The Wide Field Monitor onboard the Large Observatory For x-ray Timing (LOFT)

Abstract

The Large Observatory for X-ray Timing (LOFT) is one of the four candidate ESA M3 missions considered for launch in the 2022‐2024 time frame. It is specifically designed to perform fast Xray timing and to probe general relativity at extreme field strengths near black holes and neutron stars and probe matter at supranuclear densities in neutron stars. The LOFT scientific payload is composed of the Large Area Detector (LAD) and the Wide Field Monitor (WFM). Here we describe the LOFT WFM, a compact and light-weight coded mask instrument with a detection plane based on the large-area Silicon drift detector (SDD) technology. The instrument is designed to cover a large FoV in the same energy range as the Large Area Detector, namely almost 50% of the sky in 2‐80 keV (2‐50 keV of nominal energy range and 50‐80 keV of extended energy range). Its design would allow the detection of transient events with fluxes down to a few mCrab per day, with unprecedented spectral resolution for a Wide Field Monitor (better than 300 eV at 6 keV), a timing resolution of about 10 ms and an angular resolution of 4.7 arcmin, which translates into a sub-arcmin point-source location accuracy (PSLA) for high significance (>10s ) detections. Such performance will allow us to trigger LAD observations of the most interesting sources, and to study long-term variability of LMXBs, HMXBs and some AGNs, and to detect and localize GRBs. Moreover, the WFM is equipped with the LOFT Burst Alert System (LBAS), an onboard trigger and imaging system with a fast-link (<30 s) transmission of the position of fast transients.