New Astronomy 74 (2020) 101285 Contents lists available at ScienceDirect New Astronomy journal homepage: www.elsevier.com/locate/newast The characteristics of the coronal mass ejections preceding the associated Xray and γ-ray burst solar flares T Ramy Mawada, , Walid Abdel-Sattarb ⁎ a b Astronomy & Meteorology Department, Faculty of Science, Al-Azhar University, Nasr City, Cairo 11488, Egypt Astronomy, Space Science & Meteorology Department, Faculty of Science, Cairo University, Giza 12613, Egypt A R T I C LE I N FO A B S T R A C T Keywords: Sun Solar flare Coronal mass ejection Space weather In this study, investigated 14,786 coronal mass ejection (CME) events and 5092 Gamma-ray Burst Monitor (GBM) solar flare events (called γ-ray burst solar flare) recorded during 2008–2017, by using temporal and spatial conditions criteria, we found 845 (about 16%) CME events associated with γ-ray burst solar flare events only (hereafter, CME–γ-preflare). All the 845 events are associated with solar flares that are detected in both GBM and RHESSI simultaneously. Investigating the characteristics of these events, we found that the best time interval is 0–2 h before the flare's start time. The mean time interval for these CME–γ-preflare associated events is 61 min, with the flare's duration mean value of 12 min, which is greater than non-associated γ-ray solar flare's duration. CME width of CME-γ-preflare associated events 64° is slightly wider and slightly faster (remain lower than solar wind's speed) than non-associated CME 53°. 1. Introduction Space weather studies are focusing on the study of different solar activities which can affect the environmental conditions in Earth's magnetosphere, ionosphere and thermosphere. Many scientific studies in space science try to find the relationship between different solar activities, to have a better picture about their nature, origin and mechanism, which can help in their prediction and probable influence on Earth. Many studies were investigating the possible relationship between two of the solar activities, the solar flares and the Coronal mass ejections (CME) (e.g. Mahrous et al., 2009; Fomin et al., 2005; Aarnio et al., 2011). CME-flare relationship is an important topic to improve the Space weather forecasting of flares and CMEs as pointed out by Mahrous et al. (2009), Youssef et al. (2013), Harrison (1995, 2006), Aurass (1997), and Gopalswamy (2000). Solar flare is a brief eruption of intense high-energy radiation originating on the solar surface, its electromagnetic radiation extending over a very broad range of wavelengths from long radio waves to short γ -rays. Measurements of solar flares in Hard X-rays (HXRs) (up to about 300 keV) indicate the presence of energetic electrons (energies up to a few MeV), which produce bremsstrahlung in the dense regions of the corona and chromosphere. Observations in the microwave wavelengths ⁎ indicate synchrotron emission by relativistic electrons in ̴100 G strong magnetic fields. Electron bremsstrahlung emission exceeding tens of MeV is observed in some observations of X-class flares made by Geostationary Operational Environmental Satellite (GOES) (Trottet et al., 1998). Nuclear γ -ray lines (1–10 MeV) and continuum radiation above 100 MeV produced by accelerated protons, α particles, and heavy ions have been detected by instruments on the board of the Compton Gamma Ray Observatory (CGRO), the Solar Maximum Mission (SMM), and RHESSI (Lin et al., 2002), these lines are produced by the de-excitation of accelerated ions. The continuum radiation is resulting from interactions of (>300 MeV) protons and (>800 MeV) αparticles with ambient ions producing both charged and neutral pions (Murphy et al., 1987). Neutral pions decay produces a couple 67.5 MeV γ-rays, while decay of charged pions produces energetic positrons, electrons, and neutrinos (Ramaty and Mandzhavidze, 1993). Among detectors of Gamma-ray solar flares are the Large Area Telescope (LAT; Atwood et al., 2009) and Gamma-ray Burst Monitor (GBM; Meegan et al., 2009) instruments on the Fermi Gamma-Ray Space Telescope. The LAT is detecting high-energy γ-ray emission associated with GOES (M-class and X-class) X-ray flares accompanied by coronal mass ejections and SEP events. In some observations, LAT has detected gamma rays with energies up to several hundreds of MeV during the impulsive phase and gamma rays up to GeV energies sustained for several