Characteristics Of Variability In Mrk 509 With Swift

The nuclei or centers of extragalactic objects are usually regarded as active galactic nuclei(AGNs),which have violent activities or intense physical process-es.So much energy of AGNs is generally thought to derive from the central supermassive black holes by accreting surrounding material.Variability has long been recongnized as one of the most typical characteristics of AGNs and it is not limited to one wavelength regime but is spread across the entire electromag-netic spectrum.It is very helpful for us to understand the physical structures and mechanisms to study the variability of X-ray and UV/Optical continuum of AGNs.It also plays an important rolc in limiting the theoretical model of AGNs'central region.In order to study the characteristics of accretion disk and corona in AGNs'central region,Swift monitoring of the Seyfert 1 galaxy Mrk 509 has been car-ried out in intensive multi-band(X-ray,ultraviolet and optical)simultaneously over 9 months,with an average of about once a day from March to December in 2017.The absolute/relative variability amplitudes in UV/optical bands de-crease as the wavelengths increase.The absolute variability amplitude at hard X-ray is significantly lower than that in UV.As we study the color variance of UV/optical continuum,the trend of bluer when brighter is notable but its timescale-dependence is not apparent.The interpolated cross-correlation func-tion(ICCF)is used to measure the interband correlation and lags.The correla-tion within the UV/Optical is strong with the maximum correlation coefficient rmax=0.97-1.00.The UV/Optical interband lags are generally consistent with??? 4/3,as predicted by centrally illuminated thin accretion disk model.How-ever,the normalization coefficient ?0=1.20±0.27 indicates a disk radius of 1.20 lt-day at 1928 A,larger than the prediction of standard thin accretion disk mod-el.However,it can be considered to be consistent with the theory of standard thin accretion disk model due to the great uncertainty of theoretical prediction.The X-ray/UV correlations are found to be much weaker than those within the UV/optical,and it seems that the X-ray lags the UV,posing sever problems for the lamp-post reprocessing model.The U band shows a significantly larger than expected from the fitting with accretion disk model and surrounding bands,which could be due to Balmer continuum emission from the broad-line region(BLR).The precise mixing of disk and BLR components cannot be determined from these data alone.Finally,several models of accretion disks and corona are discussed in order to explain the time delay relationship between X-ray and UV/optical continuum.