The Focusing Optics X-ray Solar Imager (FOXSI)

1. Steven Christe1,2, L. Glesener1, S. Krucker1, B. Ramsey3, T. Takahashi4, S. Watanabe4 1 Space Sciences Lab, U.C. Berkeley, Berkeley, CA 2 NASA GSFC, Greenbelt, MD 3 NASA MSFC, Huntsville, AL 4 ISAS JAXA, Japan The Focusing Optics X-ray Solar Imager (FOXSI)

2. FOXSI Motivation • A major goal of solar physics is to understand energy release/particle acceleration on the Sun. • Hard x-ray (bremsstrahlung) observations are a powerful probe for accelerated electrons and the associated heated plasma. • But current observations do not have the sensitivity or dynamic range to observe energetic electrons in the corona where they are thought to be accelerated.

3. FOXSI Science Motivation • To understand energy release on the Sun • need to observed electrons being accelerated and traveling through the corona. Sturrock (1966) (weak) Thin target emission RHESSI HXR Obs. thermal (intense) Thick target footpoints Current flare observations (e.g. RHESSI) show only where electrons are stopped(footpoints) and hot thermal loops.

4. FOXSI Science Targets Energy Release in its many forms… Polar Jets Noise Storms Many science targets are available for future FOXSI flights! Active Region Flares Quiet Sun (coronal heating) The first FOXSI flight (Jan 2011) will focus on thermal and flare emission from active regions nanoflares in the quiet Sun. Occulted HXR Emission Type III radio bursts Axions?

5. Coronal Heating Nanoflares(thermal) • Do nanoflares heat the corona? • Are small flares the same as large flares? • To answer these questions, HXR observations require greater sensitivity. Microflares (nonthermal + thermal) ~1.8 FOXSI Hannah et al. (2008)

6. FOXSI • Short for the Focusing Optics X-ray Solar Imager • Sounding rocket mission fundedunder the NASA LCAS program in 2008. • Launch scheduled for Jan 2011. • FOXSI will leverage new technologies • HXR grazing-incidence replicated optics (as flown on the HERO balloon payload, Ramsey et al. 2002) • Double-sided Si strip detectors (developed by JAXA/ISAS for Astro-H/NeXT) • FOXSI will be ~50 times more sensitive than RHESSI and will have up to 100 times its dynamic range!

7. FOXSI Optics • HXRs undergo total internal reflection at shallow graze angle (<0.5 degree). • Using mirror shells with a Wolter I geometry (confocalparaboloid and hyperboloid) HXRs can be brought to a common focus. • Telescope shells are nested together to form telescope modules to increase area.

8. FOXSI Optics Fabrication Process by B. Ramsey at the M.S.F.C.

9. FOXSI Optics • Individual shell resolution of 7’’ (FWHM). • Telescope module resolution of 12’’. • Dynamic range of 100 for separations >30’’. FWHM 12’’ -100 -50 0 50 100 150 arcseconds

10. Effective area • FOXSI’s effective area • Blue represents the current configuration for the flight in 2011 • Redrepresents an upgraded configuration for a potential flight in 2013 • Due to increased area and smaller detectors, FOXSI will be ~50 times more sensitive than RHESSI (in this energy range). 2011 2013 The dashed line represent the area provided by the optics. The effective area is also shown.

11. FOXSI Detectors • Developed for Astro-H (NeXT) Mission • Double-sided Silicon Strip Detectors (DSSD) • 128 x 128 strips, 500 mm thick • 75 mm pitch (total 9.6x9.6 mm) • Efficiency 98% for 10 keV68% for 15 keV • CdTe DSSD in the future

12. FOXSI by the Numbers • Energy range : 4 – 15 keV • Energy resolution : 0.5 keV • FOV : ¼ Sun (960’’ x 960’’, 128x128 pixels) • Resolution : 12’’ (FWHM) • Effective area : ~4 x RHESSI (180 cm2) • Sensitivity : 50 x RHESSI • Dynamics Range : ~10 x RHESSI (~100) (for source separations >30’’)

13. FOXSI Payload Replicated optics telescope module (7 shells & 7 modules) 2 m focal length Si strip detectors (75mm)

14. FOXSI Progress (Above) Practicing bonding the VATA ASIC on the detector board. (Above) Preparing the FOXSI detector plane assembly for a thermal test. (Right) A FOXSI Si strip detectors (75mm pitch)

15. FOXSI Progress (Left) A newly minted FOXSI shell (Right) Getting ready for a Vibration test of a FOXSI telescope module (Left) FOXSI Team members (S. Krucker, B. Ramsey, L. Glesener, S. Christe) holding a FOXSI telescope module.

16. Concluding Remarks/Future Work • FOXSI will investigate the problem of coronal heating through brightening in the quiet Sun. • Using HXR focusing optics (dynamic range++) • Pixelated solid state detectors (sensitivity++) • FOXSI will be a pathfinder for the next generation of solar hard x-ray spectroscopic imagers.

17. HXR from the Quiet Sun • Heating events are observed in the “quiet” Sun network (Krucker & Benz 1998, Parnell & Jupp 2000, Ascwanden 2000). • Nonthermal HXR emission may be expected. T∼2MK, EM∼1044 cm, E∼5×1025 ergs, Dt = 60s

18. HXR from Radio-producing e- • Electrons traveling/trapped in the corona should emit thin-target HXR emission. • Same number of particles in Type III radio bursts as Type I noise storms (Benz & Wentzel 1981)

19. Concluding Remarks/Future Work • FOXSI will investigate the problem of coronal heating through brightening in the quiet Sun. • Using HXR focusing optics (dynamic range++) • Pixelated solid state detectors (sensitivity++) • FOXSI will be a pathfinder for the next generation of solar hard x-ray spectroscopic imagers.