- Email: [email protected]
Observational evidence of magnetic reconnection in solar X-ray jets
Adv. Space Res.
Vol. 26, No. 3. pp. 44%452.2WO
0 2000 COSPAR.Published by Elsevier Science Ltd.All rightsreserved
Pergamon
Printedin GreatBritain 0273-l 177BO$20.00 + 0.00
www.elsevier.nl/locate/asr
PII: SO273-1177(99)01104-7
OBSERVATIONAL RECONNECTION
EVIDENCE OF MAGNETIC IN SOLAR X-RAY JETS
and K. Shibata2
M. Shimojorts,
1Department of Astronomical Science, Graduate University for Advanced studies, d-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan 2National Astronomical Observatory, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
ABSTRACT The solar X-ray jets are one of the most interesting findings of Soft X-Ray Telescope( SXT) aboard Yohkoh. They are transitory X-ray enhancements with an apparent collimated motion. In this paper, we present the observational evidence of magnetic reconnection of solar X-ray jets. From the morphological study of solar X-ray jets using SXT, we found the following properties of solar X-ray jets. 1) Most X-ray jets are associated with flares (microflares - flares) at their footpoints. 2) When the active regions at the footpoint of jets can be resolved well, it is found that morphology changes significantly during jets. 3) 27% of the jets show a gap ( > lo4 km) between the exact footpoint of the jet and the brightest part of the associated flare. Furthermore, as a result of the coalignment between magnetograms and SXT images, we found that the jet-producing region are the mixed polarity region and the region of evolving magnetic flux (increasing or decreasing). Canfield et al. (1996) investigated some Ho surges which were associated with X-ray jets and found some new Ha phenomena (moving-blueshift feature, converging footpoint motion). They suggested that these phenomena are the results of magnetic reconnection. As the results, we propose that the solar X-ray jets are produced by energy input from the (micro)flares which are generated by magnetic reconnection. 0 2606 COSPAR. Published by Elsevier Science Ltd. INTRODUCTION The soft X-ray telescope (SXT: Tsuneta et al. 1991) aboard Yohkooh(Ogawara et al. 1991) has better temporal coverage and resolution than previous solar X-ray imagers, and has revealed many previously unknown dynamic coronal phenomena. Among various newly discovered dynamic phenomena, one of the most interesting findings is the common occurrence of X-ray jets (Shibata et al. 1992, Strong et al. 1992). The purpose these results
of this paper is to summarize the observational studies with a model of the solar X-ray jets based on magnetic
OBSERVATIONAL Statistical
Study
CHARACTERISTICS of Solar
X-Hay
OF X-RAY
of the solar X-ray jets and compare reconnection.
JETS
Jets
According to the statistical study of 100 X-ray jets by Shimojo et al. (1996), these X-ray jets are transitory X-ray enhancements with an apparent collimated motion and have the following observed characteristics: 1) Most are associated with small flares (microflares - subflares) at their footpoints. 2) The lengths lie in the range of a few x104 - 4 x lo5 km. 3) The widths are 5 x lo3 - lo5 km.
449
450
M. Shimojo and K. Shibata
4) The apparent velocities are 10 - 1000 km s-l with an average velocity of about 200 km s-l. 5) 76% of the jets show constant or converging shapes: the width of the jet is constant or decreases with distance from the footpoint. The converging type tends to be generated with an energetic footpoint event and the constant type by a wide energy range of the footpoint event. 6) 27% of the jets show a gap ( > lo4 km) between the exact footpoint of the jet and the brightest part of the associated flare. 7) When the active regions at the footpoint of jets can be resolved well, it is found that morphology changes significantly during jets. 8) The frequency distribution of the intensity of footpoint flares is nearly a power law similar to that of microflares and flares. 9) The X-ray intensity distribution along an X-ray jet often shows an exponential decrease with distance from the footpoint. This exponential intensity distribution holds from the early phase to the decay phase.
Examples of Magnetic Field Properties of X-Ray Jets SXT : 2-Dee-91 08:09:llUT
SXT : 2-Now91 05:32:00UT
SXT : 1-Nov-91 22:51:36UT
Single Pole 8% Mag : 2-Now91 14:47:00UT
12% Blpole Mag : 2-Dee-91 16:26:00UT
~~~~
SXT : 25-Feb-92 15:52:44UT
Polarity 24% Satellite Polarity 48% Mag : 25-Feb-92 16:00:00UT
Mag : l-Now91 14:47:00UT
(Contour : SXT Image)
Figure 1: Examples of magnetic properties of X-ray jets. First row shows X-ray jets images taken by Yohktoh SXT. The second row are the corresponding magnetograms with white circles indicating the footpoint of the jets. The third row shows schematic illustrations of magnetic field configuration types.
