relative importance? How long do they last? What are their physical properties?

9 Using polarimetry to approach SED fits Polarisation data gives info on internal structure of the source Magnetic fields: intensity and structure Different particle populations (zones) present PKS 43 GHz Marscher et al. ApJ 2010

10 Using polarimetry to approach SED fits In particular, one can use variability data to decompose the temporal behaviour of the Stokes parameters Q,U in terms of (Hagen-Thorn, S. Jorstad, et al.) : a dominant, variable component driving the variability; and a quiescent-state jet to which it is superposed. (in terms of superposed polarisation properties, since the two contributions cannot be physically resolved and are integrated in the measurement of the jet)

11 Using polarimetry to approach SED fits In particular, one can use variability data to decompose the temporal behaviour of the Stokes parameters Q,U PKS Barres de Almeida et al. MNRAS 2010

12 Using polarimetry to approach SED fits The resulting description of the jet (tomography) is: PKS Barres de Almeida et al. MNRAS 2010

13 Study case: PKS PKS measured by HESS and Fermi in 2009 is a rich, complex dataset.

14 Study case: PKS It was studied in detail but an interpretation of the physics was not trivial to find: lack of MWL correlations to explaing (low but clear) variability and SED cannot be fitted by 1-zone model but no clear motivation to do otherwise in the quiescent state

15 Study case: PKS It was studied in detail but an interpretation of the physics was not trivial to find PKS HESS/Fermi Collab. 2009

16 Study case: PKS We used strictly simultaneous polarimetric variability information available for this source to derive the evolution of the variable component responsible for the changes in the polarisation of the source. Dates for which simultaneous polarimetric data is available

17 Study case: PKS : Results RESULT: the component responsible for the variability in the optical polarisation has a flux of only 10% the total optical flux and is therefore not directly visible in the photometric data Barres de Almeida et al. MNRAS 2010

18 Study case: PKS : Results RESULT: but it correlates well with the X-ray behaviour only band showing variability, previously uncorrelated and not understood. X-rays (RXTE 2-10 kev) Polarised component (x10) Optical photometry

19 Study case: PKS : Results RESULT: but it correlates well with the X-ray behaviour only band showing variability, previously uncorrelated and not understood.

20 Study case: PKS : Results RESULT: but it correlates well with the X-ray behaviour only band showing variability, previously uncorrelated and not understood. we have a case for a two-zone approach to the SED fit from the optical polarisation analysis we have an input on the physical properties of one of the zones (in optical) - this in turn constrains (via variability data) the X-rays and we can derive a well-constrained and physically motivated 2-zone fit to the SED of the source

21 Study case: PKS : Results Variability behaviour of the SED can be readily understood in terms of changes in well constrained physical parameters (e.g., evolution of B).

22 Study case: PKS : Results Variability behaviour of the SED can be readily understood in terms of changes in well-constrained physical parameters (evolution of B).

23 Study case: PKS : Conclusion Variability behaviour of the SED can be readily understood in terms of changes in well-constrained physical parameters (evolution of B). CONCLUSION: The method (at least in some cases) allows to have a physically motivated approach to the SED fit which better constrains models (specially the necessity of 1/2- zones) and physical parameters (with an external input)

24 Future Studies We have collected 2 years of data on c. 20 VHE blazars, contemporaneously (sometimes simultaneously), with Liverpool Telescope in polarisation, MAGIC telescopes and Fermi. We are now putting all this info together and will apply the method of polarimetric tomography consistently to all objects where this is possible to: (a) better understand the approach, its capabilities and limitations (b) if it can contribute significantly in the study of blazars SED in general (c) what new info, population-wise it will give us on these objects.