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the onboard calibration for the spaced row charge injection of the suzaku xis

The onboard calibration for the spaced-row charge injection of the Suzaku XIS

Hideki Uchiyama, Yoshiaki Hyodo, Hiroya Yamaguchi, Hideyuki Mori, Takeshi Go Tsuru, Hironori Matsumoto, Katsuji Koyama (Kyoto Univ.), Ken'ichi Torii, Satoru Katsuda, Hiroshi Nakajima, Kazuto Hasuike, Kiyoshi Hayashida, Hiroshi Tsunemi (Osaka Univ.), Hiroshi Murakami, Tadayasu Dotani (ISAS/JAXA), Gregory Prigozhin, Steve Kissel, Eric Miller, Beverly LaMarr, Mark Bautz (MIT) and Suzaku XIS team

x ray astronomy satellite suzaku x ray imaging spectrometer xis
X-ray astronomy satellite Suzaku& X-ray Imaging Spectrometer (XIS)
  • Suzaku

The 5th Japanese X-ray satellite

  • X-ray Imaging Spectrometer (XIS)
    • X-ray CCD camera onboard Suzaku
    • 3 Front Illuminated (FI) & 1 Back Illuminated (BI) sensors
    • Positional resolution
    • ~2’ with X-ray telescope (HPD)
    • High energy resolution ~140eV@5.9keV (FWHM) in Aug. 2005 (just after launch)
    • Equipped with a charge injection (CI) structure

Suzaku satellite

CCD chip of XIS

slide3

Degradation of the energy resolution

The time dependence of the energy resolution @5.9keV

Aug. 2005

just after launch

200

Energy resolution (eV,FWHM)

May

2006

150

2×108

1.9×108

1.8×108

Time since 2000-1-1 00:00:00 (s)

The increase of charge transfer inefficiency (CTI) causes this degradation.

slide4

How the CTI causes the degradation

ACTY

ACTX

Q

Imaging area

X-ray

Charge trap caused by radiation damage in orbit

1026 pixel

Q

Transfer direction

Energy resolution

is

degraded.

Readout charge

Frame-store region

Q

Q’

Q’’

Q’

Q’’

Readout node

0

ACTY

slide5

54 rows

Transfer direction

Spaced-row Charge Injection (SCI)

Charge injection structure

ACTY

ACTX

Charge trap caused by radiation damage in orbit

Q

Imaging area

X-ray

Injected charge fills the traps.

→It decreases the CTI.

1026 pixel

Q

Q’

Q’’

Energy resolution

is

recovered!

Frame-store region

Q

Readout charge

Injected charge

Q’

Q’’

ACTY

Readout node

0

slide6

Spectra of onboard cal source 55Fe

  • We operated XIS with the SCI technique in orbit for the first time in August 2006 and verified the recovery of the energy resolution from 210eV to 150eV (@5.9keV,FWHM)

no-SCI

SCI

Mn I Kα

Mn I Kβ

Pulse height (channel)

  • We studied the gain non-uniformity in the SCI mode and developed a new correction method for it.
how the sci mitigates the gain non uniformity
How the SCI mitigates the gain non-uniformity
  • Perseus cluster of galaxies
    • It is a bright diffuse X-ray source.
    • It covers almost all of the FOV of the XIS.
    • Its spectrum has strong He-like Fe Kα line and the line center is roughly independent of the position.

→Suitable for the study of the gain non-uniformity over the chip.

    • Aug. 2006, in the both SCI & no-SCI mode, exposure time ~50 kilo seconds

XIS image of

Perseus cluster

slide8

How the SCI mitigates the gain non-uniformity

He-like Fe Kα from Perseus cluster

  • Perseus cluster

ACTY

Pulse Height channel

ACTX

He-like Fe

K α

cnts/ch/s

Pulse Height channel

The CTI became ~30% by the SCI.

slide9

The gain non-uniformity on a smaller spatial scale

Positional dependence ofMn I Kα line

  • Ground experiment of the SCI with proton-damaged CCD

500

Transfer direction

450

Pulse Height

400

Tomida et al.

1997

Charge Injected row

350

100

200

300

400

500

Transfer pixel

“Saw-tooth” gain non-uniformity appeared.

→ Does it appear in orbit?

slide10

Onboard calibration sources 55Fe

  • They irradiate the upper edge of XIS continuously.

→ We can use long exposure data.

  • The spectrum has Mn I Kα line and the line center is 5.895keV.
  • April 2007, in the SCI mode, exposure time ~1 mega seconds

XIS image of

Cal source

slide11

The gain non-uniformity on a smaller spatial scale

Charge injected row

  • Onboard calibration source 55Fe

Mn I Kα from onboard cal source

Charge injected row

C

Pulse Height channel

54 rows

B

A

A

Transfer

direction

B

Mn I Kα

C

Transfer

direction

cnts/ch/s

ACTY

PH CH

“Saw-tooth” gain non-uniformity appeared in orbit.

correction for the gain non uniformity

The slope at ΔACTY=0

PH0

PH

Saw-tooth

function

The slope at ΔACTY=54

ΔACTY

54 rows

ACTY

charge-injected rows

Correction for the gain non-uniformity
  • We modeled the positional non-uniformity of the gain by “saw-tooth” function below.
  • Three parameters, the slope at ΔACTY=0, ΔACTY=54 and PH0 specify this function uniquely.
  • Fit the observed ACTY-PH relation with the saw-tooth function to obtain the the slope at ΔACTY=0, 54 and PH0, then correct the observed PH.

Saw-tooth

Correction

result of the saw tooth correction method
Result of the saw-tooth correction method

Mn I Kαfrom onboard cal source

Mn I Kαfrom onboard cal source

fitting result of the saw-tooth function

Pulse Height channel

  • The correction reduced the gain non-uniformity at 5.9 keV from ~ 0.5% to ~ 0.1%

→The gain is uniform on the order of a few eV at 6 keV with this correction.

  • The energy resolution is also improved.

151 eV → 148 eV @5.9 keV FWHM (additional width ~ 30 eV)

Without Saw-tooth correction

With Saw-tooth correction

the current status of the suzaku xis software data processing for the sci
The current status of the Suzaku XIS software & data processing for the SCI
  • The saw-tooth correction has been built into public Suzaku analysis software and released.
  • Version 2.0 data processing incorporates the saw-tooth correction and the calibration of the SCI. The processing has already begun.
  • The calibration database for the SCI is being updated continuously now.
summary
Summary
  • Suzaku XIS operated the spaced-row charge injection technique for the first time and verified the recovery of the energy resolution.
  • The CTI became ~30% by the SCI. The gain non-uniformity over the chip was mitigated well in orbit.
  • The saw-tooth gain non-uniformity was shown in orbit in April 2007.
  • We developed the saw-tooth correction method. It made the gain in the SCI mode uniform on the order of a few eV at 6keV.
  • The software for the SCI mode has been released. The data processing for the SCI mode already started.