Athiray, P.S.

Linsay Glesener

Noriyuki Narukage

Shin-Nosuke Ishikawa

Viervering, Juliana

English

NASA Technical Reports Server

t 5th Asia Pacific Solar Physics Meeting
Pune, 5 Feb 2020
Lindsay Glesener,
Juliana Vievering, 
Juan CamiloBuitrago-Casas,
Shin-nosukeIshikawa, 
Andrew Inglis, 
Noriyuki Narukage, 
Daniel Ryan, 
Steven Christe, 
Sophie Musset,
SämKrucker
The FOXSI-3Team5th	APSPM,	Pune,	2/5/20
https://ntrs.nasa.gov/search.jsp?R=20200001484 2020-03-28T19:19:36+00:00Z
Outline
• Overview of FOXSI sounding rocket experiment
• Successful Flight campaigns and coordinated FOXSI-2 microflare observations 
• Temperature response functions for FOXSI-2
• Combined Differential Emission Measure (DEM) analysis - to determine the 
amount of plasma in the line of sight that emits the radiation as a function of 
temperature 
• Estimates of thermal energy
• Summary
5th	APSPM,	Pune,	2/5/20
High-energy aspects of the Sun beyond RHESSI
Lingering	questions…
Where	and	how	does	particle	acceleration	occur?
What	is	the	role	of	small-scale	energy	release	in	heating	
coronal	plasmas?
How	quiet	is	the	Sun	in	HXRs?
Need	for…
Better	sensitivity
Increased	imaging	
dynamic	range
Fine	time	resolution
266 I.G. Hannah et al.
Fig. 2 The energy distributions
for solar flares. The nonthermal
energy distribution is shown for
large flares >25 keV observed
with SMM/HXRBS (Crosby et al.
1993), microflares >8 keV from
CGRO/BATSE (Lin et al. 2001a)
and microflares >EC (above the
low energy cutoff) from RHESSI
(Hannah et al. 2008a). The
thermal energy distribution is
shown for microflares with
RHESSI (Hannah et al. 2008a)
and Yohkoh/SXT (Shimizu 1995)
and EUV nanoflares with TRACE
(Parnell and Jupp 2000;
Aschwanden et al. 2000) and
SOHO/EIT (Benz and Krucker
2002). This figure is deceptive as
it is comparing energy
distributions of different flare
energy components, each
involving different instrument
and selection effects, and were
obtained over different periods of
different solar cycles
distributions. In Sect. 3.3 we briefly discuss how the power-law nature of the flare parameters
arises. Conclusions and discussion are given in Sect. 4.
2 From Major to Minor Flares
2.1 Flare Classification & General Properties
The most powerful ordinary flares have energies estimated at above 1033 ergs and present
a spectacular range of phenomena, easily observed across the wavelengths. The first flare
observed was a powerful event in 1859, detectable through its small, intense white-light
emission patches as described by Carrington (1859) and corroborated by Hodgson (1859).
Remarkable terrestrial effects accompanied this flare and also followed it after an interval of
half a day. This event anticipated much of the complexity of flares as we know them today,
but it was not until the 1940s that “flare” was accepted as the term to describe these transient
phenomena (Newton 1943; Richardson 1944). Events with total energy about a millionth
smaller than large flares (about 1027 erg), became known as “microflares” (Schadee et al.
1983; Lin et al. 1984). Parker hypothesized that even smaller flares, “nanoflares,” with en-
ergies of order one billionth of large flares or about 1024 erg, could be the basic unit of a
localized impulsive energy release (Parker 1988).
Quantitative flare classification is based on the 1–8 Å SXR flux observed by GOES.
Large flares have Xn-class, indicating a peak flux of n × 10−4 W m−2, the largest events
being above X10. This classification decreases through the decades of M, C and B-class
flares down to the smallest An-class events with n×10−8 W m−2 and the sensitivity limit of
the detector. The classification of flares and the associated range of GOES fluxes is shown in
Table 1. The largest GOES flare was SOL2003-11-04T19:53 (X17.4), which saturated the
nano micro large
5th	APSPM,	Pune,	2/5/20
Focusing Optics X-ray Solar Imager (FOXSI) 
1. Photons	are	collected	on	a	small	volume	for	– high	Signal	to	Noise
2. Point	spread	function	falls	steeply,	providing	improved	dynamic	range.
Point Spread Function
0 50 100 150 200
