Determination of K,Ar, Cl,S, Si and Al flare abundances from RESIK soft X-ray spectra

The RESIK is a high sensitivity, uncollimated bent crystal spectrometer which successfully operated aboard Russian CORONAS-F solar mission between 2001 and 2003. It measured for the first time in a systematic way solar soft X-ray spectra in the four wavelength channels from 3.3 Å to 6.1 Å. This range includes characteristic strong lines of H- and He-like ions of K, Ar, Cl, Si, S and Al in the respective spectral channels. A distinguishing feature of RESIK is its possibility of making reliable measurements of the continuum radiation in flares. Interpretation of line and the continuum intensities observed in vicinity of respective strong lines provides diagnostics of plasma temperature and absolute abundances of K, Ar, Cl, S, Si and Al in several flares. We analyzed the observed intensities of spectral lines and the nearby continuum using the CHIANTI v5.2 atomic data package. A specific, so-called “locally isothermal” approach has been used in this respect allowing us to make not only flare-averaged abundance estimates, but also to look into a possible variability of plasma composition during the course of flares.     

Results of solar observations by the CORONAS-F payload

The CORONAS-F mission experiments and results have been reviewed. The observations with the DIFOS multi-channel photometer in a broad spectral range from 350 to 1500 nm have revealed the dependence of the relative amplitudes of p-modes of the global solar oscillations on the wavelength that agrees perfectly well with the earlier data obtained in a narrower spectral ranges. The SPIRIT EUV observations have enabled the study of various manifestations of solar activity and high-temperature events on the Sun. The data from the X-ray spectrometer RESIK, gamma spectrometer HELICON, flare spectrometer IRIS, amplitude–temporal spectrometer AVS-F, and X-ray spectrometer RPS-1 have been used to analyze the X- and gamma-ray emission from solar flares and for diagnostics of the flaring plasma. The absolute and relative content of various elements (such as potassium, argon, and sulfur) of solar plasma in flares has been determined for the first time with the X-ray spectrometer RESIK. The Solar Cosmic Ray Complex monitored the solar flare effects in the Earth’s environment. The UV emission variations recorded during solar flares in the vicinity of the 120-nm wavelength have been analyzed and the amplitude of relative variations has been determined.     

The statistical features of radio bursts with fine structure at 1.1–7.6 GHz

This work presents the spectral and temporal features of radio bursts with fine structures (FSs) at broad band from 1.1 to 7.6 GHz. Fifteen burst events are studied with high frequency and temporal cadence observation from the Solar Broadband Radio Spectrometer at three frequency bands. It is found that the amount and species of radio FS decrease with increasing frequency band; the pulsation, type III burst and continuum are most frequently recorded; almost in all the burst events, more radio FSs occur before the soft X-ray (SXR) maximum than after; at 1.1–2.06 GHz, all types of radio FSs have more before the SXR peak except fiber; at 2.6–3.8 GHz, pulsation, fiber and spike prefer to appear after the peak; the separation between neighboring emission lines of zebra pattern increases with increasing frequency and the magnetic field deduced from the whistler model is 29–86 G at 1.1–2.06 GHz and 89–268 G at 2.6–3.8 GHz.     

He-like Ar xvii triplet observed by RESIK

We present the observations of He-like Ar triplet lines obtained by RESIK spectrometer aboard CORONAS-F. Interpretation of intensity ratios between triplet lines of lower Z elements is known to provide useful diagnostics of plasma conditions within the emitting source. Here, we investigate whether triplet line ratios are useful for interpretation of higher Z element spectra. A high sensitivity, low background and precise absolute calibration of RESIK allow to consider in addition also the continuum contribution. This provides a way to determine the Ar absolute abundance from the observed triplet component ratios. The method is presented and the results are shown for two selected flares. Derived values of Ar absolute abundance for these flares are found to be similar: 2.6 × 10⁻⁶ and 2.9 × 10⁻⁶. They fall in the range between presently accepted Ar photospheric and coronal abundances.     

GRB observed by IBIS/PICsIT in the MeV energy range

We present the preliminary results of a systematic search for GRB and other transients in the publicly available data for the IBIS/PICsIT (0.2–10 MeV) detector on board INTEGRAL. Lightcurves in 2–8 energy bands with time resolution from 1 to 62.5 ms have been collected and an analysis of spectral and temporal characteristics has been performed. This is the nucleus of a forthcoming first catalog of GRB observed by PICsIT.     

