J/ApJ/851/91 Statistical studies of solar white-light flares (Namekata+, 2017)
Statistical studies of solar white-light flares and comparisons with superflares
on solar-type stars.
Namekata K., Sakaue T., Watanabe K., Asai A., Maehara H., Notsu Y.,
Notsu S., Honda S., Ishii T.T., Ikuta K., Nogami D., Shibata K.
<Astrophys. J., 851, 91 (2017)>
=2017ApJ...851...91N 2017ApJ...851...91N
ADC_Keywords: Stars, flare; Magnetic fields; Sun
Keywords: magnetic reconnection; stars: flare; Sun: flares; Sun: magnetic fields
Abstract:
Recently, many superflares on solar-type stars have been discovered as
white- light flares (WLFs). The statistical study found a correlation
between their energies (E) and durations (τ):
τ∝E0.39, similar to those of solar hard/soft X-ray
flares, τ∝E0.2-0.33. This indicates a universal mechanism
of energy release on solar and stellar flares, i.e., magnetic
reconnection. We here carried out statistical research on 50 solar
WLFs observed with Solar Dynamics Observatory/HMI and examined the
correlation between the energies and durations. As a result, the
E-τ relation on solar WLFs (τ∝E0.38) is quite similar
to that on stellar superflares (τ∝E0.39). However, the
durations of stellar superflares are one order of magnitude shorter
than those expected from solar WLFs. We present the following two
interpretations for the discrepancy: (1) in solar flares, the cooling
timescale of WLFs may be longer than the reconnection one, and the
decay time of solar WLFs can be elongated by the cooling effect; (2)
the distribution can be understood by applying a scaling law
(τ∝E1/3B-5/3) derived from the magnetic reconnection
theory. In the latter case, the observed superflares are expected to
have 2-4 times stronger magnetic field strength than solar flares.
Description:
Our white-light flare (WLF) catalog contains M- and X-class solar
flares that occurred from 2011 to 2015 and were observed by both Solar
Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) and
RHESSI.
The 43 flares in our catalog that occurred from 2011 to 2014 were
taken from Kuhar+ (2016ApJ...816....6K 2016ApJ...816....6K); we enlarged the sample by
adding 10 flares that occurred in 2015.
To present whether the cadence of SDO/HMI is short enough to resolve
the evolution of WLFs, we compared the obtained light curves with
those observed by the Solar Magnetic Activity Research Telescope
(SMART) at Hida Observatory of Kyoto University for one event and the
Hinode/Solar Optical Telescope (SOT) for four events.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 120 50 Physical parameters of flares
table2.dat 61 50 Detailed observations
table3.dat 46 4 Physical parameters of flares with the Hinode/
Solar Optical Telescope (SOT)
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See also:
J/A+A/327/1114 : Optical flares on EV Lac in 1967-1977 (Leto+ 1997)
J/AJ/141/50 : White-light flares on cool stars (Walkowicz+, 2011)
J/ApJ/743/48 : Stellar rotation periods & X-ray luminosities (Wright+, 2011)
J/ApJ/757/94 : Solar flares observed with GOES and AIA (Aschwanden, 2012)
J/other/Nat/485.478 : Superflares on solar-type stars (Maehara+, 2012)
J/ApJS/209/5 : Superflares of Kepler stars. I. (Shibayama+, 2013)
J/ApJ/814/35 : Flare events in M dwarf of M37 (Chang+, 2015)
J/ApJ/818/43 : Stellar surface gravity measures of KIC stars (Bastien+, 2016)
J/ApJ/832/27 : Global energetics of solar flares. III. (Aschwanden+, 2016)
J/ApJ/833/284 : Quasi-periodic pulsations in solar flares (Inglis+, 2016)
J/ApJS/224/37 : White-light flares on close binaries from Kepler (Gao+, 2016)
J/ApJS/229/30 : Revised properties of Q1-17 Kepler targets (Mathur+, 2017)
J/ApJS/232/26 : Catalog of Kepler flare stars (Van Doorsselaere+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Flare sequential running number
4- 13 A10 "Y/M/D" Obs.date Flare peak date of the GOES soft X-ray flux
15- 19 A5 "h:m" Obs.time Flare peak time of the GOES soft X-ray flux
21- 24 A4 --- Class GOES class (M1.0 to X2.8)
26- 29 I4 arcsec Loc-EW [-940/950] Event location, EW
31- 34 I4 arcsec Loc-NS [-410/560] Event location, NS
36- 41 F6.3 10+22J E [0.6/66.1] Flare energy radiated in
the white light, in 10+29erg units
43- 47 F5.2 10+22J Ec [1.7/73] Flare energy corrected values
for limb darkening, in 10+29erg units
49- 53 F5.2 10+22J e_E [0.4/13] Uncertainty on E or Ec
55- 59 F5.2 10+5ct F [1.1/40] Total counts of the white-light
flares, data numbers
61- 65 F5.2 10+5ct Fc [2.7/71.1] Total counts corrected values
for limb darkening
67- 70 F4.2 10+5ct e_F [0.1/3.5] Uncertainty in F or Fc
72- 77 F6.3 min t-decay [0.9/14.1] E-folding decay time
79- 83 F5.3 min e_t-decay [0/1.5] Uncertainty in t-decay
85- 90 F6.4 min t-HXR [0.03/8.5] Decay time of the HXR flare,
30-80keV
92- 97 F6.3 10-6 Fc/Fsun [0.6/18.4] flare count to solar ratio, ppm
99-103 F5.1 10-4T B-est [42.4/126] Estimated magnetic field
strength, gauss (1)
105-110 F6.2 10-4T B-obs [3.2/137] Observed magnetic field strength,
gauss (2)
112-115 F4.2 10+9cm L-est [1.3/6] Estimated loop length (1)
117-120 F4.2 10+9cm L-obs [1/6] Observed loop length (2)
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Note (1): Theoretically estimated values from the scaling laws.
Note (2): Observationally measured values with SDO.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Flare sequential running number
4- 13 A10 "Y/M/D" st.date Start date of white-light flare (3)
15- 22 A8 "h:m:s" st.time Start time of white-light flare (3)
24- 33 A10 "Y/M/D" end.date End date of white-light flare (3)
35- 42 A8 "h:m:s" end.time End time of white-light flare (3)
44- 45 I2 % Area [10/70] HXR Area (4)
47- 61 A15 --- Detectors RHESSI detector number(s) used.
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Note (3): The start and end time of white-light flare we defined by eye on the
basis of the pre-flare subtracted movies in Section 2.
Note (4): The contour levels of the mask of the hard X-ray images where we
extracted white-light emission as in Section 2.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [2/41] Flare sequential running number
4- 13 A10 "Y/M/D" obs.date Hinode/SOT Flare peak time
15- 19 A5 "h:m" obs.time Hinode/SOT Flare peak time
21- 25 F5.2 10+29erg Ec [5/31.6] Flare energy corrected values for
limb darkening
27- 30 F4.2 min t-HMI [2/2.8] Decay time of the HMI flare
32- 35 F4.2 min t-red [1.9/3.2] Observed e-folding decay time
w/ SOT/Red continuum
37- 40 F4.2 min t-green [2/3.2] Observed e-folding decay time
w/ SOT/Green continuum
42- 46 F5.3 min t-blue [0.9/3.3] Observed e-folding decay time
w/ SOT/Blue continuum
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Jul-2018