80 research outputs found
Design of Optical/IR Blocking Filters for the Lynx X-Ray Microcalorimeter
The Lynx mission concept, under development ahead of the 2020 Astrophysics Decadal Review, includes the Lynx X-ray Microcalorimeter (LXM) as one of its primary instruments. The LXM uses a microcalorimeter array at the focus of a high-throughput soft x-ray telescope to enable high-resolution nondispersive spectroscopy in the soft x-ray waveband (0.2 to 15 keV) with exquisite angular resolution. Similar to other x-ray microcalorimeters, the LXM uses a set of blocking filters mounted within the dewar that pass the photons of interest (x-rays) while attenuating the out-of-band long-wavelength radiation. Such filters have been successfully used on previous orbital and suborbital instruments; however, the Lynx science objectives, which emphasize observations in the soft x-ray band (<1keV), pose more challenging requirements on the set of LXM blocking filters. We present an introduction to the design of the LXM optical/IR blocking filters and discuss recent advances in filter capability targeted at LXM. In addition, we briefly describe the external filters and the modulated x-ray sources to be used for onboard detector calibration
Proximity Effects and Nonequilibrium Superconductivity in Transition-Edge Sensors
We have recently shown that normal-metal/superconductor (N/S) bilayer TESs
(superconducting Transition-Edge Sensors) exhibit weak-link behavior.1 Here we
extend our understanding to include TESs with added noise-mitigating
normal-metal structures (N structures). We find TESs with added Au structures
also exhibit weak-link behavior as evidenced by exponential temperature
dependence of the critical current and Josephson-like oscillations of the
critical current with applied magnetic field. We explain our results in terms
of an effect converse to the longitudinal proximity effect (LoPE)1, the lateral
inverse proximity effect (LaiPE), for which the order parameter in the N/S
bilayer is reduced due to the neighboring N structures. Resistance and critical
current measurements are presented as a function of temperature and magnetic
field taken on square Mo/Au bilayer TESs with lengths ranging from 8 to 130
{\mu}m with and without added N structures. We observe the inverse proximity
effect on the bilayer over in-plane distances many tens of microns and find the
transition shifts to lower temperatures scale approximately as the inverse
square of the in- plane N-structure separation distance, without appreciable
broadening of the transition width. We also present evidence for nonequilbrium
superconductivity and estimate a quasiparticle lifetime of 1.8 \times 10-10 s
for the bilayer. The LoPE model is also used to explain the increased
conductivity at temperatures above the bilayer's steep resistive transition.Comment: 10 pages, 8 figure
A Galaxy at z = 6.545 and Constraints on the Epoch of Reionization
We report the discovery of a Lyman-alpha-emitting galaxy at redshift z=6.545
serendipitously identified in the course of spectroscopic follow-up of hard
X-ray sources on behalf of the Serendipitous Extragalactic X-Ray Source
Identification (SEXSI) survey. The line flux of the galaxy, 2.1e-17 erg/cm2/s,
is similar to line fluxes probed by narrow-band imaging surveys; the 5.2
square-arcminutes surveyed implies a surface density of z~6.5 Lyman-alpha
emitters somewhat higher than that inferred from narrow-band surveys. This
source marks the sixth Lyman-alpha-emitting galaxy identified at z~6.5, a
redshift putatively beyond the epoch of reionization when the damping wings of
the neutral hydrogen of the intergalactic medium is capable of severely
attenuating Lyman-alpha emission. By comparing the Lyman-alpha emitter
luminosity functions at z~5.7 and z~6.5, we infer that the intergalactic medium
may remain largely reionized from the local universe out to z~6.5.Comment: 16 pages, 4 figures; submitted to the Astrophysical Journa
A High Spectral Resolution Study of the Soft X-ray Background with the X-ray Quantum Calorimeter
We present here a combined analysis of four high spectral resolution
observations of the Diffuse X-ray Background (DXRB), made using the University
