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SMMGRS - GRS Gamma-Ray Bursts



The Gamma-Ray Spectrometer (GRS) was one of two instruments on the Solar Maximum Mission (SMM) which independently monitored cosmic gamma-ray bursts from SMM's launch in February 1980 until the end of the mission in 1989.

The GRS was designed for investigation of the gamma-ray spectrum of solar flares (Forrest, D.J. et al. 1980, Sol. Phys., 65, 15). The main detector was an array of seven gain-controlled 7.6 cm diameter X 7.6 cm thick NaI(Tl) detectors. A complete spectrum was obtained every 16.38 seconds in the energy range 0.3-9 MeV. The number of counts in three energy windows covering the 4.2-6.4 MeV range was read out every 2.048 seconds. In addition, the number of counts in an approximately 50 keV wide window near 300 keV was read out every 64 milliseconds. The spectrometer was shielded by a 2.5 cm thick CsI(Na) annulus and a 25 cm diameter X 7.6 cm thick CsI(Na) back detector. The shield elements defined a field of view of approximately 135 degrees (FWHM) in the solar direction. The CsI back detector and the seven NaI detectors together provided a high-energy spectrometer with approximately 100 cm^2 effective area and four energy channels from 10 to 100 MeV. The number of counts in those high-energy channels was read out every 2.048 seconds. The experiment was complemented by two 8 cm^2 X 0.6 cm thick NaI(Tl) detectors which measured the X-ray portion of the spectrum every 1.024 seconds in the range from 13 keV to 182 keV.


The SMM Gamma-Ray Spectrometer (GRS) instrument is described in Norris, J.P. et al. 1986 ApJ, 301, 213 and in Vestrand, W.T et al. 1999, ApJS, 120, 409 (the latter reference also presents a catalog and atlas of solar gamma-ray flares detected above 300 keV by the GRS).


This database table was created by the HEASARC in the early 1990s based on tables supplied by the SMM Project and was subsequently revised in February 2002.


The gamma-ray burst designation based on the prefix 'GRB' and the (2-digit) year, month, and data (YYMMDD) descriptor

The date and time of the gamma-ray burst, in Universal Time.

The Universal Time of the gamma-ray burst onset in seconds of time since the midnight of the burst date.

The duration of the gamma-ray burst, in seconds.

The total gamma-ray burst fluence, in units of 10^-6 erg/cm^2.

The uncertainty in the gamma-ray burst fluence, in units of 10^-6 erg/cm^2.

The V/Vmax statistic, i.e., the ratio of the volume to the maximal volume in which the gamma-ray burst would have been detected. V/Vmax is thus a measure of the homogeneity of the spatial distribution of the cosmic GRB sources. For a spatially homogeneous distribution of GRBs, the average value of V/Vmax would be 0.5.

The angle from the direction to the center of the earth to the direction of the Sun as seen from the SMM spacecraft, in degrees.

The apparent Right Ascension (J2000) of SMM as viewed from the center of the Earth.

The apparent Declination (J2000) of SMM as viewed from the center of Earth.

This flag parameter is set to 'Y' to indicate that the GRB was found by a computerized method.

This flag parameter is set to 'Y' to indicate that the SMM spacecraft was near the South Atlantic Anomaly (SAA).

This parameter lists other experiments that detected the same gamma-ray burst, thereby confirming its cosmic nature.

Contact Person

Questions regarding the SMMGRS database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 8-Nov-2004