fl082.vandriel01 Posted: 01-Nov-92 Updated: 31-Jul-93, 24-Jul-94, 03-Apr-95, 20-Oct-95, 20-Jul-96 Events specified: N/A
L. van Driel-Gesztelyi (Kiso Observatory, E-mail:lidia@spot.mtk.nao.ac.jp) with: H.S. Hudson, B. Anwar, E. Hiei, S. Tsuneta
Primary objective: To search for the theoretically predicted negative pre-flares of white-light flares.
Motivation: Calculations which predict that an event analog to stellar negative pre-flares can also exist on the Sun were published by Henoux et al. (1990, Astron. Astrophys. 233, 577) and Aboudarham et al., (1990, Solar Phys. 130. 243.), who showed that at the beginning of a solar white-light flare (WLF) event an electron beam can cause a transient darkening before the WLF emission starts, under certain conditions. They named this event a ``black light flare'' (BLF), indicating it is a counterpart of the subsequent WLF.
It was pointed out that there are two effects at the very beginning of the bombardment, if the beam is intense and impulsive enough: (i) it enhances the hydrogen recombination emission in the upper atmosphere, and (ii) it increases the H-minus population in the lower atmosphere. The increase of causes an enhanced absorption, resulting in a transient decrease of the white-light emission (the negative flare or BLF). The predicted event lasts about 20 sec until the heating of the atmosphere turns the absorption into emission and the WLF starts.
BLFs (if they really exist on the Sun) should appear as diffuse dark patches for about 20 seconds preceding WLFs with intense and impulsive hard X-ray bursts, at the same place as, or in the vicinity of, the forthcoming bright patches. Their predicted contrast depends on the position of the flare on the solar disc and on the wavelength band of the observation. According to the calculations, a BLF could be observed best between 365-570 nm or above 820 nm, with a sampling time not longer than 10 seconds.
Yohkoh, being outside the Earth's atmosphere, provides optical images without seeing effects, at 431 nm wavelength, which is in the wavelength interval mentioned above, and its time resolution is typically 12 seconds in flare mode. Therefore Yohkoh optical images are optimal for searching for solar negative flares. We therefore propose to analyse the white-light flares observed by Yohkoh from this point of view. This study might provide the first clearly identified observations of such intriguing events.
Update 20-Jul-96
We presented a poster paper at the Yohkoh conference at Bath, England on WLFs. We continue similar investigation for other Yohkoh WLFs. The abstract is as follows:
Beam Driven Return Current Instabilities and White-light Flares}
S.A. Matthews$^{1}$ J.C. Brown$^{1}$ and L. van Driel-Gesztelyi$^{2,3}$
(1) Dept. of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, U.K. (2) Observatoire de Paris, Section de Meudon, Meudon Cedex, Principal 92195, France (3) Konkoly Observatory, Budapest, Hungary.
It has been shown that the low ionization levels in the deep chromosphere of solar flares can cause the return current driven by a thick target flare beam to be unstable to ion acoustic wave generation. We investigate the possibility that anomalous heating as a result of this instability may produce sufficient heating to power the white-light flare. Four white-light flares observed by {\it Yohkoh} are examined: October 27 1991; November 15 1991; January 26 1992 and February 14 1992.
We are about to finish the analysis of 4 WLFs comparing light curves of individual WLF patches in WL and HXR to very high temporal resolution high energy HXR observations obtained with the PHEBUS and WATCH instruments aboard the GRANATE satellite. The flares are as follows:
Date Max X-ray Opt. Loca- NOAA UT class imp. tion Reg.
920214 2310 M7.0 2B S13E02 7056 920215 2135 M5.5 1B S16W13 7056 920424 1918 M1.2 1B N13W00 7138 920716 1700 M6.8 2B S10W61 7222
Update 20-Oct-95
Our goal is still the compilation of a Yohkoh WLF catalog. We continue a systematic search for WLFs first of all among flares with hard X-ray spectra. Since we are analysing about 70 flares, the work hasn't been completed yet mainly, because of in addition to the WL and SXR data we started reducing the HXR data for all flares and since we use Tom Metcalf's new /PIXONS keyword in the HXT_MULTIMG program, the results are great, but to get them we need lots of time...
