分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: In recent years, tremendous progress has been made on complementary metal-oxide-semiconductor (CMOS) sensors for applications as X-ray detectors. To shield the visible light in X-ray detection, a blocking filter of aluminum is commonly employed. We designed three types of aluminum coating layers, which are deposited directly on the surface of back-illuminated sCMOS sensors during fabrication. A commercial 2k * 2k sCMOS sensor is used to realize these designs. In this work, we report their performance by comparison with that of an uncoated sCMOS sensor. The optical transmissions at 660 nm and 850 nm are measured, and the results show that the optical transmission reaches a level of about 10-9 for the 200 nm aluminum layer and about 10-4 for the 100 nm aluminum layer. Light leakage is found around the four sides of the sensor. The readout noise, fixed-pattern noise and energy resolution of these Al-coated sCMOS sensors do not show significant changes. The dark currents of these Al-coated sCMOS sensors show a noticeable increase compared with that of the uncoated sCMOS sensor at room temperatures, while no significant difference is found when the sCMOS sensors are cooled down to about -15 degree. The aluminum coatings show no visible crack after the thermal cycle and aging tests. Based on these results, an aluminum coating of a larger area on larger sCMOS sensors is proposed for future work.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present estimates of line-of-sight distortion fields derived from the 95 GHz and 150 GHz data taken by BICEP2, BICEP3, and Keck Array up to the 2018 observing season, leading to cosmological constraints and a study of instrumental and astrophysical systematics. Cosmological constraints are derived from three of the distortion fields concerning gravitational lensing from large-scale structure, polarization rotation from magnetic fields or an axion-like field, and the screening effect of patchy reionization. We measure an amplitude of the lensing power spectrum $A_L^{\phi\phi}=0.95 \pm 0.20$. We constrain polarization rotation, expressed as the coupling constant of a Chern-Simons electromagnetic term $g_{a\gamma} \leq 2.6 \times 10^{-2}/H_I$, where $H_I$ is the inflationary Hubble parameter, and an amplitude of primordial magnetic fields smoothed over 1 Mpc $B_{1\text{Mpc}} \leq 6.6 \;\text{nG}$ at 95 GHz. We constrain the root mean square of optical-depth fluctuations in a simple "crinkly surface" model of patchy reionization, finding $A^\tau<0.19$ ($2\sigma$) for the coherence scale of $L_c=100$. We show that all of the distortion fields of the 95 GHz and 150 GHz polarization maps are consistent with simulations including lensed-$\Lambda$CDM, dust, and noise, with no evidence for instrumental systematics. In some cases, the EB and TB quadratic estimators presented here are more sensitive than our previous map-based null tests at identifying and rejecting spurious B-modes that might arise from instrumental effects. Finally, we verify that the standard deprojection filtering in the BICEP/Keck data processing is effective at removing temperature to polarization leakage.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We characterize Galactic dust filaments by correlating BICEP/Keck and Planck data with polarization templates based on neutral hydrogen (HI) observations. Dust polarization is important for both our understanding of astrophysical processes in the interstellar medium (ISM) and the search for primordial gravitational waves in the cosmic microwave background (CMB). In the diffuse ISM, HI is strongly correlated with the dust and partly organized into filaments that are aligned with the local magnetic field. We analyze the deep BICEP/Keck data at 95, 150, and 220 GHz, over the low-column-density region of sky where BICEP/Keck has set the best limits on inflationary theories. We separate the HI emission into distinct velocity components and demonstrate a detection of dust polarization correlated with the local Galactic HI but not with the HI associated with Magellanic Stream I. We present a robust, multi-frequency detection of polarized dust emission correlated with the filamentary HI morphology template down to 95 GHz. We find the correlation for frequencies between 95-353 GHz to be between ~10-50% over multipoles $20<\ell<200$. We measure the spectral index of the filamentary dust component spectral energy distribution to be $\beta = 1.54 \pm 0.13$. We find no evidence for decorrelation in this region between the filaments and the rest of the dust field or from the inclusion of dust associated with the intermediate velocity HI. Finally, we explore the morphological parameter space in the HI-based filamentary model.