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NASA NTRS1989

Capabilities of GRO/OSSE for observing solar flares

The launch of the Gamma Ray Observatory (GRO) near solar maximum makes solar flare studies early in the mission particularly advantageous. The Oriented Scintillation Spectrometer Experiment (OSSE) on GRO, covering the energy range 0.05 to 150 MeV, has some significant advantages over the previous generation of satellite-borne gamma-ray detectors for solar observations. The OSSE detectors will have about 10 times the effective area of the Gamma-Ray Spectrometer (GRS) on Solar Maximum Mission (SMM) for both photons and high-energy neutrons. The OSSE also has the added capability of distinguishing between high-energy neutrons and photons directly. The OSSE spectral accumulation time (approx. 4s) is four times faster than that of the SMM/GRS; much better time resolution is available in selected energy ranges. These characteristics will allow the investigation of particle acceleration in flares based on the evolution of the continuum and nuclear line components of flare spectra, nuclear emission in small flares, the anisotropy of continuum emission in small flares, and the relative intensities of different nuclear lines. The OSSE observational program will be devoted primarily to non-solar sources. Therefore, solar observations require planning and special configurations. The instrumental and operational characteristics of OSSE are discussed in the context of undertaking solar observations. The opportunities for guest investigators to participate in solar flare studies with OSSE is also presented.

Kurfess, J. D.↗
NASA NTRS1990

Observations of extended and counterrotating disks of ionized gas in S0 galaxies

While many E/S0 galaxies have been found to show emission line spectra in their nuclear regions, the question of the presence and nature of extended disks of ionized gas in these galaxies has been addressed only in recent years. Typically the ionized gas is detected in the inner region on a scale of approx. 1 kpc (e.g., Phillips et al. 1986, Caldwell 1984). Here researchers present evidence that the disks of ionized gas of at least some S0 galaxies are much more extended than previously believed. In addition, with the detection of the counterrotation of gas and stars in NGC 7007 they strengthen the basis for arguments that the source of gas in S0 galaxies is external

Dettmar, Ralf-Juergen↗
NASA NTRS1992

The optically thick C III spectrum. I - Term populations and multiplet intensities at lower optical depths

The C III spectrum is studied quantitatively under both optically thin and optically thick conditions, yielding term populations and line/multiplet intensities for column lengths from zero to 10 exp 18/sq cm. The roles of escape probabilities and line profiles in the calculation are discussed in some detail. It is shown that use of the fully integrated escape factor, rather than the more appropriate monodirectional escape probability, can lead to appreciable errors in calculated intensities. The results for populations and intensities make it possible to identify two unassigned features in the solar EUV spectrum of Vernazza and Reeves (1978) as C III multiplets, and to establish that an unidentified infrared solar feature at 8500.32 A, seen in both absorption (Fraunhofer) and emission (chromospheric) spectra, is the C III transition 2s3s(1S)-2s3p(1P). Voigt parameters for the C III lines and multiplets, obtained by a modified semiclassical method are tabulated. A new, unambiguous notation for the numerous line ratios present in a typical spectrum, which is argued to be an improvement over present arbitrary notations, is proposed and used.

Bhatia, A. K.↗
NASA NTRS1993

A compact, high resolution Michelson interferometer for atmospheric spectroscopy in the near ultraviolet

A new, compact Fourier Transform Michelson interferometer (FTUV) with an apodized resolving power greater than 300,000 at 300 nm, high throughput and wide spectral coverage has been developed. The objectives include atmospheric spectroscopy (direct solar absorption and solar scattering) and laboratory spectroscopy of transient species. In this paper, we will briefly describe the prototype FTUV instrument and the results of preliminary laboratory investigations of OH and ClO spectra in emission and absorption.

Sander, Stanley P.↗
NASA NTRS1994

Observation of mass loading in the Io plasma torus

Ground-based high-resolution spectra of emission from the Io plasma torus obtained during 53 nights of observation over a seven month period are used to measure the torus rotation speed and discern regions of the torus that are slowed by mass loading of newly ionized materials. The amount of torus slowing implies that between 2000 and 3000 kg/sec are being ionized by the torus. The slowing is spread azimuthally throughout the orbit of Io, suggesting that neutral materials emanating from Io are distributed around Jupiter much more uniformly than currently believed.

