Soft X-ray irradiance study using Hinode/XRT synoptic composite images

Topics from Hinode/XRT irradiance study

Aki Takeda (Montana State University, USA) & XRT group at MSU
26 September 2023 @ Hinode-16/IRIS-13 Joint Science Meeting


Sample pages from the XRT Synoptic Composite Image Archive (SCIA) `(http://solar.physics.montana.edu/HINODE/XRT/SCIA/)`

0. Outline of this talk

Introduction --- instrument & data description
Method of Analysis
- How to derive X-ray irradiance
- Calibration challenges and difficulties
Science topics derived from irradiance study
- Revisiting Lx-B power law relation (comparison with SDO/HMI).
- Rising-Descending phase asymmetry of irradiance

1. Introduction

Hinode's X-Ray Telescope :
- launched in 2006, September 23.
- grazing incidence telescope with aperture size ≈ 35cm
- 9 X-ray analysis filters
- observing wavelength range : 5 - 200 Å
- CCD : back-illuminated 2048 × 2048 pix
- field of view : 2040 × 2040 arcsec.

Synoptic Composite Images : short/medium/long exposure images taken closely in time are processed into a single composite image to increase the dynamic range. These products are accessible from the XRT Synoptic Composite Image Archive (SCIA).
(for detail, see Takeda et al. (2016) Sol.Phys. 291, 317)

2. Method of Analysis

Step 1 : Derive filter-ratio Te and EM (isothermal corona assumed).
- collect soft X-ray full-Sun signals (< 1.1R_⦿) from 2 different analysis filters.
  - 2008.2 - 2015.6 : Al_mesh and Ti_poly
  - 2015.1 - 2021.6 : Al_mesh and Al_poly
- apply Filter Ratio Method to derive Te and EM.
  - traditional coronal elemental abundance (Feldman 1992) assumed.
Step 2 : Calculate isothermal coronal spectrum using Te and EM.
- CHIANTI atomic DB ver.10.0 (isothermal.pro)
- Coronal elemental abundance (sun_coronal_1992_feldman_ext.abund)
- CHIANTI's default ionization equilibrium data (chianti.ioneq)
Step 3 : Integrate coronal spectrum over a certain wavelength range.
- 5 -- 60 Å as the XRT irradiance.
- 1 -- 8 Å for comparison with GOES/XRS
- 2.8 -- 36.6 Å for comparison with Yohkoh/SXT
- etc.

Calibration challenges and difficulties

Proper correction of aging effect of the instruments:

Visible stray light contamination --- caused by a rupture developed on the pre-filter.

event	date	open area fraction	note
1st	9-May-2012	~0.1%	Ti_poly and C_poly filters started to be affected.
2nd	14-Jun-2015	~3.3%	Ti_poly filter single use disabled.
3rd	27-May-2017	~7.5%	Al_mesh filter started to be affected.
4th	29-May-2018	~9.9%	Al_poly filter started to be affected.
5th	8-Jun-2022	~10.8%
6th	5-May-2023	~13.5%

Subtraction of visible light component from the X-ray images.
Modification of XRT's effective area function due to the open area of the pre-filter.

Growth of contaminant layers on CCD and X-ray analysis filters.
--- caused by the evaporation of some material used in the telescope.

[CCD] the contaminant layer thickness estimation using G-band intensity was replaced with the empirical curve.
[FILTERS] additional growth of the FILTER contaminant layer after 2007 is likely.

Empirical curve assumed since May-2022 (red) [provided by K. Yoshimura]	Additional contamination layers on X-ray filters currently assumed.

Obtained Te, EM and X-ray irradiance (5-60A).

Modification by CHIANTI ver.10.1 new elemental abundance files.

CHIANTI ver. 10.0 abundance files
- sun_coronal_1992_feldman_ext.abund
- sun_coronal_2012_schmelz_ext.abund
- etc.
CHIANTI ver. 10.1 abundance files (released June 2023)
- sun_coronal_2021_chianti.abund
- etc.
Change from ver 10.0 to 10.1

(chart and plots prepared by R. Fleming)

For details, see a poster presentation (P-138) by Rhiannon Fleming et al.

