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Observations of the white light flare on 27 October, 1991
@ Pergamon Press Ltd Printed in Great Britain 0275-1062/93%24.00+.00
Chin. Astron. Astrophys. (1993)17/3,291-295 A translation of Acta Astron. Sin. (1993) 34/l, 89-91
Observations
of the white light flare
on 27 October, HUANG Zhen Urumgi Astronomical
station,
MA Lu
Chinese Academy
FANG Cheng Department
1991t
of Astronomy,
of Sciences, Xinjiang,
830011
HU Ju Nanjing university
Abstract A X6.1/3B flare, occurring near the center of solar disk on 27 October 1991, was observed simultaneously by the solar patrol telescope of the Urumgi Astronomical station with five wide-band filters and by the Solar Tower of Nanjing University with a multichannel spectrograph. The observations indicate that it is a white light flare. The observations and some preliminary results are described in this paper. Key
words:
Sun - white light flare
Since Carrington and Hodgson discovered for the first time a white light flare (WLF) in 1859, only about 80 WLFs have been reported all over the world during more than one hundred year&l. Among them, near ten have spectral data recorded . This is mainly due to the fact that the number of WLFs is at most only several percent of the total number of flares121and most of them appear at the impulsive phase of flares with a duration of only several minutes, resulting in the great difficulty to observe them. Just for this reason, there is so far much controversy about the radiative characteristics, the energy sources and the energy transport mechanism of WLFs. T_hus, the observation and the study of WLFs are ones of the frontiers of flare physics and have been attached much importance to in solar physics community131. A WLF patrol telescope was installed at the Urumgi Astronomical Station (UAS) in 1990. The aperture of the telescope is 10 cm and the focal length is 1.2 m. Six wide-band filters are placed before the focal plane with the wavelength/passband of 3602121.0 A, 3874122.1 respectively. The six filters A, 4182130.3 A, 4969131.3 A, 5654124.5 A and 6380128.5 A can be rotated by step motors, which are controlled by an IBM PC/AT computer, so six monochromatic frames can be obtained successively. A TM-46 CCD camera with 422 x 579 pixels is used to receive the signals. The size of each pixel corresponds to 1.“48 x 0.“95 t Supported by National Natural Science Foundation and National Educational Commission Ph. D. Foundation Received 1992 June 23; revised version 1992 September 23
292
Fig. 1
HUANG Zhen et al.
Temporal evolution at 3874&22.1A
of the Oct. 27, 1991 WLF observed by Urumgi
Observatory
on the solar image. The data of monochromatic images are acquired by a SR 151 image processor and stored on the disk of the computer. Much improvement of the solar tower telescope (STT) of Nanjing University was finished in 1990. The aperture of the coeiostat is 60 cm. The aperture of the objective mirror is 43 cm with a focal length of 21.7 m. With a fast multi-channel spectrograph, the spectra round Ha, H/3, H7, NaI D, CaII K and H can be photographed simultaneously. The dispersions are about 1 mm A-l. A X6.1/3B major flare occurred near the center of the solar disk (S13 E15) in AR6891 on October 27, 1991. According to the report of NOAAl*l, it is a proton flare. The Ha: emission began to increase before 05:38 UT, reached m~mum at 05:49 UT and ended after 06:58 UT. Soft X-ray burst (from GOES data) started at 05:37 UT with maximum at 05:48 UT and ended at 07:12 UT. The observations of the flare were made both with the patrol telescope at UAS and with STT at Nanjing University. The temporal variations of five wide-baud monochromatic images and four wavelength band (Ha, HP, Hy and NaI D) spectra have been obtained respectively. The temporal resolution of the observation of UAS is about 30 s., and the observational period is 04:59 N 06:53 UT. The monochromatic images at 05:40:30 UT and at 05:41:06 UT are a little dimmed due to focusing defect and need to be dealt with further. The temporal resolution of the spectral observation of STT is 10 - 15 s. The observational period is 05:39 - 06:30 UT. Fig.1 gives the temporal evolution of the flare monochromatic images observed by UAS in the waveband of 3874122.1 A. Fig.2 shows a part of the spectral series observed by STT of Nanjing University. Fig. 3 gives a slit-jaw Ha: picture of the flare, the scale of which is about the same as in Fig. 1. It can be seen from Fig.1 and Fig.2 that this flare is a WLF with two kernels , Kl and Kz. Although during the spectral observation the slit only crossed the kernel K2, the continuum emission is still obvious, especially in the blue waveband fHy ). The preliminary results of measurement indicate that at 05:40:56 UT the excess continuum emission in the
Fig. 2
Nanjing University
A part of spectral series of the Oct. 27, 1991 WLF observed by Solar Tower Telescope of
HUANG
294
Fig.
3
A Ha slit jaw image
at 05:40:40
UT of the Oct.
Tower Telescope
Fig.
