Study On Radio Radiation Properties And Physical Origin Of Mid-infrared Burst Sources

The tidal disruption event(TDE)is a kind of high-energy transient accretion phenomenon in black hole study.It also provides a unique method to study the dominant supermassive black holes in quiescent galaxies.It is crucial to study on the complete dynamic physical process of black hole accretion,relativistic jets,and interstellar gas medium in the galaxy core.TDE can generate broad-band electromagnetic radiation from high-energy gamma and X-rays to ultraviolet optical,infrared,and radio.Recent observations have actually detected dozens of TDEs from X-ray and ultraviolet optical bands,but at present there are very few detections in the radio band,the nature of which is still unclear.The mid-infrared burst is considered to be re-radiation from the absorption of optical or ultraviolet photons by dust.As a new detection window for TDEs,mid-infrared(MIR)burst galaxies provide a unique opportunity to study the dust-enshrouded TDEs.At the same time,observations in the radio band can help to reveal physical mechanism of outburst,probe the jet and non-relativistic outflows,as well as diagnose circumnuclear gas and dust properties around black holes.Based on the advantages of high-resolution,high-sensitivity observations provided by radio interference arrays,and the rich optical spectral database of galaxies from the Sloan Optical Digital Survey,this paper conducted comprehensive studies of radio properties of multiple mid-infrared burst samples selected from in the Wide-field Infrared Survey Explorer.The content of this article is summarized as the following chapters:Chapter 1 starts from the introduction of origin of radio astronomy,the search for supermassive black holes,and the theoretical mechanism of radio radiation.Firstly,we introduced several methods of searching for black holes,as well as the theory of stellar tidal disruption events by black holes,and the current research progress on these topics.Then the mechanism of radio radiation is briefly described,which mainly consists of thermal and non-thermal radiation.Non-thermal radiation is generally dominated by synchrotron radiation.In this case,there is a power-law relationship between flux density and frequency.Finally,from the application aspects of radio atmospheric window and comprehensive aperture interferometry technology in radio telescopes,we highlight the importance and advantages of radio-band observational studies in astronomy.Chapter 2 presents the main results of this paper.We performed deep VLA observations of nearby MIR bursts sources which consist of two-epochs observations at C-band and single epoch observations at L-band.First of all,we detected 12 radio radiation above 5? level out of 16 sources in the sample,corresponding to the radio detection rate of 75%.The radio emission is extremely compact and most sources cannot be resolved.We have found that star formation contribution to the radio emission is low(<10%),but active galactic nuclei(AGN),transient jets,or outflows as origins for the radio emission are possible.The current observations cannot distinguish these scenarios.In the second monitoring observations of the sub-sample,we found that except for the three AGN-type sources with slight increase in brightness,the radio flux for the remaining sources is decreased,four of which have dropped at least 1.5 times,strongly suggesting that the radio emission for them is transient.Most of detected sources have the radio spectral index less than-0.5.Our results highlight the importance of radio monitoring observations which are important to uncover the nature of nuclear MIR bursts in our sample.Chapter 3 explores the nature of galaxy transient MIR flares from the perspective of radio variability with GMRT observations.We found that the flux for all four sources in the sample has slightly increased compared to that obtained from the FIRST survey.Their radio emission is compact and not resolved by GMRT at a resolution of 2".The explanation of the transient MIR flare of the sample with the beaming jet is basically excluded,which may instead originate from the AGN or TDE heated dust emission.In addition,in the comparison of radio-loud and radio-quiet sub-samples,it is found that the variability of radio-quiet sources is more significant,which may be more sensitive to transient MIR bursts.It is expected to detect the transient jet radiation due to TDE from follow-up observations.Chapter 4 presents the VLA observations of MIR burst galaxy samples with or without newly emerging coronal lines or broad Balmer emission lines in our optical spectroscopy monitoring observation.We find that the radio detection rate is as high as 89%.All the detected radio emission is compact and likely from the centers of galaxies.It is impossible to distinguish between the radio detection properties between the strong coronal and the non-coronal lines sources.Our results suggest that there may be no necessary connection between coronal lines and radio emission.The study of this sample provides observational data to determine whether radio echo is ubiquitous between extremely strong coronal line sources,thereby further reveals the diversity or universality of the distribution of interstellar medium around supermassive black holes.Chapter 5 is the summary of results,including the innovations and deficiencies of the research in our works.We also present the research plan and prospects for future works.