X-ray Flux Enhancement Research Articles

Ionospheric response to an intense solar flare in equatorial and low latitude region

Multi-instrument data recorded at multi-stations are used to study the equatorial and low-latitude ionospheric response to an intense solar flare of class X7 (2B) in the current solar cycle 24 with the peak at 08:05 UT on 09 August 2011. Rapid changes in ionospheric total electron contents (TEC) measured by global positioning system (GPS) showed an enhancement of 2–3 TECU. The very low frequency (VLF) data recorded at a low latitude station Varanasi showed an enhancement of VLF signal amplitude during the solar flare period which is attributed to the sudden enhancement of D-region ionization. Ground based GPS measurements are also validated by analyzing the electron density profiles measured from COSMIC satellite mission. COSMIC-derived electron density profile shows a decrease below F2 peak altitude and increase above F2 peak. The D-region ionospheric perturbation observed during the solar flare could be caused by flare time enhanced level of photo-ionization due to X-ray flux enhancement, whereas for E and F-region ionosphere, enhanced EUV flux causes photo-ionization and hence perturbed the TEC.

MAGNETAR-LIKE X-RAY BURSTS FROM A ROTATION-POWERED PULSAR, PSR J1119–6127

ABSTRACT Two energetic hard X-ray bursts from the rotation-powered pulsar PSR J1119−6127 recently triggered the Fermi and Swift space observatories. We have performed in-depth spectral and temporal analyses of these two events. Our extensive searches in both observatories’ data for lower luminosity bursts uncovered 10 additional events from the source. We report here on the timing and energetics of the 12 bursts from PSR J1119−6127 during its burst active phase on 2016 July 26 and 28. We also found a spectral softer X-ray flux enhancement in a post-burst episode, which shows evidence of cooling. Here we discuss the implications of these results on the nature of this unusual high-field radio pulsar, which firmly place it within the typical magnetar population.

Demonstration of enhancement of x-ray flux with foam gold compared to solid gold

Experiments have been conducted to compare the re-emission from foam gold with a 0.3 g cc−1 density and solid gold in a SGIII prototype laser facility. Measurements of the re-emission x-ray flux demonstrate that emission is enhanced by the low density foam gold compared to the solid gold under the same conditions. The emission fraction increases with time and is concentrated on soft x-ray flux between 0.1–1 keV. The simulation results with Multi 1D agree with the experimental results. There are potential advantages to using foam walls for improving the emission and soft x-ray flux in hohlraums.

BROADBAND X-RAY PROPERTIES OF THE GAMMA-RAY BINARY 1FGL J1018.6–5856

We report on NuSTAR, XMM-Newton and Swift observations of the gamma-ray binary 1FGL J1018.6-5856. We measure the orbital period to be 16.544+/-0.008 days using Swift data spanning 1900 days. The orbital period is different from the 2011 gamma-ray measurement which was used in the previous X-ray study of An et al. (2013) using ~400 days of Swift data, but is consistent with a new gamma-ray solution reported in 2014. The light curve folded on the new period is qualitatively similar to that reported previously, having a spike at phase 0 and broad sinusoidal modulation. The X-ray flux enhancement at phase 0 occurs more regularly in time than was previously suggested. A spiky structure at this phase seems to be a persistent feature, although there is some variability. Furthermore, we find that the source flux clearly correlates with the spectral hardness throughout all orbital phases, and that the broadband X-ray spectra measured with NuSTAR, XMM-Newton, and Swift are well fit with an unbroken power-law model. This spectrum suggests that the system may not be accretion-powered.

Analysis of solar EUV and X-ray flux enhancements during intense solar flare events and the concomitant response of equatorial and low latitude upper atmosphere

We investigate the X ray and UV flux changes during flare events and the corresponding ionospheric response. The study reveals that UV flux enhancement depends on both flare intensity and position on solar disk while X-ray flux enhancement depends only on the former. The study brings out a new result that the E region response to flares directly relates to the X-ray flux enhancement and that it does not exhibit limb effect. Further, the F region response shows limb effect indicating the UV flux control on the same and it also shows seasonal variability due to solar zenith angle variability.

