Subject: Re: jemx mosaics

Hello Simon,

Sorry not having answered your mail sooner, but I am in holidays this week
(just having a look from home to the Bulge data).
I have to think about your question, but I remember we decided long ago
during a JEM-X SW meeting not to normalise the significance artificially
to 1, letting the user to take account of the FWHM of the significance
distribution, as you did I guess.

Cheers,
        Jérôme

> Hello again,
>
> Regarding my latest Infrequently Asked Question I ran a bit of a test,
> to see what happens if I simply take the set of INTEGRAL data (GRS 1915
> from rev 0295 - total 28 ScW) and then make mosaics for subsets of that
> (I did only the first 2 scws (~7ks), first 5 (18ks), first 10 (36ks) and
>  all 28 of them (100ks)).  The test for 20 ScWs is still running, but
> from the results so far I'm afraid it doesn't seem like much point in
> waiting for it to finish.
>
> So I have used fimgstat to report the statisics of the significance
> images in the 3-10 keV band and plotted the value returned for the
> standard deviation of the images against the length of the observation
> (I have only read TELAPSE from the header, not the GTI information, but
> the effect is clear).
>
> There seems to be a seriously strong linear correlation between the
> standard deviation of the distribution of all the pixel values in the
> significance image and the length of the observation - if the
> significance images were correct then the points should be scattered
> around a std of 1 regardless of observation length.
>
> My GB observations  are all about 12ksec in length so there isn't much
> range on time and they seem to have std around 1.5, which is a bit lower
>  than for the GRS observations, so I'm sure there is also an effect
> based  on what is in the field of view.  However from the GRS data there
>  clearly seems to be a problem involving the time in the calculation,
> and  thats much more serious.
>
> Sorry to drop this on you on a Friday afternoon - I'll be happy if you
> can prove me wrong !!
>
> Simon
>
>
> Carol Anne Oxborrow wrote:
>> Dear Jerome,
>>
>> could you please send me a copy of your reply to Simon? I'll try and
>> make another question and answer for the JEM-X FAQ from his and your
>> emails - that way we'll get the FAQ populated by actual (Frequently -
>> is once `frequently'?) Asked Questions.
>>
>> Thanks,
>>
>> CAO
>>
>> DANISH NATIONAL SPACE CENTER
>> Dr. Carol Anne Oxborrow
>> Email: oxborrow@space.dtu.dk	Homepage:
>> http://www.spacecenter.dk/~oxborrow Telephone (direct): +45 35 32 57
>> 33
>>
>> Main teleph.: (+45) 35 32 57 00
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>> Main E-mail:  office@spacecenter.dk
>>
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>>
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>>


-- 
Dr. Jérôme CHENEVEZ         Institut for Rumforskning og – teknologi
National Space Center       Juliane Maries Vej 30
     DTU Space              DK-2100 Copenhagen Ø
http://www.dsri.dk/~jerome  www.space.dtu.dk
Tel. +45 35 32 57 03        FAX: +45 35 36 24 75