Thin structure of temporal profiles of solar flares January 15, 17 and 20, 2005 by data of AVS-F apparatus onboard CORONAS-F satellite

The count rate temporal profiles and energy spectra of the solar flares January 15, 17, 20 2005 in hard X-ray and gamma energy bands by data of AVS-F apparatus onboard CORONAS-F satellite are discussed. The energy spectra of these solar flares contain positron line and neutron capture line. Solar flares of January 17 and 20 spectra also contain some nuclear lines. Thin structure with characteristic timescales of 33–92 s is presented on flares temporal profiles in energy bands corresponding to the observed spectral features, which are confirmed by periodogram analysis (confidence level is 99%).     

Probing the method of correcting Faraday rotation in vector magnetograms

By analyzing the vector magnetograms of Huairou Solar Observing Station (HSOS) taken at the line center (0.0 Å) and the line wing (−0.12 Å) of FeI λ5324.19 Å, we make an estimate of the measured errors in transversal azimuths (δ?) caused by Faraday rotation. Since many factors, such as the magnetic saturation and scattered light, can affect the measurement accuracy of the longitudinal magnetic field in the umbrae of sunspots, we limit our study in the region ∣B_z∣ < 800 G. The main mean azimuth rotations are about 4°, 6°, 7° and 9°, while ∣B_z∣ are in the ranges of 400–500 G, 500–600 G, 600–700 G and 700–800 G, respectively. Moreover, we find there is also an azimuth rotation of about 8° at the wavelength offset −0.12 Å of the line compared against a previous numerical simulation.     

X-ray study of accretion flow in narrow-line Seyfert 1 galaxies

We present the results of a systematic study of narrow-line Seyfert 1 galaxies (NLS1s) observed with XMM-Newton. The 2–12 keV X-ray spectra of NLS1s are well represented by a single power law with a photon index Γ ∼ 2. When this hard power law continuum is extrapolated into the low energy band, we found that all objects in our sample show prominent soft excess emission. This excess emission is well parameterized by the thermal emission expected from an optically thick accretion disk, and we found the following three peculiar features: (1) The derived disk temperatures are significantly higher than the expectation from a standard Shakura-Sunyaev accretion disk, if we assume a central mass of a black hole to be 10^6–8M_⊙. (2) The temperatures are distributed within narrow range (ΔkT ∼ 0.08 keV) with an average temperature of 0.18 keV in spite of the range of four orders of magnitude in luminosity (10^41–45 erg s⁻¹). (3) We found a peculiar temperature–luminosity relation, where the luminosity seems to be almost saturated in spite of the significant change in temperature, during the observations of the most luminous NLS1 PKS 0558-504. These results strongly suggest that the standard accretion disk picture is no longer appropriate in the nuclei of NLS1s. We discuss a possible origin for the soft excess component, and suggest that a slim disk may be able to explain the observational results, if the photon trapping effect is properly taken into account.     

AVS-F observations of γ-ray emission during January 20, 2005 solar flare up to 140 MeV

The solar flare of January 20, 2005 (X7.1, 06:36–07:26 UT, maximum at 07:01 UT by the GOES soft X-ray data) was the most powerful one in January 2005 series. The AVS-F apparatus onboard CORONAS-F registered γ-emission during soft X-ray rising phase of this flare in two energy ranges of 0.1–20 MeV and 2–140 MeV. The highest γ-ray energy registered during this flare was ∼140 MeV. Six spectral features were registered in energy spectrum of this solar flare: annihilation + αα (0.4–0.6 MeV), ²⁴Mg + ²⁰Ne + ²⁸Si + neutron capture (1.7–2.3 MeV), ²¹Ne + ²²Ne + ¹⁶O + ¹²С (3.2–5.0 MeV), ¹⁶O (5.3–6.9 MeV), one from neutral pions decay (25–110 MeV) and one in energy band 15–21 MeV. Four of them contain typical for solar flares lines – annihilation, nuclear de-excitation and neutron capture at ¹H. Spectral feature caused by neutral pions decay was registered during several flares too. Some spectral peculiarities in the region of 15–21 MeV were first observed in solar flare energy spectrum.     

The effective temperatures of O-type stars from UV spectroscopy

We present an analysis of high resolution spectra in the far-UV – UV range (∼905–2000 Å) with non-LTE, spherical, hydrodynamical, line-blanketed models, of three O-type Galactic stars, and derive their photospheric and wind parameters. These data extend previously analyzed samples and fill a gap in spectral type coverage. The combined sample confirms a revised (downward) T_eff scale with respect to canonical calibrations, as found in our previous works from UV and optical spectra, and in recent works by other authors.     

