Up to top level
AO15   AO16   AO17   AO18   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   SciSim   Simulators_other   Suggestions   Trash   Visibility   XMM-bouncing   XMM-news   XRPS   XSA   esas   incoming  

Logged in as guest

Viewing Calibration/5656
Full headers

From: jules@astro.columbia.edu
Subject: EPIC pn small window event times
Compose reply
Download message
Move To:
2 replies: 1 2
0 followups:

Private message: yes  no

Notes:

Notification:


Date: Fri, 16 Aug 2002 17:30:33 GMT
From: jules@astro.columbia.edu
To: xmmhelp@xmm.vilspa.esa.es
CC: jules@astro.columbia.edu
Subject: EPIC pn small window event times
Full_Name: Jules Halpern
Submission from: (NULL) (128.59.168.142)


I understand that pn small window frames consist of 3.97 ms of exposure,
followed by 1.69 ms of shifting and reading.  However, what absolute time
is assigned to the events in each frame?  Is it the time of the beginning
of the exposure, the time of the readout, or what?  A related question is,
how accurate is the absolute calibration of the spacecraft clock?

Reply 1

Resend
From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: jules@astro.columbia.edu
Subject: Re: EPIC pn small window event times (PR#5656)
Date: Sat Aug 17 15:52:40 2002
Dear Jules Halpern,

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

Resend
From: Matthias Ehle <xmmhelp@xmm.vilspa.esa.es>
To: jules@astro.columbia.edu
Subject: Re: EPIC pn small window event times (PR#5656)
Date: Wed Sep 11 11:40:22 2002
Dear Jules Halpern

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

you wrote:
> I understand that pn small window frames consist of 3.97 ms of exposure,
> followed by 1.69 ms of shifting and reading.  However, what absolute time
> is assigned to the events in each frame?  Is it the time of the beginning
> of the exposure, the time of the readout, or what?  

In ipn maging 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).


> A related question is,
> how accurate is the absolute calibration of the spacecraft clock?

The current status of the EPIC timing calibration can be described in the
following way:

Absolute timing means: XMM-time compared to atomic clock /other satellites  

Relative timing means: relative deviation in the observed pulse period w.r.t. 
the most accurate radio period   

The release of SAS 5.3.3 comprises for the first time all necessary components 
to support timing analysis with out-standing time resolutions of down to 29 
and 7 microseconds for PN Timing and Burst modes. Tests on data from the 
Crab pulsar taken during XMM-Newton's performance verification campaign in 
early 2000 indicate that the relative deviation in the observed pulse period 
w.r.t. the most accurate radio data available (\Delta P/P) is now considerably 
better than 10^-8, with an absolute timing accuracy of < 500 microseconds.  

For the Crab pulsar the new results now conform with estimates of the 
theoretically attainable accuracy with XMM-Newton and the expected statistical 
errors. Further investigations for periods of other objects are currently 
underway. Because of another improvement in converting the onboard time to the 
event time, the user should make sure that the data are fully reprocessed with 
the new SAS 5.3.3 and not only with the new "barycen" task in order to achieve 
the ultimate timing accuracy. 

Please, do not hesitate to contact us again if further clarifications are
needed.

Best reagrds,
Matthias.

Matthias Ehle 
XMM-Newton SOC 
User Support Group

Up to top level
AO15   AO16   AO17   AO18   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   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