Multi-band Astronomical Variable Objects Monitor Research Articles

Multi-purpose InSTRument for Astronomy at Low-resolution: MISTRAL at the Observatoire de Haute-Provence

Multi-purpose InSTRument for Astronomy at Low-resolution (MISTRAL) is the new Faint Object Spectroscopic Camera mounted at the folded Cassegrain focus of the 1.93m telescope of the Haute-Provence Observatory (OHP). We describe the design and components of the instrument and give some details about its operation. We emphasize in particular the various observing modes and the performance of the detector. A short description of the working environment is also provided. Various types of objects, including stars, nebulae, comets, novae, and galaxies, have been observed during various test phases to evaluate the performance of the instrument. The instrument covers the range of 4000 to 8000 AA with the blue setting, or from 6000 to 10000 AA with the red setting, at an average spectral resolution of 700. Its peak efficiency is about 22$<!PCT!>$ at 6000 AA . In spectroscopy, a limiting magnitude of rsim 19.5 can be achieved for a point source in one hour with a signal-to-noise ratio of 3 in the continuum (and better when emission lines are present). In imaging mode, limiting magnitudes of 20-21 can be obtained in 10-20mn (with average seeing conditions of 2.5 arcsec at the OHP). The instrument is very user-friendly and can be put into operations in less than 15mn (rapid change-over from the other instrument in use) if required by the science (e.g. for gamma-ray bursts). Some first scientific results are described for various types of objects, and in particular, for the follow-up of gamma-ray bursts. While some further improvements are still under way, in particular, to facilitate the switch from blue to red setting and add more grisms or filters, MISTRAL is ready for the follow-up of transients and other variable objects, in the soon-to-come era of the Space-based multi-band astronomical Variable Objects Monitor (SVOM) satellite and of the Rubin telescope, for instance.

Study of SVOM/ECLAIRs inhomogeneities in the detection plane below 8 keV and their mitigation for the trigger performances

Context. The Space-based multi-band astronomical Variable Objects Monitor is a Chinese-French mission dedicated to the study of the transient sky. It is scheduled to start operations in 2024. ECLAIRs is a coded-mask telescope with a large field of view. It is designed to detect and localize gamma-ray bursts in the energy range from 4 keV up to 120 keV. In 2021, the ECLAIRs telescope underwent various calibration campaigns in vacuum test-chambers to evaluate its performance. Between 4 and 8 keV, the counting response of the detection plane shows inhomogeneities between pixels from different production batches. The efficiency inhomogeneity is caused by low-efficiency pixels (LEPs) from one of the two batches, together with high-threshold pixels (HTPs) whose threshold was raised to avoid cross-talk effects. In addition, some unexpected noise was found in the detection plane regions close to the heat pipes. Aims. We study the impact of these inhomogeneities and of the heat-pipe noise at low energies on the ECLAIRs onboard triggers. We propose different strategies in order to mitigate these impacts and to improve the onboard trigger performance. Methods. We analyzed the data from the calibration campaigns and performed simulations with the ground model of the ECLAIRs trigger software in order to design and evaluate the different strategies. Most of the impact of HTPs can be corrected for by excluding HTPs from the trigger processing. To correct for the impact of LEPs, an efficiency correction in the shadowgram seems to be a good solution. An effective solution for the heat-pipe noise is selecting the noisy pixels and ignoring their data in the 4–8 keV band during the data analysis. Results. The trigger threshold is the minimum value of the signal-to-noise ratio that is required to claim that ECLAIRs has detected a candidate event that is not related to a background fluctuation. After introducing the efficiency inhomogeneity in the imaging simulation, the trigger threshold in the 4–8 keV band increased by a factor of 5.75 times and 1.43 times due to the impact of HTPs and LEPs, respectively, in the worst case (on a timescale of about 20 min). The trigger threshold value was restored to its normal value after we applied an efficiency-correction method. Introducing the heat-pipe noise in our simulations in the worst case (timescale of about 20 min) resulted in an increase in the trigger threshold of approximately 100% in the 4–8 keV band compared to observations without heat-pipe noise. Moreover, even with this increased threshold, we estimated a false-trigger rate of 99.26% in the 4–8 keV band and 4.44% in the 4-120 keV band. By accepting a loss of 2.5-5% noisy pixels in the 4–8 keV energy band, we can prevent false triggers caused by heat-pipe noise and reduce the threshold increment to about 20% for the longest timescale (about 20 min) of the ECLAIRs trigger in the 4–8 keV range.