Flaring loop parameters estimated from solar decimeter type U-like and type J-like fine structures

This work presents the analysis of five fine structures in the solar radio emission, observed between June 2000 and October 2001 by the Brazilian Solar Spectroscope (BSS), in the decimeter frequency band of 950–2500 MHz. Based on their morphological characteristics identified in the dynamic spectra, the fine structures had been classified as type U-like or type J-like bursts. Such emissions are variants of the type III bursts. They support the hypothesis of generation by plasma emission mechanism, from interaction of electron beams accelerated during solar flares, propagating along closed magnetic structures, within the trapped plasma of the solar corona. The spectral and temporal characteristics of the five fine structures had been obtained from the dynamic spectra and the parameters of the agent and the emitting source have been determined, assuming both fundamental and harmonic emissions. The analysis revealed the flux density of the structures is less than 20–80 s.f.u. For assumption of harmonic emission, the interval of values for the source parameters estimated are: the loop size is (0.3–5.1) × 10¹⁰ cm; the electron beam velocity is in the range of 0.16–0.53 c; the temperature of coronal loop top is of the order of (0.25–1.55) × 10⁷ K; and the low limit for the magnetic field is of 7–26 G. These results are in agreement with previous determinations reported in the literature.     

Application of HF Doppler measurements for the investigation of internal atmospheric waves in the ionosphere

We present results of the spectral analysis of data series of Doppler frequency shifted signals reflected from the ionosphere, using experimental data received at Kazan University, Russia. Spectra of variations with periods from 1 min to 60 days have been calculated and analyzed for different scales of periods. The power spectral density for spring and winter differs by a factor of 3–4. Local maxima of variation amplitude are detected, which are statistically significant. The periods of these amplitude increases range from 6 to 12 min for winter, and from 24 to 48 min for autumn. Properties of spectra for variations with the periods of 1–72 h have been analyzed. The maximum of variation intensity for all seasons and frequencies corresponds to the period of 24 h. Spectra of variations with periods from 3 to 60 days have been calculated. The maxima periods of power spectral density have been detected by the MUSIC method for the high spectral resolution. The detected periods correspond to planetary wave periods. Analysis of spectra for days with different level of geomagnetic activity shows that the intensity of variations for days with a high level of geomagnetic activity is higher.     

X-ray redshifts with the International X-ray Observatory (IXO)

We explore the capabilities of the future space science mission IXO (International X-ray Observatory) for obtaining cosmological redshifts of distant Active Galactic Nuclei (AGNs) using the X-ray data only. We first find in which regions of the X-ray luminosity (L_X) versus redshift (z) plane the weak but ubiquitous Fe Kα narrow emission line can deliver an accurate redshift (δz < 5%) as a function of exposure time, using a CCD-based Wide Field Imager (IXO/WFI) as the one baselined for IXO. Down to a 2–10 keV X-ray flux of 10⁻¹⁴ erg cm⁻² s⁻¹ IXO/WFI exposures of 100 ks, 300 ks and 1 Ms will deliver 20%, 40% and 60% of the redshifts. This means that in a typical 18′ × 18′ IXO/WFI field of view, 4, 10 and 25 redshifts will be obtained for free from the X-ray data alone, spanning a wide range up to z ∼ 2–3 and fairly sampling the real distribution. Measuring redshifts of fainter sources will indeed need spectroscopy at other wavebands.     

Photospheric flows in the active regions (asymmetric and localized Doppler velocities)

We observed 10 active regions through their disk passage during June 25–August 25, 1988, with the Tower Vector Magnetograph (TVM) of Marshall Space Flight Center. The TVM was used in scanning mode to measure the photospheric Doppler velocities with the Line-Center-Magnetogram (LCM) technique in the spectral line of FeI 5250.2 Å. In this paper we present the result of a subset of observations obtained while the active regions were situated away from the solar limb. A wide range of magnetic complexity and associated chromospheric activity characterized these active regions. It was found that the value of zero-crossing wavelength of the integrated Stokes-V profile of two opposite magnetic polarities were different, corresponding to Doppler velocities ranging from ∼100 m s⁻¹ to ∼1475 m s⁻¹. The measurements of relative velocities between different locations, connected by magnetic flux tubes as inferred from YOHKOH soft X-ray and TRACE 171 Å Fe IX images, showed widely different values of dominant localized flows. The region of parasite polarity, which showed recurrent chromospheric activity, was blue shifted with respect to the main “magnetic element” of the same polarity. Some of them were also the sites of sheared magnetic field configuration. The magnitude of the relative velocity between the leading and following polarity is more for the active regions of higher “field asymmetry”.     

Spectroscopic analysis of the solar flare event on 2002 August 3 with the use of RHESSI and RESIK data

We use simultaneous observations from RESIK and RHESSI instruments to compare plasma properties of a major solar flare in its rise and gradual phase. This event occurred on 2002 August 3 (peak time at 19:06 UT). The flare had a very good coverage with RESIK data and well-resolved soft and hard X-ray sources were seen in RHESSI images. Spectra of X-ray radiation from RHESSI images are studied and compared with RESIK measurements in different flare phases. Result shows large differences in flare morphology and spectra between flare rise and gradual phase.     

