Up to top level
AO15   AO16   AO17   AO18   AO19   Backgrounds   Calibration   Conference   Data   Docs   EPICMOS   EPICpn   Feedback   Gallery   Misc   OM   Pending   PhD_Theses   Publications   RGS   RadMonitor   SAS_Hardware   SAS_WS   SASv16.0   SASv16.0_Installation   SASv16.1   SASv16.1_Installation   SASv17.0   SASv17.0_Installation   SASv18.0   SASv18.0_Installation   SciSim   Simulators_other   Suggestions   Trash   Visibility   XMM-bouncing   XMM-news   XRPS   XSA   esas   incoming  

Logged in as guest

Viewing EPICpn/9320
Full headers

From: Phil Evans <pae@astro.keele.ac.uk>
Subject: Background scalings
Compose reply
Download message
Move To:
2 replies: 1 2
0 followups:

Private message: yes  no

Notes:

Notification:


Date: Wed, 15 Oct 2003 14:36:23 +0100 (BST)
From: Phil Evans <pae@astro.keele.ac.uk>
To: xmmhelp@xmm.vilspa.esa.es
Subject: Background scalings
I am trying to examine phase-resolved EPIC spectroscopy, where the source 
spectra are extracted using a (PHASE in [x:y]) type selection expression, 
a PHASE column having been created in the eventlist using PHASECALC.
I am not slecting the background spectrum based on phase, so as to 
maintain a decent S/N ratio for the background.
However, while the EXPOSURE key-value for the background file appears to 
be more-or-less the exposure time, the phase-resolved source regions have 
exactly the same value as this, and as each other, despite covering 
different phase ranges.
As far as I can tell therefore, XSPEC will assume that the source and 
background spectra have the same time exposures, and will thus 
oversubtract the background. If I manually calculate the exposure time for 
each source as (totaltime * phasecoverage), and set the EXPOSURE value to 
these, will this result in an accurately subtracted background?

Phil Evans

-- 
--------------------------

Phil Evans,
Astrophysics Research Student.
Keele University Astrophysics Group

Tel: (01782) 583530
pae@astro.keele.ac.uk
http://www.astro.keele.ac.uk/~pae


Reply 1

Resend
From: Michel G. Breitfellner <xmmhelp@xmm.vilspa.esa.es>
To: pae@astro.keele.ac.uk
Subject: Re: Background scalings (PR#9320)
Date: Fri Oct 17 14:32:24 2003
Dear Dr. Evans,

Our EPIC calibration specialist is away this week. He will look
into your question on Monday.

With best regards,
Michel G. Breitfellner
XMM-Newton User Support Group


Reply 2

Resend
From: Michel G. Breitfellner <xmmhelp@xmm.vilspa.esa.es>
To: pae@astro.keele.ac.uk
Subject: Re: Background scalings (PR#9320)
Date: Thu Oct 23 14:12:46 2003
Dear Dr. Evans,

Please, find enclosed the answer from our calibration specialist:

that's how i do it

i.e.   your obs has 10.000 sec,

you extract 20 phases,, then you have to scale the exposure of the BG by 1/20
---> EXPOSURE BG = 10.000/20=500

be aware of the dead times in Burst for example,, you have to use the right
times in the header

With best regards,
Michel G. Breitfellner
XMM-Newton User Support Group

Up to top level
AO15   AO16   AO17   AO18   AO19   Backgrounds   Calibration   Conference   Data   Docs   EPICMOS   EPICpn   Feedback   Gallery   Misc   OM   Pending   PhD_Theses   Publications   RGS   RadMonitor   SAS_Hardware   SAS_WS   SASv16.0   SASv16.0_Installation   SASv16.1   SASv16.1_Installation   SASv17.0   SASv17.0_Installation   SASv18.0   SASv18.0_Installation   SciSim   Simulators_other   Suggestions   Trash   Visibility   XMM-bouncing   XMM-news   XRPS   XSA   esas   incoming  

Logged in as guest


Please make your (short) question the subject of your request!


Web interface using JitterBug ... back to the XMM home page