What Do Hard and Soft Spectrums Really Mean?

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Discussion Overview

The discussion revolves around the definitions and implications of "hard" and "soft" spectrums in the context of astrophysics, particularly in relation to neutron star atmospheres and their spectral characteristics. Participants explore the meaning of these terms and how they relate to energy, frequency, and comparisons with black-body spectra.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • Nick seeks clarification on the terms "hard" and "soft" as they relate to spectrums, questioning what these descriptors imply in a comparative sense.
  • George Jones notes that hard gamma rays are characterized by higher energy, frequency, and shorter wavelength compared to soft gamma rays.
  • Nick references a specific paper discussing model neutron star atmospheres, questioning the meaning of "harder" in the context of their findings, particularly in relation to black-body spectra.
  • A later reply cites that the maxima of the spectra in the paper are shifted towards higher energies, indicating a difference from black-body maxima.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definitions of "hard" and "soft" spectrums, and the discussion includes multiple interpretations and clarifications without resolving the underlying questions.

Contextual Notes

The discussion highlights the dependence on specific definitions and contexts when discussing spectral characteristics, particularly in relation to astrophysical phenomena.

nicksauce
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"Hard" Spectrum

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


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


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?
 


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.
 


Ah... thank you very much.
 

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