Update of the section 4, Extensions to ObsCore Specific to High Energy Astrophysics Data

[bkhelifi]

This PR updates the section 4:

• some minor typo correction
• add the event_type

[bkhelifi]

@iannevans : I have some problem to understand the relative description of obs_mode and scan_mode and tracking_mode. Can you elaborate a bit mode? And even, could we merge them?
PS: in the scan_mode, the example of slewing mode should be moved in the tracking_mode, I guess.

In the CTAO data mode, we have split the observation configuration as follow:

• Tracking mode: fixed ICRS, fixed horizontal
• Observing mode: Wobble, OnOff, GridScan, Custom positions, slewing
• PointingMode: parallel pointing (telescopes pointing all towards the same direction), convergent and divergent
  I think that the current description is not precise enough. And we need to identify the attribute where to put our parallel/convergent/divergent.

The outcome of the discussion will have an impact on the section 6, PR #14 .

[iannevans]

When referring to datasets, telescopes, instruments etc. in general that may cover various parts of the high energy astrophysics range from soft-X-ray up to the highest energies, I recommend keeping the HEA ("High Energy Astrophysics") terminology rather than HE ("High Energy") which can be easily be misinterpreted as a restricted energy range (as opposed to VHE, UHE, etc.).

[iannevans]

@iannevans : I have some problem to understand the relative description of obs_mode and scan_mode and tracking_mode. Can you elaborate a bit mode? And even, could we merge them? PS: in the scan_mode, the example of slewing mode should be moved in the tracking_mode, I guess.

In the CTAO data mode, we have split the observation configuration as follow:

• Tracking mode: fixed ICRS, fixed horizontal
• Observing mode: Wobble, OnOff, GridScan, Custom positions, slewing
• PointingMode: parallel pointing (telescopes pointing all towards the same direction), convergent and divergent
  I think that the current description is not precise enough. And we need to identify the attribute where to put our parallel/convergent/divergent.

The outcome of the discussion will have an impact on the section 6, PR #14 .

Here we are also trying to be consistent with the proposed radio extension, which defines both scan_mode (their examples are on-off, raster map, on-the-fly map, ...) and tracking_mode (their examples are targeted, alt-azimuth, wobble, ...) parameters. obs_mode is something the HEIG group suggested. I suggest we consider converging these terms with the radio extension for user convenience (for example having wobble defined in obs_mode for HEA and in tracking_mode for radio may be confusing to end users who are unfamiliar with the individual facilities), although since these values are facility/instrument dependent there is no requirement to do so.

For Chandra for example obs_mode would be primarily relevant for the instrument configuration, which can dramatically change the data returned in some cases (e.g., ACIS CC mode continuously reads out the detector so there is only one defined spatial dimension instead of two). For tracking mode we have sidereal rate and tracking moving targets. We don't directly do any scan_modes other than target pointing (spatial scans would be implemented as a set of independent observations). I put slew data under scan_mode rather than tracking_mode since for slews the telescope isn't actually "tracking" but honestly it doesn't really fit there either ;-)