Magnetic
Field
Properties
of Solar X-Ray
Jets
From a list of X-ray jets made by Shimojo et al. (1996), we selected events for which there were magnetic field data from NSO/Kitt Peak. Using co-aligned SXT images and magnetograms, we examined the magnetic field properties of X-ray jets (Shimojo, Shibata, and Harvey, 1998a). We found that 8% of studied jets occurred at a Single Pole , 12% at a Bipole, 24% in a Mixed Polarity and 48% in a Satellite Polarity (Figure 1.). If the satellite polarity region is the same as the mixed polarity region, 72% of the magnetic evolution of jetjets occurred at the (general) mixed polarity region. We also investigated producing area in active regions NOAA 7067, NOAA 7270 and NOAA7858. It is found that X-ray jets favored regions of evolving magnetic flux (increasing or decreasing).
Evidence of Reconnection
451
in Solar X-Ray Jets
When the mixed polarity regions appeared at the east side of proceeding spot, though, these regions did not produce jets but produced loop brightenings (microflares). This result suggests that the difference between loop brightenings and jets is due to the difference of structure of the magnetic field. Multi
Wave
Length
Observation
of Solar
X-Ray
Jets
Radio Observation of Solar X-ray Jets : Aurass, Klein and Martens (1994), Kundu et al. (1995) and Raulin et al. (1996) reported that metric Type III bursts occur in association with X-ray jets. Kundu et al. (1995) reported that the positions of radio sources observed in different frequencies aligned in the direction of the X-ray jets. This result suggests that electron beams propagate along the X-ray jet, and the flare associated with the X-ray jet produces non-thermal electrons. Ha observation of Solar X-ray Jets : Shibata et al. (1992) discovered that an X-ray jet occurred simultaneously with an Ha surge. Shimojo et al. (1996) reported that about 10 % of jets are associated with Ho surges using Solar Geophysical Data. Canfield et al. (1996) investigated some Ho surges which are associated with X-ray jets and found some new Ho phenomena (moving-blueshift feature, footpoint converging motion). They suggest that these phenomena are the results of magnetic reconnection. The relation between Macrospicules and Solar X-ray Jets : Pike and Harrison (1997) observed a macrospiclue using Coronal Diagnostic Spectrometer (CDS) on board SOHO and found some features which are the same as the features of solar X-ray jets. However, the relation between macrospicules and solar X-ray jets is not so clear since there is no simultaneous observation of these phenomena.
ReconnectionOutftow --a------+ Non-thermal
Electron
Thermal Condwtion
Evaporation
Flow
Figure 2: The model of X-ray jets based on magnetic reconnection model including chromospheric evap1. Magnetic reconnection occurred between emerging flux and overlying magnetic field. 2. oration. Magnetic energy is released into the left-side loop by reconnection outflow, thermal conduction and nonthermal electrons. 3. The evaporation flow is produced by thermal conduction and non-thermal electrons in the left-side loop.