arcseconds
10-4
10-3
10-2
10-1
100
R
el
at
iv
e 
flu
x FOXSI (1-15 keV)
Yohkoh (~1.5 keV)
RHESSI (3-100 keV)
Main	Goal	of	FOXSI:	Demonstrate	use	of	focusing	optics	for	observing	the	Sun	in	hard	x-rays	
First solar dedicated Hard X-ray (HXR) telescope with direct focusing optics
5th	APSPM,	Pune,	2/5/20
FOXSI sounding rocket experiment
5th	APSPM,	Pune,	2/5/20
FOXSI sounding rocket experiment
X-ray optic modules:  
Nested shells of grazing  
incidence optics
NASA Marshall Space FlightCenter
Krucker et al, SPIE, 2013  
Christe et al, 2015  
Buitrago-Casas et al, 2017
• Replicated	Ni	optics
• Wolter-I	shape
• Nested	sets	of	7	or	10
• FWHM	~5”
5th	APSPM,	Pune,	2/5/20
FOXSI sounding rocket experiment
X-ray optic modules:  
Nested shells of grazing  
incidence optics
NASA Marshall Space FlightCenter
Krucker et al, SPIE, 2013  
Christe et al, 2015  
Buitrago-Casas et al, 2017
Semi-conductor  
detectors (Si and CdTe), 
JAXA, ISAS, Kavli IPMU
Ishikawa et al, 2016
Athiray et al, 2017
• Double-sided	Si	or	CdTe strip	detectors	
• Read	out	by	low-power,	low-noise	ASICs
Energy	range	:	4	to	20	keV
5th	APSPM,	Pune,	2/5/20
FOXSI sounding rocket: past campaigns
White Sands  
Missile Range
FOXSI-1
Nov’ 02, 2012
FOXSI-1 (2012)
First focused image
of the solar HXR
Kruckeretal,2014
Ishikawaetal,2014
5th	APSPM,	Pune,	2/5/20
FOXSI sounding rocket: past campaigns
White Sands  
Missile Range
FOXSI-1
Nov’ 02, 2012
Major upgrades:  
Additional optic
shells, CdTe detectors
FOXSI-2  
Dec'11,2014
FOXSI-2(2014)
1. Observation of quiet ARs
2. Two microflares, an order of magnitude 
fainter than previous observations
Kruckeretal,2014
Ishikawaetal,2014
Ishikawa et al, Nature Astronomy, 2017
Athiray et al, ApJ (in revision)
Vievering et al, in prep
5th	APSPM,	Pune,	2/5/20
FOXSI-1 (2012)
First focused image
of the solar HXR
FOXSI sounding rocket: past campaigns
White Sands  
Missile Range
FOXSI-1
Nov’ 02, 2012
FOXSI- 3
Sep’07, 2018
Major upgrades:  
SXR detector  
Collimator
Major upgrades:  
Additional optic
shells, CdTe detectors
FOXSI-2  
Dec'11,2014
FOXSI-1 (2012)
First focused image
of the solar HXR
FOXSI-2(2014)
1. Observation of quiet ARs
2. Two microflares, an order 
of magnitude fainter than 
previous observations
Kruckeretal,2014
Ishikawaetal,2014
Ishikawa et al, Nature Astronomy, 2017
Athiray et al, ApJ (in revision)
Vievering et al, in prep
FOXSI-3 (2018)
First photon-counting  
image of the Sun in SXR
Musset et al, 2019
5th	APSPM,	Pune,	2/5/20
Solar	microflares	with	FOXSI-2	rocket
5th	APSPM,	Pune,	2/5/20
Microflare-1
Microflare-2
Observations during second flight ~(6.5mins)
• Two solar microflares
• Coordinated observations : Hinode/XRT, SDO/AIA, IRIS, VLA
FOXSI-2 microflares
• FOXSI allows us to image an order of magnitude fainter microflares than observed by solar X-ray 
instruments
Vievering (2019, Phd Thesis)
Detector 6
-250 -200 -150 -100 -50 0 50
X (arcsec)
-50
0
50
100
150
200
250
Y 
(a
rc
se
c)
FOXSI-2 (5 - 8 keV)
Microflare 2 AR12234
Target J
Detector 6
-100 -50 0 50 100 150
X (arcsec)
-350
-300
-250
-200
-150
-100
Y 
(a
rc
se
c)
FOXSI-2 (5 - 8 keV)
Microflare 1 AR12230
Target C
19:13 19:14 19:15 19:16 19:17 19:18 19:19
0
5
10
15
20
25
30
Co
un
ts 
s-1
A B C D E J
Detector 6, AR12230
Time (HH:MM)
Targets
Microflare 1
19:13 19:14 19:15 19:16 19:17 19:18 19:19
0
5
10
15
20
25
30
Co
un
ts 
s-1
Detector 6, AR12234
Targets B C D E J
M
icr
of
lar
e 
2Quiescent
Time (HH:MM)
5th	APSPM,	Pune,	2/5/20
Background subtracted GOES X-ray 
flux indicate sub A-class microflares
SDO/AIA
-400-200 0 200 400 600 800
X (arcsec)
-400
-200
0
200
400
600
800
Y 
(a
rc
se
c)
94 Å
AR12230
AR12234
Data summary for DEM analysis
EUV (5 Channels) SXR (9 filter combinations) HXR (5 to 8 keV)  
• Brightening in EUV, SXRs and HXRs clearly suggest a multi-thermal plasma
• Unique dataset suitable for “Differential Emission Measure analysis”
Hinode/XRT
-400-200 0 200 400 600 800
X (arcsec)
-400
-200
0
200
400
600
800
Y 
(a
rc
se
c)
Be Thick
Open/
AR12230
AR12234
FOXSI-2 (Detector 6)
-400-200 0 200 400 600 800
X (arcsec)
-400
-200
0
200
400
600
800
Y 
(a
rc
