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From: evg@astro.columbia.edu
Subject: Definition of time bin for each intrument, mode.
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Date: Fri, 16 Aug 2002 09:30:32 GMT
From: evg@astro.columbia.edu
To: xmmhelp@xmm.vilspa.esa.es
CC: evg@astro.columbia.edu
Subject: Definition of time bin for each intrument, mode.
Full_Name: Eric Gotthelf
Submission from: (NULL) (128.59.168.136)


Dear XMMhelp,

I would like to determine the absolute phase of a pulsar. I need to 
know the definition of the time assignment of a time bin. Does the
arrival time of a photon refer to the start of the CCD integration, middle, 
or perhaps the end? Does this depend on instrument, mode (spacifically
the small window, 6ms EPIC mode).

I would appreciate a defintive answer to this question, and any other relative
information you think necessary for determining the absolute pulse arrival times

(e.g., what is the timing accuracy of the time stamps on XMM).

Thank you ,
Eric

------------------------------/>/</>/</--------------------------------
Eric Gotthelf
Columbia Astrophysics Laboratory      WORK: 212-854-9047
Pupin Hall, Columbia University        FAX: 212-854-8121
550 West 120th St,                   EMAIL: eric@astro.columbia.edu
New York, NY 10027, USA                WEB: www.astro.columbia.edu/~eric
------------------------------/X//X//X/--------------------------------



Reply 1

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From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: evg@astro.columbia.edu
Subject: Re: Definition of time bin for each intrument, mode. (PR#5654)
Date: Fri Aug 16 10:58:19 2002
Dear Eric,

I have forwarded your questions to the EPIC calibration scientist and will
let you have his answer as soon as possible.

Cheers,
Matthias.

Matthias Ehle 
XMM-Newton SOC 
User Support Group


Reply 2

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From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: evg@astro.columbia.edu
Subject: Re: Definition of time bin for each intrument, mode. (PR#5654)
Date: Wed Sep 11 11:24:11 2002
Dear Eric,

(sorry for the late reply which was partly due to the summer holiday season...)

you wrote:
> I would like to determine the absolute phase of a pulsar. I need to 
> know the definition of the time assignment of a time bin. Does the
> arrival time of a photon refer to the start of the CCD integration, middle,

> or perhaps the end? Does this depend on instrument, mode (spacifically
> the small window, 6ms EPIC mode).

According to the experts, the EPIC time stamps created by the SAS based on
the time correlation file (TCS) refer to the middle of each frame 
time (=integration period).

In case of the pn the following mode dependence exist:

In imaging modes the center of the integration period Tc is used as the 
photon arrival time. Tc can be calculated from the frame time (header keyword
FRMTIME in the event lists = time word Tw), minus a correction term a, which is

a function of readout mode and CCD number.                     

Tc = Tw - a(mode, CCD No)                       

In the following table we list the values for a, both in number of 40 ns cycles

and in ms. The values have been compiled from the Technical Note "Correction of

the Photon Arrival Times for the Readout Modes of the EPIC-pn Camera" by Markus
Kuster and B.rbel Kretschmar, version 1.1, Sept. 09. 2002                  

Mode            CCD No. a (in 40 ns cycles)     a (in ms)
                        
FF              0       1280846.5                51.234
FF              1       1128086.5                45.123
FF              2        975331.5                39.013
ext.FF (wait=3) 0       2853710.5               114.148
ext.FF (wait=3) 1       2700950.5               108.038
ext.FF (wait=3) 2       2548195.5               101.928
ext.FF (wait=5) 0       3902286.5               156.091
ext.FF (wait=5) 1       3749526.5               149.981
ext.FF (wait=5) 2       3596771.5               143.871
LW              0        825748                  33.030
LW              1        726529                  29.061
LW              2        627315                  25.093
SW              0         92024                   3.681

In the early mission phase the ext.FF mode was used with 5 wait cycles while
since then 3 cycles are programmed (visible in the housekeeping parameter
F1294). 

In case of the MOS the photon arrival times are randomized over the frame time.
The mode dependent frame time value is visible in the header keyword FRMTIME
in the event lists as well.

In case of the pn no randomization is done yet but randomization will become an
option in a future SAS version (I expect that epframes will get an additional
parameter here).

I hope this info is somewhat useful for your planned scientific analysis.

Cheers,
Matthias.

Matthias Ehle 
XMM-Newton SOC 
User Support Group

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