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.
The Line Emission Mapper X-ray Probe-class mission concept is based on a microcalorimeter array tuned to energies in the range 0.1 to 2 keV. The study of cosmic ecosystems defines the directed portion of the Line Emission Mapper (LEM) mission, thus LEM has been optimized for observations of diffuse X-ray-emitting gas, largely with very low surface brightness. To broaden the range of targets that general observers can study with LEM, we have investigated the particular needs for UV/optical bright stars and solar-system objects. X-ray microcalorimeters are susceptible to degraded energy resolution that can result from thermal noise from residual UV, optical, and IR radiation. Using the present baseline design of the microcalorimeter thermal filters, we compute the UV-IR loading expected from bright stars over the effective temperature range 3500 to 39,000 K and from solar-system objects. The dominant leak of out-of-band energy is in the far-UV around 1500 Å, with a secondary peak of throughput around 4000 Å. For stars with magnitudes V<10 and for all solar-system planets as well as the Moon, the loading is significant, indicating that additional UV/optical blocking is essential if bright objects are to be observed. We have investigated the efficacy of several filter options for optical-blocking filters on the LEM filter wheel, demonstrating that new technology development is not necessary to open up many of these classes of objects to investigation with the high spectral resolution of LEM.
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.
The line emission mapper (LEM) is a probe-class mission concept that is designed to detect x-ray emission lines from hot ionized gas (T > 106 K) that will enable us to test galaxy evolution theories. It will permit us to study the effects of stellar and black-hole feedback and flows of baryonic matter into and out of galaxies. The key to being able to study the hot gases that are otherwise invisible to current imaging x-ray spectrometers is that the energy resolution is sufficient to use cosmological redshift to separate extragalactic source lines from foreground Milky Way emission. LEM incorporates a large-format microcalorimeter array instrument called the LEM microcalorimeter spectrometer (LMS) with a light-weight x-ray optic with 10” half power diameter angular resolution. The LMS microcalorimeter array has pixels with 15″ pixel pitch over a 33′ field of view (FOV) optimized for the 0.3 to 2 keV energy band. The central 7′ region of the array has an energy resolution of 1.3 eV at 1 keV and the rest of the FOV has 2.5 eV energy resolution at 1 keV. The array will be read out with state-of-the-art time-division multiplexing. We present an overview of the LMS instrument, including details of the entire detection chain, the focal plane assembly, as well as the cooling system and overall mechanical and thermal design. For each of the key technologies, we discuss the current technology readiness level and the plan to advance them to be ready for flight. We also describe the current system design and our estimate for the mass, power, and data rate of the instrument. The design details presented concentrate primarily on the unique aspects of the LMS design compared with prior missions and confirm that the type of microcalorimeter instrument needed for LEM is not only feasible but also technically mature.
We summarize nearly two decades of successful operation of the Chandra High Resolution Camera (HRC). The HRC is a pair of cesium–iodide (CsI) coated microchannel plate X-ray detectors launched in July, 1999, one optimized for widefield imaging (HRC-I) and a second as a readout for X-ray transmission gratings (HRC-S). We discuss the temporal evolution of the performance of the flight instrument, the impact of extended exposure to the charged particle environment of high Earth orbit, and lessons learned from nineteen years of flight operations. We also describe our investigation of new algorithms to remove more efficiently the charged particle background from the science data, as we prepare for another decade of operation.
The Extreme Physics Explorer (EPE) is a concept timing/spectroscopy mission that would use micro-channel plate
optics (MCPO) to provide 4m2 effective area focused to ~1 arc-min onto an X-ray calorimeter. We describe science
drivers for such a mission, possible designs for the large area MCPO needed for EPE, and the challenges of the large
area MCPO design.
The International X-ray Observatory (IXO) has a top level requirement that the observing efficiency be 85%. This is a
challenging requirement, given that the observing efficiencies for CXO and XMM-Newton are between 60% and 70%.
However, the L2 orbit for IXO means that it will not be subject to the earth block/radiation zone effects that are seen for
CXO and XMM-Newton. Outside of these effects the efficiencies for CXO and XMM-Newton do approach 85%, so
this requirement appears achievable for IXO. In this paper we itemize the effects which impact the observing efficiency,
in order to guide the design of the observatory. Meeting the 85% requirement should be possible but will require careful
attention to detail.
The High Resolution Camera (HRC) is one of two focal plane instruments on the NASA Chandra X-ray Observatory which was successfully launched on July 23, 1999. The Chandra X-ray Observatory was designed to perform high resolution spectroscopy and imaging in the X-ray band of 0.07 to 10 keV. The HRC instrument consists of two detectors, HRC-I for imaging and HRC-S for spectroscopy. Each HRC detector consists of a thin aluminized polyimide blocking filter, a chevron pair of microchannel plates and a crossed grid charge readout. The HRC-I is an approximately 100 X 100 mm detector optimized for high resolution imaging and timing, the HRC-S is an approximately 20 X 300 detector optimized to function as the readout for the Low Energy Transmission Grating. In this paper we discuss the in-flight performance of the HRC-S, and present preliminary analysis of flight calibration data and compare it with the results of the ground calibration and pre-flight predictions. In particular we will compare ground data and in-flight data on detector background, quantum efficiency, spatial resolution, pulse height resolution, and point spread response function.
In this paper we present and compare flight results with the latest results of the ground calibration for the HRC-I detector. In particular we will compare ground and in flight data on detector background, effective area, quantum efficiency and point spread response function.
The Advanced X-Ray Astrophysics Facility High Resolution Camera was calibrated at NASA's X-Ray Calibration Facility during March and April 1997. We have undertaken an analysis of the effective area of the combined High Resolution Mirror Assembly/High Resolution Camera using all data presently available from these tests. In this contribution we discuss our spectral fitting of the beam-normalization detectors, our method of removing higher order contamination lines present in the spectra, and the corrections for beam non- uniformities. Using an approach based upon the mass absorption cross-section of Cesium Iodide, we determine the quantum efficiency in the microchannel plates. We model the secondary electron absorption depth as a function of energy, which we expect to be relatively smooth. This is then combined with the most recent model of the telescope to determine the ensemble effective area for the HRC. The ensemble effective area is a product of the telescope effective are, the transmission of the UV-Ion shield, and the quantum efficiency of the microchannel plates. We focus our attention on the microchannel plate quantum efficiency, using previous result for the UV-Ion shield transmission and telescope effective area. We also address future goals and concerns.
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