Another important progress in the project that we began to analyse the SXT aspect sensor throughput data in order to find out how much genuine white-light emission is present in the observed brightness enhancement and how much is due to a line emission coming mainly from the H-gamma line, wich is in the passband of the NaBand filter. Preliminary results show that line emission may lead to an about 5 % increase in brightness, therefore flares with greater change in WL brightness than that can be regarded as genuine WLFs.
Update 03-Apr-95
Our goal is the compilation of a Yohkoh WLF catalog. We continue a systematic search for WLFs first of all among flares with hard X-ray spectra. Contrary to our expectations we have found a new WLF with a really small total energy (M1.2; 920424) and another with a soft HXR spectra: the second peak, which appears as a relatively strong patch in WL, shows only a very small peak in the HXT M2 and H channels (920215). We are analysing about 70 flares, listed below. The ones which were found to be WLFs so far, are marked with an asterix. Comparing the light-curve of several WLF patches to the light-curve of the corresponding HXR kernels, we found that the WL emission peaks a few (< 10) seconds after the HXR emission.
in Max End X Ray HXR L HXT H Opt Loca- NOAA WLF YYMMDD UT UT UT Class chan. chan. Imp tion Reg.
911024 1710B 1713 1715A M3.2 264 10 1B S15E51 6891 SOFT 911024 2230 2237 2251 M9.8 1145 22 1N S12E46 6891 WLF * 911027 0547B 0541U 0850A X6.1 3756 1362 3B S13E15 6891 WLF * 911030 0644B 0644U 0649A X2.5 230 9 3B S08W25 6891 NWLF * 911102 0643 0647 0715A 590 129 NWLF Great * 911109 2051 2052 2056 M1.4 93 54 1B S14W69 6906 HARD !! 911110 0647 0648 0649A M2.2 193 79 2B S14E53 6919 HARD ! 911110 2005 2010 2013A M7.9 413 101 1N S15E43 6919 WLF * 911113 2116 2116 2129 M1.3 39 26 HARD 911115 2234 2237 2245 X1.5 1292 341 3B S13W19 6919 WLF * 911117 0156 0157U 0208 M1.5 134 37 2B S13W33 6919 HARD 911117 1832B 1833 1836A M1.9 82 18 2B S12E78 6929 HARD 911130 1340 1341 1347A C3.9 6 16 SF S08E41 6946 HARD 911202 0448 0455 0533 M3.6 61 11 SF N16E87 6952 SOFT 911203 1632 1636 1658 X2.2 4128 232 2B N17E72 6952 WLF * 911204 1742 1743 1750A M4.1 89 20 SF N18E58 6952 HARD 911205 1948 1948 1950 C7.0 17 17 SF N19E43 6952 HARD 911208 1701 1703 1217 M3.4 318 10 1B N10E57 6961 SOFT 911209 0933 0941 0951 M4.1 377 09 SOFT 911211 1504 1505 1513 M4.0 130 10 1N S05E56 6966 SOFT 911215 1828 1832 1834 M1.4 162 137 1F S8E77 6972 NWLF ? * 911216 0059 0102 0104 C7.5 26 21 SN N09W01 6966 HARD 911216 0312 0313 0316 C7.8 45 30 1B S10E69 6972 HARD 911216 0454 0456 0503 M2.7 299 57 SF N04W45 6961 HARD ! 