DISCUSSION Many properties of jets are able to be explained by a model based on magnetic reconnection. For example, the model suggests that magnetic reconnection occurs between emerging flux and the overlying magnetic field. From magnetograms, we found that the jet-producing region is a mixed polarity region and the
452
M. Shimojo and K. Shibata
small emerging flux regions. The properties of these regions are consistent with the model. Other example is that the gap between the footpoint of the jet and the brightest part is explained by the gap between jet and reconnected loop (Figure 2). And, the morphological change of footpoint X-ray structure (loops disappear or appear) is also explained by the change of the magnetic field configuration through magnetic reconnection (Shibata et al., 1994). From Ha images of the regions of X-ray jets, new phenomena which are able to be explained by magnetic reconnection are discovered by Canfield et al. (1996). These observational results suggest that the solar X-ray jets are produced by magnetic reconnection. If the mechanism of jets is same as that of normal flares, the phenomena which occur in normal flares (chromospheric evaporation, particle acceleration, etc.) may be occurring in jets. Shimojo et al. (199813) performed lD-hydrodynamic simulations of evaporation based on the reconnection model of jets and they succeeded in reproducing the X-ray intensity distribution along the jets. Therefore, it is likely that some of the solar X-ray jets are the evaporation flows which are produced by the magnetic reconnection (Figure 2). ACKNOWLEDGMENTS The Yohkoh mission is a project of the ISAS, Japan, with substantial participation from other institutions within Japan, and with important contributions from the research groups in the U.S. and the U.K, under the support of NASA and SERC. The authors would like to thank Prof. R. C. Canfield, Dr. K. L. Harvey for useful discussions and suggestions during the course of the analysis. We would also like to thank aII of the Yohkoh team members. The NSO/Kitt Peak data used here are produced cooperatively by NSF/NOAO, NASA/GSFC, and SEC/NOAA. REFERENCE Aurass, H., Klein, K.-L. and Martens, P.C.H, Solar Phys., 155,203 (1994). Canfield, R.C., et al., Astrophys. J., 462, 1016 (1996). Kundu, M.R., et al., Astrophys. J., 447, L135 (1995). Ogawara Y., et al., Solar Phys., 136, 1 (1991). Pike, C.D., and Harrison, R.A., Solar Phys., 175, 457 (1998). Raulin, J.P., et al., Astron. Astrophys., 306, 229 (1996). Shibata, K., et al., Publ. Astron. Sot. Japan, 44, L147 (1992). Shibata, K., et al., Astrophys. J., 431, L51 (1994). Shibata, K., Yokoyama, T., and Shimojo, M., Adv. Space Res., 17(4/5), 197 (1996) J. Geomag. Geoelectr., 48, 19 (1996) Shibata, K., bohrr Jets and Coronal Plumes, ESTEC, The Netherlands, 137 (1998). Shimojo, M., et al., Publ. Astron. Sot. Japan, 48, 123 (1996). Shimojo, M., Shibata, K., and Harvey, K.L., Solar Phys., 178, 379 (1998a). Shimojo, M., et al., Solar Jets and Coronal Plumes, ESTEC, The Netherlands, 163 (1998b). Strong, K. T., et al., Publ. Astron. Sot. Japan, 44, L161 (1992). Tsuneta, S., et al., Solar Phys., 136, 37 (1991). Yokoyama, T. and Shibata, K. Nature, 375, 42 (1995). Yokoyama, T. and Shibata, K. Publ. Astron. Sot. Japan, 48, (1996).
Vol. 26, No. 3. pp. 44%452.2WO
0 2000 COSPAR.Published by Elsevier Science Ltd.All rightsreserved
Pergamon
Printedin GreatBritain 0273-l 177BO$20.00 + 0.00
www.elsevier.nl/locate/asr
PII: SO273-1177(99)01104-7
OBSERVATIONAL RECONNECTION
EVIDENCE OF MAGNETIC IN SOLAR X-RAY JETS
and K. Shibata2
M. Shimojorts,
1Department of Astronomical Science, Graduate University for Advanced studies, d-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan 2National Astronomical Observatory, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
ABSTRACT The solar X-ray jets are one of the most interesting findings of Soft X-Ray Telescope( SXT) aboard Yohkoh. They are transitory X-ray enhancements with an apparent collimated motion. In this paper, we present the observational evidence of magnetic reconnection of solar X-ray jets. From the morphological study of solar X-ray jets using SXT, we found the following properties of solar X-ray jets. 1) Most X-ray jets are associated with flares (microflares - flares) at their footpoints. 2) When the active regions at the footpoint of jets can be resolved well, it is found that morphology changes significantly during jets. 3) 27% of the jets show a gap ( > lo4 km) between the exact footpoint of the jet and the brightest part of the associated flare. Furthermore, as a result of the coalignment between magnetograms and SXT images, we found that the jet-producing region are the mixed polarity region and the region of evolving magnetic flux (increasing or decreasing). Canfield et al. (1996) investigated some Ho surges which were associated with X-ray jets and found some new Ha phenomena (moving-blueshift feature, converging footpoint motion). They suggested that these phenomena are the results of magnetic reconnection. As the results, we propose that the solar X-ray jets are produced by energy input from the (micro)flares which are generated by magnetic reconnection. 0 2606 COSPAR. Published by Elsevier Science Ltd. INTRODUCTION The soft X-ray telescope (SXT: Tsuneta et al. 1991) aboard Yohkooh(Ogawara et al. 1991) has better temporal coverage and resolution than previous solar X-ray imagers, and has revealed many previously unknown dynamic coronal phenomena. Among various newly discovered dynamic phenomena, one of the most interesting findings is the common occurrence of X-ray jets (Shibata et al. 1992, Strong et al. 1992). The purpose these results
of this paper is to summarize the observational studies with a model of the solar X-ray jets based on magnetic
OBSERVATIONAL Statistical
Study
CHARACTERISTICS of Solar
X-Hay
OF X-RAY
of the solar X-ray jets and compare reconnection.
