X-ray Flare Events Research Articles

The enigmatic dance of the HD 189733A system: A quest for accretion

Context. Several studies suggest that the emission properties of a star can be significantly affected by its interaction with a nearby planet through magnetic fields or interaction between their respective winds. However, the actual observability of these effects remains a subject of debate. An illustrative example is the HD 189733A system: certain characteristics of its emissions have been interpreted as indicative of ongoing interactions between the star and its associated planet. Other studies attribute these characteristics to the coronal activity of the star. Aims. In this study we aimed to investigate whether the observed stellar X-ray flare events, which appear to be in phase with the planetary period in the HD 189733A system, could be attributed to the accretion of the planetary wind onto the stellar surface or if they resulted from an interaction between the planetary and stellar winds. Methods. We developed a 3D magnetohydrodynamic model with the PLUTO code that describes the system HD 189733A , including the central host star and its hot Jupiter along with their respective winds. The effects of gravity and the magnetic fields of both the star and the planet are taken into account. Results. Our analysis reveals that, in the cases examined in this study, the accretion scenario is only viable when the stellar magnetic field strength is at 5 G and the planetary magnetic field strength is at 1 G. In this scenario, the Rayleigh-Taylor instabilities lead to the formation of an accretion column that connects the star to the planet. Once formed the accretion column remains stable for the duration of the simulation. The accretion column produces an accretion rate of the order of 1012 g s−1 and shows an average density of about 107 cm−3. In the other case explored, the accretion column does not form because the Rayleigh-Taylor instability is suppressed by the stronger magnetic field intensities assumed for both the star and the planet. We synthesized the emission resulting from the shocked planetary wind and found that the total X-ray emission ranges from 5 × 1023 to 1024 erg s−1. Conclusions. In the case of accretion, the emission originating from the hotspot cannot be distinguished from the coronal activity. Also, the interaction between the planetary and stellar winds cannot be responsible for the X-ray emission, as the total emission produced is about four orders of magnitude lower than the average X-ray luminosity of the star.

The Influence of Solar X-ray Flares on SAR Meteorology: The Determination of the Wet Component of the Tropospheric Phase Delay and Precipitable Water Vapor

In this work, we study the impact of high-energy radiation induced by solar X-ray flares on the determination of the temporal change in precipitable water vapor (ΔPWV) as estimated using the synthetic aperture radar (SAR) meteorology technique. As recent research shows, this radiation can significantly affect the ionospheric D-region and induces errors in the estimation of the total electron content (TEC) by the applied models. Consequently, these errors are reflected in the determination of the phase delay and in many different types of measurements and models, including calculations of meteorological parameters based on SAR observations. The goal of this study is to quantify the impact of solar X-ray flares on the estimation of ΔPWV and provide an estimate of errors induced if the vertical total electron content (VTEC) is obtained by single layer models (SLM) or multiple layer models (MLM) (these models do not include ionosphere properties below the altitude of 90 km as input parameters and cannot provide information about local disturbances in the D-region). The performed analysis is based on a known procedure for the determination of the D-region electron density (and, consequently, the vertical total electron content in the D-region (VTECD)) using ionospheric observations by very low frequency (VLF) radio waves. The main result indicates that if the D-region, perturbed by medium-sized and intense X-ray flares, is not modeled, errors occur in the determination of ΔPWV. This study emphasizes the need for improved MLMs for the estimation of the TEC, including observational data at D-region altitudes during medium-sized and intense X-ray flare events.

Lifting the curtain: The Seyfert galaxy Mrk 335 emerges from deep low-state in a sequence of rapid flare events

Context. The narrow-line Seyfert 1 galaxy Mrk 335 was one of the X-ray brightest active galactic nuclei, but it has systematically faded since 2007. Aims. We report the discovery with Swift of a sequence of bright and rapid X-ray flare events that reveal the emergence of Mrk 335 from its ultra-deep multiyear low state. Methods. Results are based on our dedicated multiyear monitoring of Mrk 335 with Swift. Results. Unlike other bright active galactic nuclei, the optical–UV is generally not correlated with the X-rays in Mrk 335 on a timescale of days to months. This fact either implies the absence of a direct link between the two emission components; or else implies that the observed X-rays are significantly affected by (dust-free) absorption along our line of sight. The UV and optical, however, are closely correlated at the 99.99% confidence level. The UV is leading the optical by Δt = 1.5 ± 1.5 d. The Swift X-ray spectrum shows strong deviations from a single power law in all brightness states of the outbursts, indicating that significant absorption or reprocessing is taking place. Mrk 335 displays a softer-when-brighter variability pattern at intermediate X-ray count rates, which has been seen in our Swift data since 2007 (based on a total of 590 observations). This pattern breaks down at the highest and lowest count rates. Conclusions. We interpret the 2020 brightening of Mrk 335 as a decrease in column density and covering factor of a partial-covering absorber along our line of sight in the form of a clumpy accretion-disk wind that reveals an increasing portion of the intrinsic emission of Mrk 335 from the disk and/or corona region, while the optical emission-line regions receive a less variable spectral energy distribution. This then also explains why Mrk 335 was never seen to change its optical Seyfert type (not “changing look”) despite its factor ∼50 X-ray variability with Swift.

