据国家天文台官网消息,1月24日,500米口径球面射电望远镜(FAST)与上海65米射电望远镜天马望远镜首次成功实现联合观测,获得甚长基线干涉测量(VLBI)干涉条纹。国家天文台F A S T团队与上海天文台VLBI团队合作,利用FAST与天马望远镜进行...据国家天文台官网消息,1月24日,500米口径球面射电望远镜(FAST)与上海65米射电望远镜天马望远镜首次成功实现联合观测,获得甚长基线干涉测量(VLBI)干涉条纹。国家天文台F A S T团队与上海天文台VLBI团队合作,利用FAST与天马望远镜进行了条纹干涉实验,对致密射电源3C454.3进行了联合观测.展开更多
Fast radio bursts(FRBs) were first discovered(Lorimer et al. 2007) serendipitously during a search for radio pulses in archival data in 2007. In the intervening period, FRBs have become an active area of astrophysical...Fast radio bursts(FRBs) were first discovered(Lorimer et al. 2007) serendipitously during a search for radio pulses in archival data in 2007. In the intervening period, FRBs have become an active area of astrophysical research that has attracted a diverse community of several hundred astronomers around the world.展开更多
We investigate the influence of population density on radio-frequency inter- ference （RFI） affecting radio astronomy. We use a new method to quantify the thresh- old of population density in order to determine the m...We investigate the influence of population density on radio-frequency inter- ference （RFI） affecting radio astronomy. We use a new method to quantify the thresh- old of population density in order to determine the most suitable lower limit for site selection of a radio quiet zone （RQZ）. We found that there is a certain trend in the population density-RFI graph that increases rapidly at lower values and slows down to almost fiat at higher values. We use this trend to identify the thresholds for pop- ulation density that produce RFI. Using this method we found that, for frequencies up to 2.8 GHz, low, medium and high population densities affecting radio astronomy are below 150 ppl km-2, between i50 ppl km-2 and 5125 ppl km-~, and above 5125 ppl km-2 respectively. We also investigate the effect of population density on the environment of RFI in three astronomical windows, namely the deuterium, hydro- gen and hydroxyl lines. We find that a polynomial fitting to the population density produces a similar trend, giving similar thresholds for the effect of population density. We then compare our interference values to the standard threshold levels used by the International Telecommunication Union within these astronomical windows.展开更多
We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB20201124A with the Five-hundred-meter Aperture Spherical radio Telescope(FAST)during an extremely active epis...We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB20201124A with the Five-hundred-meter Aperture Spherical radio Telescope(FAST)during an extremely active episode on UTC 2021 September 25–28 in a series of four papers.In this second paper of the series,we study the energy distribution of 881 bursts(defined as significant signals separated by dips down to the noise level)detected in the first four days of our 19 hr observational campaign spanning 17 days.The event rate initially increased exponentially but the source activity stopped within 24 hr after the 4th day.The detection of 542 bursts in one hour during the fourth day marked the highest event rate detected from one single FRB source so far.The bursts have complex structures in the time-frequency space.We find a double-peak distribution of the waiting time,which can be modeled with two log-normal functions peaking at 51.22 ms and 10.05 s,respectively.Compared with the emission from a previous active episode of the source detected with FAST,the second distribution peak time is smaller,suggesting that this peak is defined by the activity level of the source.We calculate the isotropic energy of the bursts using both a partial bandwidth and a full bandwidth and find that the energy distribution is not significantly changed.We find that an exponentially connected broken-power law function can fit the cumulative burst energy distribution well,with the lower and higher-energy indices being-1.22±0.01 and-4.27±0.23,respectively.Assuming a radio radiative efficiency ofη_(r)=10^(-4),the total isotropic energy of the bursts released during the four days when the source was active is already 3.9×10^(46)erg,exceeding~23%of the available magnetar dipolar magnetic energy.This challenges the magnetar models which invoke an inefficient radio emission(e.g.,synchrotron maser models).展开更多
It was pointed out that Type Ⅱ supernovae would develop instabilities and asymmetric structure during its explosion. SN1987A, for the first time, provided direct and convincing observational evidence of such behavior...It was pointed out that Type Ⅱ supernovae would develop instabilities and asymmetric structure during its explosion. SN1987A, for the first time, provided direct and convincing observational evidence of such behavior. SN1993J confirmed this, too. On July 12, 1993, we obtained a low resolution (5.3 /pixel) spectrum of SN1993J using the 2.16 m telescope in Beijing Astronomical Observatory. We found that many fine structures appeared in the [OI] and H_x lines. This showed that clumping, chemical mixing and strong instabilities had occurred in the ejecta展开更多
文摘据国家天文台官网消息,1月24日,500米口径球面射电望远镜(FAST)与上海65米射电望远镜天马望远镜首次成功实现联合观测,获得甚长基线干涉测量(VLBI)干涉条纹。国家天文台F A S T团队与上海天文台VLBI团队合作,利用FAST与天马望远镜进行了条纹干涉实验,对致密射电源3C454.3进行了联合观测.