Measurement methods for gamma-ray bursts redshifts

In the era of multi-messenger astronomy, gamma-ray bursts (GRBs) with known redshifts, especially high-redshift GRBs, are a powerful tool for studying the structure and evolution of the early Universe. We review the background, the history, and the application of measurement methods of GRB redshifts in astronomy. Based on different observation targets, two measurement methods are mainly introduced. One is on GRB afterglow, the other is on GRB host galaxy. There are various processing methods belonging to measurement methods based on afterglow, including spectral measurement method of afterglow and afterglow spectral energy distribution fitting method with improved methods. There are also numerous measurement methods based on host galaxy, such as spectral measurement method of host galaxy, template matching method of host galaxy, some automatic spectroscopic redshift measurement methods, and machine learning methods. We subsequently introduce the principles, effects, and performance of these methods. We enumerate several detection and measurement instruments, which have been used in observation. The characteristics, advantages, disadvantages, and applicability of the GRB redshift measurement methods are summarized and analyzed. Furthermore, we provide a data set of 611 GRBs with measured redshift. The data set has been collected since 1997. Analysis and statistics are presented based on this data set. We summarize the characteristics of GRBs such as location, time, and accuracy. Finally, we introduce Space-based multi-band astronomical Variable Objects Monitor (SVOM) mission dedicated to searching high redshift GRBs. We also introduce the application prospect of various redshift measurement methods in SVOM mission.

The SVOM/ECLAIRs image trigger with wavelet-based background correction optimised with a one-year simulation of observations

Context. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) mission under development will carry four instruments, and in particular the coded-mask telescope named ECLAIRs, with a large field of view of about 2 sr, operating in the 4–150 keV energy band. The trigger software on board ECLAIRs will search for high-energy transients such as gamma-ray bursts and peculiar behaviour (e.g. strong outbursts) from known X-ray sources, in order to repoint the satellite to perform follow-up observations with the onboard narrow field of view instruments. Aims. The image trigger, one of the two algorithms implemented in the software on board ECLAIRs, produces images over periods of exposure ranging from 20 s to 20 min during which the Earth can cross the field of view. The Cosmic X-ray Background and contributions from known X-ray sources are expected to dominate the ECLAIRs astrophysical and instrumental background and must be taken into account and corrected prior to coded-mask image deconvolution in order to optimise the sensitivity to faint transients. Methods. To correct these background components, we implemented and studied a traditional fitting method and a new method based on wavelet decomposition of the detector image. In order to study and to assess the performance of these methods, we performed a 1-yr simulation of the image trigger on board ECLAIRs. From the images produced during this realistic observation scenario of the SVOM mission, we also defined a way to analyse the sky images to search for new sources. Results. We present the algorithms behind the image trigger on board SVOM/ECLAIRs. We show that the wavelet method we implemented provides similar results in terms of cleaning performance compared to the traditional fitting method, and has the benefit of not requiring any assumption on the shape of the background on the detector. We also calibrate the detection threshold to be adaptive and based on the quality of the reconstructed sky image.

The Simultaneous Three-channel Multicolor CCD Photometric System of the 1.2 m Telescope at Jilin Astronomical Observatory*

Abstract We will introduce the construction and design of a new simultaneous three-channel multicolor CCD photometer. This photometer has been mounted on the 1.2 m telescope at Jilin Astronomical Observatory, and is applied to study space debris, gamma-ray burst afterglows, asteroids and other rapidly variable objects. As one of the ground follow-up telescopes of the Chinese-French Space-based multi-band astronomical Variable Objects Monitor (SVOM) mission, it appears very essential to evaluate the performance of the photometry system of this photometer, which can achieve simultaneous imaging within a field of view of 21.′5 × 21.′5, 21.′5 × 21.′5 and 21.′3 × 21.′3 in the Sloan Digital Sky Survey (SDSS) g′, r′, i′ bands, respectively. Photometric calibrations were carried out by using plenty of SDSS standard stars, and the relationship between the photometric system and the Johnson-Bessel filter system was also studied. The results of the performance evaluation from observing open cluster M67 are presented.