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: As a novel X-ray focusing technology, lobster eye micro-pore optics (MPO) feature both a wide observing field of view and true imaging capability, promising sky monitoring with significantly improved sensitivity and spatial resolution in soft X-rays. Since first proposed by Angel (1979), the optics have been extensively studied, developed and trialed over the past decades. In this Letter, we report on the first-light results from a flight experiment of the Lobster Eye Imager for Astronomy ($LEIA$), a pathfinder of the wide-field X-ray telescope of the Einstein Probe mission. The piggyback imager, launched in July 2022, has a mostly un-vignetted field of view of $18.6^\circ \times 18.6^\circ $. Its spatial resolution is in the range of 4$-$7 arcmin in FWHM and the focal spot effective area is 2$-$3 cm$^2$, both showing only mild fluctuations across the field of view. We present images of the Galactic center region, Sco X-1 and the diffuse Cygnus Loop nebular taken in snapshot observations over 0.5$-$4 keV. These are truly wide-field X-ray images of celestial bodies observed, for the first time, by a focusing imaging telescope. Initial analyses of the in-flight data show excellent agreement between the observed images and the on-ground calibration and simulations. The instrument and its characterization are briefly described, as well as the flight experiment. The results provide a solid basis for the development of the present and proposed wide-field X-ray missions using lobster eye MPO.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We report detection of radio recombination line (RRL) H$_{40\alpha}$ toward 75 sources, with data obtained from ACA observations in the ATOMS survey of 146 active Galactic star forming regions. We calculated ionized gas mass and star formation rate with H40U line emission. The mass of ionized gas is significantly smaller than molecular gas mass, indicating that ionized gas is negligible in the star forming clumps of the ATOMS sample. The star formation rate (SFR$_{{\rm H}_{40\alpha}}$) estimated with RRL H$_{40\alpha}$ agrees well with that (SFR$_{\rm L_{bol}}$) calculated with the total bolometric luminosity (L$_{\rm bol}$) when SFR $\gtrsim 5 {\rm M_\odot My}r^{-1}$, suggesting that millimeter RRLs could well sample the upper part of the initial mass function (IMF) and thus be good tracers for SFR. We also study the relationships between L$_{\rm bol}$ and the molecular line luminosities (L0mol) of CS J=2-1 and HC$_3$N J=11-10 for all the 146 ATOMS sources. The Lbol-L0mol correlations of both the CS J=2-1 and HC3N J=11-10 lines appear approximately linear and these transitions have success in predicting L$_{\rm bol}$ similar to that of more commonly used transitions. The L$_{\rm bol}$-to-L$_{\rm mol}$ ratios or SFR-to-mass ratios (star formation efficiency; SFE) do not change with galactocentric distances (R$_{\rm GC}$). Sources with H$_{40\alpha}$ emission (or H$_{\rm II}$ regions) show higher L$_{\rm bol}$-to-L$_{\rm mol}$ than those without H$_{40\alpha}$ emission, which may be an evolutionary effect.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: In recent years, tremendous progress has been made on complementary metal-oxide-semiconductor (CMOS) sensors for applications as X-ray detectors. To shield the visible light in X-ray detection, a blocking filter of aluminum is commonly employed. We designed three types of aluminum coating layers, which are deposited directly on the surface of back-illuminated sCMOS sensors during fabrication. A commercial 2k * 2k sCMOS sensor is used to realize these designs. In this work, we report their performance by comparison with that of an uncoated sCMOS sensor. The optical transmissions at 660 nm and 850 nm are measured, and the results show that the optical transmission reaches a level of about 10-9 for the 200 nm aluminum layer and about 10-4 for the 100 nm aluminum layer. Light leakage is found around the four sides of the sensor. The readout noise, fixed-pattern noise and energy resolution of these Al-coated sCMOS sensors do not show significant changes. The dark currents of these Al-coated sCMOS sensors show a noticeable increase compared with that of the uncoated sCMOS sensor at room temperatures, while no significant difference is found when the sCMOS sensors are cooled down to about -15 degree. The aluminum coatings show no visible crack after the thermal cycle and aging tests. Based on these results, an aluminum coating of a larger area on larger sCMOS sensors is proposed for future work.