ARF file for GSO analysis

Dear Suzaku users,

Through the in-orbit calibration of the HXD-GSO (S. Yamada et al. in prep.) after Kokubun et al. (2007), we have succeeded in delivering more reliable HXD-GSO response matrices, ae_hxd_gso[hx,xi]nom_20100524.rsp. The still-remaining issues on the HXD-GSO responses are an uncertainty of linearity above Gd-K edge (mainly 50-70 keV) and a cross normalization between HXD-PIN and HXD-GSO. As a temporary workaround, we have prepared arf files, ae_hxd_gsohxnom_crab_20100526.arf and ae_hxd_gsoxinom_crab_20100526.arf, for all GSO users.

The figure shows HXD-PIN and HXD-GSO spectra of Crab Nebula observed on Sep. 15 in 2005 at the HXD nominal position. The adopted model for HXD-PIN (black) and HXD-GSO with thearf (red) is wabs * brokenpowerlaw with Nh = 3.8 x 10²¹ cm^-2, photon indices of 2.09 and 2.27, a break energy of 103 keV, and a nomalization of 10.9 photos keV^-1 cm^-2 s^-2 (@ 1 keV). The ratio of specta to model is shown in the bottom panel. To clarify the effect of the arf files, we also plot the ratio in the case without the arf files in blue. The 20% difference of flux from 70 to 400 keV between the data and model without the arfs and the bump-like residual around 50-70 keV due to calibration uncertainties around the Gd-K edge is more reduced by introducing the arf files, resulting in a better agreement with the HXD-PIN spectrum. Here is an example of the usage of the arf files in XSPEC:

data     1 gso_cl_dtcor.pha
backgrnd 1 gso_bgd_dtcor.pha
response 1 ae_hxd_gso[hx,xi]nom_20100524.rsp
arf      1 ae_hxd_gso[hx,xi]nom_crab_20100526.arf

1) The arfs are totally different from those previously released (i.e., ae_hxd_gso[hx,xi]nom_crab_20070502.arf); Old arfs must be used together with theold responses, while new arfs must be used with new responses.

2) New responses and arfs are incompatible with the spectra processed in the oldcalibration (see this page for details).

3) The uncertainty of the parameters of broken-powerlaw for the Crab nebula as described here is still being studied.

4) Note that the old arfs were generated so that the spectra of the Crab nebula is represented by the single powerlaw with a photon index of 2.1. This is not the case for new arfs.