Experimental Astronomy最新文献

In the current era when access to space is becoming easier and at a lower cost thanks to the standardised cubesat technology, numerous missions are expected to be launched to observe, particularly, at ultraviolet wavelengths. Given the reduced dimensions of the telescope that a cubesat can carry, most of these missions will be focused on photometric surveys of a reduced sample of targets of interest, and therefore each mission will define their own photometric bands according to their scientific objectives and orbital constraints. However, in order to provide a coherent view of the ultraviolet sky, the data should be post-processed under a common framework. In 2017, the IAU working group on ultraviolet astronomy identified the need to define such a common framework for the upcoming ultraviolet missions, and coordinated the definition of a standard set of photometric bands that could serve for homogenizing the current and future data. This paper presents the procedure adopted by the working group for the definition of the standard photometric system, that was approved by the IAU during the General Assembly Business Sessions held in August, 2021. The photometric system consists of seven bands, denoted as UV1-UV7, all included in the range 115 - 400 nm. Some of these bands are based on existing filters, while others have been defined as theoretical bands with constant throughput. This system is to be regarded as a set of synthetic bands for post-processing the data of any mission, and an example of its application to the SPARCS cubesat is also included. The photometric bands are publicly available and can be downloaded from https://www.nuva.eu/uv-photometry/.

In this paper, we estimate the Cosmic Microwave Background (CMB) temperature using the data of the monopole spectrum from the Cosmic Background Explorer/ Far-Infrared Absolute Spectrophotometer (COBE/FIRAS). Utilising the idea of straight-line fitting, we obtain the temperature and chemical potential. The temperature of the CMB is found to be (2.725007 ± 0.000024) K (only statistical error) by using the monopole spectrum. Handling the data of the monopole spectrum the chemical potential is obtained as (-1.1 ± 3.4) × 10^–5 with an upper bound |µ| < 5.7 × 10^–5 (95% confidence level). The amplitude of the CMB dipole is found to be, T_amp = (3.47 ± 0.11) mK. We estimate an upper limit for the rms value of the fluctuation in chemical potential as Δµ < 1.2 × 10^–4 (95% confidence level). The upper limit of y- distortion is calculated as y < 1.0 × 10^–4 (95% confidence level).

Two infrared thermal imagers have been installed on the TianMa radio telescope (TMRT) to continuously monitor the temperature distributions of the back-up structure (BUS). In order to compensate the measurement error of the infrared thermal imager (ITI) for a BUS, a correction formula, as a function of measuring distance and viewing angle, is proposed. According to the relationship between the locations of the measurement points in the thermographic image and those in the actual structure, the 3D coordinates of the measurement points are determined by a finite element model of the BUS. Then, the measuring distances and viewing angles are calculated using 3D coordinates of the measurement points. The measurement accuracy of the ITI improves from ±2(^{circ })C to ±0.5(^{circ })C with the proposed formula. Additionally, based on the information of rotation angle and rotation speed of the elevation, the problem of the ITI moving with the elevation of the telescope in real time is solved. The temperature data at each elevation are recorded in excel documents respectively which are integrated into a document in chronological order through compiling program. Finally, the temperature of the measurement points at different altazimuthal positions is displayed as curves or contours. The thermal states of about 40% measuring points of the BUS are simultaneously monitored by the ITI, which provides accurate temperature distribution for the prediction of thermal deformations of the BUS.

In recent years, deep learning has been successfully applied in various scientific domains. Following these promising results and performances, it has recently also started being evaluated in the domain of radio astronomy. In particular, since radio astronomy is entering the Big Data era, with the advent of the largest telescope in the world - the Square Kilometre Array (SKA), the task of automatic object detection and instance segmentation is crucial for source finding and analysis. In this work, we explore the performance of the most affirmed deep learning approaches, applied to astronomical images obtained by radio interferometric instrumentation, to solve the task of automatic source detection. This is carried out by applying models designed to accomplish two different kinds of tasks: object detection and semantic segmentation. The goal is to provide an overview of existing techniques, in terms of prediction performance and computational efficiency, to scientists in the astrophysics community who would like to employ machine learning in their research.

Solar flare intensity is strongly dependent on the phase in the solar cycle, the structure and dynamics of the magnetic field near sunspots, and also on occasional solar coronal mass ejections. In this paper we study some of the solar flares detected by the stratospheric balloon borne experiments of Indian Centre for Space Physics. We also observe a gamma-ray burst which is believed to be originated from sudden energy release in gamma rays. In the hard X-ray region of 10 − 100 keV, we present and analyze data from various classes of solar flares and a gamma-ray burst. Because of natural constraints present in balloon borne experiments we receive data up to about a height of ∼ 42 km. The Earth’s residual atmosphere at this height absorbs the lower energy part of the spectrum. Moreover, the background radiation (mainly secondary cosmic rays) introduces noise. We show how we circumvent these limitations and create the accurate light curves and the spectra of a few solar flares and a gamma-ray burst.