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Dual-phase xenon time projection chamber (TPC) detectors have demonstrated superior search sensitivities to dark matter over a wide range of particle masses. To extend their sensitivity to include low-mass dark matter interactions, it is critical to characterize both the light and charge responses of liquid xenon to sub-keV nuclear recoils. In this work, we report a new nuclear recoil calibration in the LUX detector $\textit{in situ}$ using neutron events from a pulsed Adelphi Deuterium-Deuterium neutron generator. We demonstrate direct measurements of light and charge yields down to 0.45 keV (1.4 scintillation photons) and 0.27 keV (1.3 ionization electrons), respectively, approaching the physical limit of liquid xenon detectors. We discuss the implication of these new measurements on the physics reach of dual-phase xenon TPCs for nuclear-recoil-based low-mass dark matter detection.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Hydrogen recombination lines (RRLs) are one of the major diagnostics of the physical properties of H{\sc ii} regions. We use RRL H40$\alpha$, He40$\alpha$ and 3 mm continuum emission to investigate the properties of a large sample of resolved UC H{\sc ii} regions identified in the ATOMS survey. In total, we identify 94 UC H{\sc ii} regions from H40$\alpha$ emission. The basic parameters for these UC H{\sc ii} regions such as electron density, emission measure, electron temperature, ionic abundance ratio (n$_{\rm He^+}$/n$_{\rm H^+}$), and line width are derived. The median electron density and the median n$_{\rm He^+}$/n$_{\rm H^+}$ ratio of these UC H{\sc ii} regions derived from RRLs are $\sim$9000 cm$^{-3}$ and 0.11, respectively. Within UC H{\sc ii} regions, the n$_{\rm He^+}$/n$_{\rm H^+}$ ratios derived from the intensity ratio of the He40$\alpha$ and H40$\alpha$ lines seems to be higher in the boundary region than in the center. The H40$\alpha$ line width is mainly broadened by thermal motion and microturbulence. The electron temperature of these UC H{\sc ii} regions has a median value of $\sim$6700 K, and its dependence on galactocentric distance is weak.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present the results from combining machine learning with the profile likelihood fit procedure, using data from the Large Underground Xenon (LUX) dark matter experiment. This approach demonstrates reduction in computation time by a factor of 30 when compared with the previous approach, without loss of performance on real data. We establish its flexibility to capture non-linear correlations between variables (such as smearing in light and charge signals due to position variation) by achieving equal performance using pulse areas with and without position-corrections applied. Its efficiency and scalability furthermore enables searching for dark matter using additional variables without significant computational burden. We demonstrate this by including a light signal pulse shape variable alongside more traditional inputs such as light and charge signal strengths. This technique can be exploited by future dark matter experiments to make use of additional information, reduce computational resources needed for signal searches and simulations, and make inclusion of physical nuisance parameters in fits tractable.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Hydrogen recombination lines (RRLs) are one of the major diagnostics of the physical properties of H{\sc ii} regions. We use RRL H40$\alpha$, He40$\alpha$ and 3 mm continuum emission to investigate the properties of a large sample of resolved UC H{\sc ii} regions identified in the ATOMS survey. In total, we identify 94 UC H{\sc ii} regions from H40$\alpha$ emission. The basic parameters for these UC H{\sc ii} regions such as electron density, emission measure, electron temperature, ionic abundance ratio (n$_{\rm He^+}$/n$_{\rm H^+}$), and line width are derived. The median electron density and the median n$_{\rm He^+}$/n$_{\rm H^+}$ ratio of these UC H{\sc ii} regions derived from RRLs are $\sim$9000 cm$^{-3}$ and 0.11, respectively. Within UC H{\sc ii} regions, the n$_{\rm He^+}$/n$_{\rm H^+}$ ratios derived from the intensity ratio of the He40$\alpha$ and H40$\alpha$ lines seems to be higher in the boundary region than in the center. The H40$\alpha$ line width is mainly broadened by thermal motion and microturbulence. The electron temperature of these UC H{\sc ii} regions has a median value of $\sim$6700 K, and its dependence on galactocentric distance is weak.