[Heig] [UCDList_1-7_RFM] discussion on new terms for UCDs in the high energy domain

[Dr. Ian N. Evans]

Hi Mireille,

For HEA, I prefer “pulseHeight” or “pha” rather than “pulse.amplitude”.

Historically in X-ray and space-based gamma-ray astronomy, the instrument-derived measure of photon energy is termed PHA, which was derived from “Pulse Height Analyzer” (the description of the electronic circuit that measures the quantity).  More recently PHA tends to be listed as “Pulse Height Amplitude”, but this is not the origin of the term.  PHA is more informally termed “Pulse Height”.

However, the precise quantity that defines the PHA value varies somewhat depending on the how the instrument works.
  
For some types of detectors (especially those used in earlier high energy instrumentation) the peak amplitude of the voltage pulse produced when a high energy photon was detected, digitized by an A/D converter, and normalized to some range (e.g., 0-255, 0-1023 etc.), was used to define the PHA value because for those detectors the signal peak scales approximately with input photon event energy.  

For other kinds of detectors, the integrated area under the curve of the pulse is used to define PHA value; this definition is typically used if the detector records charge per event (e.g., a CCD detector), since the integrated charge scales approximately with input photon event energy for these kind of detectors.  

In both cases the typical high-energy astrophysicist would term the measured value PHA (or pulse height) because the details of how the detector works are less important than knowing that the value is the measured proxy for energy (prior to folding through the responses).

Scientists who are responsible for actually developing calibrations or response functions may in some cases need to know the peak pulse amplitude, integrated pulse area, pulse rise and fall times, and pulse width (especially for instruments with very fast response times).  However the astrophysicist who is using the data to do science very likely doesn’t care about such nuances.

Thanks,
—Ian

> On Apr 13, 2026, at 12:26, Mireille Louys via heig <heig at ivoa.net> wrote:
> 
> Hi Heig & semantics members , 
> 
> I have summarized the UCD changes requests on this page : https://wiki.ivoa.net/twiki/bin/view/IVOA/UCDList_1-7_RFM <https://www.google.com/url?q=https://wiki.ivoa.net/twiki/bin/view/IVOA/UCDList_1-7_RFM&source=gmail-imap&ust=1776702390000000&usg=AOvVaw0NsQesG9V4sKVxZ8_NuWjd>
> These are the current terms to be discussed for improving the UCD vocabulary and exercise UCDs in the High energy domain as well. 
> 
> Your comments are welcome , via email on both lists . 
> 
> Many thanks, Mireille
> 
> -- 
> --
> Mireille Louys, MCF (Assistant Professor)
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—

Dr. Ian Evans
Astrophysicist
Chandra X-ray Center
Center for Astrophysics | Harvard & Smithsonian

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