Discovery of Relativistic Positrons in Solar Flares with Microwave Imaging

and Polarimetry

Gregory D. Fleishman, Alexander T. Altyntsev, Natalia S. Meshalkina

NJIT05 Nov. 2013

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Dale Gary, Research HighlightsI. Instrumentation

• Owens Valley Solar Array (OVSA)

• Korean Solar Radio Burst Locator (KSRBL)

• FASR Subsystem Testbed (FST)

• EOVSA Subsystem Testbed (EST)

• Expanded OVSA (EOVSA )

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Dale Gary, Research HighlightsII. Research

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Discovery of Relativistic Positrons in Solar Flares with Microwave Imaging

and Polarimetry

Gregory D. Fleishman, Alexander T. Altyntsev, Natalia S. Meshalkina

NJIT05 Nov. 2013

Plan of the talk• Where relativistic positrons come from in flares?

• What is the positron contribution to the microwave emission?

• How emission by positrons can be distinguished from that by electrons?

• Can this be done with existing microwave databases?

• Data analysis

• Discussion and conclusions

Origin of Relativistic Positrons in Flares

Acceleration of Ions

Polarimetry – a key to positron detection

Nobeyama Radioheliograph (NoRH) is well suited for our study:

NoRH produces images of intensity (I = R+L) and polarization (V = R – L) at 17 GHz while of the intensity only at 34 GHz. In addition, Nobeyama Polarimeters (NoRP) (Nakajima 1985) observe total power data (both I and V) at a number of singlefrequencies including 17 and 35 GHz. This set of observationaltools suggests the following strategy of identifying properties of solar bursts with unambiguous positron contribution:

(i) single, spatially coinciding, sources at both 17 and 34 GHz; (ii) the 34 GHz emission must come from an area where the 17

GHz V displays a unipolar distribution (i.e., the polarization of 17 GHz emission has a definite sense throughout the region of 34 GHz emission); and

(iii) the total power V must have opposite signs at 17 and 34 GHz.

Gan et al (2001).

13 Mar 2000

Yohkoh

Yohkoh

NoRP

Gan et al (2001).

V, 17 GHz, RCPBz, photosphere

Gan et al (2001).

X-ray

MW

Spectra

Polarization

24 Aug 2002>90 MeV70-150 keV

0.7-2 MeV

V.Kurt. Pr. Com.

17 May 1999

15 Jul 2004Kawate et al. 2012

03 Mar 2000

02 Sep 2001

23 Apr 1998

24 Oct 2003

?

9 Jul 2012

NO

• High-frequency microwave imaging spectropolarimetry offers a new way of detecting and studying relativistic positrons from solar flares.

• Analysis of the Nobeyama database augmented by other context data reveals around 10 events-candidates with the relativistic positron signature; a few of them unambiguously show all expected evidence, so the conclusion that the positrons dominated in producing high-frequency microwave emission in those events seems inescapable.

• New generation of the radio imaging instruments observing at many high frequencies, such as JVLA and ALMA, promises that the positron contribution to the GS emission can be routinely observed in many events.

• Being observed at many frequencies the relativistic positron energy spectrum and spatial distribution can be measured in great detail as a function of time.

Summary