I'm trying to figure out the sensitivity of the Fermi LAT, in units of spectral flux---e.g. Jansky, or a limiting magnitude which could easily be converted. I've only found sensitivity in traditional high-energy terms, e.g:(adsbygoogle = window.adsbygoogle || []).push({});

[tex]4\times10^{-6} \textrm{ photons/s/cm}^2[/tex]

for photons above 100 MeV, with a photon spectral index of -2.1

from http://arxiv.org/abs/1003.1436" [Broken].

The published spectral range of the LAT is 20 MeV to 300 GeV, thus for a spectral index of -2.1, I find that the average photon energy (above 100 MeV) should be about 606 MeV.

This gives a sensitivity of about [tex]3.9\times10^{-9} \textrm{ ergs/s/cm}^2[/tex] That seems fair.

Now, to get spectral flux, one needs to divide by the bandpass to yield units of ergs/s/cm^2/Hz, and then 1 Jy = 10^-23 erg/s/cm^2/Hz (wikipedia).

Dividing by a bandpass of 300 GeV (~7e25 Hz) gives a sensitivity of ~[tex]5\times10^{-12} \textrm{ Jy}[/tex]!!! That can't be right! This would correspond to a limiting magnitude of 37!

What am I doing wrong?

Thanks!

Z

EDIT: This value is for an integration of 100s --- not very long.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Converting between photons/s/cm^2 to spectral flux (e.g. Jy) - Fermi LAT Sensitivity?

Can you offer guidance or do you also need help?

**Physics Forums | Science Articles, Homework Help, Discussion**