4
Variation
of the relative
Zhen et al.
of Nanjing
enhancement 05:41:54
27, 1991 WLF
of continuum UT
observed
by the solar
University
emission
in two flare kernels
at
White Light Flare
295
Ha waveband relative to the undisturbed background is about 0.03 - 0.04. The observed temporal series show that the continuum emission of the WLF varied with time. The duration was about 3 - 4 minutes. The continuum emission peaked at 05:41 UT, while the maximum of the radio burst at 2840 MHz observed by the Beijing Astronomical Observatory was at 05:42:14 UT151. So th e continuum emission mainly appeared at the impulsive phase of the flare. Fig.4 gives the relative intensity enhancements (If - In)/In of the continuum measured at the two kernels of the flare ( If ) and in the photospheric undisturbed region ( I, ) at 05:41:54 UT in the five wide-band images. If is an average of the intensities at five pixels around the pixel on the kernel where the intensity attains its maximum. I,, is an average over about 1000 pixels in the undisturbed region near the flare. Due to the fact that the kernel appeared in the penumbra of a sunspot, the relative intensity enhancements in the long wavelength becomes negative. It can be seen from Fig.4 that the continuum emission of this flare is bluish which is consistent with the spectral observations (Fig.2). It is worth to mention that the YOHKOH satellite has observed for the first time some WLFs from space. The flare we observed is the one of themL61.The observation of YOHKOH was made by use of a filter with a passband of about 30 A, centered at 4308 A. The result indicated that the relative increase of the continuum emission at 05:48 UT is 0.07. A detailed analysis on the data of the flare is under way. The results will be published elsewhere. ACKNOWLEDGEMENT We would like much to thank Drs. Shen long-xiang, Qiao Qiyuan, Gao Feng, Fu Qi-Jun and Xue Yi-sheng at the Beijing Astronomical Observatory and Mr.Gao Xiu-fa and Dr.Ji Guo-ping of the Department of Astronomy, Nanjing University for their help in the observations and the data analysis. References [l]
Neidig, D. F., Wiborg, F H., G’lli 1 am, L. B., Solar Phys., 1992 (in press)
[2]
Chen, X. Z., Wang, Z. Y., Acta Astron. Sin&a, 1984, 25, 127
[ 31
Wang, J. X., Shen, L. X., Fang, C., Progress in Astronomy, 1986,4,175
[ 41
SESC PRF 843, 29 October 1991, P.6; P.8; PRF 858, 11 February 1992, P.28
[ 51
Fu, Q. J. 1992, private communication
[ 61
Hudson, H. S. et al., Publ. Astron. Sot. Japan, 1993 (in press)
Chin. Astron. Astrophys. (1993)17/3,291-295 A translation of Acta Astron. Sin. (1993) 34/l, 89-91
Observations
of the white light flare
on 27 October, HUANG Zhen Urumgi Astronomical
station,
MA Lu
Chinese Academy
FANG Cheng Department
1991t
of Astronomy,
of Sciences, Xinjiang,
830011
HU Ju Nanjing university
Abstract A X6.1/3B flare, occurring near the center of solar disk on 27 October 1991, was observed simultaneously by the solar patrol telescope of the Urumgi Astronomical station with five wide-band filters and by the Solar Tower of Nanjing University with a multichannel spectrograph. The observations indicate that it is a white light flare. The observations and some preliminary results are described in this paper. Key
words:
Sun - white light flare
Since Carrington and Hodgson discovered for the first time a white light flare (WLF) in 1859, only about 80 WLFs have been reported all over the world during more than one hundred year&l. Among them, near ten have spectral data recorded . This is mainly due to the fact that the number of WLFs is at most only several percent of the total number of flares121and most of them appear at the impulsive phase of flares with a duration of only several minutes, resulting in the great difficulty to observe them. Just for this reason, there is so far much controversy about the radiative characteristics, the energy sources and the energy transport mechanism of WLFs. T_hus, the observation and the study of WLFs are ones of the frontiers of flare physics and have been attached much importance to in solar physics community131. A WLF patrol telescope was installed at the Urumgi Astronomical Station (UAS) in 1990. The aperture of the telescope is 10 cm and the focal length is 1.2 m. Six wide-band filters are placed before the focal plane with the wavelength/passband of 3602121.0 A, 3874122.1 respectively. The six filters A, 4182130.3 A, 4969131.3 A, 5654124.5 A and 6380128.5 A can be rotated by step motors, which are controlled by an IBM PC/AT computer, so six monochromatic frames can be obtained successively. A TM-46 CCD camera with 422 x 579 pixels is used to receive the signals. The size of each pixel corresponds to 1.“48 x 0.“95 t Supported by National Natural Science Foundation and National Educational Commission Ph. D. Foundation Received 1992 June 23; revised version 1992 September 23
292
Fig. 1
HUANG Zhen et al.
