The digital frequency-domain multiplexing technique is widely used for astrophysical instruments with large detector arrays. Detailed detector characterization is required for instrument calibration and systematics control. We conduct the TES complex electrothermal-feedback response measurement with the DfMux readout system as follows. By injecting a single sideband signal, we induce modulation in TES power dissipation over a frequency range encompassing the detector response. The modulated current signal induced by TES heating effect is measured, allowing for the ETF response characterization of the detector. With the injection of an upper sideband, the TES readout current shows both an upper and a lower sideband. We model the upper and lower sideband complex ETF response and verify the model by fitting to experimental data. The model not only can fit for certain physical parameters of the detector, such as loop gain, temperature sensitivity, current sensitivity, and time constant, but also enables us to estimate the systematic effect introduced by the multiplexed readout. The method is therefore useful for in situ detector calibration and for estimating systematic effects during astronomical telescope observations, such as those performed by the upcoming LiteBIRD satellite.

Astrophysical emission lines arising from particle decays can offer unique insights into the nature of dark matter (DM). Using dedicated simulations with background and foreground modeling, we comprehensively demonstrate that the recently launched X-Ray Imaging and Spectroscopy Mission (XRISM) space telescope with powerful X-ray spectroscopy capabilities is particularly well suited to probe decaying DM, such as sterile neutrinos and axion-like particles, in the mass range of a few to tens of keV. We analyze and map XRISM's DM discovery potential parameter space by considering the Milky Way Galactic DM halo, including establishing an optimal line-of-sight search, as well as dwarf galaxies, where we identify Segue 1 as a remarkably promising target. We demonstrate that with only 100 ks exposure, the XRISM/Resolve instrument is capable of probing the underexplored DM parameter window around a few keV and testing DM couplings with a sensitivity that exceeds by two orders existing Segue 1 limits. Further, we demonstrate that XRISM/Xtend instrument sensitivity enables discovery of the nature of faint astrophysical X-ray sources, especially in Segue 1, which could shed light on star formation history. We discuss implications for decaying DM searches with improved detector energy resolution in future experiments.

We report the discovery of a geocoronal solar wind charge exchange (SWCX) event corresponding to the well-known 2006 December 13th coronal mass ejection (CME) event. Strong evidence for the charge exchange origin of this transient diffuse emission is provided by prominent non-thermal emission lines at energies of O7+, Ne9+, Mg11+, Si12+, Si13+. Especially, a 0.53 keV emission line that most likely arises from the N5+ 1s15p1 -> 1s2 transition is detected. Previously, the forecastability of SWCX occurrence with proton flares has been disputed. In this particular event, we found that the SWCX signal coincided with the arrival of the magnetic cloud inside CME, triggered with a time delay after the proton flux fluctuation as the CME shock front passed through the Earth. Moreover, a spacecraft orbital modulation in SWCX light curve suggests that the emission arises close to the Earth. The line of sight was found to always pass through the northern magnetospheric cusp. The SWCX intensity was high when the line of sight passed the dusk side of the cusp, suggesting an azimuthal anisotropy in the flow of solar-wind ions inside the cusp. An axisymmetric SWCX emission model is found to underestimate the observed peak intensity by a factor of about 50. We suggest this discrepancy is related to the azimuthal anisotropy of the solar-wind flow in the cusp. We discovered compelling observational evidence of the coronal mass ejection (CME) interacting with Earth's magnetosphere by the Suzaku satellite. The signal arises from a process called charge exchange, in which heavily charged ions within the CME interact with neutral hydrogen within Earth's magnetosphere. This specific process, known as solar wind charge exchange (SWCX), was associated with the CME event occurred on 2006 December 13th during the solar minimum. This event provided us with a unique opportunity to gain insights into the interplanetary consequences of CMEs. Despite a delay relative to the shock wave associated with the CME, the SWCX coincided with the arrival of a magnetic cloud. This suggests that solar wind ions were guided along magnetic field lines into a region near Earth called the cusp, through a process known as magnetic reconnection. Additionally, we observed that SWCX emissions were most pronounced when the satellite's line of sight passed through the dusk region of the cusp. This indicates that the CME ejecta may have followed a path along the Parker spiral-a magnetic field pattern twisted by solar rotation-resulting in the solar wind arriving from a direction distinct from that of the Sun. We discover a solar wind charge exchange event with Suzaku X-ray satellite driven by the 2006-December-13th coronal mass ejectionThe solar wind charge exchange (SWCX) occurrence time coincides with the CME magnetic cloud arrival. It is a useful knowledge in space weather forecastingWe modeled the light curve variation of the SWCX. The result indicates that the solar-wind flow is anisotropic in the cusp