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: As a novel X-ray focusing technology, lobster eye micro-pore optics (MPO) feature both a wide observing field of view and true imaging capability, promising sky monitoring with significantly improved sensitivity and spatial resolution in soft X-rays. Since first proposed by Angel (1979), the optics have been extensively studied, developed and trialed over the past decades. In this Letter, we report on the first-light results from a flight experiment of the Lobster Eye Imager for Astronomy ($LEIA$), a pathfinder of the wide-field X-ray telescope of the Einstein Probe mission. The piggyback imager, launched in July 2022, has a mostly un-vignetted field of view of $18.6^\circ \times 18.6^\circ $. Its spatial resolution is in the range of 4$-$7 arcmin in FWHM and the focal spot effective area is 2$-$3 cm$^2$, both showing only mild fluctuations across the field of view. We present images of the Galactic center region, Sco X-1 and the diffuse Cygnus Loop nebular taken in snapshot observations over 0.5$-$4 keV. These are truly wide-field X-ray images of celestial bodies observed, for the first time, by a focusing imaging telescope. Initial analyses of the in-flight data show excellent agreement between the observed images and the on-ground calibration and simulations. The instrument and its characterization are briefly described, as well as the flight experiment. The results provide a solid basis for the development of the present and proposed wide-field X-ray missions using lobster eye MPO.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Investigating the physical and chemical structures of massive star-forming regions is critical for understanding the formation and the early evolution of massive stars. We performed a detailed line survey toward six dense cores named as MM1, MM4, MM6, MM7, MM8, and MM11 in G9.62+0.19 star-forming region resolved in ALMA band 3 observations. Toward these cores, about 172 transitions have been identified and attributed to 16 species including organic Oxygen-, Nitrogen-, Sulfur-bearing molecules and their isotopologues. Four dense cores MM7, MM8, MM4, and MM11 are line rich sources. Modeling of these spectral lines reveals the rotational temperature in a range of 72$-$115~K, 100$-$163~K, 102$-$204~K, and 84$-$123~K for the MM7, MM8, MM4, and MM11, respectively. The molecular column densities are 1.6 $\times$ 10$^{15}$ $-$ 9.2 $\times$ 10$^{17}$~cm$^{-2}$ toward the four cores. The cores MM8 and MM4 show chemical difference between Oxygen- and Nitrogen-bearing species, i.e., MM4 is rich in oxygen-bearing molecules while nitrogen-bearing molecules especially vibrationally excited HC$_{3}$N lines are mainly observed in MM8. The distinct initial temperature at accretion phase may lead to this N/O differentiation. Through analyzing column densities and spatial distributions of O-bearing Complex Organic Molecules (COMs), we found that C$_{2}$H$_{5}$OH and CH$_{3}$OCH$_{3}$ might have a common precursor, CH$_{3}$OH. CH$_{3}$OCHO and CH$_{3}$OCH$_{3}$ are likely chemically linked. In addition, the observed variation in HC$_{3}$N and HC$_{5}$N emission may indicate that their different formation mechanism at hot and cold regions.
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: Nuclear reactors are one of the most intense, pure, controllable, cost-effective, and well-understood sources of neutrinos. Reactors have played a major role in the study of neutrino oscillations, a phenomenon that indicates that neutrinos have mass and that neutrino flavors are quantum mechanical mixtures. Over the past several decades reactors were used in the discovery of neutrinos, were crucial in solving the solar neutrino puzzle, and allowed the determination of the smallest mixing angle θ13. In the near future, reactors will help to determine the neutrino mass hierarchy and to solve the puzzling issue of sterile neutrinos.