Temporal evolution at 3874&22.1A
of the Oct. 27, 1991 WLF observed by Urumgi
Observatory
on the solar image. The data of monochromatic images are acquired by a SR 151 image processor and stored on the disk of the computer. Much improvement of the solar tower telescope (STT) of Nanjing University was finished in 1990. The aperture of the coeiostat is 60 cm. The aperture of the objective mirror is 43 cm with a focal length of 21.7 m. With a fast multi-channel spectrograph, the spectra round Ha, H/3, H7, NaI D, CaII K and H can be photographed simultaneously. The dispersions are about 1 mm A-l. A X6.1/3B major flare occurred near the center of the solar disk (S13 E15) in AR6891 on October 27, 1991. According to the report of NOAAl*l, it is a proton flare. The Ha: emission began to increase before 05:38 UT, reached m~mum at 05:49 UT and ended after 06:58 UT. Soft X-ray burst (from GOES data) started at 05:37 UT with maximum at 05:48 UT and ended at 07:12 UT. The observations of the flare were made both with the patrol telescope at UAS and with STT at Nanjing University. The temporal variations of five wide-baud monochromatic images and four wavelength band (Ha, HP, Hy and NaI D) spectra have been obtained respectively. The temporal resolution of the observation of UAS is about 30 s., and the observational period is 04:59 N 06:53 UT. The monochromatic images at 05:40:30 UT and at 05:41:06 UT are a little dimmed due to focusing defect and need to be dealt with further. The temporal resolution of the spectral observation of STT is 10 - 15 s. The observational period is 05:39 - 06:30 UT. Fig.1 gives the temporal evolution of the flare monochromatic images observed by UAS in the waveband of 3874122.1 A. Fig.2 shows a part of the spectral series observed by STT of Nanjing University. Fig. 3 gives a slit-jaw Ha: picture of the flare, the scale of which is about the same as in Fig. 1. It can be seen from Fig.1 and Fig.2 that this flare is a WLF with two kernels , Kl and Kz. Although during the spectral observation the slit only crossed the kernel K2, the continuum emission is still obvious, especially in the blue waveband fHy ). The preliminary results of measurement indicate that at 05:40:56 UT the excess continuum emission in the
Fig. 2
Nanjing University
A part of spectral series of the Oct. 27, 1991 WLF observed by Solar Tower Telescope of
HUANG
294
Fig.
3
A Ha slit jaw image
at 05:40:40
UT of the Oct.
Tower Telescope
Fig.
4
Variation
of the relative
Zhen et al.
of Nanjing
enhancement 05:41:54
27, 1991 WLF
of continuum UT
observed
by the solar
University
emission
in two flare kernels
at
White Light Flare
295
Ha waveband relative to the undisturbed background is about 0.03 - 0.04. The observed temporal series show that the continuum emission of the WLF varied with time. The duration was about 3 - 4 minutes. The continuum emission peaked at 05:41 UT, while the maximum of the radio burst at 2840 MHz observed by the Beijing Astronomical Observatory was at 05:42:14 UT151. So th e continuum emission mainly appeared at the impulsive phase of the flare. Fig.4 gives the relative intensity enhancements (If - In)/In of the continuum measured at the two kernels of the flare ( If ) and in the photospheric undisturbed region ( I, ) at 05:41:54 UT in the five wide-band images. If is an average of the intensities at five pixels around the pixel on the kernel where the intensity attains its maximum. I,, is an average over about 1000 pixels in the undisturbed region near the flare. Due to the fact that the kernel appeared in the penumbra of a sunspot, the relative intensity enhancements in the long wavelength becomes negative. It can be seen from Fig.4 that the continuum emission of this flare is bluish which is consistent with the spectral observations (Fig.2). It is worth to mention that the YOHKOH satellite has observed for the first time some WLFs from space. The flare we observed is the one of themL61.The observation of YOHKOH was made by use of a filter with a passband of about 30 A, centered at 4308 A. The result indicated that the relative increase of the continuum emission at 05:48 UT is 0.07. A detailed analysis on the data of the flare is under way. The results will be published elsewhere. ACKNOWLEDGEMENT We would like much to thank Drs. Shen long-xiang, Qiao Qiyuan, Gao Feng, Fu Qi-Jun and Xue Yi-sheng at the Beijing Astronomical Observatory and Mr.Gao Xiu-fa and Dr.Ji Guo-ping of the Department of Astronomy, Nanjing University for their help in the observations and the data analysis. References [l]
Neidig, D. F., Wiborg, F H., G’lli 1 am, L. B., Solar Phys., 1992 (in press)
[2]
Chen, X. Z., Wang, Z. Y., Acta Astron. Sin&a, 1984, 25, 127
[ 31
Wang, J. X., Shen, L. X., Fang, C., Progress in Astronomy, 1986,4,175
[ 41
SESC PRF 843, 29 October 1991, P.6; P.8; PRF 858, 11 February 1992, P.28
[ 51
Fu, Q. J. 1992, private communication
[ 61
Hudson, H. S. et al., Publ. Astron. Sot. Japan, 1993 (in press)