se
c)
AR12230
AR12234
Microflare 1
Microflare 2
5-8 keV
5th	APSPM,	Pune,	2/5/20
Temperature	response	function
• AIA & XRT - Standard solar soft routines
• FOXSI-2 
1. Instrument response : Optics effective 
area, Detectors spectral response matrix, 
Thermal blankets
2. Synthetic Solar spectrum at different 
isothermal temperatures (1 to 30 MK)
3. Temperature response is created by
folding the synthetic spectra through
instrument response to get the expected
counts
Instruments’ ability to detect plasma at 
different temperatures
• FOXSI is sensitive to temperatures > 5 MK 
• Good overlap in temperature sensitivity for all the instruments Note: Pixel sizes are different
for each instrument
6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4
Log[ T(MK) ]
10-30
10-28
10-26
10-24
10-22
DN
 cm
5  s
-1
  p
ixe
l-1  
(A
IA
 a
nd
 X
RT
)
10-30
10-28
10-26
10-24
10-22
Co
un
ts 
cm
5  s
-1
  p
ixe
l-1  
(F
OX
SI
-2
)
FOXSI-2
5-6 keV
6-7 keV
7-8keV
SDO/AIA
94  Å
131Å
171Å
193Å
211Å
Hinode/XRT
C_poly/Ti_poly
C_poly
Be_thin
Be_med
Al_med
5th	APSPM,	Pune,	2/5/20
10−6
10−4
10−2
100
102
104
DN
 (o
r) 
Co
un
ts 
s−
1  p
ix−
1
Predicted
Observed
−1.5
0.0
1.5
Re
sid
ua
ls
94Å 131Å 171Å 193Å 211Å 5.5 6.5 7.5
Be Thick
AIA	 FOXSI					XRT
10-4
10-2
100
102
104
DN
 (o
r) 
Co
un
ts 
s-1
 p
ix-
1
Predicted
Observed
-1.5
0.0
1.5
Re
sid
ua
ls
94Å 131Å 171Å 193Å 211Å 5.5 6.5 7.5
C Poly/Ti Poly
C Poly
5.9 6.2 6.5 6.8 7.1 7.4
log T
1016
1018
1020
1022
DE
M
(c
m
-5
 K
-1
)
Target A
5.9 6.2 6.5 6.8 7.1 7.4
log T
1016
1018
1020
1022
DE
M
(c
m
−5
 K
−1
)
Target J
Combined DEM 
analysis
Fluxi = Response(Tj,i) !	DEM(Tj)
Hinode-XRT DEM 
inversion 
• Forward fitting using 
non-linear least squares
• Monte Carlo simulations 
to emulate errors
Best DEM solution
MC solutions
Microflar -2 
unknown
AIA	 FOXSI				XRT
Microflare-1 
5th	APSPM,	Pune,	2/5/20
5.9 6.2 6.5 6.8 7.1 7.4
log T
1023
1024
1025
1026
1027
1028
EM
(c
m
−5
)
5.9 6.2 6.5 6.8 7.1 7.4
log T
1023
1024
1025
1026
1027
1028
EM
(c
m
−5
) AIA XRT
FOXSI
Combined DEM analysis : EM loci curves
Including FOXSI can better constrain high temperature emission than AIA 
& XRT alone
EM loci provide upper limits for emission measure at a temperature 
Microflare-1 Microflare-2 
5th	APSPM,	Pune,	2/5/20
Comparison of flaring emission vs quiescent emission
• Background emission peaks at 2– 4 MK
• Microflares have excess emission above 5 MK
5th	APSPM,	Pune,	2/5/20
Thermal energy estimates
Thermal energy	(x	1028 erg)
Multi-thermal	plasma
Thermal	energy	(	x	1028 erg)
Isothermal plasma
Microflare-1 Target	A 5.1 1.4
Target B 4.9 1.5
Target	C 5.1 1.2
Microflare-2 Target	J 1.6 1.0
• RHESSI microflares : 1026 – 1030 erg (Hannah et al., 2008)
• NuSTAR microflares : 1027 – 1028 erg (Wright et al., 2017)
Multi-thermal DEM provides a more comprehensive Eth estimates than 
isothermal approximation
5th	APSPM,	Pune,	2/5/20
Summary
• We produced DEMs for two sub-A class microflares jointly observed by FOXSI-2, 
XRT, and AIA 
• Coordinated FOXSI-2 observations are one of the few definitive measurements 
of the plasma temperature distribution above 5MK in microflares
• These microflares have significant emission above 5 MK
• Multi-thermal DEM analysis provides a more comprehensive thermal energy 
estimates than isothermal approximation
• Small scale energy releases are important to consider for coronal heating
Acknowledgement : FOXSI was funded by NASA’s Low Cost Access to the Space program, grant NNX11AB75G. 
5th	APSPM,	Pune,	2/5/20
• Thank	you
5th	APSPM,	Pune,	2/5/20
Complexity	in	a	FOXSImicroflare
FOXSI-2 first microflare: Estimated GOES class:A0.5
Spectroscopy:  
Isothermal fit
→ Thermal energy of
Imaging spectroscopy: Centroids at higher energy are located ~7’’ east of
the low-energy, suggesting high temperature plasma (energy release)
Images: 4-5.5 keV
Contours: 6-15 keV
Vievering et al, in prep + thesis(2019)5th	APSPM,	Pune,	2/5/20
Flight	Data	Analysis
4-15	keV
-50 0 50 100
X (arcsecs)
-300
-250
-200
-150
Y 
(ar
cs
ec
s)
A
4 5 6 7 8 9 10
Energy [keV]
0.1
1.0
10.0
Co
un
ts
 k
eV
-
1  
s-
1
T = 10.1±0.3 MK
 
