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In an effort to measure electron-impact ionization (EII) cross-sections of He-like Fe24+ at the electron beam ion trap (EBIT) facility of the National Institute of Standards and Technology (NIST), we have experimentally determined the corrections to the nominal beam energy determined by the voltages applied to the EBIT. High-resolution X-ray spectra were recorded at nominal electron beam energies between 6660 eV and 6750 eV using X-ray microcalorimetry based upon an array of 192 transition-edge sensors (TES). A large-scale collisional-radiative simulation of the non-Maxwellian EBIT plasma using relevant atomic data calculated with Flexible Atomic Code allowed us to determine the space-charge correction due to the electron beam including the neutralization factor by the ion cloud of the EBIT.

W49B is a unique Galactic supernova remnant with centrally peaked, “bar”-like ejecta distribution, which was once considered evidence for a hypernova origin that resulted in a bipolar ejection of the stellar core. However, chemical abundance measurements contradict this interpretation. Closely connected to the morphology of the ejecta is its velocity distribution, which provides critical details for understanding the explosion mechanism. We report the first ever observational constraint on the kinematics of the ejecta in W49B using the Resolve microcalorimeter spectrometer on the X-ray Imaging and Spectroscopy Mission (XRISM). Using XRISM/Resolve, we measured the line-of-sight velocity traced by the Fe Heα emission, which is the brightest feature in the Resolve spectrum, to vary by ±300 km s−1 with a smooth east-to-west gradient of a few tens of kilometers per second per parsec along the major axis. Similar trends in the line-of-sight velocity structure were found for other Fe-group elements Cr and Mn, traced by the Heα emission, and also for intermediate-mass elements Si, S, Ar, and Ca, traced by the Lyα emission. The discovery of the east–west gradient in the line-of-sight velocity, together with the absence of a twin-peaked line profile or enhanced broadening in the central region, clearly rejects the equatorially expanding disk model. In contrast, the observed velocity structure suggests bipolar flows reminiscent of a bipolar explosion scenario. An alternative scenario would be a collimation of the ejecta by an elongated cavity sculpted by bipolar stellar winds.

There are extensive negative generationally perpetuating consequences related to high school dropout including economic, health, relationship, parenting, criminal justice, community engagement, tax revenue, and public welfare effects which disproportionately impact minority groups. In 2007 the New Hampshire legislature enacted Senate Bill 18, a statewide dropout prevention measure which effectively raised the compulsory school attendance age from 16 to 18 and created alternative learning plans for students who would otherwise drop out. The purpose of this study was to explore the efficacy of that policy change, using a Theory of Change to compare measurable outcomes with the intentions of policymakers who worked to enact the change. Empirical evidence indicated that raising the compulsory school attendance age had mixed and sometimes ambiguous results that could lead to either increasing or decreasing dropout rates. This study found that raising the compulsory school attendance age in New Hampshire did not have much effect on dropout and completion rates, as state data reports demonstrated these rates were already improving before passage and implementation of SB18(2007) and continued to do so at analogous rates afterward. A survey of school districts revealed that many districts are offering a wide range of dropout prevention services and programs.

Driven by the recent detection of an unidentified emission line previously reported at 3.55-3.57 keV in a stacked spectrum of galaxy clusters, in this work we investigated the resonant dielectronic recombination (DR) process in Li-like Ar as a possible source of, or contributor to, the emission line. The Li-like transition 1s22l-1s2l3l’ was suggested to produce a 3.62 keV photon [1] near the unidentified line at 3.57 keV and was the primary focus of our study. The Electron Beam Ion Trap at NIST was used to produce and trap the highly-charged ions of argon. The energy of the quasi-monoenergetic electron beam was incremented in steps of 15 eV to scan over all of the Li-like Ar DR resonances. A Johann-type crystal spectrometer and a solid-state germanium detector were used to take x-ray measurements perpendicular to the electron beam. Our broadband results allowed us to identify the processes that produced specific spectral features, while our high-resolution spectra allowed the experimental separation of features that are less than 2 eV apart. We have used the collisional radiative model NOMAD [2] aided by atomic data calculations by FAC [3] to interpret our observations and account for corrections. Experimental results were compared to the atomic database AtomDB, used to fit the galaxy cluster spectra. We found a number of measured features due to DR in lower charge state Ar ions not included in the database, close in energy to the identified line at 3.57 keV, and suggest their inclusion for improved interpretation and diagnosis of other astrophysical spectra.