Comparative Analysis of VLF Signal Variation along Trajectory Induced by X-ray Solar Flares

Comparative qualitative analysis of amplitude and phase delay variations was carried out along the trajectory of GQD/22.1 kHz and NAA/24.0 kHz VLF signal traces, propagating from Skelton (UK) and Maine (USA) toward Belgrade, induced by four isolated solar X-ray flare events occurred during the period from September 2005 to December 2006. For monitoring, recording and for storage of VLF data at the Institute of Physics in Belgrade, Serbia, the AbsPAL system was used. For modeling purposes of propagating conditions along GQD and NAA signal propagation paths, LWPCv21 program code was used. Occurred solar flare events induced lower ionosphere electron density height profile changes, causing perturbations in VLF wave propagation within Earth-ionosphere waveguides. As analyzed VLF signals characterize by different propagation parameters along trajectories from their transmitters to the Belgrade receiver site, their propagation is affected in different ways for different solar flare events and also for the same solar flare events.

The curious temporal behavior of the frequency of different class flares

We investigate the frequency of all (X-ray flare events higher than class B1.0), B, C, M and X-class flares, respectively, derived from the National Geophysical Data Center (NGDC) list of solar flares between May 1983 and September 2014, which corresponds to the two complete solar cycles (SCs) 22 and 23 as well as the rise and maximum phases of SC 24. Analysis shows that the temporal behavior for these various class flares is quite different. The main findings of this study, confirmed by using the Hinode flare catalog where possible, are as follows. (1) The B-class flares are in complete antiphase with all, C, M and X-class flares. (2) While, there is a small decreasing trend in the peak values of the smoothed monthly C-class flare numbers from SC 22 to 24, the occurrence rate of M and X-class flares dropped by almost half and two-thirds, respectively, during SC 23 and remained almost the same during SC 24. This class-dependent temporal behavior provides support for dynamo models that involve the coexistence of a deep global and a superficial local dynamo.

UPDATED PHOTOMETRY AND ORBITAL PERIOD ANALYSIS FOR THE POLAR AM HERCULIS ON THE UPPER EDGE OF THE PERIOD GAP

Twenty-one new optical light curves, including five curves obtained in 2009 and sixteen curves detected from the AAVSO International Database spanning from 1977 to 2011, demonstrate 16 new primary minimum light times in the high state. Furthermore, seven newly found low-state transient events from 2006 to 2009 were discovered, consisting of five Gaussian-shaped events and two events with an exponential form with decay timescales of $<$0.005 days; these timescales are one order of magnitude shorter than those of previous X-ray flare events. In the state transition, two special events were detected: a "disrupted event" with an amplitude of $\sim$ 2 mag and a duration of $\sim$ 72 minutes and continuing R-band twin events larger than all known R-band flares detected in M-type red dwarfs. All 45 available high-state data points spanning over 35 yr were used to construct an updated O-C diagram of \objectname{AM Herculis}, which clearly shows a significant sine-like variation with a period of 12-15 yr and an amplitude of 6-9 minutes. Using the inspected physical parameters of the donor star, the secular variation in the O-C diagram cannot be interpreted by any decided angular momentum loss mechanism, but can satisfy the condition $\tau_{\dot{\rm M}_{2}}\simeq\tau_{\rm KH}>>\tau_{\dot{\rm R}_{\rm 2}}$, which is required by numerical calculations of the secular evolution of cataclysmic variables. In order to explain the prominent periodic modulation, three plausible mechanisms - spot motion, the light travel-time effect, and magnetic active cycles - are discussed in detail.

