IACHEC Legacy Working Group charter v.0.1 - May 7, 2014 History of this document ------------------------ v.0.1 - Matteo Guainazzi (ed.) - draft for the first WG meeting ------------------------ Scope ----- One of the main scopes of the International Consortium for High-Energy Calibration (IACHEC; http://web.mit.edu/iachec/) is the transmission of expertise, good practises, and calibration-related know-how from operational missions to missions under development. While the path to instrument calibrations, as any other scientific undertakings, cannot be entirely foreseen in advance, there are significant gains for future missions in avoiding repeating errors and inefficiencies made by past missions. This gains can be truly critical for missions on a tighter budget, or with a shorter (predicted) operational life. Calibration time is limited, calibration plans are inevitably success-oriented (to compensate for the insufficient time devoted to calibration), and time pressure during the development phase may lead to losing the overall vision of long-term sustainable mission operations. These shortcomings can be dearly paid in the later phases of mission operations. It is therefore crucially important to avoid following knowingly wrong paths. S(hort) summary of lessons learned ---------------------------------- A special session on "a path to defining a calibration legacy program" was held at the 5th IACHEC meeting [1]. A series of shortcomings in the development of calibration activities on ground and during the early phases of science operations were identified: - the lack of integration between pre-flight and operations/data center calibration team - the lack of involvement of pre-flight calibration teams in the definition of the in-flight calibration plan - the incompleteness of the information (particularly metadata) stored in the ground-based calibration archives, or even in some cases the lack of centralised calibration databases for ground-based products - systematic errors of the ground-based calibration facilities are often difficult to disentangle from the systematic errors of the instruments to be calibrated - the incomplete transmission of data products and analysis procedures of ground-based calibration data to the operations/data center calibration teams - the decoupling between ground-calibration archives and science archives containing in-flight calibration data - the lack of accurate estimates of the systematic errors associated to each element of the ground-based calibration. Once the original expertise on ground-based calibration is lost, it may become hard or simply impossible to reconstruct them - cross-calibration is hardly identified as a critical element during the mission design, is often neglected during the early phases of science operations, and is occasionally considered with skepticism by scientific management and funding agencies in charge of operations - scientific users have often access to much better data than calibration teams (unless the latter can access all the data) - the flow of information among the in-flight calibration teams often occurred in formal meetings rather than in informal venues, hampering sincere and bias-free discussions - calibration teams tend to analyze only data of their own instrument rather then analyzing the whole suite of available data The combination of these elements led in the past to discontinuities between the pre- and in-flight calibration teams, to irrecoverable loss of expertise on the ground-based calibration results and their associated systematic errors, to duplication of activities in different phases of the mission, to inefficiencies as long as to avoidable tensions among the calibration teams. The process of defining an in-flight calibration plans has been often far from straightforward. In principle an in-flight calibration plan should provide a stable reference set of sources to be observed periodically in order to tune calibration aspects for which insufficient ground calibration time was available, to evaluate the scientific performances of the instrument, and to monitor and correct their trends. The key word here is "stable". While changes in the instrument performances with respect to the physical models developed on the basis of ground calibrations could require targets with features not predicted at launch, observing regularly the same core set of sources under the same instrumental configuration is a crucial requirement to ensure that the time evolution of the instrument performances can be accurately reconstructed. This has not always been the case, and the changes that the, e.g., XMM-Newton Routine Calibration Plan has undergone over the first half of mission operations could be partly due to lack of planning or clear requirements. Data analysis procedures for calibration activities should constitute a reference for the whole community. One of the main intangible positive effects of the work done by the IACHEC community over the past few years is the consolidation of a series of good practise on how to analyse X-ray data, in particular in the spectral domain. Usage of different cosmic abundances, cross- sections, photoelectric absorption models and, above all, statistical techniques may have an effect on the calibration results comparable to the current level of (dis)-agreement between instruments. Goals and methodology --------------------- The IACHEC "Legacy Working Group" (LWG) aims at providing an agreed and consolidated platform for know-how transfer from operational missions to missions in development, in each of the following areas: 1. maintenance of ground-based calibration data and procedures 2. X-ray spectroscopic data analysis and associated statistical methods 3. definition of the in-flight calibration plans 4. cross-calibration analysis Preliminary discussion papers on some of the aforementioned topics have been already posted in the past onto the IACHEC Wiki [2,3]. For each of the aforementioned subjects the LWG will produce a White Paper (WP). After discussion and endorsement by the LWG members, the WPs shall be presented at a plenary IACHEC meeting for their discussion, amendment, and final approval during a specific half-day session. The approved WPs shall be published on the IACHEC public web page, on the IACHEC Wiki [4], in the arXiv database, as well as on any other free Internet platforms interested in disseminating information related to space instrument calibration. For Subject#2 above, scientific publications on refereed journals on behalf of the IACHEC can be envisaged. The aforementioned subject list does not explicitly include a fundamental item, on which there is an urgent need for investigation and systematization: the propagation of systematic calibration uncertainties into the standard X-ray data analysis tools. At the time this document is being written, it is assumed that this topic will be dealt with by the IACHEC "Calibration Uncertainties" WG, that is expected to meet for the first time at the 9th IACHEC meeting. Timeline -------- - 9th IACHEC meeting: start of the LWG: charter approval and membership - by summer 2014: first teleconference of the LWG, attribution of WG tasks and responsibilities, and the election of a Chair - 10th IACHEC meeting: presentation of draft WPs - by summer 2015: publication of the approved WPs References ---------- [1] D.Jerius, "Re-thinking calibrations from a mission perspective", available at: http://web.mit.edu/iachec/meetings/2010/Presentations/Jerius_Iegacy.pdf [2] Guainazzi M., Sembay S., Pollock A., "IACHEC multi-mission cross-calibration procedure", Version 1.0, available at: https://wikis.mit.edu/confluence/download/attachments/82340885/Cross_calibration.txt?api=v2 [3] Guainazzi M., "A synoptic view of in flight-calibration plans", Version 0.1, in preparation [4] Wiki of the LWG: https://wikis.mit.edu/confluence/display/iachec/Legacy+Questions+and+Answers