Date: Tue, 17 Sep 2002 12:32:04 -0400 (EDT)
From: Stephen Drake <email@example.com>
cc: Steve Snowden <firstname.lastname@example.org>
Subject: EPIC Thick filter
I had two observations of soft (about 0.2 KeV temperature for mekal
coronal plasma models), fairly faint (3 and 10 x 10-12 erg/s/cm2 in the
0.3- 3.0 keV energy range) targets with XMM, the second of which I have
just finished analyzing. The two targets (Beta Gem and Beta Hyi) are
both visually bright stars, and thus the EPIC Thick Filter was used in
both observations. Analyzing the data, I found that, in
both cases, the observed XMM EPIC PN & MOS fluxes were
3 - 10 times lower than previous ROSAT and Einstein fluxes (these sources
are too faint to get reliable RGS spectra). Since coronal
stars can vary, this may be a case of real intrinsic variability, although
it is rather unlikely in my opinion. I wanted to be able to rule out
the XMM calibration as the cause for this effect,and thus my question
is simply how accurately determined is the thick filter response?
Is there any possibility that its effective area is overestimated?
I noticed a comment in Marcus Kirsch's EPIC Calibration Status document
(XMM-SOC-CAL-TN-0018 on page 2) which states:
`Filter transmission of the MOS thick filter is currently not correctly
modelled and is under inverstigation'. This doesn't mention the PN thick
filter (as I mentioned above, I find consistent (low) fluxes for both
MOS1, MOS2,and the PN), I might note, implying that there is no known
problem with this combination.
I would appreciate any advice you can give me on this point
PS The Obids of my 2 observations are 0006010401 and 0006010301
Dr. Stephen A. Drake,
Universities Space Research Association (USRA) Scientist,
HEASARC/Code 662, Goddard Space Flight Ctr, Greenbelt, MD 20771, USA.
Tel: 301 286 6962 or Fax: 301 286 1684.