Experimental Astronomy最新文献

Probing ReionizATion of the Universe using Signal from Hydrogen (PRATUSH) is a proposed space-based radiometer that aims to detect the sky-averaged 21-cm signal from Cosmic Dawn – a crucial phase in the cosmic evolution of the Universe. PRATUSH will operate in the frequency range of 55-110 MHz. PRATUSH will conduct observations in low earth orbit in its first phase, followed by lunar orbit in the second phase. Digital correlation spectrometer is an integral subsystem of PRATUSH radiometer, enabling phase switching, digitization and generation of sky spectrum. The digital correlation spectrometer for PRATUSH laboratory model features 10-bit analog-to-digital converters (ADCs) and a Virtex-6 Field Programmable Gate Array (FPGA). A Raspberry Pi 4 Model B-based single-board computer (SBC) serves as the master controller, real-time processor and data recorder, to minimize the power, mass and volume requirement of the laboratory model. This paper presents the implementation of the PRATUSH laboratory model digital receiver, challenges arising from the use of an SBC in place of a conventional computer, and demonstrates the performance of the spectrometer when integrated with the PRATUSH laboratory model analog receiver.

The Rockets for Extended-source X-ray Spectroscopy (tREXS) grating spectrograph uses modules of reflection gratings to collect spectroscopic data from extended astronomical sources of soft X-rays. Two blazed master gratings were produced on silicon substrates with electron-beam lithography (EBL) and complementary nanofabrication processes that include KOH etching. Substrate-conformal imprint lithography (SCIL) was then used to create 191 replicas of the two grating masters for use in the flight instrument. Diffraction efficiency was measured for several replica gratings, which achieve a peak of ( varvec{>} )70% absolute efficiency near 0.22 keV and an average of ( varvec{approx } )50% absolute efficiency across the measured band, from 0.18 – 0.8 keV. Here we detail the nanofabrication of the grating masters, including the EBL parameters and tREXS-specific fabrication considerations, and the SCIL replication process used to generate the final instrument gratings. A discussion of grating characterization and areas for future improvement is also presented.

GIFTS is a 6U CubeSat designed to detect and localise gamma-ray bursts (GRBs). Its main goal is to improve the sky coverage of existing GRB observatories and contribute to the search of electromagnetic counterparts to gravitational-wave events. GIFTS will use six CeBr( _3 ) scintillator detectors oriented at different angles to localise GRBs based on the difference in the observed count rates. Each detector employs an array of 24 SiPMs for scintillator readout. A full-size prototype of one GIFTS detector was built and tested with gamma rays with energies ranging from 31 keV to 1.3 MeV. It showed an energy resolution of 5.4% at 662 keV. Monte-Carlo simulations were used to estimate the GRB detection and localisation performance of the full instrument. GIFTS was able to detect about 50% of the GRBs from the Fermi GBM catalogue, provided they were not occulted by Earth. Assuming a 60% duty factor for GRB observations, GIFTS is expected to detect about 80 GRBs/year including 12 short GRBs/year. For 90% of the detected GRBs with positive elevations, the true localisation error is less than 32( ^{circ } ). The localisation error is mainly defined by statistical fluctuations in the observed count rates and becomes smaller for brighter events. Systematic localisation errors are expected to depend mainly on the accuracy of the instrument response model used by the localisation procedure. GIFTS is under development and expected to be launch ready for the next gravitational-wave observing run (O5).

The High Altitude Detection of Astronomical Radiation (HADAR) experiment employs an innovative Cherenkov observation technique, boasting an expansive Field-of-View (FOV), and is specifically designed to capture the prompt emissions from Gamma Ray Bursts (GRBs).We propose a novel method for energy reconstruction of Very-high-energy (VHE) γ-rays in the HADAR experiment, based on the Boosted Decision Trees (BDTs) model in machine learning algorithms, referred to as BDTs-Erec. We discuss this energy reconstruction method in detail. A training dataset is generated through Monte Carlo simulation, and the TMVA tool in the ROOT framework is utilized to implement the BDTs model. This model minimizes prediction errors by incrementally adding decision trees and finally constructs 3000 BDTs, thus optimizing the accuracy of energy reconstruction. Performance comparisons are made against the traditional energy reconstruction method based on Look-Up-Tables (denoted as LUTs-Erec), indicating that BDTs-Erec significantly outperforms LUTs-Erec in prediction performance with increasing energy, while it exhibits poorer performance in the low-energy range.

In this work we study the potentialities of machine learning models in reconstructing the solar wind speed observations gathered in the first Lagrangian point by the ACE satellite in 2016–2017. We leverage a supervised model trained with the ACE observations and the galactic cosmic-ray flux variation data measured with particle detectors hosted on board the LISA Pathfinder mission also orbiting around L1 during the same years. Missing data in galactic cosmic-ray time series have been filled with the benefit of other machine learning models developed in previous work. The model presented here will be used for the European Space Agency Laser Interferometer Space Antenna (LISA) after its launch in 2035 to estimate the solar wind speed, that will not be measured on board, with the only benefit of galactic cosmic-ray variation measurements. We show that ensemble models composed of heterogeneous weak regressors are able to outperform weak regressors in terms of predictive accuracy. Machine learning and other powerful predictive algorithms open a window on the possibility of substituting dedicated instrumentation with software models acting as surrogates for diagnostics of space missions such as the LISA mission and space weather science.