The thermal X-ray spectrum of the 2003 April 26 solar flare

Observations and their analysis of the thermal X-ray spectrum of the M2 flare on 2003 April 26 are described. The spectrum observed by the RHESSI mission cover the energy range from ∼5 to ∼50 keV. With its ∼1-keV spectral resolution, intensities and equivalent widths of two line complexes, the Fe line group at 6.7 keV (mostly due to Fe xxv lines and Fe xxiv satellites) and the Fe/Ni line group at 8 keV (mostly due to higher-excitation Fe xxv lines and Ni xxvii lines) were obtained as a function of time through a number of flares. The abundance of Fe can also be determined from RHESSI spectra; it appears to be consistent with a coronal value for at least some times during the flare. Comparisons of RHESSI spectra with those from the RESIK crystal spectrometer on CORONAS-F show very satisfactory agreement, giving much confidence in the intensity calibration of both instruments.     

Acceleration of charged particles by fluctuating and steady electric fields in a X-type magnetic field

Release of stored magnetic energy via particle acceleration is a characteristic feature of astrophysical plasmas. Magnetic reconnection is one of the mechanisms for releasing energy from magnetized plasmas. Collisionless magnetic reconnection could provide both the energy release mechanism and the particle accelerator in space plasmas. Here we studied particle acceleration when fluctuating (in-time) electric fields are superposed on an static X-type magnetic field in collisionless hot solar plasma. This system is chosen to mimic the reconnective dissipation of a linear MHD disturbance. Our results are compared to particle acceleration from constant electric field superposed on an X-type magnetic field. The constant electric field configuration represents the effects of steady state magnetic reconnection. Time evolution of ion and electron distributions are obtained by numerically integrating particle trajectories. The frequencies of the electric field represent a turbulent range of waves. Depending on the frequency and amplitude of the electric field, electrons and ions are accelerated to different degrees and have energy distributions of bimodal form consisting of a lower energy part and a high energy tail. For frequencies (ω in dimensioless units) in the range 0.5 ? ω ? 1.0 a substantial fraction (20%–30%) of the proton distribution is accelerated to gamma-ray producing energies. For frequencies in the range 1 ? ω ? 100.0 the bulk of the electron distribution is accelerated to hard X-ray producing energies. The acceleration mechanism is important for solar flares and solar noise storms but it could be applicable to all collisionless astrophysical plasmas.     

An investigation of high frequency auroral plasma emissions with a tubular dipole antenna

A band of enhanced amplitudes which follows a local plasma frequency fn in raw high frequency (HF) noise spectra is usually related to plasma emissions in the upper hybrid band (fn, fu). The enhanced band in question occurs permanently in noise spectra recorded on the Intercosmos-19, APEX and CORONAS satellites in the altitude range of 500 km–3000 km. For moderately magnetized plasma with fn > 2fc (fc – electron gyro frequency), the band occurs below fn determined from the topside sounder and impedance data or from electron beam induced spectra. The simulations of an equivalent circuit composed of a dipole antenna in a cold plasma and its preamplifiers, determined the physical origin of the band as the passive circuit resonance, due to inductive character of the antenna in a frequency band (fc, fu). The resonance spectral content is highly structured due to an inflight variability of the circuit impedances. In this report we analyze the noise and impedance spectra which are the most typical in an auroral zone if fn > fc. We focus attention on determination of local electron plasma density, essential for provisional HF mode classification. We found that the natural plasma emission in the upper hybrid band does not manifest itself as the banded natural emission, which may be used for reliable determination of local plasma frequency in the altitude range of 500–3000 km. The fast magnetosonic mode predominates in the auroral emissions. The broadband and multi banded electromagnetic emissions extending from the fast magnetosonic band well above fn > fc are characteristic for the strong wave activity and are much less frequent.     

S5 0716+714: GeV variability study

The GeV observations by Fermi-LAT give us the opportunity to characterize the high-energy emission (100 MeV–300 GeV) variability properties of the BL Lac object S5 0716+714. In this study, we performed flux and spectral analysis of more than 3 year long (August 2008 to April 2012) Fermi-LAT data of the source. During this period, the source exhibits two different modes of flux variability with characteristic timescales of ∼75 and ∼140 days, respectively. We also notice that the flux variations are characterized by a weak spectral hardening. The GeV spectrum of the source shows a clear deviation from a simple power law, and is better explained by a broken power law. Similar to other bright Fermi blazars, the break energy does not vary with the source flux during the different activity states. We discuss several possible scenarios to explain the observed spectral break.