X-Ray Polarization of Solar Flares Measured with Rhessi

The degree of linear polarization in solar flares has not yet been precisely determined despite multiple attempts to measure it with different missions. The high energy range, in particular, has very rarely been explored, due to its greater instrumental difficulties. We approached the subject using the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study six X-class and 1 M-class flares in the energy range between 100 and 350 keV. Using RHESSI as a polarimeter requires the application of strict cuts to the event list in order to extract those photons that are Compton scattered between two detectors. Our measurements show polarization values between 2 and 54%, with errors ranging from 10 to 26% in 1σ level. In view of the large uncertainties in both the magnitude and direction of the polarization vector, the results can only reject source models with extreme properties.

[1]  G. Grimaldi,et al.  Il nuovo cimento , 1889 .

[2]  Consultants Bureau,et al.  Solar system research , 1967 .

[3]  Herbert W. Schnopper,et al.  Predicted performance of a rotating modulation collimator for locating celestial x-ray sources , 1968 .

[4]  V. D. Ivanov,et al.  On the polarization of the emission of X-ray solar flares , 1970 .

[5]  E. Haug,et al.  On the polarization and anisotropy of solar X-radiation during flares , 1970 .

[6]  V. D. Ivanov,et al.  New measurements of the polarization of X-ray solar flares , 1972 .

[7]  John C. Brown,et al.  The directivity and polarisation of thick target X-ray bremsstrahlung from solar flares , 1972 .

[8]  E. Haug.  Polarization of hard X-rays from solar flares , 1972 .

[9]  W. Steffen,et al.  The polarization of X-ray emission of some solar flares in July 1974 , 1976 .

[10]  Reuven Ramaty,et al.  Backscatter, anisotropy, and polarization of solar hard X-rays , 1978 .

[11]  J. C. Brown,et al.  The polarization and directivity of solar-flare hard X-ray bremsstrahlung from a thermal source , 1980 .

[12]  J. Leach,et al.  The impulsive phase of solar flares. II - Characteristics of the hard X-rays , 1983 .

[13]  K. Hurley,et al.  Directivity of 100-500 keV solar flare hard X-ray emission , 1994 .

[14]  A. Witten,et al.  Impedance tomography: imaging algorithms for geophysical applications , 1994 .

[15]  G. Skinner,et al.  Inverse problems in X-ray and gamma-ray astronomical imaging , 1995 .

[16]  P. Li.  Directivity and its energy dependence in solar flare energetic emission , 1995 .

[17]  F. Lei,et al.  Compton Polarimetry in Gamma-Ray Astronomy , 1997 .

[18]  M. McConnell,et al.  RHESSI as a Hard X-Ray Polarimeter , 2002, astro-ph/0209384.

[19]  D. A. Landis,et al.  The RHESSI Spectrometer , 2002 .

[20]  M. Aschwanden,et al.  The RHESSI Imaging Concept , 2002 .

[21]  J. Brown,et al.  Nonsolar astronomy with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) , 2003, SPIE Astronomical Telescopes + Instrumentation.

[22]  M. McConnell,et al.  Hard X-ray solar flare polarimetry with RHESSI , 2002 .

[23]  G. J. Hurford,et al.  The PMTRAS Roll Aspect System on RHESSI , 2002 .

[24]  Alex Zehnder,et al.  RHESSI Aspect Reconstruction , 2002 .

[25]  S. Boggs,et al.  Polarization of the prompt γ-ray emission from the γ-ray burst of 6 December 2002 , 2003, Nature.

[26]  D. Fox,et al.  Re-analysis of polarization in the γ-ray flux of GRB 021206 , 2003, astro-ph/0310385.

[27]  J. Coyle.  Inverse Problems , 2004 .

[28]  W. Hajdas,et al.  Gamma-Ray Burst Polarization: Limits from RHESSI Measurements , 2004, astro-ph/0405525.

[29]  W. Hajdas,et al.  RHESSI as Gamma Ray Burst Polarimeter , 2005 .

[30]  E. Kalemci,et al.  Gamma-Ray Polarimetry of Two X-Class Solar Flares , 2005, astro-ph/0510588.

[31]  A. Bogomolov,et al.  Polarization, temporal, and spectral parameters of solar flare hard X-rays as measured by the SPR-N instrument onboard the CORONAS-F satellite , 2006 .