The Line Emission Mapper (LEM) is a Probe mission concept developed in response to NASA’s Astrophysics Probe Explorer (APEX) Announcement of Opportunity. The LEM project is a collaboration between the Smithsonian Astrophysical Observatory (SAO), the NASA Goddard Space Flight Center (GSFC) and Lockheed Martin (LM). LEM is a large field of view (30′ equivalent diameter), soft X-ray mission (0.2-2.0 keV bandpass) with a large format microcalorimeter X-ray imaging spectrometer in the focal plane (1.3-2.5 eV spectral resolution) that provides unprecedented grasp (the product of effective area times field of view) in this bandpass. LEM’s sensitivity to diffuse X-ray emission will be orders of magnitude higher than existing or proposed missions. LEM’s primary science will characterize the diffuse gas in the X-ray haloes in galaxies, the outskirts of galaxy clusters and the filamentary structures between these clusters, and in the Milky Way star formation regions and Galactic halo, and Galactic and Local Group supernova remnants. To accomplish these objectives, the LEM spacecraft and mission have been designed to perform long observations of relatively faint objects and to perform an All-Sky Survey. The science payload consists of a single X-ray mirror assembly and a single focal plane instrument, the microcalorimeter operating at a temperature of 40 mK. The LEM spacecraft is a high-heritage, low-risk design that meets or exceeds all requirements, in particular the thermal requirements for the calorimeter, electronics, and mirror. The science mission profile supports high observing efficiency (> 90%), large sky coverage (45−150° field of regard), and flexible operations that maximize the science return. LEM mission and science operations follow the same successful approaches used by LM for 16 NASA missions and by SAO for 24 years of successful operation of a NASA Great Observatory, the Chandra X-ray Observatory. With multiple decades of experience developing and maintaining the Chandra X-Ray Center Data System, the LEM team will develop the software to produce and disseminate high-quality data to the entire astronomical community. In this paper, we discuss the design of the mission and spacecraft operations that supports the transformational science that LEM promises to deliver.
The Line Emission Mapper (LEM) is a Probe mission concept developed in response to NASA’s Astrophysics Probe Explorer (APEX) Announcement of Opportunity. LEM has a single science instrument composed of a large-area, wide-field X-ray optic and a microcalorimeter X-ray imaging spectrometer in the focal plane. LEM is optimized to observe low-surface-brightness diffuse X-ray emission over a 30′ equivalent diameter field of view with 1.3 and 2.5 eV spectral resolution in the 0.2−2.0 keV band. Our primary scientific objective is to map the thermal, kinetic, and elemental properties of the diffuse gas in the extended X-ray halos of galaxies, the outskirts of galaxy clusters, the filamentary structures between these clusters, the Milky Way star-formation regions, the Galactic halo, and supernova remnants in the Milky Way and Local Group. The combination of a wide-field optic with 18′′ angular resolution end-to-end and a microcalorimeter array with 1.3 eV spectral resolution in a 5′ × 5′ inner array (2.5 eV outside of that) offers unprecedented sensitivity to extended low-surface-brightness X-ray emission. This allows us to study feedback processes, gas dynamics, and metal enrichment over seven orders of magnitude in spatial scales, from parsecs to tens of megaparsecs. LEM will spend approximately 11% of its five-year prime science mission performing an All-Sky Survey, the first all-sky X-ray survey at high spectral resolution. The remainder of the five-year science mission will be divided between directed science (30%) and competed General Observer science (70%). LEM and the NewAthena/XIFU are highly complementary, with LEM’s optimization for soft X-rays, large FOV, 1.3 eV spectral resolution, and large grasp balancing the NewAthena/X-IFU’s broadband sensitivity, large effective area, and unprecedented spectral resolving power at 6 keV. In this presentation, we will provide an overview of the mission architecture, the directed science driving the mission design, and the broad scope these capabilities offer to the entire astrophysics community.
In the 2020 Astrophysics Decadal Survey, the National Academies identified cosmic feedback and structure formation as a key question that should drive research in the upcoming decade. In response to this recommendation, NASA released a call for X-ray and IR probe-class missions, with a $1B cost cap. The line emission mapper (LEM) is a mission concept designed in response to this call. LEM is a single-instrument X-ray telescope that consists of a Wolter–Schwarzschild type I X-ray optic with a 4 m focal length, coupled with an X-ray microcalorimeter with a 30′ field of view (FoV), 15″ angular resolution, and 2.5 eV energy resolution [full-width half maximum (FWHM)], with a 1.3 eV FWHM energy resolution central subarray. The high throughput X-ray mirror combined with the large FoV and excellent energy resolution allows for efficient mapping of extended emission-line dominated astrophysical objects from megaparsecs to sub-pc scales to study cosmic ecosystems and unveil the physical drivers of galaxy formation.
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