EM = (6.4±1.4)x1044 cm-3
Data
Model
4-15	keV
Data
Model
Si
CdTe
Si
CdTe
Spectral	modeling	of	CdTe
data	shows	results	that	are	
consistent	with	Si	data.
Instrument	response:
• No	major	nondiagonal
contributions
• Convolve	response	with	
gaussian probability	
distribution	account	for	
finite	energy	resolution
Note	finer	pixel	
size	for	CdTe
FOXSI-2	First	Microflare	
(optically	thin	thermal	bremsstrahlung	model)
Vievering et	al	2019	(Thesis)	(In	preparation)5th	APSPM,	Pune,	2/5/20
FOXSI-3 upgrades
Soft X-ray photon-counting detector
→Expand energy range
NAOJ and Nagoya University
Two new 10-shell optic  
modules →  increase  
effective area
Two new CdTe detectors
→ increase efficiency at  
high energies
JAXA/ISAS and Kavli IPMU
Buitrago-Casas, SPIE, 2017
Ishikawa et al, 2016  
Furukawa et al,2019
Narukage et al, SPIE,2017
Two collimators
→reduce the ghost  
ray background
TORAY5th	APSPM,	Pune,	2/5/20
Reducing	the	ghost	ray background
5th	APSPM,	Pune,	2/5/20
Reducing	the	ghost	ray background
→ Match the lab measurements
History of each simulated ray is tracked
→ Information on the origin of the ghost rays
• Point spread function of a FOXSI 7-shell module
at the Stray Light Facility at Marshall Space Flight Center:
• X-ray source at 100 meters from the optics
• Source is 30 arcmin off axis
Lab measurement of the ghost ray background
Ray-tracing simulation of ghost rays
OpticalaxisDetecto
r  FOV
Doubly 
reflecte
d  rays
5th	APSPM,	Pune,	2/5/20


FOXSI Sounding Rocket Flights and Solar Microflare Observations

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