hours after the impulsive phase (Omodei et al., 2012). The NaI Corresponding author. E-mail addresses: ramy@azhar.edu.eg (R. Mawad), walid_as72@hotmail.com (W. Abdel-Sattar). https://doi.org/10.1016/j.newast.2019.101285 Received 11 February 2019; Received in revised form 24 March 2019; Accepted 2 July 2019 Available online 01 August 2019 1384-1076/ © 2019 Published by Elsevier B.V. New Astronomy 74 (2020) 101285 R. Mawad and W. Abdel-Sattar Lysenko et al. (2018) concluded that the solar flares often happen after a preflare/preheating phase, which is almost or entirely thermal. On the other hand, there are the so-called early impulsive flares that do not show a (significant) preflare heating, but instead often show the Neupert effect (a relationship where the impulsive phase is followed by a gradual, cumulative-like, thermal response). In the γ-ray solar flare case, Ackermann et al. (2014) studied 18 solar flares detected in high-energy γ -rays (above 100 MeV) with the Fermi Large Area Telescope (LAT), they concluded that particle acceleration up to very high energies in solar flares is more common than previously thought, occurring even in modest flares, and for longer durations. Interestingly, all these flares are associated with fast coronal mass ejections (CMEs). Solar flares have been classified into impulsive [short-duration (<1 h), compact (1026–1027 cm3), and low-lying (104 km)] and gradual [long duration (a few hours), large volumes (1028–1029 cm3), and great heights (105 km)] (e.g. Pallavicini et al., 1977; Moore et al., 1999). Kay et al. (2003) have studied 69 ejective and non-ejective solar flare events and found that, while there is some relationship between the rise and decay times of flares, there are no systematic differences between the ejective and non-ejective flares. The probability of CME–flare association increases with the increase in flare's duration (Sheeley et al., 1983): 26% for duration <1 h and a complete 100% for duration >6 h. It is important to mention that some major flares associated with largescale CMEs are not long in duration events (Nitta and Hudson, 2001; Chertok et al., 2004). Vrsank et al. (2005) studied statistically 545 CME-flare associated events and 104 non-associated; they concluded that both data sets have similar characteristics. Michalek (2009) studied statistically 578 CMEflare associated events and found that two different types of CME-flare associated events (CMEs that follow and precede flare onset) have different characteristics. It is therefore needed to examine whether the mechanism of CME occurrence (e.g., magnetic reconnection which may influence CME speed and acceleration) is different in the two types of events. Investigating the CME-Preflare association during the solar period 1996–2010, found 292 CME-Preflare associated events (∼2%). These associated events have 0–1 h time interval, popular events occur within half an hour before flare starting time. Post-flares–CME associated events are wider than CME-Preflare associated events. CME-Preflare associated events are ejected from the northern hemisphere, while the non-associated CMEs are ejected from the southern hemisphere during the 23rd solar cycle. The CME-Preflare associated events are slower than the post-flare–CME associated events, and slightly faster than non-associated CME events. Post-flare–CME associated events are in average more massive than CME-Preflare associated events and all other CMEs ejected from the Sun. CME-Preflare associated events have an average speed which is approximately equivalent to the average solar wind speed approximately (Mawad and Youssef, 2018). The purpose of this study is to investigate the relationship between CMEs and the preflare (before X-Ray solar flares) detected simultaneously in γ and X –rays for a more clear understanding of the characteristics of these two important solar activities. A complete discussion of the results is given in Section 4 and the final conclusion in Section 5. detectors of the Fermi Gamma-ray Burst Monitor, the data of which are used to compile the Fermi GBM Flare List, register photons with energies predominantly in the 10–300 keV range (Meegan et al., 2009). The main contribution to this population of photons is the bremsstrahlung emission of accelerated electrons and hot plasma produced in solar flare regions (e.g., Lin et al., 2002). This type of emission is called hard X-ray emission and