Comparison of CHIANTI_2021 abundance with old corona(Feldman_1992) and hybrid(Schmelz_2012)

Te	EM	Irradiance

3. Science topics

3.1 Lx-B relation : comparison with Magnetic field flux data

Revisit of Lx - B relationship studied by Pevtsov et al. 2003.
- Lx: X-ray luminosity (X-ray irradiance)
- B: unsigned photospheric magnetic field

X-ray data : Yohkoh/SXT
- X-ray irradiance (2.8-36.6A) obtained from AlMg/Al.1 filters.
- X-ray signals collected within 1.1Rs from Sun center.
- averaged over 1 solar rotation (27.2375 days).
Magnetic flux data : KittPeak/magnetograph
- Daily magnetogram.
- Unsigned magnetic field within 0.8(?) Rs.
- averaged over 1 solar rotation (27.2375 days).
Investigating to see if the Lx-B power-law relation is scale free.

[Our analysis]

X-ray data : Hinode/XRT
- X-ray irradiance (2.8-36.6A) obtained from thin_Be/Al_poly filters.
- X-ray signals collected within 0.83 Rs from Sun center.
- averaged over 1 day.
- converted to X-ray luminosity in [erg/sec].
Magnetic flux data : SDO/HMI
- 720 sec cad. magnetogram data averaged over 1 day.
- Total unsigned magnetic field within 0.79 Rs in [Mx].
Lx vs B scatter plot (created by K. Yoshimura)
- Single power law is obtained by cutting off weak magnetic field < 60 G
- The power law index with B_cutoff = 60 G is 1.10.
- What is the magnetic field components < 60 G that are cut-off?

Quiet Sun area	Coronal Hole area	Active Region area

	Quiet Sun	Coronal Hole	Active Region
total signed magnetic flux (Mx)	-1.11 x 10²¹	6.00 x 10²¹	2.03 x 10²²
total unsigned magnetic flux (Mx)	3.00 x 10²²	3.14 x 10²²	1.12 x 10²³
% of unsig. mag. flux over 60G in Mx in pix	46.7 8.6	47.3 8.8	85.2 20.3
% of unsig. mag. flux 15 to 60G in Mx in pix	40.0 37.1	40.0 38.9	11.8 38.3
% of unsig. mag. flux under 15G in Mx in pix	13.3 54.3	12.7 52.3	3.0 41.4

"In QS and CH, more than 50% of total magnetic flux coming from more than 90% of total area are below 60 G and need to be cut-off, in order to get a single power law."

"The area to be cut off consists of neutral area (less than noise level of HMI) and a part of network boundary magnetic field (15 to 60G)." → NOT heated by the same mechanism as ARs?

For details, see the poster presentation (P-40) by Keiji Yoshimura et al.

-------------------------------------------------------
 period  :    I           II           III
-------------------------------------------------------
 constant
  to fit :  0.300       0.354         0.336
-------------------------------------------------------
[from Takeda and Boland(2023) accepted by ApJ.]

3.2 Latitude Dependence of Irradiance

new mask images.
limb irradiance at 3 latitude ranges.
past observations
- Norikura coronagraph synoptic maps (NAOJ web site)

Characteristic behavior of mid-latitude corona affects the relative importance of outer corona of the full-Sun over the solar cycle.

suggested pictures of solar cycle variation of the Corona

Descending phase Rising phase

Illustration created by R. Fleming

Solar cycle variation of coronal shape (ecliptic view)

Solar cycle variation of coronal shape (polar view)

4. Summary

We investigated the long-term variation of the filter-ratio Te, EM and soft X-ray irradiance using a series of XRT full-Sun images.
- utilize 2D information of the corona.
- can provide physical unit.
Lx-B relationship investigation.
- Single power-law is obtained by applying magnetic field cut-off of 50-75G.
- Obtained power index: 1.16 - 1.03 (cf. 1.15 in Pevtsov_2003).
- The area of supergranule and a part of network boundaries are the excluded structures to get the single power-law relation.
Asymmetric behavior of mid-latitude corona over the solar cycle.
- Propagate to the relative contribution of outer limb corona of the whole Sun over the solar cycle: small for active Sun, largest around solar minimum, and larger in rising phase than descending phase.

summary_top

Suppl. materials

XRT temperature response is an important function that connects observed
Data Number to a physical unit.

[Temperature response func.] = [Factor(geometrical, etc.)] * 
                               [Model Solar Spectra] # [XRT Effective Area]

[Effective Area] = [aperture] * [prefilter] * [mirror1] * [mirror2] *
                     [filter1] * [filter2] * [ccdqe] * [contamination]

Descending phase	Rising phase

Rising phase	solar max.	Descending phase	solar min.

Rising phase	solar max.	Descending phase	solar min.