Line Emission Radiation Research Articles

Emission-line Variability during a Nonthermal Outburst in the Gamma-Ray Bright Quasar 1156+295

Abstract We present multi-epoch optical spectra of the γ-ray bright blazar 1156+295 (4C +29.45, Ton 599) obtained with the 4.3 m Lowell Discovery Telescope. During a multiwavelength outburst in late 2017, when the γ-ray flux increased to 2.5 × 10−6 phot cm−2 s−1 and the quasar was first detected at energies ≥100 GeV, the flux of the Mg ii λ2798 emission line changed, as did that of the Fe emission complex at shorter wavelengths. These emission-line fluxes increased along with the highly polarized optical continuum flux, which is presumably synchrotron radiation from the relativistic jet, with a relative time delay of ≲2 weeks. This implies that the line-emitting clouds lie near the jet, which points almost directly toward the line of sight. The emission-line radiation from such clouds, which are located outside the canonical accretion-disk related broad-line region, may be a primary source of seed photons that are up-scattered to γ-ray energies by relativistic electrons in the jet.

Spectral Evidence for Heating at Large Column Mass in Umbral Solar Flare Kernels. I. IRIS Near-UV Spectra of the X1 Solar Flare of 2014 October 25

Abstract The GOES X1 flare SOL2014-10-25T17:08:00 was a three-ribbon solar flare observed with the Interface Region Imaging Spectrograph (IRIS) in the near-UV (NUV) and far-UV. One of the flare ribbons crossed a sunspot umbra, producing a dramatic, ∼1000% increase in the NUV continuum radiation. We comprehensively analyze the UV spectral data of the umbral flare brightenings, which provide new challenges for radiative−hydrodynamic modeling of the chromospheric velocity field and the white-light continuum radiation. The emission line profiles in the umbral flare brightenings exhibit redshifts and profile asymmetries, but these are significantly smaller than in another, well-studied X-class solar flare. We present a ratio of the NUV continuum intensity to the Fe ii λ2814.45 intensity. This continuum-to-line ratio is a new spectral diagnostic of significant heating at high column mass (log m/[g cm−2] > −2) during solar flares because the continuum and emission line radiation originate from relatively similar temperatures but moderately different optical depths. The full spectral readout of these IRIS data also allow for a comprehensive survey of the flaring NUV landscape: in addition to many lines of Fe ii and Cr ii, we identify a new solar flare emission line, He i λ2829.91 (as previously identified in laboratory and early-type stellar spectra). The Fermi/GBM hard X-ray data provide inputs to radiative−hydrodynamic models (which will be presented in Paper II) in order to better understand the large continuum-to-line ratios, the origin of the white-light continuum radiation, and the role of electron beam heating in the low atmosphere.

Line emission radiation during early-time interaction of an intense short laser pulse with an ultrathin planar aluminum target

The interaction of an intense short laser pulse with an ultrathin planar aluminum foil is investigated with a fully relativistic particle-in-cell model self-consistently coupled to an atomic dynamics model describing the non-local thermodynamic equilibrium level population dynamics and radiative behavior of a plasma evolving on a picosecond timescale. For typical experimental conditions, laser pulses with energy 1 J, intensity 1020 W cm−2, and duration 40 fs, a synthetic spectrum for the emission lines is generated as a function of time for lines emanating in the hydrogen- and helium-like ionization stages. It is found that Heα, Heβ, Lyα, and Lyβ lines have intensities above the Bremsstrahlung continuum and could serve as diagnostics for the evolving plasma condition.

OPTICAL SPECTRAL OBSERVATIONS OF A FLICKERING WHITE-LIGHT KERNEL IN A C1 SOLAR FLARE

We analyze optical spectra of a two-ribbon, long duration C1.1 flare that occurred on 18 Aug 2011 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 \AA\ to 4550 \AA\ acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, $\le$0''.5 ($10^{15}$ cm$^2$) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor (GBM) on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a "blue continuum bump" in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

SEVO ON THE GROUND: DESIGN OF A LABORATORY SOLAR SIMULATION IN SUPPORT OF THE O/OREOS MISSION

This technical note describes a novel solar simulation experiment designed to mimic the solar radiation experienced by the Organism/Organics Exposure to Orbital Stresses (O/OREOS) nanosatellite in low-Earth orbit. Thin films of organic compounds within hermetically sealed sample cells (identical to the films and cells of the spaceflight mission) were exposed to simulated AM0 solar radiation in the laboratory for a total of 6 months, and monitored for spectral changes at two-week intervals. The laboratory experiment accurately simulated ultraviolet and visible solar irradiance to within 2% from 200‐1000 nm and the Ly! (121.6 nm) emission line radiation to within 8%. Design and calibration parameters for the experiment are discussed in detail for this ground-based laboratory irradiation experiment, which was built as a complement to, and as scientific validation of, the O/OREOS SEVO experiment in space.

