Session 64 - Telescopes for the Next Millennium.
Oral session, Thursday, January 08
Jefferson,

## [64.07] ALLEGRO: A New View of the Hard X-Ray Sky

M. P. Ulmer, S. M. Matz (Northwestern U.), J. P. Finley (Purdue U.), R. B. Wilson (MSFC), G. N. Pendleton (U. of Alabama-Huntsville), J. M. Cordes (Cornell U.), V. Petrosian (Stanford), D. Dixon (UC Riverside)

ALLEGRO is a proposed new MidEx-class NASA mission. This mission combines proven and available detector technology with innovative communications hardware to produce sensitive monitoring and mapping of the whole X-ray sky at high time resolution. It will generate an abundance of data and will provide continuity in hard X-ray astronomy acting as a bridge to the next large'' hard X-ray observatory. ALLEGRO consists of 16 large (2000 cm^2), thin, broadly-collimated NaI detectors operating from 7--200 keV (with 25% resolution at 20 keV). The instrument is zenith-pointed; its combined field-of-view (>2\pi sr) covers the entire sky visible from low-Earth orbit. All detected events are transmitted to the ground, time-tagged to 125 microseconds and with full energy information. There is no time-averaging, data-selection, or triggering on-board. This will produce a long term, unbiased record of the complete X-ray sky with uniformly high resolution in both energy and time.

ALLEGRO will have four times the sensitivity of BATSE for normal gamma-ray bursts (and better for short events), with better positioning and no limitations from on-board triggering. We will make the most comprehensive observations ever of the time variability and spectral characteristics of X-ray binaries, X-ray novae, and AGN. We will be able to produce an all-sky hard X-ray survey. ALLEGRO will have 3--5 times the OSSE sensitivity for steady emission from AGN and other sources. ALLEGRO will study pulsed hard X-ray emission from over 200 known radio pulsars and search for new, unknown pulsars with a sensitivity 10 times that of OSSE. The increased sensitivity and unique timing capabilities of ALLEGRO will open up a vast unexplored range of observational phase space, allowing ALLEGRO to make important discoveries of new sources and phenomena. Further information about ALLEGRO can be found on the WWW at: http://www.astro.nwu.edu/astro/allegro/