Op#cal polariza#on of very- high energy emi5ng blazars

Transcription

1 Op#cal polariza#on of very- high energy emi5ng blazars Talvikki Hova;a Aalto University, Metsähovi Radio Observatory, Finland D. Blinov, V. Pavlidou (U. Crete) E. Lindfors, K. ilsson, V. Fallah Ramazani (Turku University) E. Angelakis, I. Myserlis (MPIfR) The work was supported by the COST ac#on by a short- term scien#fic mission (STSM) in ov to University of Crete

2 Mo#va#on In 2003 only 6 blazars had been detected at > 100 GeV energies ow the number has increased to > 50 (h;p://tevcat.uchicago.edu/) Most of these are classified as high- spectral peaking (HSP) objects based on their SED For the first #me it is possible to do popula#on studies! Main research ques#on: Are there differences in the op#cal polariza#on of TeV- detected and non- detected ISPs / HSPs? Fermi SED paper (Abdo+ 2010, ApJ, 716, 30) CTA Image credit: CTA

3 Sample and observa#ons 38 TeV- detected objects 3 LSP flat- spectrum radio quasars 7 ISP BL Lacs 28 HSP BL Lacs Observa#ons with RoboPol and ordic Op#cal telescope (OT) in 2014 ~ 1 / week sampling Control sample of 13 ISP/ HSP objects not detected at > 100 GeV RoboPol Skinakas Observatory Crete (see poster by D. Blinov RoboPol main program results) OT La Palma Spain

4 Sample and observa#ons 38 TeV- detected objects 3 LSP flat- spectrum radio quasars 7 ISP BL Lacs 28 HSP BL Lacs Observa#ons with RoboPol and ordic Op#cal telescope (OT) in 2014 ~ 1 / week sampling Control sample of 13 ISP/ HSP objects not detected at > 100 GeV RoboPol Skinakas Observatory Crete (see poster by D. Blinov RoboPol main program results) OT La Palma Spain

5 Data challenges Rapid variability But also non- detec#ons Es#ma#on of the mean polariza#on degree? Summing Stokes Q and U zeroes the mean for rota#ng sources Es#ma#on of variability? Use a modula#on index Uncertain#es?

6 Maximum likelihood approach Assump#ons: Intrinsic polariza#on degree follows a beta distribu#on Distribu#on confined to 0 p i 1 It is observed through a Rice distribu#on Accounts for upper limits Provides uncertain#es Mod. index Probability density of Beta distribu#on mean Pol. degree observa#ons Probability density of Rice distribu#on

7 Preliminary Results Density Density RBPLJ p o =0.11 m p = obs RBPLJ p o = 0.03 m p = obs ISP and HSP TeV sources Intrinsic p degree (%) ISP and HSP control sources Intrinsic p degree (%) ISP and HSP TeV sources Intrinsic mod. index ISP and HSP control sources K- S tests show no significant differences between the TeV- detected and control sources All HSP sources will be detected by the CTA? Some caveats: Only 1 season of data! eed at least 3 points and > 1 detec#ons Op#miza#on did not converge for all sources - > work in progress! Intrinsic mod. index

8 Control source - > TeV source Variability plays a significant role eed to catch the sources at the right #me Were the TeV- detected sources detected in TeV energies in 2014? Tuorla Observatory blazar monitoring program h;p://users.utu.fi/kani/1m/s4_ html

9 Polariza#on angle behavior Previously only very few EVPA rota#ons in TeV sources Sampling density important! RoboPol has detected already 3 Project with RoboPol and OT con#nues in 2015

10 Preliminary EVPA sta#s#cs ISP and HSP TeV sources devpa/dt [deg/day] ISP and HSP control sources Es#mate mean rota#on rate Δθ/Δt o significant differences between TeV and control sources (K- S test) But a tail to larger values in the TeV- detected sources devpa/dt [deg/day]

11 Conclusions ew maximum likelihood method for es#ma#ng mean polariza#on degree and modula#on index Accounts for limits Provides uncertain#es that account for small number of points o significant differences between the TeV- detected and non- detected ISP/HSP sources All could be detected by the CTA if caught in the right ac#vity phase? eed to include analysis of magnitudes and TeV- state during 2014 CTA Image credit: CTA