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ASCA Guest Observer Facility

The U.S. ASCA Guest Observer Facility

Past Activities


The U.S. ASCA Guest Observer Facility (GOF) is located at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The GOF is part of the Office of Guest Investigator Programs (OGIP) in the Exploration of the Universe Division

The primary responsibility of the U.S. ASCA GOF is to enable U.S. astronomers to make the best use of the ASCA mission. To fulfill this responsibility, the ASCA GOF staff preforms such activities as supporting the U.S. side of the ASCA proposal selection process, distributing useable data to U.S. Guest Observers, helping Guest Observers to analyze their data, and creating the mission archive.

In addition to the tasks listed above, the U.S. ASCA GOF activities include the development of software, the compilation and production of documentation for that software, and the provision of expert help. All of the U.S. ASCA GOF's activities involve close collaboration with the Japanese ASCA team.

The U.S. ASCA GOF supports guest observers at the following stages:


The scientific question that forms the basis of a proposal is, of course, the responsibility of the investigator. However, the ASCA GOF can help by providing the investigator with information and advice to help him or her ascertain whether (and how) and ASCA observation might answer that question. For this type of assistance, the ASCA GOF provides full descriptions of the satellite and its instruments in the Technical Appendix to the NRA. In addition, the U.S. ASCA GOF provides software that simulates ASCA observations (PIMMS and XSPEC).

The GOF staff members are available to answer proposers' questions and can be reached at a quick-response help-desk by sending e-mail to

Once proposals are submitted, they are subjected to a peer review, a process supported by the GOF, which supplies the reviewers with the technical evaluations of all proposals. The final stage for each AO is the creation of a joint observation program by the merging of the Japanese and U.S. lists of top-ranked proposals.


Observation Support

In their proposals, investigators are not required to specify in detail exactly how they want their observations carried out. The GOF needs only enough information to assess the feasibility of the proposed observations. However, after a successful proposal has been scheduled as an ASCA observation, the GOF will contact the investigator to discuss which modes should be used and where exactly the satellite should point.

Processing and distribution of Data, Calibrations, and Software

Data are sent to the ASCA Guest Observer Facility from ISAS on DAT tape. The data are send in a format very similar to the original telemetry. The first step in processing the data at GSFC therefore is to reformat the data into FITS (without the loss of information). This conversion of data into FITS has three advantages: 1) FITS is a widely-used standard, 2) the file contents are self-documenting, and 3) the format is machine-independent. In addition to distributing the data to the investigator, the ASCA GOF distributes all of the software and calibration files needed for reduction and analyisis.

The contents of the data distribution includes the following:

  • Original telemetry data (for completeness)
  • FITS-converted data
  • Calibrations files and software
  • Data products (light curves, images, and spectra) derived from a standard quick look analysis.
By data, we mean science data, housekeeping, orbital, and attitude information. All of the GOF software and calibrations, as well as the archival data that are no longer proprietary, are available to users via anonymous ftp.

For more information about the processing of ASCA data, see the Astrophysics Data Facility

Data analysis

ASCA data are rich and complex. To help Guest Observers produce scientific results, the ASCA Guest Observer Facility (GOF) supplies fully documented data analysis software. The GOF also staffs a quick-response help-desk, to which Guest Observers should e-mail ( any questions, comments, or suggestions about ASCA data analysis.


The ASCA mission archive is maintained and accessed through the HEASARC . A full description of the HEASARC archive and how to access it, is given on the asca gof home page.

If you have any questions concerning ASCA, visit our Feedback form.

This file was last modified on Tuesday, 08-Mar-2005 11:18:51 EST

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