The magnetic-field-dependence critical current Ic(Ha) is measured for the Mo/Au bilayer transition-edge sensors. A model based on a surface barrier delaying the first penetration of magnetic flux into a flat superconducting strip, including both the geometrical and Bean–Livingston barrier, in combination with two Josephson junction models with different characteristic lengths, is found to ubiquitously fit the Ic(Ha) curves of devices with various geometry designs. The bulk penetration depth, London depairing current density, Josephson junction critical current, self-field coupling coefficient, and conditions of the first vortex entry are investigated throughout the superconducting transition. The evidences of Josephson effect are observed in both Fraunhofer interference pattern and Shapiro steps.

Power spectra of spatial fluctuations of X-ray emission may impose constraints on the origins of the emission independent of that from the energy spectra. We generated spatial power spectrum densities (PSDs) of blank X-ray skies observed with the Suzaku X-ray observatory utilizing the modified Delta-variance method. Using the total measured count rate as the diagnostic tool, we found that a model consisting of the sum of two components, one for the unresolved faint point sources and one for the uniform flat-field emission, can represent well the observed PSD in three different energy bands (0.2-0.5, 0.5-2, and 2-10 keV); only an upper limit is obtained for the latter component in 2-10 keV. X-ray counting rates corresponding to the best-fit PSD model functions and diffuse emission fractions were estimated, and we confirmed that the sum of the counting rates of two model components is consistent with those actually observed with the detector for all energy bands. The ratio of the flat-field counting rate to the total in 0.5-2 keV, however, is significantly larger than the diffuse emission fraction estimated from the model fits of energy spectra. We discussed that this discrepancy can be reconciled by systematic effects in the PSD and energy spectrum analyses. The present study demonstrates that the spatial power spectrum analysis is powerful in constraining the origins of the X-ray emission.

The transition-edge sensor (TES) technology is widely applied to X-ray spectroscopy or imaging applications at wavelengths ranging from infrared to sub-mm, with the aim of potentially achieving unprecedented spectral resolution and detection sensitivity. As a critical component of the X-ray microcalorimeter, the TES affects the energy resolution via two main parameters: temperature sensitivity and current sensitivity. Tremendous efforts have been made to fabricate TESs with high temperature sensitivity and low current sensitivity, in order to enhance the energy resolution of the microcalorimeters. However, since the resistance of TESs is a complex function of temperature, current, and magnetic field, it is difficult to optimize the operational point of the detector from the first principle. We conducted an experiment to map the parameter space of a sample of MoAu TESs in the transition phase. The results show that the current sensitivity depends only on the resistance of the TESs, which is in line with the two-fluid model. The figure of merit of energy resolution dependence on the quasiparticle diffusion length has been compared with the prediction of the two-fluid model, which indicates that the time-averaging critical current of phase-slip centers is not a constant throughout the superconducting transition. The magnetic field could potentially enhance the energy resolution by reducing the charge imbalance relaxation time.

Supercritical accretion onto compact objects powers a massive wind that is optically thick and Eddington-limited. If most of the hard X-rays from the central disk are obscured by the wind, the source will display a blackbody-like spectrum with a luminosity scaled with the mass of the compact object. From the Chandra archive of nearby galaxies, we selected a sample of luminous and very soft sources and excluded contaminations from foreground objects and supernova remnants. They are found to be preferentially associated with late-type galaxies. The majority of sources in our sample are either too hot or too luminous to be explained by nuclear burning on the surface of white dwarfs, and are argued to be powered by accretion. The most likely explanation is that they are due to emission from the photosphere of a wind driven by supercritical accretion onto compact objects. Their blackbody luminosity ranges from 10^37 to nearly 10^40 erg/s, indicative of the presence of both neutron stars and stellar-mass black holes. The blackbody luminosity also shows a possible bimodal distribution, albeit at low significance, peaked around the Eddington limit for neutron stars and stellar-mass black holes, respectively. If this can be confirmed, it will be smoking gun evidence that supercritical accretion powers thick winds. Based on a wind model, the inferred mass accretion rate of these objects is around a few hundred times the Eddington rate, suggesting that they may be intermediate between the canonical ultraluminous X-ray sources and SS 433 in terms of the accretion rate.

