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From: rs1@mssl.ucl.ac.uk
Subject: noise in PN power spectra
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Date: Wed, 30 May 2001 09:26:51 GMT
From: rs1@mssl.ucl.ac.uk
To: xmmhelp@xvsoc01.vilspa.esa.es
Subject: noise in PN power spectra
Full_Name: Roberto Soria
Submission from: (NULL) (128.40.72.254)


Greetings again.

I am working on EPIC PN Timing mode of a bright source.
I extracted a power spectrum with standard packages, 
but the result doesn't look good: the Fourier spectrum is dominated 
by spurious white noise > 10 Hz and strong spikes at ~ 24 and 48 Hz. 

[I am sending a couple of examples as Postscript attachments 
directly to xmmhelp@xvsoc01.vilspa.esa.es in a separate email, 
please have a look at them].

Having ascertained the noise is not from the source, it appears 
that it is caused by the CCD readout. I guess I could filter it out 
by using a dark or flat field exposure in Timing mode, but I don't know 
where to find them and how to do it properly. Can you comment and 
offer suggestions please?

Thanks,
Roberto Soria
MSSL

Followup 1

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Date: Wed, 30 May 2001 10:31:09 +0100
From: Roberto Soria <rs1@mssl.ucl.ac.uk>
To: xmmhelp@xvsoc01.vilspa.esa.es
Subject: Re: noise in PN power spectra (PR#2016)
This is a multi-part message in MIME format.
--------------AC0C17FB68F04176DF126034
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This is an example of power spectrum (EPIC PN, Timing Mode, rev 176)
dominated by spurious noise (readout noise?).

Roberto


--------------AC0C17FB68F04176DF126034
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Message of length 42370 truncated


Followup 2

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Date: Thu, 31 May 2001 09:40:54 +0100
From: Roberto Soria <rs1@mssl.ucl.ac.uk>
To: Maria Santos-Lleo <xmmhelp@xvsoc01.vilspa.esa.es>
Subject: Re: noise in PN power spectra (PR#2016)
> I have sent your question to the EPIC calibration scientist.
> He tells me that you already contacted him directly and he
> asked you to contact the MPI people.

Dear Maria,

I did contact Dave Lumb, and he sent me the following reply, also cc
ugb@xray.mpe.mpg.de, kendziorra@astro.uni-tuebingen.de
It wasn't clear from his email who I should have contacted
in MPE, so I referred my problem to you at the help desk
for directions.

*************************************
DAVE LUMB'S EMAIL:
I assume your data on LMCX-3 also refers to the PN? You should be aware
that the is a genarally more noisy operation in TIMING mode and if some
component of that is instrumental it might show up in yur power spectra.

Can you let us know which observation this was from, as there have been
quite a number of tests on different instrument settings.

Because of the cyclical nature of the readout, one could expect
different timescales to appear. The most likely is cycle of one CCD
readout of the 199 rows, but that is <6msec or a freq ~170 Hz. There is
a logical sequence of 20 such cycles, which would translate to 8.5 Hz,
so neither fit the bill. Perhaps there could be some interference with
Housekeeping or other spacecraft clocks (we know something like that
happens on MOS)
I have copied this reply to the PN experts to see if they can identify
these frequencies with something intrinsic to the PN camera design
*************************************

I haven't heard anything more after this message,
so I was hoping someone could actually offer a practical
suggestion on how to fix it, or what parameters to choose
in xmmselect to minimise the problem, or something.

Many thanks for your effort & best regards,

Roberto




Followup 3

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Date: Thu, 31 May 2001 14:54:54 +0100
From: Roberto Soria <rs1@mssl.ucl.ac.uk>
To: Maria Santos-Lleo <xmmhelp@xvsoc01.vilspa.esa.es>
Subject: Re: noise in PN power spectra (PR#2016)
> Though I understand from PN experts at MPE that you have got the answer
> directly from them, I copy it here for completeness.

Thanks, I contacted Markus directly
yesterday, I didn't know you would also
end up asking him.

Hopefully Markus' paper will offer hints
for a solution. If not I'll ask him again
directly, without overloading the help desk again!

Regards,

Roberto





Reply 1

Resend
From: Maria Santos-Lleo <xmmhelp@xmm.vilspa.esa.es>
To: rs1@mssl.ucl.ac.uk
Subject: Re: noise in PN power spectra (PR#2016)
Date: Thu May 31 08:18:01 2001
Dear Roberto, 

I have sent your question to the EPIC calibration scientist. 
He tells me that you already contacted him directly and he 
asked you to contact the MPI people. 

In case you did not contact them , please let me know and 
I will do it for you. Otherwise, could you please send us 
the answer so it becames clear in the helpdesk as well ?

With many thanks and best regards

Maria


Reply 2

Resend
From: Maria Santos-Lleo <xmmhelp@xmm.vilspa.esa.es>
To: rs1@mssl.ucl.ac.uk
Subject: Re: noise in PN power spectra (PR#2016)
Date: Thu May 31 09:53:04 2001
Dear Roberto

I have asked the PN experts whether they can provide some clues
on your problem.

I will let you know

Best regards

Maria
Maria Santos-Lleo, 
XMM-Newton SOC 
User Support Group


Reply 3

Resend
From: Maria Santos-Lleo <xmmhelp@xmm.vilspa.esa.es>
To: rs1@mssl.ucl.ac.uk
Subject: Re: noise in PN power spectra (PR#2016)
Date: Thu May 31 13:40:52 2001
Dear Roberto, 

Though I understand from PN experts at MPE that you have got the answer 
directly from them, I copy it here for completeness. 

I hope this solves your problems

With best regards

Maria

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

Hi Roberto,

(...)

I've attached a technical paper to this mail describing the readout of the
CCD. The more interesting part what your question concerns is the simulated
readout of an observation in timing mode (Fig. 3a). For the simulation we
took into account the readout window function of the CCD plus additional
Poissonian noise.

The first peak you can see in the PSD (full range plot) corresponds to the
readout cycle of the CCD (5.9ms). As you can see the noise is increasing
above 10 Hz which is agreement with your data. You can't see any of the
peaks you've in your PSD in both plots.

I suppose that the two peaks you are seeing, are caused due to an aliasing
effect. The readout of the CCD is a fix window function. Whenever you
choose a binning different from the readout time of the CCD, you'll get
aliasing effects which are caused due to the superposition of the readout
window and the binning window you are using. To prevent this effect you
should use multiples of the readout time as bin size.

Anyhow, I will check for the effect you saw with some data I have in timing
mode as soon as I've extracted the data. I hope this will help you.

Markus Kuster


Reply 4

Resend
From: Maria Santos-Lleo <xmmhelp@xmm.vilspa.esa.es>
To: rs1@mssl.ucl.ac.uk
Subject: Re: noise in PN power spectra (PR#2016)
Date: Thu May 31 15:23:55 2001
Dear Roberto,

Thanks for your answer. I hope you will finally fully understand your data.

I wish you exiting XMM-Newton science !. 

Best regards

Maria

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