Brown, Michael E.↗
NASA NTRS1995

Hot shocked gas along the jets of NGC 4258 (M106)

The ROSAT High Resolution Interferometer (HRI) and Position Sensitive Proportional Counter (PSPC) detectors have been used to study the soft X-ray emission of the nearby SABbc galaxy NGC 4258 (M106). The helically twisted, nuclear jets, previously detected in radio continuum and visual emission-line studies, are found to dominate the X-ray images. After correcting pointing errors of up to +/- 7 sec in our HRI observation, we find that the southeast jet is spatially unresolved transversely along much of its 2.5 min (5 kpc) length. The northwest jet is more diffuse, and the extensive radio 'plateaus' also emit X-rays. The energy spectrum of the jets from the PSPC exposure is noisy but is best fitted as a Raymond-Smith plasma with kT = 0.3 keV, log N(sub H) approximately = 20.0/sq cm, and luminosity 1.6 x 10(exp 40) ergs/s between 0.1 and 2.4 keV. Gas at this temperature can arise from planar shocks of 500 km/s and may have been entrained as the jets scrape along the molecular clous that are known to be adjacent to the jets. The range of radial velocities from our published visual emission-line spectra of the jet are consistent with such a shock speed. We estimate that the mass of hot gas in the jets is 6 x 10(exp 4) (1/cc/n(sub e)) solar mass, with n(sub e) the average electron density. The inferred pressure of hot gas in the southeast jet may be similar to the radio equipartition pressure and to the ambient pressure of the interstellar medium (ISM). The X-ray spectral fit is poor above 0.7 keV and requires an additional hard component that peaks near the nucleus.

Cecil, G.↗
NASA NTRS1996

Results of Detailed Modeling of the Narrow-Line Region of Seyfert Galaxies

We present model line profiles of [O II] lambda3727, [Ne III] lambda3869, [O I] lambda5007, [Fe VII] lambda6087, [Fe X] lambda6374, [O I] lambda6300, H(alpha) lambda6563, and [S 2] lambda6731. The profiles presented here illustrate explicitly the pronounced effects that collisional de-excitation, and that spatial variations in both the ionization parameter and cloud column density, have on Narrow-Line Region (NLR) model profiles. The above effects were included only qualitatively in a previous analytical treatment by Moore and Cohen. By making a direct correspondence between these model profiles and the analytical model profiles of Moore and Cohen, and by comparing with the observed profiles presented in a companion paper and also with those presented elsewhere in the literature, we strengthen some of the conclusions of Moore and Cohen. Most notably, we argue for constant ionization parameter, uniformly accelerated outflow of clouds that are individually stratified in ionization, and the interpretation of emission-line width correlations with ionization potential as a column density effect. For comparison with previous observational studies, such as our own in a companion paper, we also calculate profile parameters for some of the models, and we present and discuss the resulting line width correlations with critical density (n(sub cr)) and Ionization Potential (IP). Because the models we favor are those that produce extended profile wings as observed in high spectral resolution studies, the line width correlations of our favoured models are of particular interest. Line width correlations with n(sub cr) and/or IP result only if the width parameter is more sensitive to extended profile wings than is the Full Width at Half-Maximum (FWHM). Correlations between FWHM and n(sub cr) and/or IP result only after convolving the model profiles with a broad instrumental profile that simulates the lower spectral resolution used in early observational studies. The model in agreement with the greatest number of observational considerations has electron density decreasing outward from n(sub e) approx. equals 10(exp 6)/cu cm to n(sub e) approx. equals 10(exp 2)/cu cm and, due to collisional de-excitation effects in the lowest velocity clouds, it generates broad flat-topped profile peaks in the lines of lowest critical density (e.g., [O II] lambda3727 and [S II] lambda(lambda)6716, 6731). Because the observed profile peaks of both low and high critical density lines are often very similar, our favored model requires a contribution to NLR emission-line spectra from low-velocity, low-density, and low-ionization gas not included in the model NLR.