The SVOM Mission

SVOM (Space-based multiband astronomical Variable Objects Monitor) is a sino-french mission that is dedicated to Gamma-Ray Burst (GRB) science, expected to be launched in mid 2023. The mission includes four space-based and three ground-based instruments that, working together, will discover GRBs and provide rapid multi-wavelength follow-up in order to obtain a complete coverage of the GRB emission over seven decades in energy, from the trigger up to the very late phases of the afterglow. Thanks to its characteristics, SVOM will play a crucial role in time-domain and multi-messenger astronomy.

Calibration study of the Gamma-Ray Monitor onboard the SVOM satellite

The Gamma-Ray Monitor (GRM), which is one of the four main scientific instruments onboard the Space-based multi-band astronomical Variable Objects Monitor (SVOM) satellite, is dedicated to the spectrum measurement and study of Gamma-Ray Bursts (GRBs) in the 15 keV to 5 MeV energy band, as well as to perform real-time triggering and localization of the transient bursts in orbit. In order to fully understand the performance of the developed spectrometer and optimize the calibration scheme for the flight model (FM), several calibration campaigns, such as energy–channel relation and energy resolution, detection efficiency, temperature response, high-voltage effect and the non-uniformity tests of detector crystal, have been implemented during the development phase of the qualification model (QM) of GRM, utilizing radionuclides, hard X-ray beam and synchrotron radiation facility. The data analysis results show good agreement with the expected output by Monte Carlo simulations. The detailed optimization scenario for FM calibration is also presented in this paper.

In-orbit background simulation study of SVOM/GRM

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a Chinese-French satellite dedicated to the observation and study of Gamma-Ray Bursts (GRBs) and other variable sources. Among the four scientific payloads onboard SVOM, the Gamma-Ray Monitor (GRM) is designed to detect GRBs in the 15 keV to 5 MeV energy range. The final performance of GRM can be affected by the space environment background during the flight. In this paper, the authors present the in-orbit background simulation results by using the GEANT4 Monte-Carlo simulation toolkit. Additionally, we studied the Earth occultation effect of the space background due to the anti-solar pointing strategy of SVOM. The total background count rate of each spectrometer of GRM fluctuates between about 840 counts/s and 1341 counts/s, and is dominated by the cosmic X-ray background. Finally, we discuss the emission lines of the background and their potential use for in-orbit calibration of GRM. Our simulation study results can help to understand the impact of the space radiation environment on GRM with the latest geometrical model and can be further compared and updated with the real in-orbit measurement in the future.

SVOM: a Joint Gamma-ray Burst Detection Mission

SVOM (Space-based multi-band astronomical Variable Objects Monitor) is an international cooperation project led by the Chinese National Space Agency (CNSA) and the Centre National d’Etudes Spatiales of France (CNES). SVOM focuses on the detection of Gamma-ray bursts (GRBs). It is developed by the Chinese Academy of Sciences (CAS), CNES, and several other French laboratories. With the multi-band observation, fast manoeuvrability, flexible operation, and the capability of ground follow-up observation, the SVOM project will be the most important GRB detection mission after the SWIFT project, and will open a wide exploration field. In this paper, the project management, science objectives, the satellite platform and payloads, the ground segment, and operation concept are illustrated.

Optical design of the visible telescope for the SVOM mission.

This paper describes the optical design of the visible telescope (VT), which is the primary payload for the Chinese-French Space-based multi-band astronomical Variable Objects Monitor (SVOM) mission, for the detection and observation of high-redshift gamma-ray bursts. The VT aims at reaching a limiting magnitude of +22.5Mv with the exposure time of 300 s in the 630 km Sun-synchronous orbit with an inclination of 30°. The VT, also known as the fine guidance sensor for the SVOM, aims to measure the relative performance error (RPE) of the platform during the tracking and provide the RPE to the platform to correct its stability. The optical design is presented in this paper. The mirror manufacture and test results are presented. The optical system performance, tolerance budget, thermal analysis, and stray light design of VT are fully analyzed. Finally, the diffraction encircled energy and point source transmittance are tested in the lab for the finished telescope.

Progress on SVOM Satellite Development

SVOM (Space-based multiband astronomical Variable Objects Monitor) is a Chinese-French space mission dedicated to studying Gamma-Ray Bursts. The satellite has four instruments to detect and localize the prompt GRB emission and measure the evolution of the afterglow in the visible band and in X-rays, and a VHF communication system enabling the fast transmission of SVOM alerts to the ground. The ground segment includes an array of wide-angle cameras and two follow-up telescopes. It was planned to be in orbit in 2021, and now has to be delayed about six months because of COVID-19 epidemic.