In an effort to measure electron-impact ionization (EII) cross-sections of He-like Fe[sup.24+] at the electron beam ion trap (EBIT) facility of the National Institute of Standards and Technology (NIST), we have experimentally determined the corrections to the nominal beam energy determined by the voltages applied to the EBIT. High-resolution X-ray spectra were recorded at nominal electron beam energies between 6660 eV and 6750 eV using X-ray microcalorimetry based upon an array of 192 transition-edge sensors (TES). A large-scale collisional-radiative simulation of the non-Maxwellian EBIT plasma using relevant atomic data calculated with Flexible Atomic Code allowed us to determine the space-charge correction due to the electron beam including the neutralization factor by the ion cloud of the EBIT.

Astrophysics is a broad and dynamic field that has led to an ever increasing number of incredible discoveries. Just in the past decade or so astrophysicists have detected gravitational waves (and the electromagnetic counterpart) from a neutron star merger, imaged a black hole for the first time, discovered thousands of new planets orbiting stars, and have shown that the expansion of the Universe is accelerating. Many of these discoveries come from new facilities with advanced technologies, an increase in computational capabilities, and creative new analytical techniques. These continued improvements have led to higher quality data that often reveals that our understanding of the processes responsible for the observations is far from complete. It is the field of laboratory astrophysics (experimental and theoretical) that aims to advance our understanding of the underlying processes for more reliable interpretations of astrophysical observations. With this motivation in mind, this work first describes the electron beam ion trap (EBIT), a facility well suited for systematic atomic studies. The EBIT has a nearly mono-energetic electron beam and allows for the injection of a variety of species, including astrophysically relevant elements such as Fe or Ar. Since ions are present almost everywhere in the Universe, and are responsible for much of the measured emission, it is important to note that the tunable electron beam energy can reach up to about 30 keV and is capable of producing basically all charge states of astrophysically relevant elements. The narrow electron beam energy profile allows the user to select the charge state and to an extent the excited state, and is well suited for systematic studies. The EBIT contains a series of electrodes used to manipulate the electron beam and electrostatically trap the ions. The space charge of the electron beam and shape of the trapping electrodes work to radially trap ions. Observation ports are located radially around the trap and are oriented perpendicular to the direction of the electron beam. The non-thermal uni-directional electron beam interacts with stationary ions in the trap. This setup leads to non-statistically populated magnetic sublevels that produce polarized and anisotropic emission, and provides a unique opportunity to study magnetic sublevels which are typically inaccessible in spectroscopic observations. In the second part of this work we take advantage of this capability of the EBIT and report the measurement of the linear polarization of He-like and Li-like Ar transitions. Measurements were taken with two Johann-type crystal spectrometers in different orientations corresponding to the dispersion plane parallel and perpendicular to the electron beam direction. The Li-like transitions result from the resonant dielectronic recombination process while the He-like transitions are produced from electron impact excitation. Our results show a strong positive polarization of the w, j, k, and q transitions (in notation of Gabriel (1972)), and a negative polarization of the a, x, y, and z lines. Since the polarization depends on the magnetic sublevel specific direct excitation or dielectronic capture cross-sections, our results can be used to benchmark different methods used to calculate these cross-sections. In this work we compare measurements with polarization values calculated using the density matrix formalism. For dielectronic recombination, the Flexible Atomic Code (FAC) (Gu 2008) was used to produce the atomic data (Qd values, autoionization energies, and cross-sections) required to calculate the polarization and produce the synthetic spectra. Since measurements were taken at the resonance energy, cascade effects were ignored. For transitions resulting from direct excitation the collisional-radiative model NOMAD (Ralchenko & Maron 2001) was used to solve the system of steady-state rate equations for the magnetic sublevel populations, and included excitation up to n = 5. For both direct excitation and dielectronic recombination the theoretical predictions agree well with measured values. The final part of this work was motivated by an exciting 2014 study (Bulbul et al. 2014) that reported a possible dark matter signature at 3.55 keV - 3.57 keV in the stacked spectra of galaxy clusters. To help rule out possible atomic origins suggested by the authors, we measured Ar emission from 1s^(2)2l-1s2l3l′ satellite transitions near 3.6 keV x-ray energy. X-rays were measured simultaneously with a high count-rate, high-purity Ge detector and a high energy-resolution Johann-type crystal spectrometer. The collisional-radiative model NOMAD was used to create synthetic spectra for comparison with both our EBIT measurements and with spectra produced with the AtomDB database (Foster et al. 2012) and the Astrophysical Plasma Emission Code (APEC) (Smith et al. 2001) used in the 2014 work. Excellent agreement was found between the NOMAD and EBIT spectra at each electron beam energy, providing a high level of confidence in the atomic data used. Comparison of the NOMAD and APEC spectra revealed a number of missing lines at 3.56 keV, 3.62 keV, 3.64 keV, and 3.66 keV in the APEC spectra. These features are primarily due to Be-like Ar DR data missing in the database. At an electron temperature of Te = 1.72 keV, the inclusion of 1s2l2l'2l'' and 1s2l2l'3l'' data in AtomDB increased the total flux in the 3.5 keV to 3.66 keV energy band by a factor of 2. While important, this extra emission is not enough to fully explain the unidentified line found in the galaxy cluster spectra (Gall et al. 2019) leaving the possibility open for dark matter related origin.