Mid- and low-latitude response of the ionosphere to solar proton events on January 2012

We present and discuss the ionosphere behavior under the impact of two X-ray solar flares (M8.7 and X1.7) that occurred on January 23 and 27, respectively, and were accompanied by Solar Proton Events (SPEs). The ionosphere response to these solar phenomena was detected using riometers (30 and 38.2 MHz), ionosonde and VLF systems operating at the Comandante Ferraz Brazilian Station in Antarctica and at the Itapetinga Radio Observatory in São Paulo (SP)/Brazil. The results suggest the ionosphere was affected by both SPEs, as evidenced by absorption detected in the cosmic noise, F2 layer critical frequency and VLF amplitude measurements. These absorptions started before the beginning of the main X-ray flare events and > 100 MeV proton events detected by GOES, suggesting the ionosphere was impacted by protons with energies above 2 GeV in Antarctica and above 10-12 GeV in SP as estimated from the particle geomagnetic rigidity (Rc) at each place. The results also suggest a long-lasting presence (hours) of high energy protons.

Cross Comparison of Solar X‐Ray Data Between FY‐2C/D Satellite and GOES Satellite

AbstractFengyun 2 (FY‐2) satellite is the first generation of geostationary meteorological satellite of China. The solar X‐ray detector aboard on FY‐2C/D has capability to observe the solar X‐ray flux of &gt;5.18 keV and &gt;3.27 keV, respectively. For the purpose of examining the effectiveness of FY‐2C/D X‐ray data, we compare them with the similar data of GOES, and find that these two categories of data are well consistent in temporal characters and X‐ray flux during solar flare events. By the cross comparison of the X‐ray peak flux for 85 solar flare events from November 2004 to June 2010, it is found that the linear correlative coefficient is 0.795 between FY‐2C and GOES data in 1~8 Å, and the corresponding coefficients between FY‐2D and GOES data in 0.5~3 Å and 1~8 Å are 0.921 and 0.989, respectively. The results indicate that the FY‐2C/D solar X‐ray data are quite reliable for monitoring, warning and researching of the solar X‐ray flare events.

A SEARCH FOR STAR-DISK INTERACTION AMONG THE STRONGEST X-RAY FLARING STARS IN THE ORION NEBULA CLUSTER

The Chandra Orion Ultradeep Project observed hundreds of young, low-mass stars undergoing highly energetic X-ray flare events. The 32 most powerful cases have been modeled with the result that the magnetic structures responsible for these flares can be many stellar radii in extent. In this paper, we model the observed spectral energy distributions of these 32 stars in order to determine, in detail for each star, whether there is circumstellar disk material situated in sufficient proximity to the stellar surface for interaction with the large magnetic loops inferred from the observed X-ray flares. Our spectral energy distributions span the wavelength range 0.3-8 um (plus 24 um for some stars), allowing us to constrain the presence of dusty circumstellar material out to >10 AU from the stellar surface in most cases. For 24 of the 32 stars in our sample the available data are sufficient to constrain the location of the inner edge of the dusty disks. Six of these (25%) have spectral energy distributions consistent with inner disks within reach of the observed magnetic loops. Another four stars may have gas disks interior to the dust disk and extending within reach of the magnetic loops, but we cannot confirm this with the available data. The remaining 14 stars (58%) appear to have no significant disk material within reach of the large flaring loops. Thus, up to ~40% of the sample stars exhibit energetic X-ray flares that possibly arise from a magnetic star-disk interaction, and the remainder are evidently associated with extremely large, free-standing magnetic loops anchored only to the stellar surface.

Statistical analysis of the X-ray flares (M ≥ 1) during the maximum period of solar cycle 22

The data of the X-ray flare events of class M 1 during the interval of 1987 to 1992 corresponding to the maximum period of the 22nd solar cycle have been investigated to study the North-South (N S) and West- East (W E) asymmetries. During that period it has been shown the existence of a real N S asymmetry. That con- rms recent studies done by using other indicators, such as sunspot areas (Oliver & Ballester 1994). The E Wa sym- metry during that period is not signicant but a non uni- form flare distribution in longitude has been evidenced. That result is also in good agreement with the work made by Joshi (1995) using H flares for the same time period. We have shown that the behaviour of the reverse ten- dency of Solar Cycle 21 to exhibit a predominance of the southern hemisphere in the N S asymmetry compared to the previous Solar Cycles (19 and 20) is maintained for Solar Cycle 22. A long period cycle of the N S asymme- try could be suspected.

