The Einstein Observatory (also known as HEAO-2 or HEAO-B) was operational from 1978 November 13 until 1981 April 25 when the Einstein attitude control system failed. The Monitor Proportional Counter (MPC) was a non-focal plane instrument that monitored the 1 to 20 keV X-ray flux of the source(s) being observed simultaneously by the operational focal plane instrument. The MPC was a collimated proportional counter filled with argon and carbon dioxide. It had a circular field of view, 1.5 degrees in diameter (FWHM), which was co-aligned with the telescope. A 1.5 mil Be window sealed the gas in the detector and shielded the detector from ultraviolet radiation. The active area of the MPC was 667 square cm. The MPC obtained useful data from 1978 November 19 until 1981 April 17, with the exception of a 3-month period from 1980 Aug 27 to 1980 Dec 08 when operation was intermittent, due to Einstein Observatory attitude control problems. The characteristics of the MPC have been described in detail by Gaillardetz et al.(1979) and by Grindlay et al. (1980). One duplicate entry was removed from the HEASARC implementation of this catalog in June 2019. This is a service provided by NASA HEASARC .

The A2 experiment was flown on the HEAO-1 satellite, between August, 1977 until January 1979. The experiment consisted of six multi-layer multi-anode collimated gas proportional counters. These were two LEDs (Low Energy Detectors), a MED (Medium Energy Detector), and three HEDs (High Energy Detectors). The first 6-months of mission were dedicated to an all-sky scan after which a pointing phase started. This database accesses the spectra (and associated files) obtained from the A2 MED (small and large field of view) and HEDs (1 and 3 small and large filed of view) detectors during the pointed phase. The spectra were generated for all HEAO-1 A2 pointed observations except for those in more unusual HEAO-1 modes (RAM-11 and "radical RAMs"). Thus the set of spectra created are only a subset (though a fairly complete one) of the entire catalog of HEAO-1 A2 pointed observations. This is a service provided by NASA HEASARC .

This table is the Einstein Solid State Spectrometer catalog of observations and data products. It incorporates the most recent ice model that is described in the article on the SSS calibration by Christian, Swank, and White that appeared in the HEASARC journal, Legacy, No. 1. Also available as "associated" data products are the quasi-simultaneous observations made by the Einstein Monitor Proportional Counter. There are 634 distinct SSS observations in this database, 95% of which have associated MPC data products. The remaining SSS observations cover time intervals in which all MPC data was flagged as bad by the pCHIP program that was used to generate the MPC spectra and lightcurves. This is a service provided by NASA HEASARC .

The A2 experiment was flown on the HEAO-1 satellite, between August, 1977 until January 1979. The experiment consisted of six multi-layer multi-anode collimated gas proportional counters. These were two LEDs (Low Energy Detectors), a MED (Medium Energy Detector), and three HEDs (High Energy Detectors). The first 6-months of mission were dedicated to an all-sky scan after which a pointing phase started. This database table accesses all the background files available at HEASARC obtained from the A2 MED (small and large field of view) and HEDs (1 and 3 small and large filed of view) detectors during the pointed phase. This is a service provided by NASA HEASARC .