The Microchannel X-ray Telescope (MXT) is an innovative compact X-ray instrument on board the SVOM astronomical mission dedicated to the study of transient phenomena such as gamma-ray bursts. During 3 weeks, we have tested the MXT flight model at the Panter X-ray test facility under the nominal temperature and vacuum conditions that MXT will undergo in-flight. We collected data at series of characteristic energies probing the entire MXT energy range, from 0.28 keV up to 9 keV, for multiple source positions with the center of the point spread function (PSF) inside and outside the detector field of view (FOV). We stacked the data of the positions with the PSF outside the FOV to obtain a uniformly illuminated matrix and reduced all data sets using a dedicated pipeline. We determined the best spectral performance of MXT using an optimized data processing, especially for the energy calibration and the charge sharing effect induced by the pixel low energy thresholding. Our results demonstrate that MXT is compliant with the instrument requirement regarding the energy resolution (< 80 eV at 1.5 keV), the low and high energy threshold, and the accuracy of the energy calibration (± 20 eV). We also determined the charge transfer inefficiency ((sim 10^{-5})) of the detector and modeled its evolution with energy prior to the irradiation that MXT will undergo during its in-orbit lifetime. Finally, we measured the relation of the energy resolution as function of the photon energy. We determined an equivalent noise charge of (4.9 pm 0.2 mathrm {e}^{-}_{text {rms}}) for the MXT detection chain and a Fano factor of 0.131 ± 0.003 in silicon at 208 K, in agreement with previous works. This campaign confirmed the promising scientific performance that MXT will be able to deliver during the mission lifetime.

The iXRD is the primary science payload on Sharjah-Sat-1, a 3U CubeSat expected to be launched in Q4, 2022. Its main scientific goal is monitoring bright hard X-ray sources and transients in 20 - 200 keV band. The iXRD consists of a CdZnTe crystal (6.45 cm² area, 5 mm thickness), a Tungsten collimator with square holes with an opening angle of 4.26^∘, readout and control electronics and power supply circuitry, a back-shield and mechanical structures. Some of the design elements of iXRD have been inherited from the XRD on BeEagleSat with significant improvements in terms of collecting area, X-ray background and electronic noise. In this article, the design of the iXRD is discussed in detail taking into account mechanical, electronic, control software and data handling aspects. Its expected performance is determined after ground calibration. Depending on the pixel size, the energy resolution is 4 - 7 keV at 60 keV and the minimum detectable energy is 19 - 23 keV.

The Einstein Probe (EP) satellite is designed for X-ray time-domain astronomy. The Follow-up X-ray Telescope (FXT) is one of the scientific payloads onboard EP. It will mainly be used for the follow-up X-ray observation, and it will also be used for the sky survey and Target of Opportunity (ToO) observation. The focal plane detector of FXT provided by the Max Planck Institute for Extraterrestrial Physics (MPE) adopts a PNCCD sensor. For detector cooling, a helium pulse tube refrigerator is used, provided by the Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS), to keep the detector working at a temperature of −90 ± 0.5 °C. The PNCCD driving and data acquisition electronics are developed by the Institute of High Energy Physics (IHEP), CAS. To observe different celestial sources, we designed six filter wheel positions and three scientific operating modes for the PNCCD detector: the full-frame mode, the partial-window mode, and the timing mode. In the full-frame mode, the system frame rate is 20 frame/s and the energy resolution of the whole system reaches 92 eV @ 1.49 keV (FWHM). The frame rate of partial-window mode is 500 frame/s. In the timing mode, the time resolution is about 94 μs. This paper mainly introduces the design and test results of the focal plane camera.

The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (PILOT) is a balloon-borne experiment that aims to measure the polarized emission of thermal dust at a wavelength of 240µm (1.2 THz). The PILOT experiment flew from Timmins, Ontario, Canada in 2015 and 2019 and from Alice Springs, Australia in April 2017. The in-flight performance of the instrument during the second flight was described in [1]. In this paper, we present data processing steps that were not presented in [1] and that we have recently implemented to correct for several remaining instrumental effects. The additional data processing concerns corrections related to detector cross-talk and readout circuit memory effects, and leakage from total intensity to polarization. We illustrate the above effects and the performance of our corrections using data obtained during the third flight of PILOT, but the methods used to assess the impact of these effects on the final science-ready data, and our strategies for correcting them will be applied to all PILOT data. We show that the above corrections, and in particular that for the intensity to polarization leakage, which is most critical for accurate polarization measurements with PILOT, are accurate to better than 0.4% as measured on Jupiter during flight#3.

The Einstein Probe (EP) mission is a science mission designed for the time domain astronomy, which is approved by the Chinese Academy of Sciences (CAS) in 2017 and is to be launched in 2023 with a duration time of more than 3 years. The Follow-up X-ray Telescope (FXT) is an important payload onboard EP, which employs the Wolter I focusing mirror as the X-ray collection unit and the PNCCD as the focal plane detector. The Phase C study has been finished in 2021. During the Phase C, the structural and thermal model (STM) of the mirror assembly of FXT, provided by the European Space Agency (ESA), a mirror assembly developed by the Institute of High Energy Physics (IHEP), a qualification model (QM) PNCCD and other components, are integrated and tested in IHEP. All optical performances meet the goal requirement of EP, such as the field of view of 60 arcmins, the angular resolution of less than 30 arcsec HEW on-axis, and the focal length of ab. 1600 mm. After that, the FXT is assembled, integrated, and tested on the EP satellite platform. Furthermore, these performances are not changed after the mechanical and thermal tests on the spacecraft platform.