Spitzer Documentation & Tools

Purpose: For IRAC observations that needed to measure the flux density or variations in the flux density of a point source to a certain precision, it was important to include the Poisson noise of the source in the estimation of the signal-to-noise ratio. The online sensitivity estimator SENS-PET that estimated the detection signal-to-noise ratio only included the read noise of the instrument and the Poisson noise of the background in the calculation of the uncertainty. The snirac tool (and a separate snirac_warm tool for the warm mission) includes the source flux density as well in the uncertainty estimate. A separate memo discusses in detail how to estimate the uncertainty in a measurement of the source flux density for the benefit of observers who are interested in variations in source brightness (as in observations of extrasolar planet transits, etc).

Author: Don Hoard, Sean Carey
Date Contributed: March 2007

This software is not considered part of the pipeline and no installation support from IRSA should be expected. We are however very interested in your feedback in order to improve or replace the algorithm and are glad to work with you in test cases and analysis. Questions and comments should be directed to the Helpdesk.

Information and Download

Memo on IRAC signal-to-noise ratio calculation - Updated 14 April 2010

Download snirac.pro (PRO, 23 KB)- March 2007 - For cryogenic observations.

Download snirac_warm.pro (PRO, 30 KB) - 17 July 2013 - For post-cryogenic observations.