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Date: Tue, 31 Jul 2012 21:52:31 GMT From: cabotmail@gmail.com To: xmmhelp@sciops.esa.int Cc: cabotmail@gmail.com Subject: Decreasing Centroids
Full_Name: Sam Cabot Submission from: (NULL) (71.9.146.218) Dear Sir/Madam, I am currently analyzing absorption lines at ~21.6 and ~22.04 Angstroms in most RGS1 observations of Cygnus X-2. I noticed that the centroid wavelengths of my lines tend to decrease over the large amounts of time between observations, even though interstellar absorption should remain constant. Could you please tell me if there is any record of this issue perhaps in relation to the gain of the instrument? I can supply a plot if you would like. Thank you. -Sam.
From: Enrico Piconcelli <xmmhelp@sciops.esa.int> To: cabotmail@gmail.com Subject: Re: Decreasing Centroids (PR#50662) Date: Wed Aug 1 08:56:46 2012
Dear Sam, The document on the status of RGS calibration (available at http://xmm2.esac.esa.int/docs/documents/CAL-TN-0030.pdf) reports a wavelength accuracy of 7 mAngstrom for RGS1/2 (Table 1). Furthermore, it has been verified that the wavelength scale is stable over a long timescale. Therefore, if the shift you found is larger than this value, it is not an instrumental effect but a physical property of the material responsible for the absorption. Furthermore, please consult the SAS thread "How to reduce RGS data and extract spectra of point-like sources" to verify that all data reduction has been correctly performed (e.g., http://xmm.esac.esa.int/sas/current/documentation/threads/rgs_thread.shtml). I hope that helps. Let me know if you need further information regarding this issue. Best wishes, -Enrico Piconcelli XMM-Newton User Support Group > Full_Name: Sam Cabot > Submission from: (NULL) (71.9.146.218) > > > Dear Sir/Madam, > > I am currently analyzing absorption lines at ~21.6 and ~22.04 Angstroms in most > RGS1 observations of Cygnus X-2. I noticed that the centroid wavelengths of my > lines tend to decrease over the large amounts of time between observations, even > though interstellar absorption should remain constant. Could you please tell me > if there is any record of this issue perhaps in relation to the gain of the > instrument? I can supply a plot if you would like. Thank you. > -Sam. > >
Date: Wed, 1 Aug 2012 10:39:38 -0400 Subject: Re: Decreasing Centroids (PR#50662) From: S Cabot <cabotmail@gmail.com> To: Enrico Piconcelli <xmmhelp@sciops.esa.int>
Enrico, The shift is indeed over 7 mAngstrom. I will do some investigating and check my reduction procedure then. Thank you for your help. Best regards, -Sam. On Wed, Aug 1, 2012 at 4:56 AM, Enrico Piconcelli <xmmhelp@sciops.esa.int> wrote: > > Dear Sam, > > The document on the status of RGS calibration (available at > http://xmm2.esac.esa.int/docs/documents/CAL-TN-0030.pdf) reports a wavelength > accuracy of 7 mAngstrom for RGS1/2 (Table 1). Furthermore, it has been verified > that the wavelength scale is stable over a long timescale. > Therefore, if the shift you found is larger than this value, it is not an > instrumental effect but a physical property of the material responsible for the > absorption. > > Furthermore, please consult the SAS thread "How to reduce RGS data and extract > spectra of point-like sources" to verify that all data reduction has been > correctly performed (e.g., > http://xmm.esac.esa.int/sas/current/documentation/threads/rgs_thread.shtml). > > I hope that helps. Let me know if you need further information regarding this > issue. > > Best wishes, > -Enrico Piconcelli > XMM-Newton User Support Group >> Full_Name: Sam Cabot >> Submission from: (NULL) (71.9.146.218) >> >> >> Dear Sir/Madam, >> >> I am currently analyzing absorption lines at ~21.6 and ~22.04 Angstroms in > most >> RGS1 observations of Cygnus X-2. I noticed that the centroid wavelengths of > my >> lines tend to decrease over the large amounts of time between observations, > even >> though interstellar absorption should remain constant. Could you please tell > me >> if there is any record of this issue perhaps in relation to the gain of the >> instrument? I can supply a plot if you would like. Thank you. >> -Sam. >> >> > > This message and any attachments are intended for the use of the addressee or addressees only. The unauthorised disclosure, use, dissemination or copying (either in whole or in part) of its content is not permitted. If you received this message in error, please notify the sender and delete it from your system. Emails can be altered and their integrity cannot be guaranteed by the sender. > > Please consider the environment before printing this email. >