Development of Image Analysis Software of MAXI
Satoshi Eguchi, Yoshihiro Ueda, Kazuo Hiroi (Kyoto University), Mutsumi Sugizaki (Riken),
Motoko Suzuki, Hiroshi Tomida (JAXA/TKSC), and the MAXI team- Abstract Monitor of All-sky X-ray Image (MAXI) is an X-ray all-sky monitor, attached to the Japanese experiment module Kibo on theInternational Space Station. The main scientific goals of the MAXI mission include the discovery of X-ray novae followed by prompt
alerts to the community (Negoro et al., in this conference), and production of X-ray all-sky maps and new source catalogs withunprecedented sensitivities. To extract the best capabilities of the MAXI mission, we are working on the development of detailed
image analysis tools. We utilize maximum likelihood fitting to a projected sky image, where we take account of the complicateddetector responses, such as the background and point spread functions (PSFs). The modeling of PSFs, which strongly depend on
the orbit and attitude of MAXI, is a key element in the image analysis. In this poster, we present the status of our softwaredevelopment.

1. Introduction
Monitor of All-sky X-ray Image(MAXI) is a Japanese X-ray
all-sky monitor, which wascarried to the International
Space Station (ISS) with thespace shuttle Endeavour on 2009
July 16. It is attached to thepayloadoftheJapanese
MAXI
experiment module Kibo. The
main scientific goals of the mission are the detection of X-ray novae,
production of new source catalogs, and monitoring of time variabilitiesof X-ray sources.
Accurate determination of the position and flux by considering thecomplex detector responses is a key process in all scientific analysisof the MAXI data. In this poster, we present our analysis method,which utilizes maximum-likelihood image fitting to a projected skyimage.

Figure 1

2. The MAXI Simulator
The MAXI simulator is a software that generates fully simulated dataof the MAXI instruments by Monte Carlo method. The original role ofthe simulator is creating the test data for developing and debugging of
the alert system and data analysis software.
To achieve the complex functions required for the simulator, we
code the progam in C++ language, utilizing its concept of object
oriented programming (OOP). Figure 2 illustrates the schematic
structure of the MAXI simulator. MAXI carries two-type cameras, 12Gas Slit Cameras (GSCs) and 2 Solid State Cameras (SSCs). We
create an abstract camera class, and then derive the two concrete
camera classes corresponding to the GSC and SSC, to treat their
responses in the same manner. We apply this class relation to thephoton generetors and event containers. This abstraction enables us
to divide the MAXI simulator into a set of reusable classes and therest. Hence, it can be used as a framework of general satellite
simulators.

3. Image Analysis Based on Maximum Likelihood Fit
To extract the best sensitivities
from the observation data, we havedeveloped an analysis method byemploying image fitting with themaximum likelihood algorithm. Firstly,
we project the positions in RA andDEC of photon events in the vicinityof a target in the "sky coordinates", asin the case of an image analysis ofpointing satellite's data. To derive theflux, position and their errors, we
perform 2-dimensional fitting to thissimulated
imagebyamodel
consisting of the point spreadfunction (PSF) and background (theFigure 4
non X-ray background and the cosmic
Background X-ray background).
One complexity in the analysis of
MAXI data is that the PSF andbackground are position dependent,
being determined by the orbit andattitude condition. To take this into
account, we also utilize the MAXI
Total
simulator to construct the PSF andbackground models with a sufficiently
larger number of photons to suppress

Figure 3

the statistical fluctuation.
In the fitting, the normalization of the PSF (i.e., flux) andbackground level are set to free parameters, as well as its position.
Here we assume that the shape of the PSF does not significantly
differ in the region of interest, and ignore its position dependence
for simplicity.
Figure 3 displays a smoothed image in the vicinity of the target,
located in the center, for the 1-week simulation. Figure 4 displays its
projection onto the X-axis in a central region (with error bars),
superposed with the best-fit model.

4. Summary and Future Work
Figure 2

We present the image analysis technique for the detection of faintsources using the data generated by the MAXI simulator. We havestarted to apply this method to the real observation data. Figure 5 isa false color all-sky image in Galactic coordinate in the 2-10 keVband. The red color represents the real observation data, while thegreen color the simulation data (one week). Basically, the all sky
map pattern is well reproduced, except for systematic difference insource positions and shape of the point spread functions, which are
due to insufficient calibration at this moment.
A current problem of this method utilizing the MAXI simulator is along CPU time required to compute PSF models. We plan to develop
another softwate that can compute PSFs more quickly with
sufficient accuracy. This task shall be utilized in producing MAXI
source catalogs.

Figure 5