SPD/AAS Poster 094.1627-31 May 2007Mark Weber

Smithsonian Astrophysical Observatory

On-Orbit Measurement of the Hinode / XRT Point Response FunctionMark Weber, J. Cirtain, E.E. DeLuca, L. Golub, P. Martens, and the XRT Team (SAO, NASA, JAXA, NAOJ)

ABSTRACTThe Hinode X-Ray Telescope (XRT) provides unprecedented

observations of the solar corona in x-rays, due in part to its fine

resolution. The optical point spread function (PSF) was

measured before launch at the NASA X-Ray Calibration Facility

to have a FWHM of 0.92 arc-seconds. In this poster we describe

our work to verify the PSF measurements using on-orbit data of

Mercury and Lunar transits observed with XRT. Hinode is a

Japanese mission developed and launched by ISAS/JAXA, with

NAOJ as a domestic partner, and with NASA and STFC (UK) as

international partners. It is operated by these agencies in

cooperation with ESA and the NSC (Norway). The presenter is

supported under NASA contract NNM07AA02C.

METHODPlanetary transits can provide very sharp shadow masks

against the illumination of the Sun, facilitating a determination of

the telescope’s point response function (PRF). The drop-off of

the calibrated signal measured inward from the shadow’s limb

primarily represents the convolution of the PRF with the “true”

image. We assume the core of the PRF is a Gaussian, convolve

it with a model of a back-illuminated shadow, and compare to

the observations. We vary the model parameters and iterate

with this forward fitting technique to determine the best-fit PRF.

Since Hinode’s launch, XRT has observed a Mercury transit and

several solar eclipses by the Moon. In this poster, we present

results for a transit image and an eclipse image. We selected

images for longer exposure duration to achieve a better S/N,

and for uniform illumination along the best shadow edge.

Mercury Transit

XRT Al_poly/Open 08-Nov-06 23:50:31 16.39s 512x512

1 pixel = 1 arcsecond.

Mercury traversed the FOV horizontally about 1 arcsec

during this 16.4 sec exposure.

Mercury’s ang diam = 10 arcsec.

Analysis of three columns of pixels perpendicular to

planetary velocity.

Solar Eclipse

velocity

3 central

columns

Surface plot of intensity inside the subregion box.Mercury’s shadow has an obvious effect.Edge blurring along the direction of velocity is minimal, but we analyzed the perpendicular edge, anyway.

DN

/ s

ec

arcseconds

Mercury’s

diameter

3 pixel columns

through shadow

DN

/ s

ec

arcseconds

Light-curves along 3 central columns through shadow.

The mean of these curves is analyzed on the right

(Northern) edge.

We varied the sigma of a 2D Gaussian convolved with

a 2D circular step-function shadow to fit the drop-off.

Dashed line = mean of three columns in previous plot.Diamonds = data points used for fitting the model.Error bars on data = deviation of data about mean (probably a bit generous).Solid line = best model fitBest fit = Gaussian sigma of 0.6 +/- 0.07 arcsec.

FWHM = 1.0 +/- 0.12 arcsecD

N /

se

cD

N /

se

c

arcseconds

arcseconds

velocity

5 rows at sharp

edge

5 pixel rows across

limb

XRT Al_poly/Open 19-Mar-07 04:25:51 16.39s 1024x10241 pixel = 1 arcsecond.The Moon traversed the FOV about 50 arcsec during this 16.4 sec exposure, so there is only a short section of sharp limb to analyze.Analysis of 5 rows of pixels across sharp edge. They are shown offset in this image to leave the limb visible.

Surface plot of intensity inside the subregion box.The lunar shadow has an obvious effect, and has been rotated from the previous image for convenience.Edge blurring is clearly visible at both ends.

Light-curves along 5 rows across the sharpest edge.The mean of these curves is analyzed over the range between the vertical markers.We varied the sigma of a 2D Gaussian convolved with a 2D straight step-function shadow to fit the drop-off.

Dashed line = mean of five rows in previous plot.Diamonds = data points used for fitting the model.Error bars on data = deviation of data about mean (probably a bit generous).Solid line = best model fitBest fit = Gaussian sigma of 1.4 +/- 0.06 arcsec.

FWHM = 2.4 +/- 0.1 arcsec

DiscussionBefore integration into the Solar-B (Hinode) spacecraft, the XRT

optics were tested at the X-Ray Calibration Facility at NASA’s

Marshall Space Flight Center. During those tests, a core PRF of

about 0.9 arcsec was carefully measured.

The analysis of the on-orbit PRF measurements are on-going;

this poster only presents preliminary results. The analysis of the

Mercury transit shows a PRF in agreement with the laboratory

measurements. Mercury moved very slowly during the

exposure, so a sharp edge could be found and measured.

During the solar eclipse, the Moon moved far across the FOV

during the 16.4 sec exposure. We have attempted to do the

analysis at the sharpest edge, cutting perpendicular to the

tangent of motion. The model presented here does not account

for motion blurring or the possible effect of lunar mountains. The

large disagreement of this result with the lab results, and the

obviously larger variation among the light curves, indicate that a

more sophisticated model is necessary to analyze this data.