High Energy Astrophysics Group

MIRAX/HXI

Monitor e Imageador de Raios-X

We have proposed the MIRAX/HXI Mission of Opportunity twice as part of NASA Explorer Announcements of Opportunity (in 20XX and 20XX). Neither proposal was funded for development, but the MIRAX schedule has slipped, and one more proposal is in preparation.

The Brazilian Monitor e Imageador de Raios-X (MIRAX) X-ray astronomy mission is one of three small scientific satellites to be developed at the Instituto Nacional de Pesquisas Espaciais (INPE) in San Jose dos Campos, Brazil over the next decade under the auspices of the Brazilian Space Agency (AEB). MIRAX is dedicated to the study of transient phenomena in the central regions of the Milky Way. Continuously observing 1000 square degrees of the Galactic Plane centered on the Galactic Center with good spatial and energy resolution and with sensitivity ten times better than the RXTE/ASM and CGRO/BATSE, will allow the detection, localization, identification, and spectral/temporal analysis of a large number of short-lived, unpredictable phenomena that otherwise would be missed or poorly sampled by low duty cycle all-sky missions. In addition, MIRAX will be uniquely capable of studying longer-lived phenomena on a timescale of months to years. MIRAX observations will support multi-wavelength investigations in other wave bands.

Recently, the Lattes mission in Brazil was developed to carry both the MIRAX complement of instruments and the EQUARS instruments which study the upper atmosphere. Since EQUARS requires nadir pointing, the MIRAX instruments will scan the sky in a zenith pointed mode. The launch date is in early 2015, and the mission will be operated from the INPE mission operations center.

The MIRAX detector complement contains two sets of coded mask imaging telescopes --- the Soft X-ray Imagers (SXI) covering 1-10 keV and the Hard X-ray Imagers (HXI) sensitive from 10-200 keV. The SXI was originally to be the 2-dimensional imaging gas proportional counter BeppoSAX Wide Field Camera (WFC), and the HXI are arrays ofCdZnTe (CZT) detectors recently developed at UCSD. The WFC was the flight spare and it finally died in the clean room before the mission developed. In its place will a set of silicon drift detectors with strip-like readout developed by scientists from the BeppoSAX team. The new SXI will have a 108 degree field of view perpendicular to the scan plane and a 6 degree field along it. In this manner, the full sky can be scanned every 96 minute spacecraft orbit. The prime goals of the SXI will be the study of gamma ray bursts, with an emphasis in the spectral characteristics in the 2-20 keV band. In addition, the SXI team will provide two sets of non-imaging hard X-ray/gamma ray detectors that will trigger on each gamma ray burst to provide spectral coverage from 50 keV to several MeV. A secondary goal is to provide an all-sky monitoring for alerts to other missions and monitoring of all sources.

The HXI will still be a set of CZT detectors with coded mask imaging capability. With an offset mounting of about 30 degrees, the HXI 40x40 degree field of view will scan across the Galactic center region each satellite revolution and provide spectral, temporal, and location information on persistent and transient sources there. The HXI will also extend the spectral coverage of SXI sources in the HXI field of view.