PK'S SPECTRAL CRAB FITS

Date: Thu, 24 Jun 2004 19:05:45 +0200
From: Peter Kretschmar 
Subject: More on Crab fits
To: Carol Anne Oxborrow , Juhani Huovelin , Niels Lund , Niels J?rgen Westergaard , Soren Brandt , Stefan Larsson , Sami Maisala , Carl Budtz-Joergensen , Jerome Chenevez , Silvia Mart?nez N??ez 
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   Dear all,

   the last two days, I've amused myself again with extracting
Crab spectra using the latest ISSW and response and fitting them.
The fit was done using a fixed slope of -2.10 but free normalization.
As you can see this works quite reasonably in an energy range 4-20 keV
for both data from within 4 deg off-center and data with 4-5 degrees
offset in the later Crab calibration observations. Revolution 45 is
not shown here, but looks similar. There is a slight 'downturn'
for JMX2 spectra in both later Crab calibrations.

   Turning to earlier data, before rev 45 the picture looks still
good in rev 43  with now JMX1 showing a more marked 'downturn'
below 4-5 keV. But the 'outer' spectra for rev 42, which are
just about 5 degrees off-axis look really bad - see last attachment.
So for the moment I would still recommend to staty within ~4 degrees
if you want to use JEM-X spectra.

   Should some of these plots go into the SVR, possibly in a clearer
presentation? Do you agree from this with my general judgement?

   Cheers,
   Peter

P.S.  You can find my results generally under
       /net/luxor19/scratch1/pkretsch/Cons/obs/CrabRRRR
       where RRRR is the 4-digit revolution number.

figure
figure
figure

Date: Fri, 25 Jun 2004 10:23:35 +0200
From: Jerome Chenevez 
To: Peter Kretschmar 
Subject: Re: More on Crab fits

Good morning Peter,

Thank you for these results.

>
> So for the moment I would still recommend to staty within ~4 degrees
> if you want to use JEM-X spectra.
>
>    Should some of these plots go into the SVR, possibly in a clearer
> presentation? Do you agree from this with my general judgement?

As far as I am concerned, I agree of course. But as your results seem to
point out, perhaps we could be a bit more nuanced by indicating a period
before which it is not reasonnable to use JEM-X spectra over 4 degrees, and
after which we are more confident in those spectra. It might also be a good
idea to find out what could be the reason for this change.
I am more concerned by the quality decrease above 20 keV. But perhaps this is
not an issue because people use IBIS spectra above 20 keV?

Cheers,
               Jérôme
               
Date: Fri, 25 Jun 2004 10:45:30 +0200
From: Peter Kretschmar 
Subject: Re: More on Crab fits
To: Jerome Chenevez 

> As far as I am concerned, I agree of course. But as your results 
 > seem to point out, perhaps we could be a bit more nuanced by
 > indicating a period before which it is not reasonable to use
 > JEM-X spectra over 4 degrees, and after which we are more
 > confident in those spectra. It might also be a good idea
 > to find out what could be the reason for this change.

   I'm not sure it's really a question of time, rather of angle
but maybe we should try to nail this question down better.
Btw - I fully agree with the idea of a very close dither around
the Crab next time!

> I am more concerned by the quality decrease above 20 keV. 
 > But perhaps this is not an issue because people use IBIS
 > spectra above 20 keV?
> 
   Well, it would be better if we were more confident about
our spectra in this range, especially if one searches for
spectral features, like I do.

   Cheers,
   Peter
               


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