Superflares Research Articles

What Are the Causes of Super Activity of Solar Active Regions?

Flare productivity varies among solar active regions (ARs). This study analyzed 20 ARs of contrasting sunspot areas and flare productivities to understand the super flare productivity of certain ARs. We used the flare index (FI) as an indicator of flare activity. We examined the pattern of morphological evolution of magnetic features. Further, we derived a set of magnetic feature parameters to quantitatively characterize ARs. Our study found that the correlation coefficient is the highest (r = 0.78) between FI and the length of the strong gradient polarity inversion line (SgPIL), while the coefficient is the lowest (r = 0.14) between FI and the total unsigned magnetic flux. For the selected ARs, this study also found that the super flare productive ARs have SgPILs (R value) longer (greater) than 50 Mm (4.5). These results suggest that flare productivity is mainly controlled by the size of the subregion that comprises close interaction of opposite magnetic polarities and is weakly correlated with the size of the whole ARs. Further, even though magnetic flux emergence is important, this study shows that it alone is insufficient to increase flare productivity. New emergence can drive either the interaction of like or opposite magnetic polarities of nonconjugate pairs (i.e., polarities not from the same bipole). In the former case, the magnetic configuration remains simple, and flare productivity would be low. In the latter case, the convergence of opposite magnetic fluxes of nonconjugate pairs results in a magnetic configuration with long SgPIL and an increase in flare productivity.

Tidally-induced Magnetar Super Flare at the Eve of Coalescence with Its Compact Companion

In the late inspiral phase of a double neutron star (NS) or NS–black hole system in which one NS is a magnetar, the tidal force on the magnetar arisen from its companion will increase dramatically as the binary approaches. The tidal-induced deformation may surpass the maximum that the magnetar’s crust can sustain just seconds or subseconds before the coalescence. A catastrophic global crust destruction may thus occur, and the magnetic energy stored in the magnetar’s interior will have the opportunity to be released, which would be observed as a superflare with energy 100s of times larger than giant flares of magnetars. Such a mechanism can naturally explain the recently observed precursor of GRB 211211A, including its quasiperiodic oscillation. We predict that in the coming gravitational wave O4/O5 period, there could be a fraction of detected double NS mergers associated with such super flares. If observed, copious information on the structure and magnetic field in an NS interior can be obtained, which is hard to study elsewhere.

Torus-stable zone above starspots

ABSTRACT Whilst intense solar flares are almost always accompanied by a coronal mass ejection (CME), reports on stellar CMEs are rare, despite the frequent detection of stellar ‘super flares’. The torus instability of magnetic flux ropes is believed to be one of the main driving mechanisms of solar CMEs. Suppression of the torus instability, due to a confining background coronal magnetic field that decreases sufficiently slowly with height, may contribute to the lack of stellar CME detection. Here, we use the solar magnetic field as a template to estimate the vertical extent of this ‘torus-stable zone’ (TSZ) above a stellar active region. For an idealized potential field model comprising the fields of a local bipole (mimicking a pair of starspots) and a global dipole, we show that the upper bound of the TSZ increases with the bipole size, the dipole strength, and the source surface radius where the coronal field becomes radial. The boundaries of the TSZ depend on the interplay between the spots’ and the dipole’s magnetic fields, which provide the local- and global-scale confinement, respectively. They range from about half the bipole size to a significant fraction of the stellar radius. For smaller spots and an intermediate dipole field, a secondary TSZ arises at a higher altitude, which may increase the likelihood of ‘failed eruptions’. Our results suggest that the low apparent CME occurrence rate on cool stars is, at least partially, due to the presence of extended TSZs.

Evaluation of onion (Allium cepa L.) genotypes for growth and yield parameters under eastern dry zone of Karnataka

A field experiment was conducted to know the performance of onion (Allium cepa L.) genotypes in Eastern Dry Zone of Karnataka during 2015-16 at College of Horticulture, Kolar, Karnataka. Twenty five genotypes (13 varieties, 10 hybrids and 2 synthetics) were collected and evaluated in Rabi season. The research work was carried out to identify the elite genotypes suitable for Rabi season cultivation for higher bulb yield. The performance of the different genotypes with respect to growth and bulb yield were studied. The hybrid Flare (38.50 t/ha), Super Flare (37.00 t/ha) and S-780 (36.40 t/ha) were found best for obtaining quality bulb yield. In the studies, onion F1 hybrids were found to be superior to the synthetics and open pollinated varieties for higher bulb yield. Therefore, it is concluded that onion F1 hybrids need to be popularise for commercial cultivation for increasing productivity in the country.

Do the solar flares originating from an individual active region follow a random process or a memory-dependent correlation?

