A superbubble is a hot, dilute, and X-ray-emitting gas cavity produced by stellar winds and supernova explosions. It is an intriguing feature for the study of stellar feedback processes. We report a study of possible superbubbles in the Andromeda Galaxy (M31). We identify one out of 83 extended sources as a strong superbubble candidate, SB1, from the M31 X-ray source catalogue. SB1 is located in the northern disc of M31 and exhibits soft, extended X-ray emission surrounded by an H alpha shell. The XMM-Newton spectral analysis reveals that SB1 has a temperature of similar to 0.14 keV and an X-ray luminosity of L-X similar to 3.5x 10(37)ergs(-1) in the 0.3-10.0 keV band. Two stellar clusters are found at the west rim of SB1. The estimated age of SB1 is similar to that of an overlapping young stellar cluster, and the colour-magnitude diagram reveals the presence of young stellar objects with an age of less than 10 Myr. We propose that SB1 is a superbubble, likely having triggered star formation in this cluster by compressing the accumulated gas, thereby leading to the formation of gas-dense regions.

The Hot Universe Baryon Surveyor (HUBS) is a proposed space-based X-ray telescope for detecting X-ray emissions from the hot gas content in our universe. With its unprecedented spatially-resolved high-resolution spectroscopy and large field of view, the HUBS mission will be uniquely qualified to measure the physical and chemical properties of the hot gas in the interstellar medium, the circumgalactic medium, the intergalactic medium, and the intracluster medium. These measurements will be valuable for two key scientific goals of HUBS, namely to unravel the AGN and stellar feedback physics that governs the formation and evolution of galaxies, and to probe the baryon budget and multi-phase states from galactic to cosmological scales. In addition to these two goals, the HUBS mission will also help us solve some problems in the fields of galaxy clusters, AGNs, diffuse X-ray backgrounds, supernova remnants, and compact objects. This paper discusses the perspective of advancing these fields using the HUBS telescope.

We introduce the New-ANGELS program, an XMM-Newton survey of a similar to 7.2 deg2 area around M31, which aims to study the X-ray populations in the M31 disk and the X-ray-emitting hot gas in the inner halo of M31 up to 30 kpc. In this first paper, we report the catalog of 4506 detected X-ray sources and attempt to cross-identify or roughly classify them. We identify 352 single stars in the foreground, 35 globular clusters, and 27 supernova remnants associated with M31, as well as 62 active galactic nuclei, 59 galaxies, and one galaxy cluster in the background. We uniquely classify 236 foreground stars and 17 supersoft sources based on their X-ray colors. X-ray binaries (83 low-mass and one high-mass) are classified based on their X-ray colors and X-ray variabilities. The remaining X-ray sources either have too low signal-to-noise ratios to calculate their X-ray colors or do not have a unique classification, so are regarded as unclassified. The X-ray source catalog is published online. Studies of the X-ray source populations and the contribution of X-ray sources in the unresolved X-ray emissions based on this catalog will be published in companion papers.

We present an X-ray spectrum of the diffuse X-ray background (DXRB) between 1.5 and 120 keV, as measured with the Low-Energy Detector (LE) and the High-Energy Detector (HE) aboard the Insight-HXMT satellite, based on 'blank-sky' observations. LE covers a nominal energy range of 1-15 keV and HE 20-250 keV, but calibration issues and data quality narrowed the energy range for this work. The LE background was directly measured with `blind' detector modules, while the HE background was derived from Earth-occultation data. With the LE data alone, the measured DXRB spectrum can be well described by a power law; fitting the LE and HE data jointly, however, a spectral cut-off must be introduced in the model to account for the measurements above 30 keV. Modelling the combined spectrum with a cut-off power law, the best-fit photon index is 1.40, normalisation $9.57$~$\rm ph~cm^{-2}~s^{-1}~keV^{-1}~sr^{-1} $ (at 1 keV), and cut-off energy 55 keV, after correcting for the effects of the Earth albedo and atmospheric emission (which are significant in the HE band). Based on the best-fit cut-off power law, we derived the spectral energy distribution (SED) of the DXRB. The shape of the SED is in general agreement with the published measurements, but the overall normalization is lower by varying amounts, except for the HEAO-1 result, with which our result is in good agreement.

