National Aeronautics and Space Administration

The Einstein (HEAO-2) HRI and IPC Instruments

High Level Data Products- the Images

HRI Images

Available through the HRIIMAGE database are 870 High Resolution Imager FITS file images produced by the Harvard CfA and GIF images produced at the HEASARC. The images are within a 24 arcmin FOV of the target center and contain x-ray photons in the range 0.15-3.5 keV.

IPC Images

Available through the IPCIMAGE database are 4132 IPC FITS-format images that were produced by the Harvard CfA and GIF images produced at the HEASARC. The images have a 75 arcmin square FOV centered on the nominal target and contain x-ray photons in the range 0.2-3.5 keV. There are 3935 individual images and 197 merged images of fields in which multiple images were obtained within this database.

Screened HRI & IPC event files: These data provide information on x-ray arrival times and full resolution pixel positions for each x-ray detected. For the IPC the photon pulse height bin is also included. The HRIPHOT has 869 HRI photon event files. Included in this data base are 53 exposures using the Objective Grating Spectrometer(OGS). For these exposures the HRI was used to readout the resulting spatially dispersed spectrum. The IPCPHOT database contains 4092 IPC event files. All of these event files were produced at the Harvard CfA.

The HRI event FITS files were generated in the IRAF/PROS data analysis package, using the task xray.xdataio.einbb.xpr2fits. Versions 2.9.3 of IRAF and 1.1.1 of PROS were used. Inputs to xpr2fits were HRI xpr, tgr, and mhdr files generated in Einstein HRI Rev. 1 standard processing.

The HRI event files contain three extensions:

• Timing Gap Record (TGR) - describe the engineering or aspect status relevant to inclusion or exclusion of data.
• Good Time Interval (GTI) - start and stop time intervals. Correspond to the time ranges listed in TGR for accepted data.
• Events - entries contain the time, aspect-corrected pixel position, and pulse height for the x-ray event. Times are in units of seconds from 0 hours, U.T., Jan. 1, 1978.

For the HRI the filenames are of the form hHHMMDdd.xpa where h stands for HRI, HHMM denotes the RA of the field center, D is either N or S for North or South declinations and dd is the declination in degrees. xp stands for X-ray photon. For cases where this notation does not provide a unique filename the final letter is incremented from a to b and so on. The notation for the IPC data is identical with the first character replaced with an i.

Unscreened IPC event files: These event files plus auxiliary files are available through the IPCUNSCRND database. The screening process for the Einstein IPC data excluded the outer regions of the detector and periods of poor aspect solution or high background. Since this excluded data may still be useful for bright sources, these files include the full photon data.

The filenames for the event files have the same format as the screened IPC data except for the extension. The unscreened event files end in upa. For cases where this notation does not provide a unique filename the the final letter is incremented from a to b and so on. Each entry in this database has associated 4 data files in FITS format and one in ascii. The FITS files and their extensions are: the unscreened photons list ('up'), the source detection file ('sd'), the barycenter timing file ('bt') and/or the background file ('bk'). The ascii file ('ls') contains a summary of the observation.

The 'up' file contains seven extensions, including an observation log, GTIs the events and others. The 'sd' contains a minimum of four extensions, which store the information about the detected sources. In addition there are two extensions for each detected source containing the spectrum. The 'bt' file has three extensions, which include the solar system barycenter time correction and ephemeris.