The XIS team has released a set of blank sky background files suitable for the preparation of AO-2 proposals.
The spectral files have been created from the north ecliptic pole (NEP) observations on September 2, 2005 and February 10, 2006. These two sets of observations have the same aim point, RA = 272.8, Dec = 66.0. Because the observation in 2005 was affected by a solar flare, first 51 ks of that observation was not used.
The spectra were extracted from a circular region of a radius of 6 mm centered at the XIS/HXD nominal positions. Because the unit of the BACKSCAL keyword changes with the coordinate system, spectra were created for both the DET and SKY coordinates. Two spectra, one for the BI sensor (XIS1) and the other for the sum of FI sensors (XIS0,2,3), have been extracted for each coordinate system and for each extraction region.
Net exposures are 162.5 ks for XIS1 and 151.5 ks for XIS0,2,3.
Note that the XIS team has also released night earth data, which contains the particle (but not cosmic X-ray) background.
This release consists of the following 8 files.
The background spectra for XIS0+2+3 have been changed (2006 Nov. 17). Please use the latest one (NEP_***_fi_rev.pi).
The earlier versions of the background spectra for the 3 FI instruments contained the summed data as well as summed exposure times. Therefore, the count rates in these files were the average of the 3 FI instruments. This is inconsistent with the ARF files which contain the sum of effective areas of the 3 FI XISs.
The new versions are different in that the exposure times have been divided by 3 (the number of instruments summed). Therefore, they now contain the summed count rates, consistent with the ARFs.
These (either the sky or detector coordinate versions) are suitable for simulation purposes. Use with a matching set of RMF and ARF files.