Subject: Re: jemx mosaics

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
> Fax:          (+45) 35 36 24 75
> Main E-mail:  office@spacecenter.dk
>
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