Design and implementation of electron diverters for lobster eye space-based X-ray optics.

Micropore optics have recently been implemented in a lobster eye geometry as a compact X-ray telescope. Fields generated by rare-earth magnets are used to reduce the flux of energetic electrons incident upon the focal plane detector in such a setup. We present the design and implementation of the electron diverters for X-ray telescopes of two upcoming missions: the microchannel X-ray telescope onboard the space-based multiband astronomical variable objects monitor and the soft X-ray instrument onboard the solar wind magnetosphere ionosphere link explorer. Electron diverters must be configured to conform to stringent limits on their total magnetic dipole moment and be compensated for any net moment arising from manufacturing errors. The two missions have differing designs, which are presented and evaluated in terms of the fractions of electrons reaching the detector, as determined by relativistic calculations of electron trajectories. The differential flux of electrons to the detector is calculated, and the integrated electron background is determined for both designs.

Optimal slew path planning for the Sino-French Space-based multiband astronomical Variable Objects Monitor mission

The planning algorithm to calculate a satellite’s optimal slew trajectory with a given keep-out constraint is proposed. An energy-optimal formulation is proposed for the Space-based multiband astronomical Variable Objects Monitor Mission Analysis and Planning (MAP) system. The innovative point of the proposed planning algorithm lies in that the satellite structure and control limitation are not considered as optimization constraints but are formulated into the cost function. This modification is able to relieve the burden of the optimizer and increases the optimization efficiency, which is the major challenge for designing the MAP system. Mathematical analysis is given to prove that there is a proportional mapping between the formulation and the satellite controller output. Simulations with different scenarios are given to demonstrate the efficiency of the developed algorithm.

The SVOM mission

The Chinese–French space mission SVOM (Space‐based multiband astronomical Variable Objects Monitor) is mainly designed to detect and localize γ‐ray burst (GRB) events. The satellite, to be launched in late 2021, will carry a set of γ‐ray, X‐ray, and optical imagers. Thanks to its pointing strategy, quick slew capability, and fast data connection to Earth, ground‐based observations with large telescopes will allow us to measure redshifts for an unprecedented number of GRBs. While the association of long GRBs with core‐collapse supernovae (SNe) is well established, short GRBs are most likely due to neutron star (NS)–NS or NS–BH (black hole) mergers and are thus expected to occur simultaneously with bursts of gravitational waves. We discuss here the overall science goals of the SVOM mission in the framework of the multiwavelength and multimessenger panorama of the next decade.

Scientific prospects for spectroscopy of the gamma-ray burst prompt emission with SVOM

SVOM (Space-based multi-band astronomical Variable Objects Monitor) is a Sino-French space mission dedicated to the study of Gamma-Ray Bursts (GRBs) in the next decade, capable to detect and localise the GRB emission, and to follow its evolution in the high-energy and X-ray domains, and in the visible and NIR bands. The satellite carries two wide-field high-energy instruments: a coded-mask gamma-ray imager (ECLAIRs; 4–150 keV), and a gamma-ray spectrometer (GRM; 15–5500 keV) that, together, will characterise the GRB prompt emission spectrum over a wide energy range. In this paper we describe the performances of the ECLAIRs and GRM system with different populations of GRBs from existing catalogues, from the classical ones to those with a possible thermal component superimposed to their non-thermal emission. The combination of ECLAIRs and the GRM will provide new insights also on other GRB properties, as for example the spectral characterisation of the subclass of short GRBs showing an extended emission after the initial spike.