Based on measurements over a period of more than 650 days, we investigated the long-term stability of superconducting Mo–Cu bilayer films in the laboratory environment. The samples are based on sputtered films, which were grown for fabricating transition-edge sensor (TES) arrays. The results show an increasing trend of their superconducting transition temperature ( T c ) and transition width with time. There appears to be a turning point between 150 and 200 d, after which the rate of increasing becomes smaller. We suspect that oxidation occurred at the interface of the bilayer, through exposed edges, until the edges are fully oxidized. If proven, the slower rising trend would reflect the subsequent evolution of the bilayer films through, e.g. further oxidation of the interface, which might change T c through the proximity effect. We quantified the proximity effect with our bilayer samples of different Cu-to-Mo thickness ratios. As a function of the thickness ratio, the measured T c values are fitted well with the Martinis equation, provided that the transmission coefficient (between the layers) and T c , M o of the Mo layer are both allowed to vary. Based on the best-fit model, we found that a change of about 1% in the transmission coefficient would be sufficient to account for the slower variation in the bilayer transition temperature. We also noticed that the best-fit value of T c , M o is significantly higher than that measured for our bare Mo films. This could also be explained by surface oxidation of the Mo film samples. The implications of our results on TES-related applications are discussed.

We report a large-scale (r approximate to 20 degrees) X-ray-bright and Sunyaev-Zeldovich (SZ)-bright diffuse enhancement toward M31, which might be a Local Hot Bridge connecting the Milky Way (MW) with M31. We subtract the Galactic emission from the all-sky O VII and O VIII emission-line measurement survey, and find that the emission of these two ions is enhanced within r approximate to 20 degrees projected around M31. The mean emission enhancements are 5.6 +/- 1.3 L.U., and 2.8 +/- 0.6 L.U. for O VII and O VIII, respectively (>4 sigma for both ions). We also extract the SZ signal around M31, which suggests a surface brightness y of 2 - 4 x 10(-7), an enhancement >2.5 sigma (and a best fit of 5.9 sigma). These three measurements trace the hot gas with a temperature log T (K) > 6, showing similar plateau shapes (flat within approximate to 15 degrees, and zero beyond approximate to 30 degrees). A single-phase assumption leads to a temperature of log T (K) = 6.34 +/- 0.03, which is determined by the O VII/O VIII line ratio. Combining X-ray and SZ measurements, we suggest that this feature is unlikely to be the hot halo around M31 (too massive) or in the MW (too high pressure and X-ray bright). The plateau shape may be explained by a cylinder connecting the MW and M31 (the Local Hot Bridge). We constrain its length to be about 400 kpc, with a radius of 120 kpc, a density of approximate to 2 x 10(-4)-10(-3) cm(-3), and a metallicity of 0.02-0.1 Z(circle dot). The baryon mass is greater than or similar to 10(11) M-circle dot, and the oxygen mass is about greater than or similar to 10(8) M-circle dot, which contribute to the baryon or metal budget of the Local Group.

The Hot Universe Baryon Surveyor (HUBS) is a satellite mission that is proposed to probe "hidden" baryons in the universe and thus to fill a void in observational astronomy that seriously affects our understand of galaxy formation and evolution. The HUBS payload is highly optimized for detecting diffuse X-ray emission from the baryons, with the combination of large field of view and high spectral resolution. To assess the scientific capabilities of HUBS, we created mock observations with data from a state-of-the-art cosmological hydrodynamical simulation (IllustrisTNG). The targets include systems that are representative of galaxies, galaxy groups, and galaxy clusters at various redshifts. We generated the X-ray spectra and images of the selected sources from the mock observations, taking into account galactic foreground emission, X-ray emission from cosmologically distant background sources, as well as emission from other sources along the lines of sight. The results from analyzing the mock observations show that the assumed design of HUBS is appropriate for achieving its primary scientific objectives. In this paper, we present the results and discuss issues related to observing strategies.

In the context of detector development for a proposed X-ray satellite mission, known as Hot Universe Baryon Surveyor (HUBS), we have studied stability in the properties of Mo/Cu bilayer superconducting films in a radiation environment. For this work, test devices were fabricated from the Mo/Cu films for four-terminal measurements. They were irradiated with 1MeV protons at room temperatures, with fluence ranging from 1.0 $$\times 10^{12}$$ to 1.0 $$\times 10^{15}$$ protons/cm $$^{2}$$ . It was found that the superconducting transition temperature of the devices showed no systematic change with increasing irradiation fluence, but their residual resistance at low temperatures showed a decreasing trend when the fluence exceeded about 1.0 $$\times 10^{14}$$ protons/cm $$^{2}$$ . The former might be attributed mainly to defect migration and subsequent recombination at room temperatures, while the latter probably to the effects of annealing caused by heating of the bilayer material upon irradiation. Low-temperature irradiation experiments are required to reach firm conclusions. The results are compared with those of other investigations, and future plans are discussed.