The knowledge of the point spread function (PSF) of the Mikhail Pavlinsky Astronomical Roentgen Telescope–X-ray Concentrator (ART-XC) telescope aboard the Spectrum-Roentgen-Gamma (SRG) observatory plays an especially crucial role in the detection of point X-ray sources in the all-sky survey and the studies of extended X-ray objects with low surface brightness. In this work, we calibrate the far off-axis shape of the ART-XC PSF using in-flight data of Sco X-1 and the Crab Nebula, in all-sky survey or scan mode, respectively. We demonstrate that the so-called “slewing” ART-XC PSF (in contrast to the on-axis PSF), in convolution with the detector pixels, is consistent with ground calibration performed at the Marshall Space Flight Center, and can be used to model the PSF up to large off-axis distances in all-sky survey or scan modes. The radial profile of the Crab Nebula in the 4−12 keV band shows an extended structure out to ( sim )150” and is consistent with Sco X-1 at larger off-axis angles. Finally, we performed an analytic parametrization of the slewing ART-XC PSF as a function of energy.

The Follow-up X-ray Telescope (FXT) is a primary scientific instrument on board the Einstein Probe (EP) astronomical satellite, which was launched in January 2024. FXT consists of two nested Wolter I-type telescopes (FXT-A and FXT-B) with a focal length of 1600 mm. The focal plane detector utilizes a PNCCD with a resolution of 384(times )384 pixels. One of the key functions of FXT is to perform the real-time triggering and localization of transients and burst sources. We have developed specialized real-time trigger software that operates within the Payload Data Processing Unit of EP. This onboard software can effectively search for and locate sources, while transmitting source information in real time via the Beidou short message unit and the Very High Frequency (VHF) unit. This paper provides a comprehensive description of the design and development of the onboard software, covering software requirements, module design, and workflow. Additionally, the paper introduces both ground-based and in-orbit testing of this software, and the test results demonstrate that the software meets all design requirements.

Transition-edge sensor (TES) as a type of low-temperature superconducting bolometers offers excellent signal-to-noise-ratio, and is one of the most up-to-date technologies used for cosmic microwave background (CMB) observations. The Ali CMB polarization telescope (AliCPT) project in China uses TES bolometers as the focal plane detector through an international collaborative effort. To increase collecting efficiency of the telescope, and include bolometers of different frequency bands, large-scale production of TES bolometer arrays needs to be accomplished in the future. In this work, we developed single pixel TES bolometers, the saturation power and noise equivalent power (NEP) of which satisfy the requirements of 90 GHz and 150 GHz CMB applications. Each of the bolometers consist of a 1200 ppm AlMn alloy TES for CMB science observation and an Al TES for laboratory optical tests. Dark characterization is applied on these bolometers. Their heat capacities are in the range of 0.7(sim )1.6 pJ/K and the NEP values are below 30 aW/(sqrt{Hz}). The T(_{c}) values are about 360 mK and can be adjusted to about 410 mK by additional annealing.

The first pathfinder of the CATCH mission, CATCH-1, was launched in June 2024. It is equipped with a light-weight, narrow-field optimized Lobster Eye X-ray Optics. By sacrificing a portion of the field of view to achieve a large effective area, the telescope’s sensitivity is enhanced. This paper presents the equipment and procedures employed for calibrating the optics assembly. A comprehensive on-ground calibration for the Lobster Eye X-ray Optics is conducted before its launch using multi-target X-ray sources and the pnCCD Color X-Ray Camera in the 100 m X-Ray Test Facility. The results are derived from calibration measurements taken before and after the mechanical testing and mainly include measurements of the focal length, point spread function, angular resolution, and the effective area for incident X-rays at 0.28 keV, 0.93 keV, 1.49 keV, 2.98 keV, and 4.51 keV. The results indicate that the mirror’s performance remains stable and no observable variation before and after the mechanical testing. At 0.93 keV, the mirror’s angular resolution is (6.11^{prime }) (FWHM), and the effective area is 40.75 (textrm{cm}^{2}), meeting the expected performance of CATCH-1 X-ray optics.

The reconstruction of the photoelectron tracks in X-ray polarimetric detectors based on Gas Pixel Detectors (GPD) is crucial for polarization detection. In addition to traditional moment analysis methods, the convolutional neural network (CNN) is also a noteworthy approach. However, most existing CNN methods for polarization detection have only been effectively validated on simulated data, and the few methods validated on experimental data have not yielded satisfactory results. We have improved the CNN algorithm for reconstructing the emission direction of photoelectron tracks in X-ray polarimetric detectors. We tested this algorithm using calibration data from the detectors of the PolarLight mission and the Polarimetry Focusing Array (PFA) onboard the enhanced X-ray Timing and Polarimetry (eXTP) mission. The results indicate that the optimized deep learning model increased the modulation factor by approximately 0.02 over the 2-8 keV energy range and only introduced a small systematic error. This can enhance the sensitivity of polarization detector in the low-energy range. Additionally, the computational resources required for the model are much lower than the previous CNN models.