With the improving energy resolution of transitionedge sensor (TES) based microcalorimeters, performance verification and calibration of these detectors has become increasingly challenging, especially in the energy range below 1 keV where fluorescent atomic X-ray lines have linewidths that are wider than the detector energy resolution and require impractically high statistics to determine the gain and deconvolve the instrumental profile. Better behaved calibration sources such as grating monochromators are too cumbersome for space missions and are difficult to use in the lab. As an alternative, we are exploring the use of pulses of 3 eV optical photons delivered by an optical fiber to generate combs of known energies with known arrival times. Here, we discuss initial results of this technique obtained with 2 eV and 0.7 eV resolution X-ray microcalorimeters. With the 2 eV detector, we have achieved photon number resolution for pulses with mean photon number up to 133 (corresponding to 0.4 keV).

We have specialized astronomical applications for X-ray microcalorimeters with superconducting transition edge sensors (TESs) that require exceptionally good TES performance, but which operate in the small-signal regime. We have therefore begun a program to carefully characterize the entire transition surface of TESs with and without the usual zebra stripes to see if there are reproducible local "sweet spots" where the performance is much better than average. These measurements require precise knowledge of the circuit parameters. Here, we show how the Shapiro effect can be used to precisely calibrate the value of the shunt resistor. We are also investigating the effects of stress and external magnetic fields to better understand reproducibility problems.

Transition-edge sensors (TES) are widely used as sensing elements in X-ray microcalorimeters. Further improvement of their energy resolution hinges on a thorough understanding of the transition surface (as function of temperature, current, and magnetic field) to achieve high sensitivity (α) and low noise (small β), as well as the capability to repeatably fabricate the proximity superconducting/normal metal bilayers with a predictable transition surface. One aspect that is poorly understood is the impact of film stress on the transition. Data from Mo films deposited using e-beam evaporation onto heated substrates, as well as sputtered films, show a strong correlation between film stress and superconducting transition temperature (≈-0.2K/GPa, corresponding to shift of about -0.1 K for a 0.1% change in biaxial strain). However, this correlation is of opposite sign and much larger than one would expect from the pressure dependence of bulk Mo. Furthermore, modifications in fabrication details of the devices, such as membrane perforations and absorber attachment, have been observed to result in large qualitative differences in the transition surface for otherwise identical TES geometry. It seems reasonable to ask whether associated changes in film stress distribution can cause these differences. To shed some light on this issue, we have subjected a bare Mo film as well as Mo/Cu bilayers to in-situ tunable uniaxial stress produced by a piezo-electric stack. Our results indicate that the direct strain induced changes to the transition temperature are rather small (about +0.3 mK for a 0.1% strain change on a Mo film) and consistent in sign and order of magnitude with that derived from the bulk.

We have measured the resistance R(T, I, B ext) of a superconducting transition edge sensor over the entire transition region on a fine scale, producing a 4-dimensional map of the resistance surface. The dimensionless temperature and current sensitivities ( α ≡ ∂ log R / ∂ log T | I and β ≡ ∂ log R / ∂ log I | T ) of the TES resistance have been determined at each point. α and β are closely related to the sensor performance, but show a great deal of complex, large amplitude fine structure over large portions of the surface that is sensitive to the applied magnetic field. We discuss the relation of this structure to the presence of Josephson "weak link" fringes.

Ion mobility spectrometry (IMS) is a key trace detection technique for toxic pollutants and explosives in the atmosphere. Ultraviolet radiation photoionization source is widely used as an ionization source for IMS due to its advantages of high selectivity and non-radioactivity. However, UV-IMS bring problems that UV rays will be launched into the drift tube which will cause secondary ionization and lead to the photoelectric effect of the Faraday disk. So air is often used as working gas to reduce the effective distance of UV rays, but it will limit the application areas of UV-IMS. In this paper, we propose a new structure of curved drift tube, which can avoid abnormally incident UV rays. Furthermore, using curved drift tube may increase the length of drift tube and then improve the resolution of UV-IMS according to previous research. We studied the homogeneity of electric field in the curved drift tube, which determined the performance of UV-IMS. Numerical simulation of electric field in curved drift tube was conducted by SIMION in our study. In addition, modeling method and homogeneity standard for electric field were also presented. The influences of key parameters include radius of gyration, gap between electrode as well as inner diameter of curved drift tube, on the homogeneity of electric field were researched and some useful laws were summarized. Finally, an optimized curved drift tube is designed to achieve homogenous drift electric field. There is more than 98.75% of the region inside the curved drift tube where the fluctuation of the electric field strength along the radial direction is less than 0.2% of that along the axial direction.