The estimation of instrumental background is the basis of essentially all data analysis on observations with Insight-HXMT. The current Insight-HXMT/HE background model made by Liao et al. depends on the data from the HE blind detector, i.e., using historical data to make a preliminary estimation of the background spectra and using the real-time data from the blind detector to make a further modification. In order to decouple the dependence of background method on the blind detector, a parametric physical model has been developed to rebuild the light curve and spectrum of the HE blind detector. In this parametric model, several physical processes between the space environment and the satellite are considered to rebuild the prompt and delayed background signals of the HE blind detector. With the genetic algorithm and Markov Chain Monte Carlo procedure, the model parameters are determined by fitting the data from the HE blind detector. For all 62 energy bands in the range 28–334 keV for an exposure of 10 ks, the average systematic error of the background energy spectrum is ∼2.2% and the average total error of spectrum estimation ∼3.4%. It is found that more accurate background can be attained using this model than using the data from the Insight-HXMT/HE blind detector for exposures of less than 2 ks. These results show that the background of the Insight-HXMT/HE blind detector can be reproduced reliably with this parametric model and this method can also be applied to the background estimation of other detectors in principle.

In the process of minimizing stress in sputtered molybdenum (Mo) films for fabricating transition-edge sensor devices, we have investigated correlations between the stress and film deposition parameters. At a fixed sputtering power, the tensile stress of our film samples decreases toward both low and high ends of Ar pressure, suggestive of two physical mechanisms at work: an ‘atomic peening’ effect at low Ar pressure and the development of voids at high Ar pressure. We have also carried out correlative studies of the stress and electrical properties (including superconducting critical temperature and residual resistivity) of the film samples, and found that the results are complex. We have made extensive comparisons with the published results, and attempted to explain the discrepancies in terms of film deposition techniques, sample preparation and treatment, and dynamical ranges of measurements. It is fairly clear that the microscopic properties, including porosity and disorder, of Mo films may have significant impact on the correlations.

Hot Universe Baryon Surveyor (HUBS)1 is being conceptualized in China as a high throughput and highresolution spectroscopic X-ray mission dedicated to studying cosmic “missing” baryons, which are thought to exist in the gas of very low density and temperature of roughly one million degrees in the halo of galaxies or in large-scale structures. To detect weak emission from the “missing” baryons, HUBS will employ an X-ray microcalorimeter based on transition-edge sensors (TES) array that operates at very low temperatures. The key characteristics of the detector technology are excellent energy resolution and high quantum efficiency, which makes it an ideal choice for constructing a non-dispersive X-ray imaging spectrometer. We are developing X-ray microcalorimeters for HUBS, based on superconducting Mo/Cu bilayer films. In this work, we present results on characterization of the Mo/Cu films and TES devices at temperatures below 200 mK, including their I − V characteristics, pulse signals and energy resolutions. We have also studied correlations between the superconductivity and other properties of the films (including residual resistivity ratio, stress, crystalline structure, interface properties, etc.). Preliminary results are presented in this work.

Hot Universe Baryon Surveyor (HUBS) is being conceptualized in China as a high throughput and high-resolution spectroscopic X-ray mission dedicated to studying cosmic missing baryons, which are thought to exist in the gas of very low density and temperature roughly one million degrees in the halo of galaxies or in large-scale structures. To detect weak emission from the missing baryons, HUBS will employ a TES-based X-ray microcalorimeter array that operates at very low temperatures. The key characteristics of the detector technology are excellent energy resolution and high quantum efficiency, which makes it an ideal choice for constructing a non-dispersive X-ray imaging spectrometer. We are developing X-ray microcalorimeters for HUBS, based on superconducting Mo/Cu bilayer films. In this work, we present results on the characterization of the Mo/Cu films and TES devices at temperatures below 100 mK, including their R-T curves, I-V characteristics, energy resolutions, etc. We have also studied correlations between the superconducting transition temperature and other properties of the films (including residual resistivity ratio, stress, crystalline structure, interface properties, and so on), and looked into factors that might affect the energy resolution of the detectors. Preliminary results will be presented.