Karen Gelmis

Bio: Karen Gelmis is an academic researcher from Marshall Space Flight Center. The author has contributed to research in topics: Observatory & Gamma-ray burst. The author has an hindex of 4, co-authored 5 publications receiving 174 citations.

Lynx X-Ray Observatory: an overview

Abstract: Lynx, one of the four strategic mission concepts under study for the 2020 Astrophysics Decadal Survey, provides leaps in capability over previous and planned x-ray missions and provides synergistic observations in the 2030s to a multitude of space- and ground-based observatories across all wavelengths. Lynx provides orders of magnitude improvement in sensitivity, on-axis subarcsecond imaging with arcsecond angular resolution over a large field of view, and high-resolution spectroscopy for point-like and extended sources in the 0.2- to 10-keV range. The Lynx architecture enables a broad range of unique and compelling science to be carried out mainly through a General Observer Program. This program is envisioned to include detecting the very first seed black holes, revealing the high-energy drivers of galaxy formation and evolution, and characterizing the mechanisms that govern stellar evolution and stellar ecosystems. The Lynx optics and science instruments are carefully designed to optimize the science capability and, when combined, form an exciting architecture that utilizes relatively mature technologies for a cost that is compatible with the projected NASA Astrophysics budget.

The Lynx X-Ray Observatory: Concept Study Overview and Status

Abstract: Lynx, one of four strategic mission concepts under study for the 2020 Astrophysics Decadal Survey, will provide leaps in capability over previous and planned X-ray missions, and will provide synergistic observations in the 2030s to a multitude of space- and ground-based observatories across all wavelengths. Lynx will have orders of magnitude improvement in sensitivity, on-axis sub-arcsecond imaging with arcsecond angular resolution over a large field of view, and high-resolution spectroscopy for point-like and extended sources. The Lynx architecture enables a broad range of unique and compelling science, to be carried out mainly through a General Observer Program. This Program is envisioned to include detecting the very first supermassive black holes, revealing the high-energy drivers of galaxy and structure formation, characterizing the mechanisms that govern stellar activity - including effects on planet habitability, and exploring the highest redshift galaxy clusters. An overview and status of the Lynx concept are summarized.

Lynx Mission Concept Status

Abstract: Lynx is a concept under study for prioritization in the 2020 Astrophysics Decadal Survey. Providing orders of magnitude increase in sensitivity over Chandra, Lynx will examine the first black holes and their galaxies, map the large-scale structure and galactic halos, and shed new light on the environments of young stars and their planetary systems. In order to meet the Lynx science goals, the telescope consists of a high-angular resolution optical assembly complemented by an instrument suite that may include a High Definition X-ray Imager, X-ray Microcalorimeter and an X-ray Grating Spectrometer. The telescope is integrated onto the spacecraft to form a comprehensive observatory concept. Progress on the formulation of the Lynx telescope and observatory configuration is reported in this paper.

The Lynx X-ray Observatory: revealing the invisible universe

Abstract: We have been studying Lynx, an X-ray Observatory with factors of 10 to 1000 greater imaging and spectroscopic capabilities than any other existing or planned facility. We present a Design Reference Mission (DRM) driven by the need to solve fundamental problems in three broad areas of astrophysics. The Lynx Observatory will provide discovery space for all of astrophysics, and also address questions which will only be revealed as our knowledge increases. Studies supported by the Advanced Concepts Office at MSFC for the observatory design and operations take advantage of the highly successful architecture of the Chandra Observatory. A light-weight mirror with 30 times the Chandra effective area, and modern microcalorimeter and CMOS based X-ray imagers will exploit the 0.5 arcsec imaging capability. Operating at Sun/Earth L2, we expect 85% to 90% of the time to be spent acquiring data from celestial targets. Designed for a five year baseline mission, there are no expected impediments to achieving a 20 year goal. This paper presents technical details of the Observatory and highlights of the mission operations.

The LargE Area burst Polarimeter (LEAP) – A NASA mission of opportunity for the ISS

Abstract: The LargE Area Burst Polarimeter (LEAP) will radically improve our understanding of some of the most energetic phenomena in our Universe by exposing the underlying physics that governs astrophysical jets and the extreme environment surrounding newborn compact objects. LEAP will do this by making the highest fidelity polarization measurements to date of the prompt gamma-ray emission from a large sample of Gamma-Ray Bursts (GRBs). The science objectives are met with a single instrument deployed as an external payload on the ISS – a wide FOV Compton polarimeter that measures GRB polarization from 50–500 keV and GRB spectra from ~10 keV to 5 MeV. LEAP measures polarization using seven independent polarimeter modules, each with a 12x12 array of optically isolated high-Z and low-Z scintillation detectors readout by individual PMTs. LEAP is one of two NASA Missions of Opportunity proposals that are currently in a Phase A Concept Study, with a final selection due later this year.