it is not directly related to gamma-ray emission produced by energetic protons and ions in solar flare regions. Coronal mass ejections (CMEs) are the ejection of plasma and magnetic field into space and thought to be one of main causes of geomagnetic disturbances (Gosling, 1993). Scientific studies are interested in the study of CMEs’ arrival time and their possible influence on the Earth (e.g. Rollett et al., 2016; Mawad et al., 2016; Korsós and Ruderman, 2016; Xie et al., 2009; Gopalswamy and Xie, 2008). Many scientific studies were interested in investigating the origin of CMEs to understand the possible relationship between CMEs and other solar phenomena: - CMEs and solar flares (Mahrous et al., 2009; Fomin et al., 2005; Aarnio et al., 2011), - CMEs and Sunspots (Korsós and Ruderman, 2016), - CMEs and (filament and prominence) (Mawad et al., 2015; Alissandrakis et al., 2013; Jing et al., 2003), - CMEs and coronal holes (Wood et al., 2012; Gopalswamy et al., 2009). - CMEs and solar jets (Liu et al., 2005; Liu, 2008; Wang et al., 1998). Coronal mass ejections with large-scale eruptions of plasma and magnetic field often accompanied by localized energy release in the form of flares, because of dissipative reconfiguration of the magnetic field. Previous studies on the relation between the CME and solar flares depend on the flare's location, as the source location of the CMEs and assume it can indicat`e the earth-direction possibility (e.g. Mahrous et al., 2009; Youssef et al., 2013; Mawad et al., 2015, 2016). Mawad and Youssef (2018) summarized the founded previous studies in three association cases between CMEs and x-ray solar flares relationships as follows: 1 Simultaneously associated CME-Flare: This means that the CME's onset time (not emergence time of the CME) can be detected during the X-Ray solar flares detected lifetime by instruments (between start and end time of the solar flare. reported by many researchers such as Mahrous et al. (2009), Harrison (1995, 2006), Aurass (1997), Gopalswamy (2000), Vršnak et al. (2005) and Youssef et al. (2013). It should be noted that, The CME emerged before it appeared into LASCO C2 FOV. In this regard, CME can be detected before the detection time of the solar flares. 2 Associated post-flare – CME: This means that the CMEs can be detected after peak and end times of the X-Ray solar flares. reported by Youssef et al. (2013), Lysenko et al. (2018) and Suryanarayana (2018). 3 Associated CME-Preflare: This means that the CMEs can be detected before the X-Ray solar flares onset time. This case reported by Mawad and Youssef (2018), and Suryanarayana (2018). 2. Data sources The flare–CME association relationship is based on three hypothesis: 1) Flares produce CMEs (see, e.g. Dryer, 1996), 2) Flares are byproducts of CMEs (Hundhausen, 1999), and 3) Flares and CMEs are part of the same magnetic eruption process (Harrison, 1995; Zhang et al., 2001). Mahrous et al. (2009) investigated the CME-flare simultaneously associated during the 23rd solar cycle, they found that the time interval between the triggering time of the X-ray flare and the lifting-off time of CME associated events occur in the range 0.4 h ≤ Δt ≤ 1 h. Youssef et al. (2013) found that the CME happened during 1–2 h after the starting time of the solar flares, a similar result was also reported by Compagnino et al. (2017). The dataset used in this analysis was acquired from 3 different sources: 1 The observations of X-ray solar flares recorded by RHESSI. 2 X-ray and γ-ray burst solar flare observations from the Gamma-ray Burst Monitor (GBM) obtained by Fermi above 10 keV (all flares ≥ GOES CeClass). 3 The CME records obtained from Large Angle and Spectrometric Coronagraph on board of the Solar and Heliospheric Observatory 2 New Astronomy 74 (2020) 101285 R. Mawad and W. Abdel-Sattar ΨFlare = arctan[Sin λ /Tan β ] (1) The angular separation ΔF of these position-matched CMEs and flares is given by: ∆F = [ΨCME − ΨF ] (2) Where ΨCME is the position angle of the CME (the angle measured on the solar disk between the solar north pole and the line directed to the ejection of the CME), ΨF is the flare's position angle (Mahrous et al., 2009; Youssef et al., 2013; Mawad et al., 2015). 