IACHEC Legacy Working Group Charter v0.2 - 2014 May 9 History of this document ------------------------ v0.1 - 7/5/14 - Matteo Guainazzi (ESA) - draft for the first WG meeting v0.2 - 9/5/14 - Andy Pollock (ESA) - Consolidation of lessons learned ------------------------ Scope ----- A principal part of the scope of the International Consortium for High-Energy Calibration (IACHEC; http://web.mit.edu/iachec/) is the transmission of expertise, good practice, and calibration-related methods from operational missions to missions under development. While the path to instrument calibration, as any other scientific undertaking, cannot be entirely foreseen, there are significant gains for future missions in being able to avoid any errors and inefficiencies made in the past. These gains can be critical for missions on tight budgets, or with shorter (predicted) operational lives. Calibration plans are inevitably success-oriented in mitigation of the limited 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]. Based on shortcomings identified there from personal experience, a set of ideas has been drawn up to help inform the development of calibration activities on the ground and during the early phases of science operations: - continuity between pre-flight and operational calibration teams - mitigation of inevitable losses of expertise - involvement of pre-flight calibration teams in the definition of the in-flight calibration plan - definition and dissemination of a complete calibration data model - establishment of a configuration control system - establishment of a single consolidated archive as the unique destination of all data products without exception - derivation of ground-based calibration products strictly conforming to the calibration data model - deposit of all ground-based calibration products without exception in the consolidated mission archive subject to configuration control - calibration data model . accurate systematic error budgets and their interdependence . calibrated instruments . all elements of the ground-based calibration . ground-based calibration facilities themselves . ground and flight calibration analysis procedures - recognition of cross-calibration as a critical element of mission design . strictly simultaneous data are the highest priority . particular relevance during the early phases of science operations . combat any skepticism among scientific management and funding agencies in charge of operations - enable confidential access to all scientific data for calibration purposes . specifically calibration data is only a small fraction of the total - facilitate cooperative calibration workshops to complement formal reporting procedures . encourage interchange between instrument teams . take into account all available data should other instruments be available The absence of one or more of these elements has 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 practices 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, available at [4] [4] Wiki of the LWG: https://wikis.mit.edu/confluence/display/iachec/IACHEC+Legacy+Working+Group