Agile telescopes to monitor optical transients and sky variability: From TAROT to ARAGO

Abstract

Gamma-ray bursts afterglows are now routinely detected by ground and space facilities. However, only one detection of a prompt transient occurred at optical wavelengths. TAROT (Rapid Action Telescope for Transient Objects) has both a large field of view and the ability to slew within 1 second to observe without delay the source position. We present here the current status of GRB observations as well as other variable objects with TAROT. Since GRB 990123 was the only GRB optical counterpart detected so far, we started the ARAGO (Advanced Robotic Agile Guest Observatory, formerly TAROT-2) program: this autonomous observatory features a radically new technology 1.5 m telescope, a wide 4 square degrees field of view, and a slewing speed of 60 degrees/second. Not only ARAGO will be able to detect fast transients, but it can survey the variable sky in a frequency range starting from 1Hz down to 10—8Hz (period 1 year). Among its various objectives (extrasolar planets, AGNs, SNs …), ARAGO will be able to detect at least 20 orphan optical transients per year, a number conservatively based on the BATSE detection rate.