Long GRBs as a tool to investigate star formation in dark matter halos

First stars can only form in structures that are suitably dense, which can be parametrized by the minimum dark matter halo mass Mmin. Mmin must play an important role in star formation. The connection of long gamma-ray bursts (LGRBs) with the collapse of massive stars has provided a good opportunity for probing star formation in dark matter halos. We place some constraints on Mmin using the latest Swift LGRB data. We conservatively consider that LGRB rate is proportional to the cosmic star formation rate (CSFR) and an additional evolution parametrized as (1+z)α, where the CSFR model is a function of Mmin. Using the χ2 statistic, the contour constraints on the Mmin–α plane show that at the 1σ confidence level, we have Mmin<1010.5M⊙ from 118 LGRBs with redshift z<4 and luminosity Liso>1.8×1051 ergs−1. We also find that adding 12 high-z(4<z<5) LGRBs (consisting of 104 LGRBs with z<5 and Liso>3.1×1051 ergs−1) could result in much tighter constraints on Mmin, for which, 107.7M⊙<Mmin<1011.6M⊙ (1σ). Through Monte Carlo simulations, we estimate that future five years of Sino–French spacebased multiband astronomical variable objects monitor (SVOM) observations would tighten these constraints to 109.7M⊙<Mmin<1011.3M⊙. The strong constraints on Mmin indicate that LGRBs are a new promising tool for investigating star formation in dark matter halos.

Onboard GRB trigger algorithms of SVOM-GRM

The Gamma-Ray Monitor (GRM) is a high energy detector onboard the future Chinese-French satellite named the Space-based multi-band astronomical Variable Object Monitor which is dedicated to studies of gamma-ray bursts (GRBs). This paper presents an investigation of the algorithms that look for GRBs by searching for a significant increase in the photon count rate for the computer onboard GRM. The trigger threshold and trigger efficiency, which are based on a given sample of GRBs, are calculated with the algorithms. The trigger characteristics of onboard instruments GRM and ECLAIRs are also analyzed. In addition, the impact of solar flares on GRM is estimated, and a method to distinguish solar flares from GRBs is investigated.

Influence of the Earth on the background and the sensitivity of the GRM and ECLAIRs instruments aboard the Chinese-French mission SVOM

SVOM (Space-based multi-band astronomical Variable Object Monitor) is a future Chinese-French satellite mission which is dedicated to Gamma-Ray Burst (GRB) studies. Its anti-solar pointing strategy makes the Earth cross the field of view of its payload every orbit. In this paper, we present the variations of the gamma-ray background of the two high energy instruments aboard SVOM, the Gamma-Ray Monitor (GRM) and ECLAIRs, as a function of the Earth position. We conclude with an estimate of the Earth influence on their sensitivity and their GRB detection capability.

Prospects for detecting gamma-ray bursts at very high energies with the Cherenkov Telescope Array

We discuss the prospects for the detection of gamma-ray bursts (GRBs) by the Cherenkov Telescope Array (CTA), the next generation, ground-based facility of imaging atmospheric Cherenkov telescopes (IACTs) operating above a few tens of GeV. By virtue of its fast slewing capabilities, the lower energy threshold compared to current IACTs, and the much larger effective area compared to satellite instruments, CTA can measure the spectra and variability of GRBs with excellent photon statistics at multi-GeV energies. Employing a model of the GRB population whose properties are broadly consistent with observations by the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) onboard Fermi, we simulate follow-up observations of GRBs with the Large Size Telescopes (LSTs), the component of CTA with the fastest slew speed and the best sensitivity at energies below a few hundred GeV. For our fiducial assumptions, we foresee that the LSTs can detect ~0.1 GRBs per year during the prompt phase and ~0.5 per year in the afterglow phase, considering only one array site and both GBM and the Space-based multi-band astronomical Variable Object Monitor (SVOM) as the alert instruments. The detection rates can be enhanced by a factor of about 5 and 6 for the prompt emission and the afterglow, respectively, assuming two array sites with the same sensitivity and that the GBM localization error can be reduced to less than 1 deg. The expected distribution of redshift and photon counts are presented, showing that despite the modest event rate, hundreds or more multi-GeV photons can be anticipated from a single burst once they are detected. We also study how the detection rate depends on the intrinsic GRB properties and the delay time between the burst trigger and the follow-up observation.

SVOM Visible Telescope: Performance and Data Process Scheme

AbstractVT (Visible Telescope) is an instrument onboard SVOM (Space-based multi-band astronomical Variable Objects Monitor) satellite working in the visible band, which will play an important role in follow-up of two categories of GRBs: very distant events at higher redshift and faint/soft nearby events in SVOM mission. To fulfill these primary science requirements, decent sensitivity and wavelength coverage are fundamental for VT design. VT performance and data process strategy were successfully studied on its feasibility in Phase A, which is presented in this poster. Additionally, preliminary VT image simulator is also introduced here.