JETS
Jets
According to the statistical study of 100 X-ray jets by Shimojo et al. (1996), these X-ray jets are transitory X-ray enhancements with an apparent collimated motion and have the following observed characteristics: 1) Most are associated with small flares (microflares - subflares) at their footpoints. 2) The lengths lie in the range of a few x104 - 4 x lo5 km. 3) The widths are 5 x lo3 - lo5 km.
449
450
M. Shimojo and K. Shibata
4) The apparent velocities are 10 - 1000 km s-l with an average velocity of about 200 km s-l. 5) 76% of the jets show constant or converging shapes: the width of the jet is constant or decreases with distance from the footpoint. The converging type tends to be generated with an energetic footpoint event and the constant type by a wide energy range of the footpoint event. 6) 27% of the jets show a gap ( > lo4 km) between the exact footpoint of the jet and the brightest part of the associated flare. 7) When the active regions at the footpoint of jets can be resolved well, it is found that morphology changes significantly during jets. 8) The frequency distribution of the intensity of footpoint flares is nearly a power law similar to that of microflares and flares. 9) The X-ray intensity distribution along an X-ray jet often shows an exponential decrease with distance from the footpoint. This exponential intensity distribution holds from the early phase to the decay phase.
Examples of Magnetic Field Properties of X-Ray Jets SXT : 2-Dee-91 08:09:llUT
SXT : 2-Now91 05:32:00UT
SXT : 1-Nov-91 22:51:36UT
Single Pole 8% Mag : 2-Now91 14:47:00UT
12% Blpole Mag : 2-Dee-91 16:26:00UT
~~~~
SXT : 25-Feb-92 15:52:44UT
Polarity 24% Satellite Polarity 48% Mag : 25-Feb-92 16:00:00UT
Mag : l-Now91 14:47:00UT
(Contour : SXT Image)
Figure 1: Examples of magnetic properties of X-ray jets. First row shows X-ray jets images taken by Yohktoh SXT. The second row are the corresponding magnetograms with white circles indicating the footpoint of the jets. The third row shows schematic illustrations of magnetic field configuration types.
Magnetic
Field
Properties
of Solar X-Ray
Jets
From a list of X-ray jets made by Shimojo et al. (1996), we selected events for which there were magnetic field data from NSO/Kitt Peak. Using co-aligned SXT images and magnetograms, we examined the magnetic field properties of X-ray jets (Shimojo, Shibata, and Harvey, 1998a). We found that 8% of studied jets occurred at a Single Pole , 12% at a Bipole, 24% in a Mixed Polarity and 48% in a Satellite Polarity (Figure 1.). If the satellite polarity region is the same as the mixed polarity region, 72% of the magnetic evolution of jetjets occurred at the (general) mixed polarity region. We also investigated producing area in active regions NOAA 7067, NOAA 7270 and NOAA7858. It is found that X-ray jets favored regions of evolving magnetic flux (increasing or decreasing).
Evidence of Reconnection
451
in Solar X-Ray Jets
When the mixed polarity regions appeared at the east side of proceeding spot, though, these regions did not produce jets but produced loop brightenings (microflares). This result suggests that the difference between loop brightenings and jets is due to the difference of structure of the magnetic field. Multi
Wave
Length
Observation
of Solar
X-Ray
Jets
Radio Observation of Solar X-ray Jets : Aurass, Klein and Martens (1994), Kundu et al. (1995) and Raulin et al. (1996) reported that metric Type III bursts occur in association with X-ray jets. Kundu et al. (1995) reported that the positions of radio sources observed in different frequencies aligned in the direction of the X-ray jets. This result suggests that electron beams propagate along the X-ray jet, and the flare associated with the X-ray jet produces non-thermal electrons. Ha observation of Solar X-ray Jets : Shibata et al. (1992) discovered that an X-ray jet occurred simultaneously with an Ha surge. Shimojo et al. (1996) reported that about 10 % of jets are associated with Ho surges using Solar Geophysical Data. Canfield et al. (1996) investigated some Ho surges which are associated with X-ray jets and found some new Ho phenomena (moving-blueshift feature, footpoint converging motion). They suggest that these phenomena are the results of magnetic reconnection. The relation between Macrospicules and Solar X-ray Jets : Pike and Harrison (1997) observed a macrospiclue using Coronal Diagnostic Spectrometer (CDS) on board SOHO and found some features which are the same as the features of solar X-ray jets. However, the relation between macrospicules and solar X-ray jets is not so clear since there is no simultaneous observation of these phenomena.