The HEAO 1 A-2 experiment's operations began on day 224 of 1977 (12 August 1977) and ended on day 739 of 1977 (9 January 1979). The A-2 experiment performed two independent, low-background, high-sensitivity surveys of the entire sky 6 months apart, the first scan during days 248 to 437 of 1977 (5 September 1977 - 13 March 1978) and the second scan during days 73 to 254 of 1978 (14 March 1978 - 11 September 1978). The authors analyzed the A-2 data in order to obtain a complete flux-limited sample of extragalactic X-ray sources. The region between galactic latitudes of -20 and +20 degrees was excluded to minimize contamination from galactic sources. A circle of 6 degrees radius around the Large Magellanic Cloud sources was also excluded to prevent confusion problems. Therefore, there remained 65.5% of the sky (8.23 steradians) covered by this survey. The lowest statistical significance for the existence of the sources included in this catalog is 5 sigma, as required by the maximum likelihood methods used by the authors to determine the log N - log S parameters. Taking into account this statistical significance requirement, the authors estimated the completeness level of the first and second scans to be 1.25 and 1.8 R15 ct/s, respectively. 1 R15 ct/s is approximately 2.17 x 10^-11 erg/cm²/s in the 2-10 keV energy band for a power-law spectrum with a photon index of 1.65. This catalog contains data for 68 non-galactic sources (61 extragalactic and 7 unidentified sources) which were listed in Table 1 of the published catalog. The identified sources fall into several categories, including narrow emission line galaxies, broad emission line galaxies, BL Lacertae objects, and clusters of galaxies. This table was last revised by the HEASARC in November 2004 when 2 sources (H1257-042 and H1325-020) which had for some reason been omitted from the previous HEASARC version (the provenance of which is somewhat uncertain) were added back in to the table. This is a service provided by NASA HEASARC .

The A2 experiment was flown on the HEAO-1 satellite, from August, 1977 until January 1979. The experiment consisted of six multi-layer, multi-anode collimated gas proportional counters. These were two LEDs (Low Energy Detectors), a MED (Medium Energy Detector), and three HEDs (High Energy Detectors). The first 6-months of mission were dedicated to an all-sky scan after which a pointing phase started. This database table accesses the lightcurves available at HEASARC obtained from the A2 MED (small and large field of view) and HEDs (3 units, each with small and large field of view) detectors during the scanning phase. This is a service provided by NASA HEASARC .

The UCSD/MIT Hard X-Ray and Low-Energy Gamma-Ray Instrument, A4, was flown on the HEAO 1 satellite, between August 1977 until January 1979. The experiment consisted of a collection of collimated sodium iodide scintillators, two of which the Low Energy detectors (LED, LED-3 and LED-6), were optimized for the lower energy part of the hard X-ray range between 13 to 180 keV. The first 6-months of mission were dedicated to an all-sky scan after which a pointing phase started. In pointing mode the A4-LED instrument look axis was kept in a 1 deg dead band centered on the target position. Instead in the "ping-pong" mode the look axis was regularly alternated with a secondary target a few degrees away, usually for background determination. This database table accesses the spectra (and associated files) obtained from the A4-LED detectors in the ping-pong mode. This is a service provided by NASA HEASARC .

The A2 experiment was flown on the HEAO-1 satellite, from August, 1977 until January 1979. The experiment consisted of six multi-layer, multi-anode collimated gas proportional counters. These were two LEDs (Low Energy Detectors), a MED (Medium Energy Detector), and three HEDs (High Energy Detectors). The first 6-months of mission were dedicated to an all-sky scan after which a pointing phase started. This database table accesses the lightcurves available at HEASARC obtained from the A2 MED (small and large field of view) and HEDs (3 units, each with small and large field of view) detectors during the pointed phase. This is a service provided by NASA HEASARC .

This database table gives access to the IPC unscreened data set, which includes files in the event list format together with auxiliary files. This data set was generated by the Einstein Data Center and delivered to the HEASARC on CD-ROM. The Einstein Observatory (HEAO-2) operated from November 1978 to April 1981. Einstein carried the first fully imaging X-ray telescope in space and operated in pointing mode. The Imaging Proportional Counter had a bandpass of 0.2-3.5 keV and was one of two detectors onboard used for imaging. During the Einstein lifetime more than 4000 targets were observed with the IPC. This database table was last updated by the HEASARC in August 2005. Galactic coordinates were added and some parameters were renamed to adhere to the HEASARC's current parameter naming conventions. This is a service provided by NASA HEASARC .

The HRIIMAGE database table contains information from the High Resolution Imager aboard HEAO 2, the Einstein Observatory. 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 (HRI), 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. One duplicate entry was removed from the HEASARC implementation of this catalog in June 2019. This is a service provided by NASA HEASARC .