UV and optical spectrum variability of T Tau and RY Tau

AbstractIn this report we have presented results of spectral observations of classical T Tauri type stars T Tau and RY Tau. Observational dates were obtained from following sources: spectrograms of the UV range from the IUE archive data, and spectrograms of the visual range obtained in the 2 m telescope of ShAO of the NAS of Azerbaijan (Ismailov et al. 2010). For both of stars on the Scargle method we have searched a periodicity of variations in equivalent widths of emission lines in the optical and UV ranges. In the RY Tau firstly was detected the periodic variability in MgII λ2800 Å emission doublet intensities with a period of 23 days. The observed period had also revealed with the equivalent widths and displacements of components of Hα and H+Hϵ and K CaII emission.The lines were found to be shifted to short wavelengths as the emission line intensities increased in both UV and optical spectral ranges. The lack of a correlation between the brightness variation and the emission line intensity also suggests that, on the whole, the contribution from the radiation in emission lines for the star RY Tau is insignificant.On the analysis of T Tau we conclude that there is a significant variation of spectral emission lines in the optical and UV on a time scale of about 33 days and that this variations is periodic. Both of stars shows the periodicity also for observed group of such lines as CIV λ1450 Å, HeII λ 1640 Å, SII λ1756 Å (Ismailov et al. 2010, Ismailov et al. 2011).Additionally we have carried out spectral energy distributions of this stars in the range 0.36-100 μm which have indicated the excess of spectral radiation in the IR range of spectrum. These excesses of radiations can be explained by the thermal radiation of still unformed bodies at the circumstellar environment. The periodic variability in the spectrum together with the excess of the spectral radiation may be occurred by protoplanets and/or protostars in these young systems. It is showed that possible, planet formation processes mainly to be completed at the time of the formation of classical T Tauri type stars.

SCATTERED NEBULAR LIGHT IN THE EXTENDED ORION NEBULA

We have combined 327.5 MHz radio observations and optical spectroscopy to study conditions in the Extended Orion Nebula. We see a steady progression of characteristics with increasing distance from the dominant photoionizing star Theta1OriC. This progression includes a decrease in the F(Halpha)/F(Hbeta) ratio, an increase in the relative strength of scattered stellar continuum, decrease in electron density determined from the [S II] doublet, and increase in the ratio of Emission Measures derived from the Hbeta line and the 327.5 MHz radio continuum. We conclude that beyond about 5' south of Theta1OriC that scattered light from the much brighter central Huygens region of the nebula significantly contaminates local emission. This strengthens earlier arguments that wavelength and model dependent scattering of emission line radiation imposes a fundamental limit on our ability to determine the physical conditions and abundances in this and arguably other similar Galactic Nebulae. The implications for the study of extra-galactic HII regions are even more severe. We confirm the result of an earlier study that at least the eastern boundary of the Extended Orion Nebula is dominated by scattered light from the Huygens region.

Radiation Fields in Blazars — a Possible Extension of the Small Scale Symbiosis (Disk/Jet) into a Large Scale (Dust/Dust) Symbiosis

AbstractIn blazar models both protons and electrons may be efficiently accelerated in jets and produce γ-rays. Here we discuss the interactions of these γ-rays with different radiation fields. The external radiation fields within a few parsecs from the black hole involved in such interactions could be the direct radiation from the accretion disk coupled with the jet, the infrared radiation from a dusty torus, and the emission line radiation from the broad line region surrounding the accretion disk. The optical thickness for absorption of γ-ray photons in the external radiation fields is analysed for blazars and quasars.Based on the unification theory of active galactic nuclei we briefly review the evidence for the existence of small scale dust tori in blazars/FR I. We propose that the existing jet–accretion disk symbiosis extrapolates to a large scale symbiosis between other important dusty constituents of the blazar/FR I family.