ABSTRACT We investigate the waiting time statistics of solar flares both in a flare-productive active region (AR 12673) of the solar cycle 24 and in a three-dimensional magnetohydrodynamic (MHD) simulated AR. The statistical models of a discrete random process and a continuous memory-dependent process are applied to interpret the waiting time distributions (WTDs) of solar flares. Our results indicate that the occurrence of a solar flare in an individual AR maintains a certain amount of memory, and probably arises from MHD turbulence rather than from intermittent avalanches in a self-organized criticality system. It differs from the occurrence of ‘super flares’ when treating the star/Sun as a single non-linear system.

The 6 September 2017 X9 Super Flare Observed From Submillimeter to Mid‐IR

AbstractActive Region 12673 is the most productive active region of solar cycle 24: in a few days of early September 2017, four X‐class and 27 M‐class flares occurred. SOL2017‐09‐06T12:00, an X9.3 flare also produced a two‐ribbon white light emission across the sunspot detected by Solar Dynamics Orbiter/Helioseismic and Magnetic Imager. The flare was observed at 212 and 405 GHz with the arcminute‐sized beams of the Solar Submillimeter Telescope focal array while making a solar map and at 10 μm, with a 17 arcsec diffraction‐limited infrared camera. Images at 10 μm revealed that the sunspot gradually increased in brightness while the event proceeded, reaching a temperature similar to quiet Sun values. From the images we derive a lower bound limit of 180‐K flare peak excess brightness temperature or 7,000 sfu if we consider a similar size as the white light source. The rising phase of mid‐IR and white light is similar, although the latter decays faster, and the maximum of the mid‐IR and white light emission is ∼200 s delayed from the 15.4‐GHz peak occurrence. The submillimeter spectrum has a different origin than that of microwaves from 1 to 15 GHz, although it is not possible to draw a definitive conclusion about its emitting mechanism.

The biological impact of superflares on planets in the Habitable Zone

AbstractYounger and fully convective stars are much more active than our Sun, producing many superflares. Here we estimate the impact of the superflares UV radiation on living organisms on the surface of orbiting planets in the habitable zone of the star. For this we study two active stars, Kepler-96 (solar type) and TRAPPIST-1 (M dwarf). Kepler-96, with an age of 2.4 Gyr, is at the same stage of the Sun when the first multicellular organisms appeared on Earth. The biological impact of super flares are studied on a hypothetical Earth at 1AU of Kepler-96 and on planets TRAPPIST-1e, f, and g for three atmospheres scenarios: an Archean and Present-day atmospheres with and without ozone. We estimated the survival rates of two bacteria and concluded that life would only survive on the surface of these planets if their atmosphere had an ozone layer, or in shallow waters of an ocean.

Could Earth be fried by a ‘superflare’ from the sun?

Could Earth be fried by a ‘superflare’ from the sun?

When is the sun’s next ‘superflare’ due?

When is the sun’s next ‘superflare’ due?

Distribution of strong and super flares by phases of solar activity cycles

The phase distribution of all strong X-ray flares from 1976 to 2013 and the flares in the current 24th cycle have been investigated. It is concluded that, until around 2019, mid-level M-class flares and strong (up to X8 class) flares can be expected. Stronger flares may also occur. Superflares like the Carrington event are unlikely.

Keplersuper-flare stars: what are they?

The Kepler mission has led to the serendipitous discovery of a significant number of `super flares' - white light flares with energies between 10^33 erg and 10^36 erg - on solar-type stars. It has been speculated that these could be `freak' events that might happen on the Sun, too. We have started a programme to study the nature of the stars on which these super flares have been observed. Here we present high-resolution spectroscopy of 11 of these stars and discuss our results. We find that several of these stars are very young, fast-rotating stars where high levels of stellar activity can be expected, but for some other stars we do not find a straightforward explanation for the occurrence of super flares.

Evaluation of solar radio bursts' effect on GPS receiver signal tracking within International GPS Service network

The direct interference from solar radio bursts (SRB) has not usually been considered as a potential threat to global positioning system (GPS) signal tracking, since the flux densities of most bursts are below 40,000 solar flux units (sfu), a threat threshold to GPS L1 frequency proposed by Klobuchar et al. (1999). Recent analysis indicated that a much lower threshold should be adopted for codeless or semicodeless dual‐frequency GPS receivers. In this investigation, severe signal corruptions were found at dayside International GPS Service GPS receiver stations during a large solar radio burst that accompanied the super flare of 28 October 2003. Almost no GPS L2 signals were tracked during the solar flux peak time for areas near the subsolar point. Correlation analysis was performed between the rate of loss of lock on GPS L2 frequency and solar radio flux density at different bands, and a correlation index as high as 0.75 is revealed in the 1415 MHz solar radiation band, which is located between the two GPS operating frequencies L2 (1227.60 MHz) and L1 (1575.42 MHz). The correlation analysis indicates that GPS signal losses of lock were primarily caused by microwave in‐band interference and that the threat threshold of SRB effects on the GPS system should be re‐evaluated, since the flux density of the burst at 1415 MHz was just 4,000–12,000 sfu, which is far below the previously proposed threat threshold. The signal‐tracking performance of different types of GPS receivers during such a super flare event is also presented.