"Hard" Spectrum

[nicksauce]

What exactly is meant when a spectrum is said to be "hard" or "soft", or "harder"/"softer" compared to a different spectrum?


Cheers,
Nick

[George Jones]

Hard gamma rays, for example, have higher energy, higher frequency, and shorter wavelength than soft gamma rays.

[nicksauce]

Thanks George Jones. I'm not entirely sure if that answers my question though.

For example consider the following from "Model neutron star atmospheres with low magnetic fields" Zavlin, Pavlov, Shibanov 1996. Astron. Astrophys 315, 141-152. http://arxiv.org/abs/astro-ph/9604072

In the abstract they write "... We show that the model atmosphere spectra are substantially different from the black-body spectra. For light element atmospheres, the flux is greater than the blackbody flux, and the spectrum is harder..."

What is the meaning of harder in this context?

[George Jones]

From the paper
The maxima of the spectra ... , i.e., they are shifted by a factor of 1.6 - 1.8 from the corresponding blackbody maxima towards higher energies.

[nicksauce]

Ah... thank you very much.