The Focusing Optics X-ray Solar Imager (FOXSI)Steven Christe1,2, L. Glesener1, S. Krucker1, B. Ramsey3, T. Takahashi4, S. Watanabe4

1 Space Sciences Lab, U.C. Berkeley, Berkeley, CA2 NASA GSFC, Greenbelt, MD3 NASA MSFC, Huntsville, AL4 ISAS JAXA, Japan

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.

FOXSI Motivation

FOXSI Science Motivation

thermal

(intense) Thick target footpoints

(weak) Thin target emission

Current flare observations (e.g. RHESSI) show only where electrons are stopped(footpoints) and hot thermal loops.

To understand energy release on the Sun• need to observed electrons being accelerated and traveling through the corona.

RHESSI HXR Obs.

Sturrock (1966)

FOXSI Science TargetsPolar JetsNoise

Storms

Type III radio bursts

Axions?

Quiet Sun(coronal heating)

Active Region Flares

Energy Release in its many forms…

Occulted HXR Emission

The first FOXSI flight (Jan 2011) will focus on1. thermal

and flare emission from active regions

2. nanoflares in the quiet Sun.

Many science targets are available for future FOXSI flights!

Do nanoflares heat the corona?

Are small flares the same as large flares?

To answer these questions, HXR observations require greater sensitivity.

Coronal HeatingNanoflares (thermal) Microflares (nonthermal +

thermal)

Hannah et al. (2008)

~1.8

FOXSI

Short for the Focusing Optics X-ray Solar Imager Sounding rocket mission funded

under 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!

FOXSI

HXRs undergo total internal reflection at shallow graze angle (<0.5 degree).

Using mirror shells with a Wolter I geometry (confocal paraboloid and hyperboloid) HXRs can be brought to a common focus.

Telescope shells are nested together to form telescope modules to increase area.

FOXSI Optics

FOXSI Optics Fabrication

Process by B. Ramsey at the M.S.F.C.

Individual shell resolution of 7’’ (FWHM).

Telescope module resolution of 12’’.

Dynamic range of 100 for separations >30’’.

FOXSI Optics

-100

-50 0 50

100

150arcsecon

ds

FWHM 12’’

Effective area

20132011

FOXSI’s effective area Blue represents the

current configuration for the flight in 2011

Red represents 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).

The dashed line represent the area provided by the optics. The effective area is also shown.

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 keV

68% for 15 keV CdTe DSSD in the future

FOXSI Detectors

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’’)

FOXSI by the Numbers

FOXSI Payload

2 m focal length Si strip

detectors (75mm)

Replicated optics telescope module (7 shells & 7 modules)

FOXSI Progress

(Above) Preparing the FOXSI detector plane assembly for a thermal test.

(Above) Practicing bonding the VATA ASIC on the detector board.

(Right) A FOXSI Si strip detectors (75mm pitch)

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.

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.

Concluding Remarks/Future Work

Heating events are observed in the “quiet” Sun network (Krucker & Benz 1998, Parnell & Jupp 2000, Ascwanden 2000).

Nonthermal HXR emission may be expected.

HXR from the Quiet Sun

T∼2MK, EM∼1044 cm, E∼5×1025 ergs, Dt = 60s

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)

HXR from Radio-producing e-

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.

Concluding Remarks/Future Work