The direct demodulation method

Since it is very difficult to fold the hard X-ray photons, none of the current telescopes can obtain a hard X-ray map directly, i.e., the data are far different from a direct map. An image reconstruction method is therefore needed to derive a hard X-ray map from the observational data. The main image reconstruction method for the HXMT mission is the Direct Demodulation method (DD method) developed by T.P. Li and M. WU in early 1990s. This method solves the observation equations under non-linear control, allowing sensitive image reconstruction with high spatial resolution from the observational data of a simple collimated telescope.

Since early 1990s, using the DD method, we have analyzed various space X-ray data, published more than 30 papers and got a lot of important results. This proves the power of the DD method. In the following we give a few examples and main references.

Fig.1: Comparison of the X-ray intensity maps for a region of the Galaxy obtained from EXOSAT-ME scan observations with the usually used cross-correlation method (left) and the direct demodulation method (right).

Fig.2: Hard X-ray map (right) of the Galactic center region from the HEAO1-A4 all-sky survey data (left) with the direct demodulation method.

Reference:
1. Improving the spatial resolution of XMM-Newton EPIC images by direct demodulation technique, Feng, H., Chen, Y., Zhang, S.N., Lu, F.J., & Li, T.P. 2003, A&A, 402, 1151
2. Observations of the supernova remnant G54.1+0.3: X-ray spectrum and evidence for an X-ray jet, Lu, F.J., Aschenbach, B., & Song, L.M. 2001, A&A, 370, 570
3. Direct Demodulation imaging analysis of the combined two sets of SCC data of RXTE ASM, Chen, Y., Song, L.M., Li, T.P., & Cui, W. 2000, ACASn, 41, 214
4. Direct demodulation technique for rotation modulation collimator imaging, Chen, Y., Li, T.P., & Wu, M. 1998, A&AS, 128, 363
5. COMPTEL observation of the flaring quasar PKS0528+134, Zhang, S., Li, T.P., & Wu, M. 1998, A&A, 340, 62
6. X-ray map from the EXOSAT galactic plane survey and a direct demodulation technique, Lu, F.J., Li, T.P., Sun, X.J., Wu, M., & Page, C.G. 1996, A&AS, 115, 395
7. Image reconstruction in high energy astrophysics by direct demodulation method, Lu, F.J., Li, T.P., Sun, X.J., & Wu, M. 1995, in Proceedings of the international conference on computing in high energy physics' 95, Nguyen, T.D., & Shellard, R. eds, P.848
8. Reconstruction of objects by direct demodulation, Li, T.P., & Wu, M. 1994, Ap&SS, 215, 213
9. A direct restoration method for spectral and image analysis, Li. T.P., & Wu, M. 1993, Ap&SS, 206, 91
10. Modulation imaging based on a direct de-convolution technique, Li, T.P., Wu, M., Lu, Z.G., Wang, J.Z., Zhang, C.S. 1993, Ap&SS, 205, 381
11. A direct method for spectral and image restoration, Li, T.P., & WU, M. 1992, Astronomical data analysis software and systems, ASP conference series, Vol. 25, 1992, Diana M. Worrall et al. eds, P.229
12. Galactic gamma-ray sources in the 40-50 MeV range, Li, T.P., & Wu, M. 1990, ACASn, 31, 390