分类： 天文学 >> 天文学 提交时间： 2023-02-19
Qichun Liu
Jie Lin
Xiaofeng Wang
Shenghong Gu
Jianrong Shi
Liyun Zhang
Gaobo Xi
Jun Mo
Yongzhi Cai
Liyang Chen
Zhihao Chen
Fangzhou Guo
Xiaojun Jiang
Gaici Li
Wenxiong Li
Han Lin
Weili Lin
Jialian Liu
Cheng Miao
Xiaoran Ma
摘要： Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by the TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with $G_{\rm BP}-G_{\rm RP}$ > 2.0 mag, however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (F_peak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., $F_{{\rm peak}} \propto {\rm ED}^{0.72\pm0.04}$, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while -- for the more popular non-thermal electron heating model -- a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter $F_{{\rm peak}} \propto {\rm ED}$ relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger H alpha emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass having frequent flares are found to show H alpha emission of similar strength in their spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xutao Zheng
Huaizhong Gao
Jiaxing Wen
Ming Zeng
Xiaofan Pan
Dacheng Xu
Yihui Liu
Yuchong Zhang
Haowei Peng
Yuchen Jiang
Xiangyun Long
Di'an Lu
Dongxin Yang
Hua Feng
Zhi Zeng
Jirong Cang
Yang Tian
GRID Collaboration
摘要： Recently, silicon photomultipliers (SiPMs) have been used in several space-borne missions, owing to their solid state, compact size, low operating voltage, and insensitivity to magnetic fields. However, operating SiPMs in space results in radiation damage and degraded performance. In-orbit quantitative studies on these effects are limited. In this study, we present in-orbit SiPM characterization results obtained by the second detector of the Gamma-Ray Integrated Detectors (GRID-02), which was launched on 6 November 2020. An increase in dark current of $\sim$100 $\mu$A/year per SiPM chip (model MicroFJ-60035-TSV) at 28.5 V and 5 $^{\circ}$C was observed. Consequently, the overall noise level (sigma) of the GRID-02 detector increased by $\sim$7.5 keV/year. The estimate of this increase is $\sim$40 $\mu$A/year per SiPM chip at -20 $^{\circ}$C, highlighting the positive effect of using a cooling system.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Qichun Liu
Jie Lin
Xiaofeng Wang
Shenghong Gu
Jianrong Shi
Liyun Zhang
Gaobo Xi
Jun Mo
Yongzhi Cai
Liyang Chen
Zhihao Chen
Fangzhou Guo
Xiaojun Jiang
Gaici Li
Wenxiong Li
Han Lin
Weili Lin
Jialian Liu
Cheng Miao
Xiaoran Ma
摘要： Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by the TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with $G_{\rm BP}-G_{\rm RP}$ > 2.0 mag, however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (F_peak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., $F_{{\rm peak}} \propto {\rm ED}^{0.72\pm0.04}$, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while -- for the more popular non-thermal electron heating model -- a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter $F_{{\rm peak}} \propto {\rm ED}$ relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger H alpha emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass having frequent flares are found to show H alpha emission of similar strength in their spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xutao Zheng
Huaizhong Gao
Jiaxing Wen
Ming Zeng
Xiaofan Pan
Dacheng Xu
Yihui Liu
Yuchong Zhang
Haowei Peng
Yuchen Jiang
Xiangyun Long
Di'an Lu
Dongxin Yang
Hua Feng
Zhi Zeng
Jirong Cang
Yang Tian
GRID Collaboration
摘要： Recently, silicon photomultipliers (SiPMs) have been used in several space-borne missions, owing to their solid state, compact size, low operating voltage, and insensitivity to magnetic fields. However, operating SiPMs in space results in radiation damage and degraded performance. In-orbit quantitative studies on these effects are limited. In this study, we present in-orbit SiPM characterization results obtained by the second detector of the Gamma-Ray Integrated Detectors (GRID-02), which was launched on 6 November 2020. An increase in dark current of $\sim$100 $\mu$A/year per SiPM chip (model MicroFJ-60035-TSV) at 28.5 V and 5 $^{\circ}$C was observed. Consequently, the overall noise level (sigma) of the GRID-02 detector increased by $\sim$7.5 keV/year. The estimate of this increase is $\sim$40 $\mu$A/year per SiPM chip at -20 $^{\circ}$C, highlighting the positive effect of using a cooling system.
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