Dust outflows from quiescent spiral disks

We have conducted a search for chimneys'' in a sample of 10 highly-inclined spiral galaxies ( $i=86-90^{\circ}$) which we had previously observed in the H$\alpha$ emission line (Rand 1996). We have procured B-band CCD images for this purpose and employed unsharp-masking techniques to accentuate the structure of the dust lane. A scattering+absorption radiation transfer model enabled us to separate 5 galaxies from the sample which are sufficiently inclined ( $i>87^{\circ}$) for us to reliably identify and quantify dust clouds residing at over 2 scale-heights above the disk. Three of these galaxies possess numerous curvi-linear chimney structures stretching up to 2 kpc from the midplane and the fraction of total galactic dust contained in such structures is of order 1%. Optical extinction offers a lower limit to the amount of dust contained in the extraplanar layer but, by examining the transparent submm thermal emission from NGC 891, we fix an upper limit of 5%. Our results are consistent with a similar recent study by Howk & Savage (1999) which indicates that about half of quiescent spiral disks possess detectable dust chimneys. We have compared our optical images with the corresponding H$\alpha$ emission-line radiation. We do not find a detailed spatial correspondance between dust chimneys and either sites of recent star-formation or the extraplanar diffuse ionized gas. This is somewhat surprising given that FIR-bright galaxies, such as M 82, are known to entrain dust at the working surface of the starburst-driven outflow (traced in H$\alpha$). It is possible a global correlation exists, with disks experiencing overall higher rates of star-formation also possessing the greatest number of chimneys. This may indicate a timescale difference between the two phenomena with the H$\alpha$ phase lasting $\sim 10^{6}$ yr but chimneys requiring $\sim 10^{7}$ yr to form. Additionally, we have investigated the edge-on disk NGC 55 which, being ten times closer than galaxies in our main sample, allows us to examine in greater spatial detail the relationship between chimneys and recent star-formation. Our discussion touches upon high latitude dust and supershells observed in the Milky Way. We rule out quiescent disks as prolific sources of intergalactic grains and metals but note that the rate at which dust is expelled from the main dust layer is comparable to the rate at which it is produced by disk stars (suggesting that it may be an important regulatory process).

H imaging polarimetry of the protoplanetary nebula M2-9

After correction for interstellar polarization, our Hα polarization map of the protoplanetary nebula M2-9 shows that a significant fraction of the emission-line radiation from the nebular lobes is scattered radiation originating in the central core. We find no evidence for a spatially extended illuminating source on scales of ≥ 1-2 arcsec. In order to explain our polarization results, we present a geometrical model for the system which has diametrically opposed cavities previously created in a pre-existing dusty envelope. The illumination of the cavity walls leads to the reflection nebula properties of M2-9. We find that the high-excitation emission-line knots, supposedly undergoing regular rotation about the major axis on a time-scale of decades, have not moved significantly since 1977

Unified theories of active galactic nuclei: the hard X-ray spectrum of NGC 1068

We have reanalysed the Ginga observation of the archetypal Seyfert 2 galaxy NGC 1068. The X-ray spectrum can be decomposed into four components: a hard X-ray power law, iron Kα emission-line radiation, reflection from an accretion disc or molecular torus, and emission-line radiation at ∼ 8 keV. Although reflection is not required, its inclusion is consistent with the data and increases the underlying intrinsic power-law energy index to α E ∼ 0.9, similar to the typical slope found for Seyfert 1 galaxies. Reflection is unlikely to produce all the observed equivalent width of the Ginga Fe Kα emission line, but can account for all of the component seen at 6.4 keV by BBXRT

The structure of the Cygnus A radio galaxy

view Abstract Citations (50) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Structure of the Cygnus A Radio Galaxy Pierce, M. J. ; Stockton, A. Abstract Interference-filtered CCD optical images were obtained of Cygnus A at a wavelength of 6100 A using a FWHM 100 A bandpass and at 6495 A with a FWHM of 170 A. The data yielded a radial surface brightness profile of the region, emission line and absorption spectra, velocity field, and ratios of H-alpha flux/continuum flux near H-beta. The analytic procedures applied to the data are described. Interactions among stars, dust, emitting gas and a featureless continuum were in evidence. The continuum and emission-line radiation exhibited different distributions, with the latter displaying clumped and filamentary features. The featureless continuum radiation arose from an extended region; the generating source was not resolved. Publication: The Astrophysical Journal Pub Date: June 1986 DOI: 10.1086/164240 Bibcode: 1986ApJ...305..204P Keywords: Astronomical Spectroscopy; Galactic Structure; Radio Galaxies; Continuous Spectra; Emission Spectra; Galactic Nuclei; H Alpha Line; Interstellar Extinction; Interstellar Gas; Astrophysics; GALAXIES: INDIVIDUAL NAME: CYGNUS A; GALAXIES: STRUCTURE; RADIO SOURCES: GALAXIES full text sources ADS | data products SIMBAD (1) NED (1)