ReconnectionOutftow --a------+ Non-thermal
Electron
Thermal Condwtion
Evaporation
Flow
Figure 2: The model of X-ray jets based on magnetic reconnection model including chromospheric evap1. Magnetic reconnection occurred between emerging flux and overlying magnetic field. 2. oration. Magnetic energy is released into the left-side loop by reconnection outflow, thermal conduction and nonthermal electrons. 3. The evaporation flow is produced by thermal conduction and non-thermal electrons in the left-side loop.
DISCUSSION Many properties of jets are able to be explained by a model based on magnetic reconnection. For example, the model suggests that magnetic reconnection occurs between emerging flux and the overlying magnetic field. From magnetograms, we found that the jet-producing region is a mixed polarity region and the
452
M. Shimojo and K. Shibata
small emerging flux regions. The properties of these regions are consistent with the model. Other example is that the gap between the footpoint of the jet and the brightest part is explained by the gap between jet and reconnected loop (Figure 2). And, the morphological change of footpoint X-ray structure (loops disappear or appear) is also explained by the change of the magnetic field configuration through magnetic reconnection (Shibata et al., 1994). From Ha images of the regions of X-ray jets, new phenomena which are able to be explained by magnetic reconnection are discovered by Canfield et al. (1996). These observational results suggest that the solar X-ray jets are produced by magnetic reconnection. If the mechanism of jets is same as that of normal flares, the phenomena which occur in normal flares (chromospheric evaporation, particle acceleration, etc.) may be occurring in jets. Shimojo et al. (199813) performed lD-hydrodynamic simulations of evaporation based on the reconnection model of jets and they succeeded in reproducing the X-ray intensity distribution along the jets. Therefore, it is likely that some of the solar X-ray jets are the evaporation flows which are produced by the magnetic reconnection (Figure 2). ACKNOWLEDGMENTS The Yohkoh mission is a project of the ISAS, Japan, with substantial participation from other institutions within Japan, and with important contributions from the research groups in the U.S. and the U.K, under the support of NASA and SERC. The authors would like to thank Prof. R. C. Canfield, Dr. K. L. Harvey for useful discussions and suggestions during the course of the analysis. We would also like to thank aII of the Yohkoh team members. The NSO/Kitt Peak data used here are produced cooperatively by NSF/NOAO, NASA/GSFC, and SEC/NOAA. REFERENCE Aurass, H., Klein, K.-L. and Martens, P.C.H, Solar Phys., 155,203 (1994). Canfield, R.C., et al., Astrophys. J., 462, 1016 (1996). Kundu, M.R., et al., Astrophys. J., 447, L135 (1995). Ogawara Y., et al., Solar Phys., 136, 1 (1991). Pike, C.D., and Harrison, R.A., Solar Phys., 175, 457 (1998). Raulin, J.P., et al., Astron. Astrophys., 306, 229 (1996). Shibata, K., et al., Publ. Astron. Sot. Japan, 44, L147 (1992). Shibata, K., et al., Astrophys. J., 431, L51 (1994). Shibata, K., Yokoyama, T., and Shimojo, M., Adv. Space Res., 17(4/5), 197 (1996) J. Geomag. Geoelectr., 48, 19 (1996) Shibata, K., bohrr Jets and Coronal Plumes, ESTEC, The Netherlands, 137 (1998). Shimojo, M., et al., Publ. Astron. Sot. Japan, 48, 123 (1996). Shimojo, M., Shibata, K., and Harvey, K.L., Solar Phys., 178, 379 (1998a). Shimojo, M., et al., Solar Jets and Coronal Plumes, ESTEC, The Netherlands, 163 (1998b). Strong, K. T., et al., Publ. Astron. Sot. Japan, 44, L161 (1992). Tsuneta, S., et al., Solar Phys., 136, 37 (1991). Yokoyama, T. and Shibata, K. Nature, 375, 42 (1995). Yokoyama, T. and Shibata, K. Publ. Astron. Sot. Japan, 48, (1996).