Statistical analysis of solar EUV and X-ray flux enhancements induced by solar flares and its implication to upper atmosphere

The 0.1-0.8 nm X-ray flux data and 26-34 nm EUV flux data are used to statistically analyze the relationship between enhancement in X-ray flux and that in EUV flux during solar flares in 1996-2006. The EUV enhancement does not linearly increase with X-ray flux from C-class to X-class flares. Its uprising amplitude decreases with X-ray flux. The correlation coefficients between enhancements in EUV and X-ray flux for X, M and C-class flares are only 0.66, 0.58 and 0.54, respectively, which suggests that X-ray flux is not a good index for EUV flux during solar flares. Thus, for studying more accurately solar flare effect on the ionosphere/thermosphere system, one needs to use directly EUV flux measurements. One of important reasons for depressing relationship between X-ray and EUV is that the central meridian distance (CMD) of flare location can significantly affect EUV flux variation particularly for X-class flares: the larger value of CMD results in the smaller EUV enhancement. However, there are much smaller CMD effects on EUV enhancement for M and C-class flares. The solar disc images from SOHO/EIT are utilized to estimate the percentage contribution to total EUV enhancement from the flare region and from other region. The results show the larger percentage contribution from other region for the weaker flares, which would reduce the loss of EUV radiation due to limb location of flare and then weaken the CMD effect for weaker flares like M and C-class.

Preflare Eruption Triggered by a Tether‐cutting Process

We have examined the preflare activity of an M1.2 flare that occurred in NOAA active region 8440 on 1999 January 16, using images from the Soft X-Ray Telescope (SXT) on board Yohkoh, 1600 A UV images from the Transition Region and Coronal Explorer (TRACE), X-ray flux data from the GOES satellite, and magnetograms from Big Bear Solar Observatory (BBSO). During the preflare phase, we note a weak GOES X-ray flux enhancement just 4 minutes before the main flare begins. The SXT images show that this enhancement occurs at one footpoint of a soft X-ray loop bundle, which exactly coincides with the kernel of the major flare. The series of TRACE images provides the following pieces of evidence for small-scale magnetic reconnections associated with the preflare activity. (1) A small-scale UV sigmoid is seen at the X-ray loop footpoint before the preflare activity, and it is located along the polarity inversion line. (2) The brightest among the UV brightenings is exactly coincident and cospatial with the soft X-ray brightening observed by the Yohkoh SXT and GOES. (3) There were several interactions and brightenings among small UV loops. After these brightenings, the connectivity of the UV loops was apparently changed. As a result, a large rising loop structure was formed, with a maximum rising speed of about 40 km s−1. (4) The main flare occurred in this structure. In the aspects of the overall configuration and morphological change of UV loops, the preflare activity is quite consistent with the tether-cutting model with a single-bipole magnetic explosion. We suggest that the preflare activity and the main flare in this event not only have similar physical mechanisms, but also have a causal relation.

Unusual sudden ionospheric disturbance from solar flare of 4 November 2003

An interpretation of the nature of the sudden ionospheric disturbance in terms of response to X-ray flux enhancement in the band 1–20 Å has been made by many authors. Last decades investigations revealed presence of important qualitative distinctions in spatially temporal pattern of geomagnetic response to solar flares featuring harder radiation spectra (with quanta energies above 100 keV). These distinctions can not be adequately described by classical theory implying ionization growing on E and D ionosperic layers and intensification of Sq-current system. In this respect, solar flare on 4 November 2003 characterizing by existence of two separate (time lag ~45 min) spectral maximums in X-rays range (average quantum energy <100 keV) and in γ-rays range (average quantum energy >100 keV), represents convenient proving ground for study of specifics the geomagnetic response to bursts marked by different hardness. In current article, we show that this flare has a number of unusual features including specific variation of accompanying current system and magnetospheric manifestation that is observed in trapped radiation fluxes and magnetic field on geosynchronous orbit. Possible physical mechanism leading to intensification of magnetospheric–ionospheric current system is discussed.

