[Isocops] [Ibexhigts] another background subtraction file

Nathan Schwadron nschwadron at me.com
Tue Dec 7 20:40:34 EST 2010


OK, thanks Paul 

This will be the basis of a new cull. 

Nathan

On Dec 7, 2010, at 7:36 PM, Paul Janzen wrote:

> Not really sure who all's on this list, but here goes...
> 
> Two files are necessary to handle good/loose culls for IBEX-Hi:  the file
> listing good times (typically HiCullGoodTimes) and the file listing
> backgrounds (frequently HiCullBGCRAN).  This email is about the second
> file:  numerous variants are in the SVN repository, and I've just gone and
> added another, as promised in September.
> 
> There are two backgrounds which we subtract at present: the cosmic ray
> background, and "loose" cull offsets.  The cosmic ray background can be
> treated two ways:  either as a constant 57 mHz, which is what we've been
> doing for the most part, or as a background that changes per orbit, either
> scaled by neutron monitors or calculated by the ratio of qualified triples
> to unqualified triples.  The latter should be more accurate.  The former is
> less work and more conservative.
> 
> If the CR bg is calculated by the ratio of triples on IBEX-Hi, then both
> the loose cull offset and the CR background can be calculated directly from
> IBEX data and the good times file, and do not need to appear as magic
> numbers (with the exception of orbits 55 and 56, and a few early orbits
> where the spin rate was crazy).  For the time being, though, magic numbers
> in files fit into the processing scheme, so that's what I'm using.  The
> ISOC will eventually generate these numbers itself.
> 
> The list of background files in idsup/culldata so far is:
> HiCullBGCR : includes only cosmic ray bg at a constant 57 mHz; for use
>     with good times but not useful with loose culls.
> HiCullBGCRAN : includes 57 mHz cosmic rays and Additional Noise -- i.e.,
>     the loose culls.  This is the one I have been updating as new loose
>     culls come in.
> 
> HiCullBGCRvar : an old attempt to incorporate a variable CR background
>     based on unqualified triples.  It goes to orbit 76 and does not
>     supply uncertainties.  It also does not handle loose culls.
> 
> HiCullBGCRAN-2009-11-30
> HiCullBGCRAN-2010-02-15
> HiCullBGCRAN55
> HiCullBGCRAN.pj :
>     old versions of HiCullBGCRAN that I don't think anyone is using.
> 
> The one I've added is:
> 
> HiCullBGCRANvar : includes a variable CR background (based on unqualified
>    triples) and the loose cull offsets, as calculated by a program from
>    the IBEX-Hi data.  Also includes sigma, much of which is systematic as
>    opposed to statistical.  I will keep this one up to date too.
> 
> As per what I presented at the September meeting, I believe (barring
> errors) that HiCullBGCRANvar is what should be used for the most accurate
> heliospheric data.  It's basically HiCullBGCRAN but handling the CR
> background "better"; it also does a slightly better job on early loose
> culls because it no longer assumes (as the original pass through orbits
> 31-34 did) that the additional isotropic noise is of constant brightness in
> time.  If you use HiCullBGCRANvar, though, bear in mind that it will change
> all your numbers back through orbit 14 or so, somewhat.  And in the
> interests of full disclosure, the second background test is not
> reassuringly consistent with this variable background, (although a few other
> things are).
> 
> If you want to see what happens, set
>  hi_bg_file
> in your scripts to
>  /usr/local/ibex/ops/config/idsup/culldata/HiCullBGCRANvar
> and let'er rip.  Probably hi_bg_file is set to HiCullBGCRAN now.
> 
> If not, this additional file need not change your life.
> 
> 
> For reference, I note that there are a bunch of files
>  ops/config/idsup/HiCull*
> which are obsolete but kicking around, too.  Their format is somewhat
> different from the present bg file...
> 
> 
> Paul Janzen.
> 
> Please restrict discussions on this email list to non-ITAR sensitive topics.
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