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Motivation and Requirements
MotivationsThere are four distinct categories of motivations for archiving high energy astrophysics data: historical studies, theoretical follow-up, surveys and assurance.
Historical studies are the most obvious archival activity. An observer discovers a new phenomenon, or is studying one previously known, and needs to check earlier data to independently confirm its existence and/or track its long-term variability. These studies can be the most difficult type of archival activity because they involve combining and/or comparing datasets from different telescopes. The major issues to consider for historical studies are ease of access to data, and the ability to perform cross-instrument calibration. An activity related to historical studies is the use of archival data as part of a justification to propose the use of a new telescope.
Theoretical follow-up is the need to test new models against existing data. In many cases, the interpretation of a phenomenon can take many years, with theoreticians repeatedly building models and testing them against the data. Theoreticians previously had to work closely with the original investigator to test their models, or they had to make "eye-ball" fits to published data. The major issue for theoretical studies then is that the theoretician does not have a detailed of the instrument characteristics or analysis techniques. He or she simply wants a data product and the associated calibration to test against the model in a clearly-described, easy-to-read data format.
Surveys provide the opportunity to combine many observations of a single class of object (e.g., AGN) made by many different investigators using the same telescope and instrument. The current principal investigator approach to allocating observation time means that large, uniform samples of particular object types are rarely available to a single observer. Only after the data enter the public domain can a survey of the properties of a particular class of object be made. The main issue regarding surveys that the HEASARC faces is to ensure that a user can access a sample of all objects of a particular class.
Assurance is the ability to guarantee both that an observation is analyzed (and, if appropriate, published), and that unjustified repeat observations are not made. Observation time on satellites is very limited (and expensive). Making the data available after some fixed amount of time ensures that all interested parties in the field get access to that data. It also ensures that the data are eventually looked at. The issue here is that in many cases an observation never may be published because the result is not sufficiently noteworthy. It is essential to provide a simple overview of the main results of the observation to aviod unnecessary repeated analysis of the raw data.
RequirementsThe four categories of motivations described above and the issues related to them place the following requirements on the HEASARC:
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