National Aeronautics and Space Administration

1. Introduction

   The HEASARC is a multi-mission astronomy archive for the high energy astronomy data from the extreme ultraviolet through gamma-rays. Except at the very highest energies these wavebands are detectable only using detectors on satellites, rockets and high-altitude balloons.

   The HEASARC currently contains data and/or catalogs from more than 20 past and current EUV, X-ray and gamma-ray missions. Active missions for which data are available include:

   ROSAT, ASCA, BeppoSAX, CGRO, EUVE, and RXTE. Past missions for which data are available include: HEAO-1, Einstein (HEAO-2), and EXOSAT.

   The HEASARC is NASA's primary archive for high-energy data, and its holdings are a matchless compendium of data on the high-energy sky as seen over the past several decades. The HEASARC's mission is to assure that these data remain accessible and useful to astronomers. Data and services are geared not only for specialists in these wavelengths but is also intended for use in multiwavelength studies of the universe. This is a challenging task given the diversity of the HEASARC's data holdings.

   The HEASARC's staff of scientists, programmers, technical, and support staff, together with their counterparts at the various mission Guest Observer Facilities (GOFs), project data facilities, and Science Data Centers (SDCs), have developed a number of on-line services to provide access to the HEASARC's archive. Access is available in a number of ways: the Web, and anonymous ftp.

   Most services are available through the Web and users will typically begin by accessing the HEASARC Web page (http://heasarc.gsfc.nasa.gov/). Access to the Xray account or the FTP is primarily useful for expert users and occasionally for users with poor connections.

2. The HEASARC's Web Services

   Most of these can be accessed directly from the HEASARC's home page and/or from the HEASARC's menubar. They include:

   • Catalog Search and Access to the of the HEASARC's data holdings via our W3Browse (http://heasarc.gsfc.nasa.gov/W3Browse/) interface. There are two kinds of catalogs included in W3Browse, catalogs of observations by various instruments, and catalogs of objects. To access the archive a user will typically search an observation catalog and then request the data associated with the observations selected. Object catalogs are more typically searched to find matching objects, to classify sources, or similar tasks. A few object catalogs are associated with archival data. E.g., the WGACAT catalog contains a table of objects detected in ROSAT PSPC observations and users can request the observational data on which the detection was based. The W3Browse database also contains more than a hundred object catalogs, ranging from the historical (e.g., the Messier Catalog of Extended Objects) to the modern (e.g., the Hubble Space Telescope Guide Star Catalog). New catalogs are constantly being added.

     Users can search tables in several different ways. These include searches near a specified target or position (in which case many catalogs may be searched simultaneously), searches by selection criteria on any field in a table, or cross-correlations between two tables (which has recently been fully implemented).

     A discussion of the functionality of W3Browse is available at: http://heasarc.gsfc.nasa.gov/W3Browse/w3browse-help.html.

   • Convenient access to the status of observations included in accepted ROSAT, ASCA, RXTE, and (soon) CGRO proposals via Argus (http://heasarc.gsfc.nasa.gov/). The progress of observations through the scheduling/observing/processing/release cycle in monitored in Argus which also provides convenient access to the abstracts of proposals.
   • Images of the sky at all wavelengths using the SkyView Virtual Telescope (http://skyview.gsfc.nasa.gov/). SkyView allows astronomers (and the general public) to easily generate images using data ranging from 30 MHz radio observations through 20 GeV gamma rays. Users may simply request an image by specifying a position, or can make very detailed request for the size, scale, orientation, projection and coordinate system for the data. The entire optical sky is available at 1.7" resolution using the Digitized Sky Survey generated at ST ScI. Other notable surveys in the NVSS and FIRST data in the radio, IRAS and COBE in the IR, EUVE and the ROSAT WFC in the EUVE, the ROSAT Pointed PSPC mosaic and HEAO 1 A-2 in the X-ray and Comptel and EGRET in gamma-rays. Most surveys cover the entire sky. Interfaces of a variety of complexities are available including a Java applet/application.
   • Access to astronomical resources distributed over the Web using Astrobrowse (http://heasarc.gsfc.nasa.gov/ab). The HEASARC's new Astrobrowse service allows users to query resources distributed all over the Web. Basically any resource that is queryably by position is eligible for entry into Astrobrowse. Currently over 1,000 resources are available. With a single query a user can request data from NED, SIMBAD, IPAC, CADC, ST ScI, CDS and even the HEASARC. Astrobrowse is a major new effort at the HEASARC and shows great promise in easing the burden of searching the Web for information on astronomical objects.
   • A set of Web tools (accessible from the HEASARC menubar by clicking on the Tools button, or at http://heasarc.gsfc.nasa.gov/Tools/Tools.html) that are aimed to make the astronomers' lives easier, including tools for
   
   (i) coordinate conversions,
   (ii) date and time conversions,
   (iii) calculating the viewing periods when astronomical sources can be observed by current high-energy satellites,
   (iv) simulating spectra for ASCA, RXTE, BeppoSAX, and AXAF instruments (particularly useful for those users who are preparing observing proposals for these missions),
   (v) estimating the total Galactic neutral hydrogen column density, and
   (vi) providing information on count rates and necessary exposure times for observations by a wide range of instruments on past, current, and future missions.
   • Access to the Remote Proposal System facility that provides proposers for ASCA, RXTE, ROSAT, and CGRO Guest Investigator Annoncements of Opportunity (AOs) an automated way to submit the cover pages of their proposal forms electronically, either via e-mail or by Web forms. Use of the HEASARC's RPS service is now mandatory for most missions except in special circumstances. Many of the utilities described above are extremely useful in preparing proposals.

   • Information about and access to a wide range of high-energy astrophyics software either written by or made available through the HEASARC ( /docs/corp/software.html), including the XANADU (xspec, ximage, and xronos), FTOOLS, and FITSIO software.

   • Educational and public outreach activities in both general and high-energy astronomy, aimed both at younger children (the 'Star Child' site at http://starchild.gsfc.nasa.gov) and at older children and the general public (the 'Imagine the Universe' site at http://imagine.gsfc.nasa.gov/).

   • Aliasing of the anonymous FTP area, including the HEASARC archive, through HTTP. A file visible in FTP as ftp://heasarc.gsfc.nasa.gov/xx can be accessed over the Web as http://heasarc.gsfc.nasa.gov/FTP/xx

3. Other HEASARC On-line Services

   Users can access HEASARC catalogs and archives through the Browse catalog browser. Some capabilities of this system, particularly the ability to select and manipulate samples extracted from various catalogs, and to view and analyze selected data directly using xspec, ximage, and xronos, are not yet available in W3Browse but are planned for implementation.

   In most other respects, since the HEASARC has frozen the Browse software for the last 2 years, it has been superseded by the analogous Web-based services utility (discussed above): access to most RXTE and CGRO tables is not supported through Browse, for example.

   The HEASARC's data holdings are also accessible via the anonymous ftp protocol (ftp to heasarc.gsfc.nasa.gov and log in as anonymous). Typically only users familiar with the detailed structure of the archive will find this convenient since most FTP clients, especially for UNIX, are rather clumsy.

4. Other publications

   The HEASARC periodically distributes scientific data and educational and public outreach material on CD-ROMs: please refer to the article at the end of this issue to see what CD-ROMs are currently available and how to order them.

   The HEASARC also periodically (typically about once a year) publishes a new issue of its journal, Legacy, which contains articles both of general interest to the high-energy astrophysics community as well as articles describing specific HEASARC services, datasets, and/or software.

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