Motivated by possible atomic origins of the unidentified emission line detected at 3.55 keV to 3.57 keV in a stacked spectrum of galaxy clusters (Bulbul et al. 2014), an electron beam ion trap (EBIT) was used to investigate the resonant dielectronic recombination (DR) process in highly-charged argon ions as a possible contributor to the emission feature. The He-like Ar DR-induced transition 1s\\(^2\\)2l - 1s2l3l\\(^\\) was suggested to produce a 3.62 keV photon (Bulbul et al. 2014) near the unidentified line at 3.57 keV and was the starting point of our investigation. The collisional-radiative model NOMAD was used to create synthetic spectra for comparison with both our EBIT measurements and with spectra produced with the AtomDB database/Astrophysical Plasma Emission Code (APEC) used in the Bulbul et al. (2014) work. Excellent agreement was found between the NOMAD and EBIT spectra, providing a high level of confidence in the atomic data used. Comparison of the NOMAD and APEC spectra revealed a number of missing features in the AtomDB database near the unidentified line. At an electron temperature of \\(T_e\\) = 1.72 keV, the inclusion of the missing lines in AtomDB increases the total flux in the 3.5 keV to 3.66 keV energy band by a factor of 2. While important, this extra emission is not enough to explain the unidentified line found in the galaxy cluster spectra.

Astrophysical observations of the cosmos allow us to probe extreme physics and answer foundational questions on our universe. Modern astronomy is increasingly operating under a holistic approach, probing the same question with multiple diagnostics including how sources vary over time, how they appear across the electromagnetic spectrum, and through their other signatures, including gravitational waves, neutrinos, cosmic rays, and dust on Earth. Astrophysical observations are now reaching the point where approximate physics models are insufficient. Key sources of interest are explosive transients, whose understanding requires multidisciplinary studies at the intersection of astrophysics, gravity, nuclear science, plasma physics, fluid dynamics and turbulence, computation, particle physics, atomic, molecular, and optical science, condensed matter and materials science, radiation transport, and high energy density physics. This white paper provides an overview of the major scientific advances that lay at the intersection of physics and astronomy and are best probed through time-domain and multimessenger astrophysics, an exploration of how multidisciplinary science can be fostered, and introductory descriptions of the relevant scientific disciplines and key astrophysical sources of interest.

Gall interviews author Mattilda Bernstein Sycamore about her 2020 book, The Freezer Door. Sycamore mentions \"When I start writing a new book, I am not thinking about what I'm doing. I just write and write, and I don't take a look at the whole thing until I have a sense that I might have arrived somewhere I never know where exactly, but a place where the text might reveal something surprising. Then I basically just cut and rearrange and cut and rearrange and cut a really neurotic editor. In the case of The Freezer Door, I probably wrote for a couple years before I thought of it as a potential manuscript. It was an absurd amount of text, something like a thousand pages, and I don't consider that type of thing a draft, I consider it the material. I wrote it all in one continuous document at first, but as I edited, it became way more fragmented. I wasn't imposing any kind of structure. It's structured by feeling, and the breaks in the text are where there is a break in feeling, when the text can no longer hold especially the parts that just break entirely and become a conversation between an ice cube and ice cube tray. (laughter) That narrative first starts after the line, I don't understand why nothing heals; The feeling that one cannot exist in the world breaks the text, and the page ends there. The narrative switches to an ice cube and an ice cube tray who are in a relationship and trying to negotiate their intimacy. For me those sections function as an opening into a different way to feel. It's funny, because I consider the book nonfiction. But is that nonfiction?\"