HEAO 1 observations of quiescent X-ray emission from flare stars

view Abstract Citations (19) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS HEAO 1 observations of quiescent X-ray emission from flare stars. Tsikoudi, V. Abstract The HEAO A-2 data were searched at the positions of the 70 known flare stars for evidence of X-ray emission. Thirteen of them appear to be detected at the equal to or greater than 3 sigma level. Their X-ray luminosities in the 2-20 keV energy band are in the range 5 x 10 to the 28th - 6 x 10 to the 29th ergs/s and L(x)/L(bal) approximately 0.0001 to 0.01. There were no detectable X-ray flare events during the time of HEAO 1 observations. This detection, therefore, refers to the quiescent state X-ray emission from the coronae of these stars. It appears that intense coronae belonging to fairly active flare stars are being observed. X-ray variability over periods of 6 months was observed for several of them. Publication: The Astrophysical Journal Pub Date: November 1982 DOI: 10.1086/160417 Bibcode: 1982ApJ...262..263T Keywords: Emission Spectra; Flare Stars; Radiant Flux Density; Stellar Coronas; X Ray Sources; Heao 1; Stellar Evolution; Stellar Luminosity; Variability; Astrophysics full text sources ADS | data products SIMBAD (50) NED (11) Related Materials (1) Erratum: 1983ApJ...272..381T

The quantitative properties of three soft X-ray flare kernels observed with the AS&amp;E X-ray telescope on Skylab

The physical parameters for the kernels of three solar X-ray flare events have been deduced using photographic data from the S-054 X-ray telescope on Skylab as the primary data source and 1–8 and 8–20 A fluxes from Solrad 9 as the secondary data source. The kernels had diameters of ∼5–7″ and in two cases electron densities at least as high as 3 × 1011 cm−3. The lifetimes of the kernels were 5–10 min. The presence of thermal conduction during the decay phases is used to argue: (1) that kernels are entire, not small portions of, coronal loop structures, and (2) that flare heating must continue during the decay phase.

Observations of the structure and evolution of solar flares with a soft X-ray telescope

132 soft X-ray flare events have been observed with The Aerospace Corporation/Marshall Space Flight Center S-056 X-ray telescope that was part of the ATM complement of instruments aboard Skylab. Analyses of these data are reported in this paper. The observations are summarized and a detailed discussion of the X-ray flare structures is presented. The data indicated that soft X-rays emitted by a flare come primarily from an intense well-defined core surrounded by a region of fainter, more diffuse emission. Loop structures are found to constitute a fundamental characteristic of flare cores and arcades of loops are found to play a more important role in the flare phenomena than previously thought. Size distributions of these core features are presented and a classification scheme describing the brightest flare X-ray features is proposed.The data show no correlations between the size of core features and: (1) the peak X-ray intensity, as indicated by detectors on the SOLRAD satellite; (2) the rise time of the X-ray flare event, or (3) the presence of a nonthermal X-ray component.An analysis of flare evolution indicates evidence for preliminary heating and energy release prior to the main phase of the flare. Core features are found to be remarkably stable and retain their shape throughout a flare. Most changes in the overall configuration seem to be the result of the appearance, disappearance or change in brightness of individual features, rather than the restructuring or re-orientation of these features.Brief comparisons with several theories are presented.

Electron loss processes in the lower D-region during the decay of solar X-ray flare events

Data concerning the recovery of the lower D-region during the decay of solar X-ray events, are examined. A simple discussion of such results in terms of a two positive-ion model, has shown possible ranges for some significant parameters of the D-region, in agreement with previous experimental determinations.

Soft X-Ray (λ &lt;14 ) Emission by the Sun Since 1 July 1966.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Soft X-Ray (λ <14 ) Emission by the Sun Since 1 July 1966. van Allen, J. A. Abstract By means of three thin mica-window Geiger- Mueller tubes on the earth satellite Explorer 33, a nearly continuous patrol of the soft x-ray emis- sion by the sun has been maintained with 1-ni in time resolution for the following periods: 1July 1966-22 September 1966 9 October 1966-8 December 1966 27 December 1966-18 March 1967 and is continuing at the date of writing. Typical sensitivity is 10-6 erg (cm2 sec)-' and the dynamic range of intensity is 10~. A catalogue of x-ray flare events and detailed intensity-time profiles of selected events are presented. Four noteworthy events which are precursors of the arrival of solar-emitted particles are as follows: Ratio of maximum intensity Time of to that of Time of max. ambient Date onset intensity quiet sun 7 July 1966 00:23 UT 00:42 UT 28 28August 15:22 15:31 70 2 September 05:46 05:58 60 13 February 1967 17:55 18:24 12 Some preliminary absolute intensities (N <14 A) are (a) Mean quiet sun (September 1966): 4X 10-~ erg (cm2 sec)-'. (b) Maximum intensity of 28 August 1966 event: 3X10-2 erg (cm2 sec)-'. (c) Time-integrated emission of 28 August 1966 event (assuming 2~ sr at the sun): 0.7 X 1029 ergs. The x-ray flare events are intimately related to the Ha flare reports and to terrestrial SI D's (sudden ionospheric disturbances). Publication: The Astronomical Journal Pub Date: 1967 DOI: 10.1086/110468 Bibcode: 1967AJ.....72Q.833V full text sources ADS |