4. Results and discussion Studying 14,786 CME events and 5092 GBM solar flare events recorded during 2008–2017, we found 833 CME events associated with γray burst solar flare events (CME-γ-preflare), using the spatial and temporal criteria mentioned above. A complete list of these flares is shown in Table 2. All the 845 events (100%) are associated with solar flares that are detected in both GBM and RHESSI. 4.1. The rate of associated events Fig. 1. Histogram of CME-γ-preflare time interval. After applying the association criteria, we obtained the total number of CME-γ-preflare pairs in our sample. The final sample contains 845 CME-γ-preflare associated events (about 16%) with total 14,786 CMEs and 5092 GBM solar flare events observed during the solar period 2008–2017. Mawad and Youssef (2018) and Suryanarayana (2018) in their work found that CMEs can occur before the start time of X-ray solar flare events, which is in agreement with our results. By the same conditions criteria used, Mawad and Youssef (2018) found 292 CME – preflare associated events. Previous studies for rates of CMEs associated with flares found different association rates or ratio, 40% (Munro et al., 1979), 34% (St. Cyr and Webb, 1991) and 11% (Aarnio et al., 2011). Our result (16%) can be considered a decent result compared to previous studies, this is due to investigating a longer period and a larger dataset, however we applied more restrictions to the selection of events. SOHO/LASCO (CDA) catalog have been used. In the solar period 2008–2017 we have 14,786 CME events and 5092 GBM solar flare events recorded. 3. CME-γ-preflare matching criteria For selecting the CME-γ-preflare associated events, we applied both spatial and temporal criteria, by requiring that both flare and CME occur within a specific time window and angular separation. 3.1. Temporal condition We initially set the time window to select CMEs which occur before Gamma-Ray Burst (GBM) solar flare detection. We found the popular time interval is 2 h before γ-ray burst solar flare as shown in Fig. 1. 4.2. CME–γ-preflare time interval and duration 3.2. Spatial condition Found that the time interval for the CME-γ-preflare association is 61.5 ± 1.2 min. The flare's duration has a mean value of 12.7 ± 0.44 min with standard deviation value 12.7, which is greater than the duration of non-associated γ-ray burst solar flares mean value (12.4 ± 0.44 min) during the selected period of study, as shown in Table 1. The popular CME-γ-preflare association events occur in 1–2 h interval Mawad and Youssef (2018) found that a clear interval peak of CME – X-Ray Preflare is seen within 0–2 h, but they suggested an interval of 0–1 h as a time window for their study. Also, they noticed that most of CME events happened in half an hour before x-ray flare start time, The position of the CMEs is obtained in 2-dimensional projectivecircular coordinates (in position angle) on the solar disk plane. The solar flare's locations obtained by RHESSI are recorded in projectiveCartesian coordinates in x and y (in arc seconds). To convert the solar flare's position into heliographic coordinates, we used the IDL module called: coord_cart_helio. In order to apply the spatial condition, we need to convert the calculated spherical coordinate of the solar flares (longitude λ and latitude β) into 2-dimensional plane coordinate (position angle). This can be done using the following equation: Table 1 Summary of the statistical study. Interval Duration Width Position Angle Initial speed Acceleration Mass Kinetic Energy Associated Mean Standard Deviation Standard Error Non-associated Mean Standard Deviation Standard Error 61.5 (m) 12.4 (m) 64.4° 223.8° 351 (Km/s) 3.5 (m/s2) 1.3 × 1015 (g) 2.28 × 1030 (erg) 34.8 12.9 53.6° 84.7° 269.2 34 2.3 × 1015 9.14 × 1030 1.2 0.44 1.8° 2.9° 8.9 1.2 9 × 1013 9.1 × 1030 10.6 53.5 173 322.18 4.81 1.3 × 1015 3.5 × 1030 12.5 63.11 105.6 240.78 44.46 3.36 × 1015 2.52 × 1031 0.17 0.52 0.87 2 0.37 3.5 × 1013 2.6 × 1029 3 New Astronomy 74 (2020) 101285 R. Mawad and W. Abdel-Sattar Mawad and Youssef (2018) found the mean width values of the associated events are 63°.3, 88°.4, 81.1° and 74°.3 for B, C, M and X solar flare classes respectively of CME-Preflare associated events during the period 1996–2010, which is in agreement with our results. Mawad and Youssef (2018) found the majority of the CME-Preflare associated events exhibit an angular width ranging from 0°−60°. The popular angular width of associated CMEs is in the range 30°−60°, while the non-associated CMEs exhibit an angular width ranging from 0–30°. For the CME-Preflare associated events, the