Moore, David↗
NASA NTRS1997

Broad Absorption Line Quasars Observed by the ROSAT PSPC

Recent results from the ROSAT All-Sky Survey have shown that Broad Absorption Line (BAL) QSOs are either highly absorbed or underluminous in the soft X-ray bandpass. Here we extend this work by analyzing all known bona fide BAL QSOs observed within the inner 20 min of the ROSAT Position Sensitive Proportional Counter. This sample includes both targeted and serendipitous exposures ranging from 8 to 75 ks. Despite these deep exposures, most of the BAL QSOs are undetected and have unusually weak X-ray emission, as evidenced by large optical-to-X-ray slopes alpha(sub ox). Large values of alpha(sub ox)(approx. greater than 1.8) may prove to be a defining characteristic of BAL QSOs. We predict that samples of QSO candidates with large alpha(sub ox) will yield a higher percentage of BAL QSOs, particularly at low redshift. As a corollary, X-ray selected QSO samples should yield fewer BAL QSOs. The optical/UV emission line spectra of BAL and non-BAL QSOs are quite similar, suggesting that their intrinsic spectral energy distributions are similar as well. Absorption thus seems the likely reason for the X-ray-quiet nature of BAL QSOs. To constrain the total absorbing column of the BAL clouds, we compare our measured soft X-ray fluxes or upper limits with those expected from normal radio-quiet QSOs of comparable optical continuum magnitude and redshift. From sensitive X-ray observations, we derive column densities of approx. less than 2 x 10(exp 22)/sq cm for intrinsic cold absorbers of solar metallicity. These new results suggest columns at least an order of magnitude larger than the columns previously estimated from optical/UV spectra alone.

Green, Paul J.↗
NASA NTRS1999

Broad Absorption Line QSOS: Seeing Past the Disguise

Broad absorption line quasars (BALQSOs) have proven to be elusive soft X-ray sources. Their highly ionized, high column density clouds flow out from the nucleus at 0.1c. On the other hand, the optical/UV emission line spectra of BAL and non-BAL QSOs are quite similar, suggesting similar intrinsic continua. Absorption thus seems the likely reason for the soft X- ray quiet nature of BALQSOs, but this is unproven to date. With hard (2-60 kev) X-raY observations with RXTE, of PG1700+508, we hoped to answer the fundamental question; are BALQSOs highly absorbed or rather are they intrinsically underluminous in X-rays? Together with Kendra J. Michaud, we analyzed our broadband XTE PCA observations of this object to help answer the question of whether BALQSOs represent a separate class of QSOs or merely a different line of sight to the nucleus. Despite difficulties in obtaining a convincing background subtraction, we believe that the result is an XTE non-detection. While the sensitivity of XTE exposure limits the utility of an upper limit, we plan to publish these results within a year.

Green, P.↗
NASA NTRS2001

ASCA Observations of PSR 1929+10 and PSR 0950+08

The ASCA X-ray spectra of the old pulsars PSR 1929+10 and PSR 0950+08 are adequately fitted by simple blackbodies. Between 0.5 and 5.0 keV, PSR 1929+10 is best fitted with T = (5.14 +/- 0.53) x 10(exp 6) K and L = 1.54 x 10(exp 30) ergs/s; PSR 0950+08 has T = (5-70 +/- 0.63) x 10(exp 6) K and L = 4.67 x 10(exp 29) ergs/s. The inferred areas are 2 orders of magnitude smaller than canonical polar cap sizes. There is some evidence for a dearth of photons above 5 keV, which would disfavor alternative power-law models for the spectra. Pulsed emission is detected from PSR 1929+10 with 99.8% significance and pulsed fraction 0.35 +/- 0.18. Marginal evidence of pulsed X-ray emission from PSR 0950+08 is present with 99.0% significance and pulsed fraction 0.34+/- 0.18. Relativistic ray tracing shows that if the geometry deduced from the polarization of the radio pulse is adopted for the surface thermal emission, a central dipole cannot reproduce the large pulsed modulations observed unless the radius of the neutron star is as large as 18 km. A mechanism of polar cap heating by the impact of relativistic particles is suggested that can produce small areas with T approx. 5 x 10(exp 6) K on old, spun-down pulsars with weak magnetic fields (B approx. 3 x 10(exp 11) G).