911218 1017 1027 1034 M3.5 379 13 SOFT 911226 1048B 1048 1051A M4.6 359 35 HARD 911226 2135 2137 2156 M4.2 164 42 1B S16W23 6985 NWLF * 911228 1225 1227 1231 M3.3 126 15 HARD 911230 2306 2307 2311 M4.6 170 29 2B S15W32 6965 HARD 920110 1816 1817 1820 C6.2 4 15 HARD 920113 1724 1729 1739 M2.0 51 15 HARD 920114 1633 1636 1639 C4.8 8 15 SF S15E43 7008 HARD 920126 1523 1528 1543 X1.0 765 141 3B S16W66 7012 WLF * 920129 2233 2233 2236 C3.1 37 15 SN S03E01 7031 HARD 920202 1133 1133 1139 C5.5 60 27 SN S11E41 7042 HARD 920205 1315 1316 1320 M2.2 63 15 1B S15W29 7039 HARD 920206 0312 0325 0344 M7.6 807 13 SN N05W82 7030 SOFT 920206 2050B 2054 2122 M4.1 122 10 SOFT 920207 1143 1154 1211 72 29 NWLF * 920208 0722 0722 0723 C3.2 23 15 SF S15W40 7042 HARD 920214 2304 2307 2307 M7.0 1085 202 2B S13E02 7056 WLF * 920215 2128 2135 2149 M5.5 158 27 1B S16W13 7056 NWLF * 920219 0335 0350 0403 M3.7 78 10 SF N04E85 7067 SOFT 920401 0049 0053 0109 M5.6 204 15 SF S09W45 7116 HARD (?) 920401 1012 1014 1019 M2.3 50 19 HARD 920415 2334 2334 2336 C2.8 25 17 SB S17W13 7128 HARD 920424 1244 1251 1301 M1.4 27 17 1B N09E05 7138 HARD 920424 1917 1918 1921 M1.2 26 21 1B N13W00 7138 HARD * 920508 1545B 1545U 1549A M7.4 36 16 4B S26E08 7158 SOFT 920625 0334 0334 0335 19 15 HARD 920625 1752 1754 1807 M1.4 199 15 1B N10W70 7205 HARD 920707 1120 1120 1121 M4.1 6 10 SB S11E57 7220 SOFT 920708 0944 0947 1002 X1.2 1251 101 1B S11E46 7220 WLF * 920716 1655 1658 1703 M6.8 206 61 2B S10W61 7222 WLF ? (*) 920803 0629 0631 0639 M4.8 19 10 1N S09E68 7248 SOFT 920811 1347 1347 1351 C7.2 66 20 1N S11W45 7248 HARD 920811 2224 2225 2234 M1.4 99 18 HARD ! 920820 0903 0904 0937 M2.9 182 16 1B N16W27 7260 NWLF * 920820 1426 1432 1434 M4.0 76 09 1B N15W29 7260 SOFT 920820 2033 2034 2049 M3.0 176 09 1B N16W33 7260 SOFT 920905 1122 1127 1132 M4.0 160 13 1N S08W21 7270 HARD 920906 0513 0515 0522 M2.4 114 10 2N S09W39 7270 SOFT 920906 0902 0904 0911 M3.3 142 15 1N S11W38 7270 HARD 920906 1147 1151 1152 M4.0 129 09 1N S11w42 7270 SOFT 920907 0348 0348 0406 M3.6 164 08 2B S10W49 7270 SOFT 920907 2003 2008 2012 M5.7 5 09 2B S11W57 7270 SOFT 920909 0206 0210 0220 M3.1 84 09 SOFT 920910 2251 2252 2301 M3.2 129 102 2B N12E41 7276 HARD !!! 920911 0254 0259 0304 M1.0 43 15 HARD 920911 0604 0604 0614 M1.4 69 51 7276? NWLF ? * 921004 2213 2221 2236 M2.4 35 17 SN S05W90 7293 HARD ? 921027 0144 0145* 0151 M1.1 97 15 HARD 921028 1008 1010 1013 C2.6 42 10 1F S23W40 7321 HARD 921030 1730B 1731 1733 X1.7 223 28 2B S22W61 7321 SOFT gradual 921105 0618 0619 0825 M2.0 68 15 HARD
Update 24-Jul-94
Our goal is the compilation of a Yohkoh WLF catalog. We do a systematic search for WLFs first of all among flares with hard X-ray spectra. We have found the following WLFs so far:
bigskip {\bf Table I}: List of {\sl Yohkoh} white--light flares \begin{verbatim}
in Max End X Ray Opt Loca- NOAA Radio Type of
YYMMDD UT UT UT Class Imp tion Reg. Flux Radio Burst
(15.4)
911024 2224 2241 2251 M9.8 1N S12E46 6891 340 III
911027 0537 0548 0712 X6.1 3B S13E15 6891 13000 II,III,IV
911110 2004 2013 2033 M7.9 1N S15E43 6919 1500 II,III,V
911115 2233 2239 2254 X1.5 3B S13W19 6919 1900 II,III
911203 1631 1639 1724 X2.2 2B N17E72 6952 2300
920126 1521 1533 1606 X1.0 3B S16W66 7012 650
920214 2304 2310 2342 M7.0 2B S13E02 7056 2800 L
920708 0942 0950 1026 X1.2 1B S11E46 7220 4200
920716 1653 1700 1712 M6.8 2B S10W61 7222 690 II,V
