Image Differencing Example: fuzzy IRAC-4 galaxy

IRAC-4: galaxy located at RA,DEC = (90.054809 -66.346513) deg

DATE_OBS = 2005-07-25; T02:17:37.078 DATE_OBS = 2007-10-20; T21:58:47.899 Difference: (2005-07-25) - (2007-10-20); here is a zoomed version

Comments: The smalled barred galaxy is well resolved by IRAC (radius ~ 10 arcsec), but would not have been resolved by WISE W3 or W4.

There is a small glitch (cosmic ray) near the eastern edge of the galaxy in the second epoch. The difference shows (therefore) a 'negative' dip for this transient. Flip-side, the difference image shows a positive detection either related to a CR in the 1st epoch or pixel-phase difference (i.e., non-perfect registration & subtraction). This "detection" is an example of what may be falsely identified as an extragalactic transient.

Last update - [15 April 2009]
T.H. Jarrett (IPAC/SSC)