Satellite observations of lightning-induced hard X-ray flux enhancements in the conjugate region

Abstract. Preliminary examination of October-December 2002 SONG (SOlar Neutron and Gamma rays) data aboard the Russian CORONAS-F (Complex Orbital Near-Earth Observations of the Activity of the Sun) low-altitude satellite has revealed many X-ray enhanced emissions (30–500 keV) in the slot region (L ~ 2–3) between the Earth's radiation belts. In one case, CORONAS-F data were analyzed when the intense hard X-ray emissions were seen westward of the South Atlantic Anomaly in a rather wide L shell range from 1.7 to 2.6. Enhanced fluxes observed on day 316 (12 November) were most likely associated with a Major Severe Weather Outbreak in Eastern USA, producing extensive lightning flashes, as was documented by simultaneous optical observations from space. We propose that whistler mode signals from these lightning discharges cause precipitation of energetic electrons from terrestrial trapped radiation belts, which, in turn, produce atmospheric X-rays in the Southern Hemisphere.

Response of the equatorial electrojet to solar flare related X-ray flux enhancements

Abstract The response of ionospheric E-region electric fields and currents to solar flare related X-ray flux enhancements are studied at the magnetic equatorial location of Trivandrum (8.5°N, 77°E; dip 0.5°N) using VHF (54.95 MHz) coherent backscatter radar observations in the altitude region of 95–110 km conducted during daytime. The amplitude of the Solar Flare Effects (SFE) observed in the earth’s magnetic field variations at Trivandrum have been examined in relation to that at Alibag and it is found that the ratio of the SFE amplitudes at the two stations lies in the range of 1.8–2.6. The backscattered power of the VHF radar showed a substantial reduction during the peak phase of all the strong X-rank flares studied. It has also been observed that there is a sharp fall in the ratio of the field line integrated Hall conductivity (σ2) to the field line integrated Pedersen conductivity (σ1) in the dynamo region "Equation missing" during strong flare times in relation to normal times. The time variations of mean Doppler frequency (f D ) of the backscattered signals have been observed to indicate a fall close to the peak phase of the strong flare events. Another new result is the radar observed presence of westward electric field for a long duration of 2–3 hours during a partial counter electrojet (CEJ) event that occurred on one of the days (8 July 1992) studied. The implications of the observations are discussed in detail.

Studies on enhancement of x-ray flux in the compact electron cyclotron resonance plasma x-ray source

The electron cyclotron resonance (ECR) plasma x-ray source has a potential application for medical imaging. The plasma and x-ray characterization studies on the ECR x-ray source based on cylindrical cavity operated in TE111 mode were reported earlier by us. In order to enhance the x-ray flux and the effective energy of the x-ray spectrum, the use of rectangular cavity in ECR x-ray source is studied. In this article, the theoretical analysis of electron acceleration in TE101 rectangular cavity used as a cyclotron resonance accelerator is presented. The electron orbital values of rectangular cavity are compared with that of cylindrical cavity (TE111 mode). It is found that there is an increase in final energy of electron (170 keV), reduction in electron transit time, and increase in distance between the successive orbits in the rectangular cavity than the cylindrical cavity. An ECR x-ray source based on rectangular cavity has been designed and constructed and the experimental system is described.

Comparing Elemental Sensitivities Obtained With an Aperture and a Monolithic Polycapillary Optic Using a Commercial Micro-X-Ray Fluorescence (MXRF) Instrument

Abstract Recent MXRF reports have demonstrated marked x-ray flux enhancements over traditional aperturecollimating systems when using a total reflection capillary optic. In the present work, several standard reference materials (SRMs) were examined with a Kevex Omicron MXRF system to compare the elemental sensitivities achieved with an aperture x-ray guide to those obtained with a monolithic polycapillary optic (X-ray Optical Systems). This study is relevant to the MXRF community using commercial aperture-based instruments where trace elemental concentrations in a sample sometimes mandate the need for a higher primary x-ray dose, but the flexibility of incorporating various sized apertures for other samples is still maintained. By scanning the x-ray beam over a nickel/gold knife edge, the capillary focal spot diameter at the time of this work was determined to be ∼400 μm, while a 300 μm aperture provided a beam size of ∼550 μm due to beam divergence past the aperture.

X-ray flux enhancement in thin-film waveguides using resonant beam couplers.

We present experimental evidence for achieving significant x-ray flux enhancement by coupling a highly collimated and monochromatic synchrotron x-ray beam into a Si/polyimide/${\mathrm{SiO}}_{2}$ thin-film waveguide. The observed 20-fold flux increase agrees with theoretical predictions and was limited only by absorption of the 1 \AA{} x rays in the waveguide structure.