CME width increases as the flux of its associated solar flare increase as for the PFA associated events. The post-flare–CME associated events are wider than associated CME-Preflare associated events. These results indicate that, as the flare's flux increases, the width of the associated CME increases. These results are similar to the results obtained by Youssef et al. (2013) and with some differences with results obtained by Aarnio et al. (2011) [see, e.g. Mawad and Youssef (2018)]. Youssef et al. (2013) found that CME width equals 103, 107, 146 and 215° for post-flare classes B, C, M, and X respectively. The conclusion here is that the X-ray post-flare is wider than GBM post-flare – CME associated event. Yashiro et al. (2004) found that the annual averages of non-halo CME width range are between 47° and 61°. The CDAW catalog contains inconsistencies in the reporting of LASCO CMEs due to changes in personnel that used their own criteria (observer bias). These observer biases resulted in many more narrow CMEs added to the catalog after 2004 which significantly skewed CME width rates (Robbrecht et al., 2009; Yashiro et al., 2008). The previous studies of CME-Flare associated events did not consider the effect of observer bias on the CME width property. Consequently, we used the width which is obtained from CDAW catalog for comparison purpose only. Fig. 2. CME Angular width of CME-γ-preflare associated events. which is in agreement with our results. Mahrous et al. (2009) found that the lift-off time within the range of 0.4–1.0 h of CME–flare simultaneously associated events. Youssef et al. (2013) found that the CME happened after the starting time of the solar flares during a time interval of 1–2 h as reported by Compagnino et al. (2017). 4.3. CME's angular width 4.4. The CME mass–width relationship To check whether the CME-γ-preflare is wider than the non-associated CME, we found that many CMEs show an increase in width as they move out, therefore measurements are made when the width approaches a certain value. The mean value of the CME width distribution of CME-γ-preflare associated events is 64.4° ± 1.8°, which is slightly wider than non-associated CME (53°.5 ± 0.5), as shown in Fig. 2 and Table 1. We notice that the mass of CME-γ-preflare associated and non-associated events have the same mass and kinetic energy, as shown in Table 1. Mawad and Youssef (2018) found that mean mass of CMEPreflare associated events is 1.3 × 1015 g, while the mean mass for nonassociated CME events is 1.18 × 1015 g. The mean mass distribution of the CMEs ejected from the Sun by the x-ray post-flare is 2.6 × 1015 g. This result indicates that the CMEs occurred after the x-ray solar flare is Fig. 3. The relationship between CME's width and mass of CME-γ-preflare associated events. 4 New Astronomy 74 (2020) 101285 R. Mawad and W. Abdel-Sattar associated events. Mawad and Youssef (2018) found that the mean acceleration for CME-Preflare associated events has a negative value (−1.67 m/s2) during the solar period 1996–2006, while the non-associated CME events show a positive mean acceleration of 3.062 m/s2 during the period 1996–2010 in their study of X-ray solar flares only. Youssef et al. (2013) found that the post-flare–CME associated events have negative mean acceleration (−2.72 m/s2). Flare-CME associated simultaneously have both accelerated and decelerated CME events (Mawad et al., 2016). Youssef et al. (2013) concluded that the post-flare–CME associated events are in average more decelerated than CME-Flare associated simultaneously events and other CMEs. on average more massive than associated CME-preflare and other CMEs. The CME mass increases with the increase in flare's flux. Youssef et al. (2013) indicated that CMEs occurred after the solar flare (post-flare – CME associated events) is on average more massive than other CMEs. The mass of the CME-γ-preflare associated events is plotted as a function of the CME width in Fig. 3. The linear fitting that describes this relationship is of the form: M = −7.12 × 10+14 + 2.7 × 10+13 × W, (3) Where M is the mass of CME in grams and W is the angular width of CME in degrees. The correlation coefficient of the linear fitting is R = 0.63. Mawad and Youssef (2018) found the same linear correlation of CME-Preflare associated events during 1996–2010 with a correlation coefficient R = 0.52 for their 292 associated events. This result implies that the wide CMEs are more massive than narrow CMEs; this is in a good agreement with the result obtained by Youssef et al. (2013) and Aarnio et al. (2011), but the correlation coefficient obtained in this work is higher than their results. 