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As a new member of GECAM mission, the GECAM-C (also called High Energy Burst Searcher, HEBS) is a gamma-ray all-sky monitor onboard SATech-01 satellite, which was launched on July 27th, 2022 to detect gamma-ray transients from 6 keV to 6 MeV, such as Gamma-Ray Bursts (GRBs), high energy counterpart of Gravitational Waves (GWs) and Fast Radio Bursts (FRBs), and Soft Gamma-ray Repeaters (SGRs). Together with GECAM-A and GECAM-B launched in December 2020, GECAM-C will greatly improve the monitoring coverage, localization, as well as temporal and spectral measurements of gamma-ray transients. GECAM-C employs 12 SiPM-based Gamma-Ray Detectors (GRDs) to detect gamma-ray transients . In this paper, we firstly give a brief description of the design of GECAM-C GRDs, and then focus on the on-ground tests and in-flight performance of GRDs. We also did the comparison study of the SiPM in-flight performance between GECAM-C and GECAM-B. The results show GECAM-C GRD works as expected and is ready to make scientific observations., Comment: 18 pages, 16 figures

Fast and reliable localization of high-energy transients is crucial for characterizing the burst properties and guiding the follow-up observations. Localization based on the relative counts of different detectors has been widely used for all-sky gamma-ray monitors. There are two major methods for this counts distribution localization: $\chi^{2}$ minimization method and the Bayesian method. Here we propose a modified Bayesian method that could take advantage of both the accuracy of the Bayesian method and the simplicity of the $\chi^{2}$ method. With comprehensive simulations, we find that our Bayesian method with Poisson likelihood is generally more applicable for various bursts than $\chi^{2}$ method, especially for weak bursts. We further proposed a location-spectrum iteration approach based on the Bayesian inference, which could alleviate the problems caused by the spectral difference between the burst and location templates. Our method is very suitable for scenarios with limited computation resources or time-sensitive applications, such as in-flight localization software, and low-latency localization for rapid follow-up observations.

Utility preference robust optimization (PRO) has recently been proposed to deal with optimal decision making problems where the decision maker's (DM) preference over gains and losses is ambiguous. In this paper, we take a step further to investigate the case that the DM's preference is not only ambiguous but also potentially inconsistent or even displaying some kind of randomness. We propose a distributionally preference robust optimization (DPRO) approach where the DM's preference is represented by a random utility function and the ambiguity is described by a set of probability distributions of the random utility. An obvious advantage of the new DPRO model is that it no longer concerns the DM's preference inconsistency. In the case when the random utility functions are of piecewise linear structure, we propose two statistical methods for constructing the ambiguity set: an ellipsoidal method and a bootstrap method both of which are fundamentally based on the idea of confidence region with the sample mean of the random parameters, and demonstrate how the resulting DPRO can be solved by a cutting surface algorithm and an MISOCP respectively. We also show how the DPRO models with general random utility functions may be approximated by those with piecewise linear random utility functions. Finally, we apply the proposed DPRO model in car manufacturing and facility location planning and show how the random samples may be extracted by multinomial logit method and conjoint analysis/machine learning. The paper is the first attempt to use distributionally robust optimization methods for PRO., Comment: 47 pages, 9 figures, 4 tables

Each satellite of the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM, mission) consists of 25 SiPM based gamma-ray detectors (GRDs). Although SiPM based GRD has merits of compact size and low bias-voltage, the drift of the SiPM gain with temperature is a severe problem for GRD performance. An adaptive voltage supply source was designed to automatically adjust the SiPM bias voltage to compensate the temperature effects and keep the gain stable. This approach has been proved to be effective during both the on-ground and in-flight tests. The in-flight measured variation of the SiPM gain is within 2%. To reduce the gain non-uniformity of GRDs, an iterative bias voltage adjustment approach is proposed and implemented. The gain non-uniformity is reduced from 17% to 0.6%. In this paper, the gain stabilization and consistency correction approach are presented and discussed in detail., Comment: 14 pages, 21 figures

The population of satellite galaxies in a host galaxy is a combination of the cumulative accretion of subhaloes and their associated star formation efficiencies, therefore, the luminosity distribution of satellites provides valuable information of both dark matter properties and star formation physics. Recently, the luminosity function of satellites in nearby Milky Way-mass galaxies has been well measured to satellites as faint as Leo I with $M_{V} \sim -8$. In addition to the finding of the diversity in the satellite luminosity functions, it has been noticed that there is a big gap among the magnitude of satellites in some host galaxies, such as M101, where the gap is around 5 in magnitude, noticeably larger than the prediction from the halo abundance matching method. The reason of this gap is still unknown. In this paper, we use a semi-analytical model of galaxy formation, combined with high-resolution N-body simulation, to investigate the probability and origin of such big gap in M101-alike galaxies. We found that, although M101 analogues are very rare with probability of \sim 0.1%-0.2% in the local universe, their formation is a natural outcome of the CDM model. The gap in magnitude is mainly due to the mass of the accreted subhaloes, not from the stochastic star formation in them. We also found that the gap is correlated with the total satellite mass and host halo mass. By tracing the formation history of M101 type galaxies, we find that they likely formed after $z \sim 1$ due to the newly accreted bright satellites. The gap is not in a stable state, and it will disappear in ~7 Gyr due to mergers of bright satellites with the central galaxy., Comment: 8 pages, 11 figures, accepted by MNRAS

