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Suzaku News #011: Low energy efficiency of Suzaku

To: GO community
Subject: Low energy efficiency of Suzaku

December 20, 2005

The good low energy response of the back illuminated (BI) CCD, i.e. 
the high detection efficiency and the gaussian-like good energy 
spread function, is an important unique feature of Suzaku. However, 
we recently found evidence that the effective area below 1 keV of 
both back- and front-illuminated sensors is decreasing with time (see 
figures in the Suzaku web page, 
http://www.astro.isas.jaxa.jp/suzaku/). On the average at 0.6 keV the 
effective area is about 50% that just after launch. We are working 
hard to understand the cause of decrease and to find possible 
recovery methods.   The present best estimate of the e-folding time 
constant is 160 days at the OVII line
(570 eV), but it can be shorter at lower energies and is longer at 
higher energies.  However, at present we cannot predict the future 
long-term behavior of efficiency well. Because of this we will put 
the priority on the low energy observations as soon as possible 
during AO1. And we will provide the response functions (rmf files) of 
the XIS as of October 26, 2005 on the Suzaku web page soon.  Please 
note in your proposal which response function is used to estimate the 
observation times.

Please note that the energy resolution has not changed.

Best wishes,

Kazuhisa Mitsuda (ISAS/JAXA)
Hideyo Kunieda (ISAS/JAXA and Nagoya University)
Nick White (NASA/GSFC)

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