Image Differencing Example: fuzzy IRAC-4 galaxy |
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.