With an extensive analysis,we study the temporal evolution of magnetic flux during three successive M-class flares in two adjacent active regions：NOAA 10039 and 10044.The primary data are full disk longitudinal magne...With an extensive analysis,we study the temporal evolution of magnetic flux during three successive M-class flares in two adjacent active regions：NOAA 10039 and 10044.The primary data are full disk longitudinal magnetograms observed by SOHO/MDI.All three flares are observed to be accompanied by magnetic flux changes.The changes occurred immediately or within 1 ～ 10 minutes after the starting time of the flares,indicating that the changes are obvious consequences of the solar flares.Although changes in many points are intrinsic in magnetic flux,for some sites,it is caused by a rapid expansion motion of magnetic flux.For the second flare,the associated change is more gradual compared with the ＇step-function＇ reported in literature.Furthermore,we use the data observed by the Imaging Vector Magnetograph（IVM） at Mees Solar Observatory to check possible line profile changes during the flares.The results from the IVM data confirm the flux changes obtained from the MDI data.A series of line profiles were obtained from the IVM＇s observations and analyzed for flux change sites.We find that the fluctuations in the width,depth and central wavelength of the lines are less than 5.0 even at the flare＇s core.No line profile change is observed during or after the flare.We conclude that the magnetic field changes associated with the three solar flares are not caused by flare emission.展开更多
White-light flares are considered to be the most energetic flaring events that are observable in the optical broad-band continuum of the solar spectrum. They have not been commonly observed. Observations of white-ligh...White-light flares are considered to be the most energetic flaring events that are observable in the optical broad-band continuum of the solar spectrum. They have not been commonly observed. Observations of white-light flares with sub-arcsecond resolution have been very rare. The continuous high resolution observations of Hinode provide a unique opportunity to systematically study the white-light flares with a spatial resolution around 0.2 arcsec. We surveyed all the flares above GOES magnitude C5.0 since the launch of Hinode in 2006 October. 13 of these kinds of flares were covered by the Hinode G-band observations. We analyzed the peak contrasts and equivalent areas （calculated via integrated excess emission contrast） of these flares as a function of the GOES X-ray flux, and found that the cut-off visibility is likely around M1 flares under the observing limit of Hinode. Many other observational and physical factors should affect the visibility of white-light flares; as the observing conditions are improved, smaller flares are likely to have detectable white-light emissions. We are cautious that this limiting visibility is an overestimate, because G-band observations contain emissions from the upper atmosphere. Among the 13 events analyzed, only the M8.7 flare of 2007 June 4 had near-simultaneous observations in both the G-band and the blue continuum. The blue continuum had a peak contrast of 94% vs. 175% in G-band for this event. The equivalent area in the blue continuum is an order of magnitude lower than that in the G-band. Very recently, Jess et al. studied a C2.0 flare with a peak contrast of 300% in the blue continuum. Compared to the events presented in this letter, that event is probably an unusual white-light flare： a very small kernel with a large contrast that can be detected in high resolution observations.展开更多
基金Supported by the National Natural Science Foundation of China (Grants Nos. 10833007,10933003 and 10928307)the National Basic Research Program of China (973 Program) under grant 2011CB811402
文摘With an extensive analysis,we study the temporal evolution of magnetic flux during three successive M-class flares in two adjacent active regions：NOAA 10039 and 10044.The primary data are full disk longitudinal magnetograms observed by SOHO/MDI.All three flares are observed to be accompanied by magnetic flux changes.The changes occurred immediately or within 1 ～ 10 minutes after the starting time of the flares,indicating that the changes are obvious consequences of the solar flares.Although changes in many points are intrinsic in magnetic flux,for some sites,it is caused by a rapid expansion motion of magnetic flux.For the second flare,the associated change is more gradual compared with the ＇step-function＇ reported in literature.Furthermore,we use the data observed by the Imaging Vector Magnetograph（IVM） at Mees Solar Observatory to check possible line profile changes during the flares.The results from the IVM data confirm the flux changes obtained from the MDI data.A series of line profiles were obtained from the IVM＇s observations and analyzed for flux change sites.We find that the fluctuations in the width,depth and central wavelength of the lines are less than 5.0 even at the flare＇s core.No line profile change is observed during or after the flare.We conclude that the magnetic field changes associated with the three solar flares are not caused by flare emission.
基金The work is sup-ported by NSF under grant ATM 07-45744NASA under grants NNX07AH78G, NNX08AJ23Gand NNX08AQ90G
文摘White-light flares are considered to be the most energetic flaring events that are observable in the optical broad-band continuum of the solar spectrum. They have not been commonly observed. Observations of white-light flares with sub-arcsecond resolution have been very rare. The continuous high resolution observations of Hinode provide a unique opportunity to systematically study the white-light flares with a spatial resolution around 0.2 arcsec. We surveyed all the flares above GOES magnitude C5.0 since the launch of Hinode in 2006 October. 13 of these kinds of flares were covered by the Hinode G-band observations. We analyzed the peak contrasts and equivalent areas （calculated via integrated excess emission contrast） of these flares as a function of the GOES X-ray flux, and found that the cut-off visibility is likely around M1 flares under the observing limit of Hinode. Many other observational and physical factors should affect the visibility of white-light flares; as the observing conditions are improved, smaller flares are likely to have detectable white-light emissions. We are cautious that this limiting visibility is an overestimate, because G-band observations contain emissions from the upper atmosphere. Among the 13 events analyzed, only the M8.7 flare of 2007 June 4 had near-simultaneous observations in both the G-band and the blue continuum. The blue continuum had a peak contrast of 94% vs. 175% in G-band for this event. The equivalent area in the blue continuum is an order of magnitude lower than that in the G-band. Very recently, Jess et al. studied a C2.0 flare with a peak contrast of 300% in the blue continuum. Compared to the events presented in this letter, that event is probably an unusual white-light flare： a very small kernel with a large contrast that can be detected in high resolution observations.