文摘Fast radio bursts(FRBs) were first discovered(Lorimer et al. 2007) serendipitously during a search for radio pulses in archival data in 2007. In the intervening period, FRBs have become an active area of astrophysical research that has attracted a diverse community of several hundred astronomers around the world.
基金made possible by the usage of the University of Malaya’s grants UMRG(RG118-10AFR),IPPP(PV025-2011A)and HIR(H-21001-F000028)Universiti Sultan Zainal Abidin(UniSZA)and the Ministry of Higher Education(MOHE)for their sponsorship
文摘We investigate the influence of population density on radio-frequency inter- ference （RFI） affecting radio astronomy. We use a new method to quantify the thresh- old of population density in order to determine the most suitable lower limit for site selection of a radio quiet zone （RQZ）. We found that there is a certain trend in the population density-RFI graph that increases rapidly at lower values and slows down to almost fiat at higher values. We use this trend to identify the thresholds for pop- ulation density that produce RFI. Using this method we found that, for frequencies up to 2.8 GHz, low, medium and high population densities affecting radio astronomy are below 150 ppl km-2, between i50 ppl km-2 and 5125 ppl km-~, and above 5125 ppl km-2 respectively. We also investigate the effect of population density on the environment of RFI in three astronomical windows, namely the deuterium, hydro- gen and hydroxyl lines. We find that a polynomial fitting to the population density produces a similar trend, giving similar thresholds for the effect of population density. We then compare our interference values to the standard threshold levels used by the International Telecommunication Union within these astronomical windows.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11988101 and 11725313)supported by the Open Project Program of the Key Laboratory of FAST,Chinese Academy of Sciences+11 种基金support from the National Natural Science Foundation of China(NSFC,Grant No.U2031117)the Youth Innovation Promotion Association CAS(id.2021055)CAS Project for Young Scientists in Basic Research(grant YSBR-006)the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupported by the Key Research Project of Zhejiang Lab No.2021PE0AC0supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11988101 and 11833009)the Key Research Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSWSLH021)supported by the Cultivation Project for the FAST scientific Payoff and Research Achievement of CAMSCASsupported by National SKA Program of China 2020SKA0120200National Natural Science Foundation of China(NSFC,Grant No.12041303)the CAS-MPG LEGACY projectfunding from the MaxPlanck Partner Group。
文摘We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB20201124A with the Five-hundred-meter Aperture Spherical radio Telescope(FAST)during an extremely active episode on UTC 2021 September 25–28 in a series of four papers.In this second paper of the series,we study the energy distribution of 881 bursts(defined as significant signals separated by dips down to the noise level)detected in the first four days of our 19 hr observational campaign spanning 17 days.The event rate initially increased exponentially but the source activity stopped within 24 hr after the 4th day.The detection of 542 bursts in one hour during the fourth day marked the highest event rate detected from one single FRB source so far.The bursts have complex structures in the time-frequency space.We find a double-peak distribution of the waiting time,which can be modeled with two log-normal functions peaking at 51.22 ms and 10.05 s,respectively.Compared with the emission from a previous active episode of the source detected with FAST,the second distribution peak time is smaller,suggesting that this peak is defined by the activity level of the source.We calculate the isotropic energy of the bursts using both a partial bandwidth and a full bandwidth and find that the energy distribution is not significantly changed.We find that an exponentially connected broken-power law function can fit the cumulative burst energy distribution well,with the lower and higher-energy indices being-1.22±0.01 and-4.27±0.23,respectively.Assuming a radio radiative efficiency ofη_(r)=10^(-4),the total isotropic energy of the bursts released during the four days when the source was active is already 3.9×10^(46)erg,exceeding~23%of the available magnetar dipolar magnetic energy.This challenges the magnetar models which invoke an inefficient radio emission(e.g.,synchrotron maser models).
文摘It was pointed out that Type Ⅱ supernovae would develop instabilities and asymmetric structure during its explosion. SN1987A, for the first time, provided direct and convincing observational evidence of such behavior. SN1993J confirmed this, too. On July 12, 1993, we obtained a low resolution (5.3 /pixel) spectrum of SN1993J using the 2.16 m telescope in Beijing Astronomical Observatory. We found that many fine structures appeared in the [OI] and H_x lines. This showed that clumping, chemical mixing and strong instabilities had occurred in the ejecta