The Physics of Galaxy Cluster Outskirts

Abstract: As the largest virialized structures in the universe, galaxy clusters continue to grow and accrete matter from the cosmic web. Due to the low gas density in the outskirts of clusters, measurements are very challenging, requiring extremely sensitive telescopes across the entire electromagnetic spectrum. Observations using X-rays, the Sunyaev–Zeldovich effect, and weak lensing and galaxy distributions from the optical band, have over the last decade helped to unravel this exciting new frontier of cluster astrophysics, where the infall and virialization of matter takes place. Here, we review the current state of the art in our observational and theoretical understanding of cluster outskirts, and discuss future prospects for exploration using newly planned and proposed observatories.

Astrophysics with the Laser Interferometer Space Antenna

Abstract: The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA's first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultracompact stellar-mass binaries, massive black hole binaries, and extreme or intermediate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.

Unveiling the gravitational universe at μ-Hz frequencies

Abstract: We propose a space-based interferometer surveying the gravitational wave (GW) sky in the milli-Hz to μ-Hz frequency range. By the 2040s, the μ-Hz frequency band, bracketed in between the Laser Interferometer Space Antenna (LISA) and pulsar timing arrays, will constitute the largest gap in the coverage of the astrophysically relevant GW spectrum. Yet many outstanding questions related to astrophysics and cosmology are best answered by GW observations in this band. We show that a μ-Hz GW detector will be a truly overarching observatory for the scientific community at large, greatly extending the potential of LISA. Conceived to detect massive black hole binaries from their early inspiral with high signal-to-noise ratio, and low-frequency stellar binaries in the Galaxy, this instrument will be a cornerstone for multimessenger astronomy from the solar neighbourhood to the high-redshift Universe.

Constraining Gas Motions in the Intra-Cluster Medium

Abstract: The detailed velocity structure of the diffuse X-ray emitting intra-cluster medium (ICM) remains one of the last missing key ingredients in understanding the microphysical properties of these hot baryons and constraining our models of the growth and evolution of structure on the largest scales in the Universe. Direct measurements of the gas velocities from the widths and shifts of X-ray emission lines were recently provided for the central region of the Perseus Cluster of galaxies by Hitomi, and upcoming high-resolution X-ray microcalorimeters onboard XRISM and Athena are expected to extend these studies to many more systems. In the mean time, several other direct and indirect methods have been proposed for estimating the velocity structure in the ICM, ranging from resonant scattering to X-ray surface brightness fluctuation analysis, the kinematic Sunyaev-Zeldovich effect, or using optical line emitting nebulae in the brightest cluster galaxies as tracers of the motions of the ambient plasma. Here, we review and compare the existing estimates of the velocities of the hot baryons, as well as the various overlapping physical processes that drive motions in the ICM, and discuss the implications of these measurements for constraining the viscosity and identifying the source of turbulence in clusters of galaxies.

Illuminating the dark ages: cosmic backgrounds from accretion onto primordial black hole dark matter

Abstract: Cold dark matter as the sum of different mass Primordial Black Holes (PBH) can explain a number of unsolved astrophysical mysteries. Here I assume a broad PBH mass distribution providing the bulk of the dark matter, consistent with all constraints and estimate the baryon accretion onto PBH contributing to cosmic background radiations, mainly the correlation signal between the Cosmic X-ray and the Cosmic infrared background fluctuations in deep Chandra and Spitzer surveys. I assume Bondi capture and advection dominated disk accretion with reasonable baryon densities and effective relative velocities between baryons and PBH, as well as appropriate accretion and radiation efficiencies, and integrate over the PBH mass spectrum and cosmic time. The X-ray contribution is indeed consistent with the residual X-ray background signal and the X-ray/infrared fluctuations. The flux peaks at z~17-30, consistent with constraints requiring the signal to come from high redshifts. The PBH contribution to the infrared background fluctuations is only about 1%. Magnetic fields are an essential ingredient in the Bondi capture process, and PBH can play a role in amplifying early seed fields and maintaining them until the galactic dynamo processes set in. The contribution of the assumed PBH population to the re-ionization history of the universe does not conflict with the Planck ionization limits. X-ray heating from PBH can provide a contribution to the entropy floor in groups of galaxies. The tantalizing EDGES redshifted 21-cm absorption line feature can be connected to the radio contribution to the cosmic background radiation. Finally, the number of intermediate-mass black holes and the diffuse X-ray emission in the Galactic Center are consistent with the assumed PBH dark matter. Some of the discrete sources in the deepest Chandra observations of the Galactic Ridge could indeed be accreting PBH.