The origin of cosmic rays. II - The cosmic-ray distribution and the spiral structure of NGC 3310. III - Particle acceleration by global spiral shocks

view Abstract Citations (18) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Origin of Cosmic Rays. II. The Cosmic-Ray Distribution and the Spiral Structure of NGC 3310 Duric, N. Abstract The optical and radio continuum properties of the spiral arms of NGC 3310 are analyzed and intercompared. The likely presence of a strong density wave in NGC 3310 is demonstrated, and a number of observational results constraining the relationship between synchrotron emission, emission line radiation, and starlight are developed. The role of supernova remnants in the production of relativistic particles is investigated and found to be inconsistent with the constraints. The generation of cosmic rays by global spiral shocks via a Fermi-type shock acceleration process is shown to agree with all the major constraints, suggesting that the rotation of the galaxy powers the acceleration of particles to cosmic ray energies. A medium with temperature of 10,000 K, partially to fully ionized, is shown to support the diffusive shock acceleration mechanism. Publication: The Astrophysical Journal Pub Date: May 1986 DOI: 10.1086/164147 Bibcode: 1986ApJ...304...96D Keywords: Cosmic Rays; Galactic Structure; Radiation Distribution; Spiral Galaxies; Astronomical Maps; Density Wave Model; Galactic Rotation; Particle Acceleration; Synchrotron Radiation; Space Radiation; COSMIC RAYS: GENERAL; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3310; GALAXIES: STRUCTURE; PARTICLE ACCELERATION; RADIO SOURCES: GALAXIES; SHOCK WAVES full text sources ADS | data products SIMBAD (10) NED (10) Related Materials (2) Part 1: 1986ApJ...304...82D Part 3: 1986ApJ...304..111D

The 1980 low state of AM Herculis

view Abstract Citations (70) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The 1980 low state of AM Her. Latham, D. W. ; Liebert, J. ; Steiner, J. E. Abstract A series of spectrophotometric scans obtained with a 4.5 m multiple mirror telescope and a 2.3 m reflector is reported. Broad-band polarimetry obtained with the 2.3 reflector is also discussed. All observations were obtained between 1980 June 15-September 5, during which time the object was apparently in a consistent low state near 15th magnitude. Ultraviolet observations with the International Ultraviolet Explorer satellite were obtained on June 30. Attention is given to the polarized continuum radiation, the emission-line radiation, the secondary star, and the magnetic white dwarf photosphere. Much of the absorption observed in connection with the Zeeman absorption spectrum may be explained by hydrogen in a dominant magnetic field strength near 13 megagauss. Publication: The Astrophysical Journal Pub Date: June 1981 DOI: 10.1086/158985 Bibcode: 1981ApJ...246..919L Keywords: Binary Stars; Circular Polarization; Magnetic Stars; Stellar Spectra; Stellar Spectrophotometry; X Ray Sources; Absorption Spectra; Continuous Radiation; Dwarf Stars; Emission Spectra; Infrared Stars; Line Spectra; Near Infrared Radiation; Polarized Radiation; Radial Velocity; Stellar Magnetic Fields; Stellar Mass Accretion; Astronomy full text sources ADS | data products SIMBAD (1)

High time-resolution observations of UV CET stars.

view Abstract Citations (47) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High time-resolution observations of UV Ceti stars. Moffett, T. J. ; Bopp, B. W. Abstract Simultaneous, high time-resolution spectroscopic and photometric observations of eight flare events on four UV Ceti-type stars are presented. These observations firmly establish the existence of two phases during a flare: the spike phase, which is dominated by continuum emission, and the slow phase, which shows strong emission-line radiation with decreasing continuum radiation. The time sequence of spectral features during a flare is that the continuum reaches maximum strength first, followed 1 to 19 minutes later by maximum strength in the Balmer emission lines, and finally the peak of the Ca ii K-line strength some 4 to 52 minutes after the continuum peak. The flare phenomenon is spectroscopically complex, with no apparent simple relation between the various flare parameters. The emission lines produce a time-varying contribution to the broad-band color indices of flare light. Subject headings: stars: emission4ine - stars: flare Publication: The Astrophysical Journal Supplement Series Pub Date: May 1976 DOI: 10.1086/190374 Bibcode: 1976ApJS...31...61M full text sources ADS | data products SIMBAD (4)