HRIPHOT - Einstein HRI Photon Event Data
The HRIPHOT database contains information from the High Resolution Imager
aboard HEAO-2, the Einstein Observatory, in Event List Format. Einstein
incorporated a high-resolution X-ray telescope and a focal plane assembly
capable of positioning at its focus one of four instruments: a high-
resolution imaging detector (HRI), a broader-field imaging proportional
counter (IPC), a solid state spectrometer (SSS), and a Bragg crystal
spectrometer (FPCS). Einstein (HEAO-2) was launched on November 13, 1978,
and operated successfully until April 1981.
The High Resolution Imager has been described by Henry et al.
(Proc SPIE, 106,196,1977).
The HRI used a pair of cascaded microchannel plates as an X-ray image
converter and photoelectron multiplier, and a crossed-wire grid as a
two-dimensional position-sensitive charge detector. The detector provided
an arrival time and position for each X-ray event occurring within the
24-arcmin FOV and within the energy range 0.15 to 3.5 keV. The spatial
resolution of the HRI was 3 arcsec at the telescope focus and the temporal
resolution was 7.8125 microsec. The nominal sensitivity of the HRI was
10 Uhuru counts per second, but this value depends on the assumed value of
the low-energy cutoff parameter Ea. An Objective Grating Spectrometer
(OGS) could be used in conjunction with the HRI. 53 sequences with this
configuration are included in the 870 HRI photon events files of this
The only data products associated with this database table are FITS events
files. The file names for these data products have the format `hhhmmDdd.xp*`.
The letters `hhmm` denote the RA hour and minute. The `D` is either `N` or `S`
for North or South, and `dd` is the declination in degrees. The `*` is a
letter, such as A, B, C, etc., that is used to distinguish the files when the
rest of the file name is not unique. This occurs when more than one pointing
was made at a given position.
Start time of observation in the format yy.ddd
Stop time of observation in the format yy.ddd
The RA reference point value of the FITS image file.
The right ascension (1950.0) in decimal degrees of the center of the image.
The DEC reference point value of the FITS image file.
The declination (1950.0) in decimal degrees of the center of the image.
Galactic Longitude of field center of the FITS image file.
Galactic Latitude of field center of the FITS image file.
The detector roll angle in degrees
The number of photons collected during the exposure.
Satellite On-Time (sec)
Observation mode of current observation (point, slew or scan)
Information on the nature of the target. Entries include catalog names
(e.g., 4U0248-85) and observer's notes.
The file name of the original XPR file used to create the FITS file.
The XPR files conform to a standard of Hxxxx.XPR in which xxxx is the
observation sequence number.
File name of the FITS events file in the data archive. The files
have the format `hhhmmDdd.xp*`. The letters `hhmm` denote the RA hour
and minute. The `D` is either `N` or `S` for North or South, and `dd`
is the declination in degrees. The `*` is a letter such as A, B, C,
etc., to distinguish the files when the rest of the file name is not
unique. This occurs when more than one pointing was made at a given
Questions regarding the HRIPHOT database table can be addressed to the
HEASARC User Hotline.
If you have any problems, please consult the help
page or mail email@example.com