ASCA Now Available On NDADS

Volume 11, Number 1, March 1995
By Nancy Oliversen
The Advanced Satellite for Cosmology and Astrophysics (ASCA), launched on February 20, 1993, is a joint Japanese and U.S. mission. The mission's purpose is to perform X-ray astronomical observations in the energy band from 1 to 12 KeV. ASCA carries four large-area X-ray telescopes and four X-ray detectors: two are Gas Imaging Spectrometer (GIS) detectors, which are gas imaging scintillation proportional counters and two are Solid State Imaging Spectrometers (SIS), which are Charge Coupled Device (CCD) cameras. ASCA is the first X-ray mission to combine imaging capability with a broad passband, good spectral resolution, and a large effective area. The mission is also the first satellite to use CCDs for X-ray astronomy. The primary scientific purpose of ASCA is the X-ray spectroscopy of astrophysical plasmas--especially the analysis of discrete features such as emission lines and absorption edges in stars, pulsars, galaxies, and supernova remnants.

ASCA data are being archived at the National Space Science Data Center on the NASA Data Archive and Distribution System (NDADS) near-line system. Data first became publicly available on November 15, 1994, and consist of data from the initial 8-month Performance Verification (PV) period of the mission. Data from the Guest Observer part of the program, which began after the completion of the PV period of the mission, should begin to become publicly available in May 1995. Data will initially be released in 1-month batches, around the 15th of each month. As the archive population becomes routine, the releases will be made more frequent, on a weekly basis.

ASCA Data on NDADS

The ASCA/NDADS archive can be accessed in several ways. Requests can be submitted via an E-mail interface to NDADS or via the World Wide Web (WWW).

ASCA data on NDADS are organized by the 8-digit observation sequence number. The data files for a single observation sequence have been grouped into six data-types (AUX, RAW, TELEM, SCREENED, UNSCREENED, and PRODUCT) and archived on NDADS in UNIX TAR containers. Most of the component files within each TAR container have been compressed (*.Z extension) using the UNIX compress utility. The size of each TAR container varies substantially depending on the particular sequence number and data type, but may be as large as 50-200 mB and have several hundred component files. The individual ASCA data files are archived in FITS format.

Also archived on NDADS are six logs (listings) of the files within each TAR container. These logs are derived from the original "Bills of Lading" (BOLs) delivered from the project and contain the following fields; original file name delivered by the project, compressed byte count, decompressed byte count, original release date as supplied by the ASCA project, an archive flag used to ingest the data, and the astrophysical object name. These logs are archived as ASCII files separate from the TAR container files (NDADS data-type of 'LOG'). Further details on the ASCA data are available from the ASCA WWW pages referenced below.

NDADS E-Mail Requests

ASCA data can be requested electronically through the Automated Retrieval Mail System (ARMS). To request information on the NDADS ASCA data holdings, send the following E-mail message (nothing needs to be entered in the body of the message):
  To:       NDADSA::ARCHIVES    (or archives@ndadsa.gsfc.nasa.gov)
  Subject:  HOLDINGS ASCA
The NDADS holdings file also contains more detailed information on the ASCA data formats, such as how to request ASCA data from NDADS and how to extract the individual data files once the user has copied the files to their home computer or another location.

NDADS requests for ASCA data should include the NDADS entry-id's (8-digit observation sequence number's), the data-type (AUX, SCREENED UNSCREENED, PRODUCT, LOG, TELEM, and RAW) and the project name (ASCA). For example:

  To:       NDADSA::ARCHIVES     (or archives@ndadsa.gsfc.nasa.gov)
  Subject:  REQUEST Project_Name Data_Type
In the body of the mail message list the sequence number(s) you wish to request. A request for a particular object may also be submitted instead of the 8-digit observation sequence number. If a particular object was observed multiple times then more than one observation sequence will be returned. Requests for more than one data-type must be submitted separately.

World Wide Web Interface

The ASCA data on NDADS and related information can be accessed via the WWW. The URL for the ASCA Astrophysics Data Facility (ADF) home page is:
http://nssdca.gsfc.nasa.gov/asca/asca.html
and then connect to "ASCA Data Archives at the ADF/NSSDC." This allows you to connect to a form for requesting ASCA data. You may then electronically transfer the data via default DECnet or ftp to the node of your choice. This process is similar to the NDADS/ARMS E-mail procedure.

ASCA Data at the HEASARC

ASCA data are also available through the WWW online service of the High Energy Astrophysics Science Archive Research Center (HEASARC). Information on how to access the ASCA archive is available through the ASCA Guest Observer Facility (GOF) at GSFC. The URL for the ASCA GOF is:
http://heasarc.gsfc.nasa.gov/0/docs/asca/ascagof.html
and then connect to "How to access the ASCA archive."

Obtaining ASCA Data Through the Mail

NSSDC can write ASCA data from its NDADS platters to media for mailing to requestors. Contact NSSDC's Request Coordination Office for details, including prices.

Questions concerning how to access ASCA data on NDADS may be sent to Nancy Oliversen at noliversen@nssdca.gsfc.nasa.gov.

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Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 04 Dec 1996 [EDG]