IRAC Instrument Handbook - IRSA - California Institute of Technology

IRAC Instrument Handbook
Figure 2.9: IRAC point source sensitivity as a function of frame time, for medium background. To convert to
MJy/sr, see equation 2.8.
where σ is the noise from equation 6.1 and
2
F b = STexσ
(2.6)
In the bright source limit, F >> Fb, then the signal-to-noise ratio becomes
/ N = ST F
(2.7)
S ex
If the exposure time is in seconds and the source flux is in µJy, then for IRAC channels 1, 2, 3, and 4,
respective ly, S/N is 0.88, 0.95, 0.65, and 0.95 times Tex F .
Instrument Description 22 Sensitivity and Saturation