4.7. The CME speeds Found that the CME initial speeds of the CME-γ-preflare associated events are meanly lower than solar wind mean speed and have the value ∼352 km/s as shown in Fig. 6, while non-associated CME has a mean value ∼322 km/s. This means that the γ-ray burst is playing role in increasing slightly the speed of CME, but the CME speed remains lower than the solar wind mean speed. The dominant CME initial speed of the CME-γ-preflare associated events is ∼300 Km/s. Mawad and Youssef (2018) found that the CME initial and linear speeds of the selected 292 CME-Preflare associated events during 1996–2010 are mainly near the solar wind mean speed and have the value ∼ (490 ± 17) km/s. The fastest associated CME-Preflare is the M – class solar flare. Youssef et al. (2013) found that the average CME linear speed of the selected 388 post-flare–CME associated events have 880 km/s, while the CMEs non-associated with flares speed was (400 ± 2) km/s. Gosling et al. (1976), and Aarnio et al. (2011) found that the CME-flare associated events have a higher linear speed than those not associated with flares. 4.5. CME's position angle From Fig. 4, we notice that the most of CMEs associated with X-ray and γ-ray burst solar flares are ejected near the solar equator, most of the events are originated in the west side of the solar disk near the solar equator. CME-γ-preflare associated events have a mean value of CME position angle 224°, while the non-associated event has a position angle of 173°, which indicates that the non-associated events tend towards the solar pole. 4.6. The CME acceleration 5. Conclusion Found the mean value of the CME acceleration of the CME-γ-preflare associated events to be (3.5 ± 1.2) m/s2, which is smaller than non-associated events ∼ (4.8 ± 0.37) m/s2 during the selected period 2008–2017 as shown in Fig. 5. The γ-ray bust solar flare accelerates CMEs but are less than non-associated or only X-ray solar flare Studied 14,786 CME events and 5092 GBM solar flare (called γ-ray burst solar flare) events recorded during 2008–2017, found 845 (about 16%) CME events associated with γ-ray burst solar flare events only Fig. 4. Position angle of CME-γ-preflare associated events. 5 New Astronomy 74 (2020) 101285 R. Mawad and W. Abdel-Sattar Fig. 5. CME acceleration of CME-γ-preflare associated events. position angle 224°, while the non-associated event has a position angle of 173°. The mean value of the CME acceleration of the CME-γ-preflare associated events is 3.5 m/s2 less than non-associated events ∼ 4.8 m/s2. The γ-ray burst solar flare accelerates CMEs but less than non-associated or only X-ray solar flare associated events. The CME initial speeds of the CME-γ-preflare associated events are meanly lower than solar wind mean speed and have the value ∼ 351 km/s, while non-associated CME has a mean value ∼ 322 km/s. The complicated process of the magnetic reconnection associated with the γ-ray burst solar flares should have played one important role in slightly increasing the speed of CME, but the CME speed remains lower than the solar wind mean speed. The mass of the CME-γ-preflare associated events is investigated as a function of the CME width. The linear fitting that describes this (CME-γ-preflare), using our spatial and temporal criteria. These 845 associated events are all (100%) associated with solar flares that are detected in both GBM and RHESSI (hard X-ray and maybe associated γray burst). Found that the time interval for the CME-γ-preflare association is 61.5 min. The flare's duration has a mean value of 12.4 min greater than non-associated γ-preflare solar flares mean value (10.6 min) during the selected period of study. The popular CME-γ-preflare association events occur in the interval 1–2 h The mean value of the CME width distribution of CME-γ-preflare associated events is 64°, which is slightly wider than non-associated CME (53°). The most of CMEs associated with γ and X -rays solar flares are originated in the west side of the solar disk near the solar equator. CME-γ-preflare associated events have a mean value of CME 6 New Astronomy 74 (2020) 101285 R. Mawad and W. 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