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The Science

GOYA (the Gamma-ray burst Observer Yearned- Always), is a mission proposed for the Spanish MINISAT platform.

GOYA consists of several instruments devoted to the observation of the X/gamma-ray sky:

The leitmotive for proposing this mission has been the mystery that surrounds the gamma-ray bursts (GRBs) since their discovery in 1973. The proposed mission will contribute significant new observations in the following fields:

The main objective of GOYA is the detection and localization of GRBs. WIFICAM should be able to localize about 40 GRBs/year, with a 1 degree localization accuracy. A rapid observation (within 10 s) of the GRB error box by XTEL will observe the X-ray tail of the bursts and simultaneously improve the source localization accuracy. After final processing, the accuracy of the GRB positions will be reduced to 2'. The soft X-ray observations will also provide the spectrum in the 0.5-10 keV energy range. When combined with the spectrum in the 5-200 keV range, it will be possible to determine the value of the H column towards the burst source. For a fraction of the bursts (those with -20 < b < +20) we should be able to distinguish whether they arise from nearby sources or if they are far (or beyond) the Galaxy.

The rapid observation by the optical camera (reaching V = 14.5 on 1 s exposure and V = 20 on 1000 s), will allow to search for a flaring GRB optical counterpart. The detection of a flaring counterpart, until now never observed, would be an important step towards an understanding of the GRB origin. Nevertheless, even if no optical counterpart is found by OCAM, the imposed limits to the optical emission will constrain many of the theories proposed so far, and the optical observations of the background star field are also essential for achieving the source localization accuracy.

The wide field X/gamma-ray cameras (5-200 keV), will continously monitor 50 % of the X/gamma-ray sky in the 5-200 keV energy band, with a sensitivity of 1 mCrab in 10E5 s. New X-ray sources will be discovered (about 30 X-ray transients every year). The rapid follow-up observations by the on-board movable telescopes will provide accurate source positions and allow sensitive searches for optical or radio counterparts from the ground.

During quiescent periods the narrow field instruments will be devoted to observations of the Galactic Centre and other interesting objects.

Undoubtely, the monitoring of the sky by GOYA will provide a very important support for ESA's INTEGRAL mission, provided the two missions overlap in time.


next up previous
Next: The Mission Up: GOYA executive summary Previous: GOYA executive summary

Alberto J. Castro-Tirado
Wed Mar 5 22:02:51 MET 1997