Absence of Impact Polarization in H Michele Bianda Istituto Ricerche Solari Locarno (IRSOL) Switzerland Collaborators: A. Benz, D. Gisler, G. Küveler, R. Ramelli, J.O. Stenflo

Outline Introduction to impact polarization Observations Technical setup Difficulties in observing polarization Polarimeter: ZIMPOL

Impact polarization Directed particle beam colliding with plasma  impact polarization Created in flares?

Observations I Q/I M1.0 flare 2 August 2002 1051 UT 190 arc sec 140 arc sec I Q/I M1.0 flare 2 August 2002 1051 UT No impact polarization observed V/I

Observations I Q/I M3.9 flare 18 November 2003 0831 UT 190 arc sec 140 arc sec I Q/I M3.9 flare 18 November 2003 0831 UT No impact polarization observed V/I

Time evolution in flaring region

Observations of X17.1 flare, 28 Oct 2003 purple: slit position green: TRACE 195 Å yellow and blue: RHESSI

Observations of X17.1 flare, 28 Oct 2003

Observations of X17.1 flare, 28 Oct 2003

Difficulties observing polarization in visible light Polarization measurement: Combining intensity images with different polarization properties Difference of images “polarization”, if not recognized as instrumental effect. Impact polarization: fast evolving structure high intensity gradients

Polarimeter techniques Two beam technique: + simultaneous − different optical paths − different CCDs One beam technique: + same path + same CCD − not simultaneous ( seeing!) I1 I2 I1 I2 R

ZIMPOL concept (1) Fast polarization modulation and on-chip demodulation how? I1 0° I2 switched at 42 kHz 90°

ZIMPOL concept (2) Demodulation at 42 kHz Same CCD pixel for different polarization states

Conclusions Impact polarization not detected by ZIMPOL at IRSOL; more than 30 events were observed

Profiles from imaging observations