Bug #1549
Spectral parameters for diffuse map are biased
| Status: | Closed | Start date: | 10/13/2015 | |
|---|---|---|---|---|
| Priority: | Normal | Due date: | ||
| Assigned To: |  Knödlseder Jürgen | % Done: | 100% | |
| Category: | - | |||
| Target version: | 1.0.0 | |||
| Duration: |
Description
The Prefactor and Index parameters for a diffuse map are biased. This can be seen in the following pull histograms:
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The model simulated here was the Cen A map with a Crab spectrum:
<?xml version="1.0" standalone="no"?>
<source_library title="source library">
<source name="Crab" type="DiffuseSource">
<spectrum type="PowerLaw">
<parameter name="Prefactor" scale="1e-16" value="5.7" min="1e-07" max="1000.0" free="1"/>
<parameter name="Index" scale="-1" value="2.48" min="0.0" max="+5.0" free="1"/>
<parameter name="Scale" scale="1e6" value="0.3" min="0.01" max="1000.0" free="0"/>
</spectrum>
<spatialModel type="SpatialMap" file="cena_lobes_parkes.fits">
<parameter scale="1" name="Prefactor" min="0.001" max="1000.0" value="1" free="0"/>
</spatialModel>
</source>
<source name="Background" type="CTAIrfBackground" instrument="CTA">
<spectrum type="PowerLaw">
<parameter name="Prefactor" scale="1.0" value="1.0" min="1e-3" max="1e3" free="1"/>
<parameter name="Index" scale="1.0" value="0.0" min="-5.0" max="+5.0" free="1"/>
<parameter name="Scale" scale="1e6" value="1.0" min="0.01" max="1000.0" free="0"/>
</spectrum>
</source>
</source_library>
This bug is possible related to #1248.
Recurrence
No recurrence.
Related issues
History
#1
Updated by Knödlseder Jürgen about 9 years ago
- Status changed from New to In Progress
- Assigned To set to Knödlseder Jürgen
- Target version set to 1.0.0
#2
Updated by Knödlseder Jürgen about 9 years ago
- Description updated (diff)
#3
Updated by Knödlseder Jürgen about 9 years ago
- % Done changed from 0 to 10
The mean prefactor is 5.635348e-16 which presents a -1.1% offset with respect to the nominal value. The mean index is 2.474517 which presents a -0.2% offset with respect to the nominal value.
The Monte Carlo simulations of diffuse models rely on the GSkyMap::flux() method and specifically its precision. The flux computation has a precision of about 1%, hence the observed bias is fully compatible with that precision. It is thus plausible that the diffuse map computation is in fact correct and that the observed bias is due to the limited accuracy of the GSkyMap::flux() method.
#4
Updated by Knödlseder Jürgen about 9 years ago
- Status changed from In Progress to Closed
- % Done changed from 10 to 100
This issue can now also be closed. Improvement can only be achieved by improving the accuracy of the GSkyMap::flux() method.