Wang, F. Y.-H.↗
NASA NTRS1998

Results from the Mars Global Surveyor Thermal Emission Spectrometer

The Thermal Emission Spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase, together with about a 35 percent dust component provides the best fit to the spectrum. Qualitative upper limits can be placed on the concentration of carbonates (<10 percent), olivine (<10 percent), clay minerals (<20 percent), and quartz (<5 percent) in the limited regions observed. Limb observations in the northern hemisphere reveal low-lying dust hazes and detached water-ice clouds at altitudes up to 55 kilometers. At an aerocentric longitude of 224 degrees a major dust storm developed in the Noachis Terra region. The south polar cap retreat was similar to that observed by Viking.

unmanned↗
NASA NTRS2005

Gamma-ray Bursts: The Prompt Emission

Gamma-ray bursts are the largest explosions in the Universe. The radiation is thought to come from a hypernova initiated from the collapse of a massive star or perhaps the merger of two compact stars such s neutron stars and/or black holes. Most of the observed energy is radiated as gamma rays, usually lasting from a fraction of a second to several hundred seconds. The energy generation process is usually referred to as the "central engine". Observed properties of this prompt emission, including spectra, time profiles and durations will be discussed. The history of these observations and future GRB spacecraft will also be described.

Fishman, Jerry↗
NASA NTRS2011

The Effect of Blazar Spectral Breaks on the Blazar Contribution to the Extragalactic Gamma-Ray Background

The spectral shapes of the contributions of different classes of unresolved gamma-ray emitters can provide insight into their relative contributions to the extragalactic gamma-ray background (EGB) and the natures of their spectra at GeV energies, We calculate the spectral shapes of the contributions to the EGB arising from BL Lacertae type objects (BL Lacs) and flat-spectrum radio quasars (FSRQs) assuming blazar spectra can be described as broken power laws, We fit the resulting total blazar spectral shape to the Fermi Large Area Telescope measurements of the EGB, finding that the best-fit shape reproduces well the shape of the Fermi EGB for various break scenarios. We conclude that a scenario in which the contribution of blazars is dominant cannot be excluded on spectral grounds alone, even if spectral breaks are shown to be common among Fermi blazars. We also find that while the observation of a featureless (within uncertainties) power-law EGB spectrum by Fermi does not necessarily imply a single class of contributing unresolved sources with featureless individual spectra, such an observation and the collective spectra of the separate contributing populations determine the ratios of their contributions. As such, a comparison with studies including blazar gamma-ray luminosity functions could have profound implications for the blazar contribution to the EGB, blazar evolution, and blazar gamma-ray spectra and emission.

Venters, Tonia M.↗
NASA NTRS2010

The First Detection of (O IV) from an Ultraluminous X-Ray Source with Spitzer. 2. Evidence for High Luminosity in Holmberg II ULX

This is the second of two papers examining Spitzer Infrared Spectrograph observations of the ultraluminous X-ray source (ULX) in Holmberg II. Here, we perform detailed photoionization modeling of the infrared lines. Our analysis suggests that the luminosity and morphology of the [Oiv] 25.89 micronmeters emission line is consistent with photoionization by the soft X-ray and far ultraviolet (FUV) radiation from the accretion disk of the binary system and inconsistent with narrow beaming. We show that the emission nebula is matter bounded both in the line-of-sight direction and to the east, and probably radiation-bounded to the west. A bolometric luminosity in excess of 10(exp 40) erg s(exp -1) would be needed to produce the measured [O iv] flux. We use modeling and previously published studies to conclude that shocks likely contribute very little, if at all,to the high-ionization line fluxes observed in the Holmberg II ULX. Additionally, we find that the spectral type of the companion star has a surprisingly strong effect on the predicted strength of the [O iv] emission. This finding could explain the origin of [O iv] in some starburst systems containing black hole binaries.

GALAXIES↗
NASA NTRS2011

Fading of Jupiter's South Equatorial Belt

One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.

near-infrared↗