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ASCA Guest Observer Facility

The US ASCA Guest Observer Facility

--by Charles Day & Koji Mukai, GSFC


The US ASCA Guest Observer Facility is located at the NASA Goddard Space Flight Center, Greenbelt, MD, and is a part of the Office of Guest Investigator Programs (OGIP) in the Laboratory for High Energy Astrophysics. Its responsibility is to enable US astronomers to make the best use of the ASCA mission. This role entails supporting the US side of the proposal selection process, distributing usable data to US Guest Observers, helping Guest Observers to analyze their data, and creating the mission archive. In practice , it involves the development of software, the compilation and production of documentation and the provision of expert help. It also involves close collaboration with the Japanese ASCA team.

The description in the next section shows how the GOF is involved in the key stages of a GO's ASCA project:

  • Proposals
  • Observations
  • Processing and distribution of data, calibrations and software
  • Data analysis
  • Archive

In this process, communication between the GOF and the Guest Observers is obviously very important. In Section 3 we list the GOF staff, describe the e-mail helpdesks and bulletins, as well as the items available via anonymous ftp.

From ASCA Proposal to ASCA Archive


The scientific question that forms the basis of a proposal is, of course, the responsibility of the PI. What the GOF does is to provide information and advice to help the PI ascertain whether and how an ASCA observation can answer the question. For this, we provide full descriptions of the satellite and its instruments (the Technical Appendix to the NRA) as well as software that simulates ASCA observations (PIMMS and XSPEC). The GOF staff are available to answer proposers' questions and can be reached at a quick-response helpdesk by sending e-mail to Once submitted, proposals are subjected to a peer review, a process supported by the GOF that supplies the reviewers with technical evaluations of all the proposals. The final stage for each AO is the creation of a joint observation program by the merging of the Japanese and US lists of top-ranked proposals.


In their proposals, PIs 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. However, after a successful proposal has been scheduled as an observation, the GOF will contact the PI to discuss which modes should be used and exactly where the satellite should point.

Processing and Distribution of Data, Calibrations and Software

Data are sent to the GOF from ISAS on DAT tape in a format very close to the original telemetry. The first stage of the processing preformed at GSFC is the reformatting of the data into FITS (without the loss of any 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. As well as the data themselves, the GOF distributes all the software and calibration files needed for reduction and analysis to the PIs. A choice of distribution media is available. The contents of the distribution package are:

  • Original telemetry data (for completeness)
  • FITS-converted data
  • Data reduction software
  • Calibration files and software
  • Data products (light curves, images, spectra) derived from subjecting the data to an automatic, standard analysis
  • Data analysis software

By "data" we mean science data, housekeeping, orbital and attitude information. All the GOF software and calibrations, as well as archival data (when no longer proprietary), are available to users via anonymous ftp (see below).

Data analysis

ASCA data are rich and complex. To help GOs produce scientific results, the GOF supplies fully-documented data analysis software. The software is described in the article by Arnaud et al. in this Newsletter. The GOF also staffs a quick-response helpdesk to which GOs should e-mail any questions, comments, suggestions or complaints about data analysis (


The ASCA mission archive will have the same "look and feel" as other mission archives under the HEASARC (e.g., ROSAT). That is, the data and calibrations will be archived in databases that are structured in the same standard way and accessible via the same software. Also available will be the mission log, mission timelines, various catalogs and data products. Archival ASCA data will become publicly available one year after the original PI received the data; the mission logs and timelines are updated continuously and are available now (see below).


E-mail bulletins

During the period between the posting of an ASCA NRA and the corresponding deadline for proposals (about four months), the GOF usually finds it necessary to communicate with potential proposers. For example, analysis of PV phase data might reveal a problem with one of the detectors, or a target of opportunity might be observed. To contact potential proposers, we send e-mail bulletins to all those people who requested the ASCA Technical Appendix (indispensable if one wants to write a proposal). These bulletins are also available via anonymous ftp (see below). If you did not request the AO-1 Technical Appendix, then you will not be on the current distribution list. To be included, please send an e-mail to:

To communicate with GOs, the GOF will use a smaller distribution list comprising PIs whose proposals were successful. These bulletins also will be available via anonymous ftp.

E-mail helpdesks

To respond quickly to questions and comments from proposers and GOs, the GOF has two quick-response helpdesks, ascanra and ascahelp. The members of the GOF staff take it in turns to staff the helpdesk hotseats and will respond to inquiries as a quickly as possible.

For questions about the NRA and proposals:
For questions about data and software:

Proposers and GOs should, as far as possible, direct the queries to the two helpdesks, since this approach will guarantee the fastest response. However, for issues not covered by the helpdesks, the GOF staff can be contacted directly. Please see the list of GOF staff.

Items Available to Proposers via ftp

A lot of information about ASCA is available to users via anonymous ftp at:

in the directory asca and its subdirectories. Each directory contains a README file, which describes its contents and which appears on the screen as a .message file when one enters the directory. Reproduced below are the README files for the top-level asca directory and for the subdirectory asca/nra_info.

The asca directory contains the following subdirectories:

ASCA calibration files in FITS
ASCA data (science and housekeeping) in FITS
documents describing the mission, instruments, calibrations, etc.
NASA Research Announcement and related information
calibration issues, software bugs, etc.
ASCA bibliography
ASCA-specific software
long-term and short-term timelines

At present (1993 October 1), only calib_data, nra_info and timelines contain anything.

All directories and subdirectories contain README files that describe their contents briefly and that appear (as .message files) on the screen when you enter the directories.

Comments and questions should be sent to

The nra_info directory contains the following subdirectories:

appendices A, C & E of the NRA
e-mail messages sent to proposers
Portable Interactive Multi-Mission Simulator
Information about the Performance Verification phase of the ASCA mission
GIS and SIS response matrices for simulations
Remote Proposal Submission
VIEWING, which generates observing windows for ASCA

PIMMS, RPS and VIEWING are all programs. Their corresponding directories contain source code, makefiles and documentation.

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