The main scientific goal of the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is to monitor various types of Gamma-Ray Bursts (GRB) originated from merger of binary compact stars, which could also produce gravitational wave, and collapse of massive stars. In order to study the response of GECAM Gamma-Ray Detectors (GRDs) to high-energy bursts and test the in-flight trigger and localization software of GECAM before the launch, a portable GRB simulator device is designed and implemented based on grid controlled X-ray tube (GCXT) and direct digital synthesis (DDS) technologies. The design of this GRB simulator which modulates X-ray flux powered by high voltage up to 20 kV is demonstrated, and the time jitter (FWHM) of the device is about 0.9 $\mu$s. Before the launch in December, 2020, both two GECAM satellites were irradiated by different types of GRBs (including short and long bursts in duration) generated by this GRB simulator. The light curves detected with GECAM/GRDs are consistent with the programmed input functions within statistical uncertainties, indicating the good performance of both the GRDs and the GRB simulator., Comment: 15 pages, 12 figures, accepted to be published in Experimental Astronomy on 09 July 2021

Observational work have shown that the two brightest satellite galaxies of the Milky Way (MW), the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), are rare amongst MW analogues. It is then interesting to know whether the presence of massive satellite has any effect on the whole satellite population in MW analogues. In this article, we investigate this problem using a semi-analytical model combined with the Millennium-II Simulation. MW-analogous galaxies are defined to have similar stellar mass or dark matter halo mass to the MW. We find that, in the first case, the halo mass is larger and there are, on average, twice as many satellites in Milky Way analogs if there is a massive satellite galaxy in the system. This is mainly from the halo formation bias. The difference is smaller if MW analogues are selected using halo mass. We also find that the satellites distribution is slightly asymmetric, being more concentrated on the line connecting the central galaxy and the massive satellite and that, on average, LMC have brought in 14.7 satellite galaxies with $M_{r}<0$ at its accretion, among which 4.5 satellites are still within a distance of 50kpc from the LMC. Considering other satellites, we predict that thereare 7.8 satellites with 50kpc of the LMC. By comparing our model with the early data of Satellites Around Galactic Analogs (SAGA), a survey to observe satellite galaxies around 100 Milky Way analogues, we find that SAGA has more bright satellites and less faint satellites than our model predictions. A future comparison with the final SAGA data is needed., Comment: 9 pages, 10 figures, published in MNRAS

Based on the neutron and proton degrees of freedom, the low-lying energy levels, the $E2$, $M1$ and $E0$ transition strengths of nucleus $^{124}$Te have been calculated by the neutron-proton interacting boson model. The calculated results are quite consistent with the experimental data. By comparing the key observables of states at the critical point of $\textrm{U}_{\pi \nu}(5)$--$\textrm{O}_{\pi \nu}(6)$ transition with experimental data and calculated results, we show that the $^{124}$Te is a possible nucleus at the critical point of the second order phase transition from vibration to unstable rotation and such a critical point contains somewhat triaxial rotation. The 0$^+_2$ state of $^{124}$Te can be interpreted as the lowest state of the first excited family of intrinsic levels in the critical point symmetry., Comment: 19 pages, 1 figure, 3 tables

The properties of the low-lying states, especially the relevant shape coexistence in $^{80}$Ge close to one of most neutron-rich doubly magic nuclei at $N=50$ and $Z=28$ have been investigated within the framework of the proton-neutron interacting model (IBM-2). Based on the fact that the relative energy of the $d$ neutron boson is different from proton bosons', the calculated energy levels of low-lying states, $E2$ transition strengths can reproduce the experimental data very well. Particularly, the first excited state 0$^+_2$ is reproduced quite nicely, which is intimately related with the shape coexistence phenomenon. And the $\rho^2(E0, 0^+_2\rightarrow0^+_1)$ transition strength has been predicted. The experimental data and theoretical results indicate that both collective spherical and $\gamma$-soft vibration structures coexist in $^{80}$Ge. Key words: $^{80}$Ge, low-lying states, $E0$ transition strengths, shape coexistence, IBM-2., Comment: 13 pages, 1 figure, accepted by Chinese Physics C