of Wisconsin-Madison/Goddard Space Flight Center X-ray Quantum Calorimeter
(XQC) sounding rocket payload. The observed spectra support the existence of a
keV Local Hot Bubble and a keV Hot Halo, with discrepancies
between repeated observations compatible with expected contributions of
time-variable emission from Solar Wind Charge Exchange (SWCX). An additional
component of keV emission observed only at low galactic latitudes can
be consistently explained by unresolved dM stars.Comment: 21 pages, 6 figures, accepted for publication in Ap
The Serendipitous Extragalactic X-Ray Source Identification (SEXSI) Program. III. Optical Spectroscopy
We present the catalog of 477 spectra from the Serendipitous Extragalactic
X-ray Source Identification (SEXSI) program, a survey designed to probe the
dominant contributors to the 2-10 keV cosmic X-ray background. Our survey
covers 1 deg^2 of sky to 2-10 keV fluxes of 10^-14 erg cm^-2 s^-1, and 2 deg^2
for fluxes of 3 x 10^-14 erg cm^-2 s^-1. Our spectra reach to R <24 and have
produced redshifts for 438 hard X-ray sources. The vast majority of the 2-10
keV-selected sample are AGN with redshifts between 0.1 and 3. We find that few
sources at z<1 have high X-ray luminosities, reflecting a dearth of high-mass,
high-accretion-rate sources at low redshift, a result consistent with other
recent wide-area surveys. Half of our sources show significant obscuration,
with N_H>10^22 cm^-2, independent of unobscured luminosity. We classify 168
sources as emission-line galaxies; all are X-ray luminous objects with optical
spectra lacking both high-ionization lines and evidence of a non-stellar
continuum. The redshift distribution of these emission-line galaxies peaks at a
significantly lower redshift than does that of the sources we spectroscopically
identify as AGN. We conclude that few of these sources can be powered by
starburst activity. Stacking spectra for a subset of these sources, we detect
[Ne V] emission, a clear signature of AGN activity, confirming that the
majority of these objects are Seyfert 2s in which the high-ionization lines are
diluted by stellar emission. We find 33 objects lacking broad lines in their
optical spectra which have quasar X-ray luminosities (Lx>10^44 erg s^-1), the
largest sample of such objects identified to date. In addition, we explore 17
AGN associated with galaxy clusters and find that the cluster-member AGN sample
has a lower fraction of broad-line AGN than does the background sample.Comment: Accepted to ApJ; 57 pages, 25 figures, 5 table
Multiabsorber Transition-Edge Sensors for X-Ray Astronomy
We are developing arrays of position-sensitive microcalorimeters for future x-ray astronomy applications. These position-sensitive devices commonly referred to as hydras consist of multiple x-ray absorbers, each with a different thermal coupling to a single-transition-edge sensor microcalorimeter. Their development is motivated by a desire to achieve very large pixel arrays with some modest compromise in performance. We report on the design, optimization, and first results from devices with small pitch pixels (<75 m) being developed for a high-angular and energy resolution imaging spectrometer for Lynx. The Lynx x-ray space telescope is a flagship mission concept under study for the National Academy of Science 2020 decadal survey. Broadband full-width-half-maximum (FWHM) resolution measurements on a 9-pixel hydra have demonstrated E(FWHM) = 2.23 0.14 eV at Al-K, E(FWHM) = 2.44 0.29 eV at Mn-K, and E(FWHM) = 3.39 0.23 eV at Cu-K. Position discrimination is demonstrated to energies below <1 keV and the device performance is well-described by a finite-element model. Results from a prototype 20-pixel hydra with absorbers on a 50-m pitch have shown E(FWHM) = 3.38 0.20 eV at Cr-K1. We are now optimizing designs specifically for Lynx and extending the number of absorbers up to 25/hydra. Numerical simulation suggests optimized designs could achieve 3 eV while being compatible with the bandwidth requirements of the state-of-the art multiplexed readout schemes, thus making a 100,000 pixel microcalorimeter instrument a realistic goal
- …