New flares, should be confirmed later:
911030 0644B 0644U 0649A X2.5 3B S08W25 6891 911102 0643 0647 0715A GREAT 911215 1828 1832 1834 M1.4 1F S8E77 6972 DOUBTFUL 911226 2135 2137 2156 M4.2 1B S16W23 6985 920207 1143 1154 1211 920215 2128 2135 2149 M5.5 1B S16W13 7056 920820 0903 0904 0937 M2.9 1B N16W27 7260 920911 0604 0604 0614 M1.4 7276? DOUBFULCandidates (flares with hard X-ray spectra - not on-line)
911110 0648 911113 2116 911117 1830 911228 1226 911230 2307 920401 1013 920424 1918 920811 1347 920811 2225 920905 1127 920906 0904 920910 2252 920911 0259 921004 2219 921027 0145* 921028 1010 921105 0619It seems that optical continuum emissiom may occur in flares as small as M2-3, if the flare is sufficiently hard.
Update 31-Jul-93
A DIAGNOSTCS OF SOLAR ATMOSPHERIC MODELS: SEARCH FOR ``BLACK FLARES''
L. van Driel-Gesztelyi$^{1}$, H.S. Hudson$^{2}$, B. Anwar $^{3}$ E. Hiei $^{4}$, and S. Tsuneta $^{5}$\\
$^{1}$ Kiso Observatory, Institute of Astronomy, University of Tokyo, Japan \\ $^{2}$ Institute for Astronomy, University of Hawaii, USA \\ $^{3}$ National Institute of Aeronautics and Space, Bandung, Indonesia \\ $^{4}$ National Astronomical Observatory of Japan, Tokyo, Japan \\ $^{5}$ Institute of Astronomy, University of Tokyo, Japan \\
Calculations which predict that an event analog to stellar negative pre-flares can also exist on the Sun were published by Henoux {\it et al.} (1990, {\it Astron. Astrophys.} {\bf 233}, 577) and Aboudarham {\it et al.}, (1990, {\it Solar Phys.} {\bf 130}. 243.), who showed that at the beginning of a solar white-light flare (WLF) event a nonthermal ionisation by particle beams can cause a transient darkening of the solar continuum before the WLF emission starts, under certain conditions. They named this event a ``black light flare'' (BLF), indicating it is a counterpart of the subsequent WLF.
According to the proposed BLF model,
BLFs (if they really exist on the Sun) should appear as diffuse dark patches for about 20 seconds preceding WLFs with intense and impulsive hard X-ray bursts, at the same place as, or in the vicinity of, the forthcoming bright patches. Their predicted contrast depends on the position of the flare on the solar disc and on the wavelength band of the observation. According to the calculations, a BLF could be observed best between 365-570 nm or above 820 nm, with a sampling time not longer than 10 seconds.
We are searching data from the SXT instrument on board {\sl Yohkoh} for BLF effects. Because {\sl Yohkoh} is outside the Earth's atmosphere, the SXT aspect camera can provide optical images without seeing effects at 431 nm wavelength, which is in the optimum wavelength interval mentioned above. The time resolution is typically 12 seconds during a major flare. Therefore the {\sl Yohkoh} optical images are quite suitable to search for solar negative flares. Successful observations of this phenomenon on the Sun would greatly strengthen our knowledge of the lower solar atmosphere and its effects on solar luminosity variations.