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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
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NASA NTRS2002

A Synoptic Study of an X-Ray Nova in Outburst (ADP 2000)

This ADP grant funds and ongoing RXTE Cycle 6 and Cycle 7 project with the same title. The ongoing RXTE project proposes an aggressive campaign of multiwavelength observations of the first X-ray nova that rises above an X-ray intensity of 1 Crab. The RXTE pointed X-ray observations are central to this observing campaign, which includes also very extensive optical and radio observations in both hemispheres. This is a Target of Opportunity program; that is, it is triggered by the RXTE Project Scientist only upon the appearance of such a bright X-ray nova.

McClintock, Jeffrey↗
NASA NTRS2001

ASCA Observation of the Superluminal Jet Source GRO J1655-40 in the 1997 Outburst

We report on the results of an ASCA observation of the Galactic jet source GRO 51655-40 performed from 1997 February 25 to February 28 covering a full orbital period (2.62 d). The averaged 2-10 keV flux was about 1.1 Crab. An absorption line feature centered at 6.8 keV was detected both in the GIS and SIS spectra. We interpret this as a blend of two resonance-absorption K alpha lines from H-like and He-like iron ions. We can consistently explain both the ASCA spectra and the simultaneous RXTE/PCA spectrum by a combination of K-absorption lines and K-absorption edges of iron ions. The fact that the absorption line is stably present over the whole orbital phase implies that the distribution of the highly ionized plasma is not affected by the companion star, which is consistent with its presence around the black hole. A curve of growth analysis shows that the plasma contains velocity dispersion along the line-of-sight larger than 300 km/s attributed to bulk motions. It is probably a part of a geometrically thick accretion flow in turbulent motions with velocities of 500-1600 km/s at an estimated radius of sim 10(exp 10)/cm.

Yamaoka, Kazutaka↗
NASA NTRS1999

Evolution of the Iron K-Alpha Emission Line in the Black Hole Candidate GX339-4 During and Outburst Decay Phase

The evolution of the iron K-alpha line emission feature was found from the black hole candidate GX339-4 when its X-ray flux (2 to 10 keV) decreased significantly. With RXTE observations, a broad line emission feature around 7 keV was detected in its quiescent and low flux state; while in the high flux state, an emission line feature around 6.4 keV was detected. A similar 6.4 keV line feature was also detected with previous ASCA observations in a high flux state. We consider that the evolution could be the evidence of the variations in the geometric structure and the physical properties of the accretion flow when the accretion rate changed. This is because that the 7 keV line feature can be produced by the radiative recombination cascade, collisional excitation, and fluorescence of Fe XXVI and Fe XXV, which can exist in a very high temperature plasma; while the 6.4 keV line feature can be produced by fluorescent K-alpha line emission of neutral iron atoms in the cold accretion disk. (copyright) 1999 American Astronomical Society. All rights reserved.

Feng, Y.↗
NASA NTRS1995

Outburst of Jupiter's synchrotron radiation after the impact of comet Shoemaker-Levy 9

Jupiter's nonthermal microwave emission, as measured by a global network of 11 radio telescopes, increased dramatically during the Shoemaker-Levy 9 impacts. The increase was wavelength-dependent, varying from approximately 10 percent at 70 to 90 centimeters to approximately 45 percent at 6 and 36 centimeters. The radio spectrum hardened (flattened toward shorter wavelengths) considerably during the week of impacts and continued to harden afterward. After the week of cometary impacts, the flux density began to subside at all wavelengths and was still declining 3 months later. Very Large Array and Australia Telescope images of the brightness distribution showed the enhancement to be localized in longitude and concentrated near the magnetic equator. The evidence therefore suggests that the increase in flux density was caused by a change in the resident particle population, for example, through an energization or spatial redistribution of the emitting particles.

Jupiter↗
NASA NTRS2004

RXTE Timing and Spectroscopy of a Black Hole X-Ray Binary in Outburst

This program was executed primarily to observe the black hole transient GX339-4. Observations were made simultaneously with XMM-Newton in 2004 March, and observations simultaneous with Chandra will continue to be made in the fall of 2004. As the total data set has not yet been obtained, a great deal of work remains. Preliminary examination of the data has shown extremely exciting spectral features (Fe K-alpha emission lines) and timing features (strong QPOs and flaring variability) of exactly the sort we hoped to obtain. We expect that the results of these observations will be finalized over the next year. The results will be presented in 2-3 publications in refereed journals. We have requested a no-cost extension of this grant to analyze and report our findings.

Miller, Jon M.↗
NASA NTRS2005

RXTE timing and spectroscopy of black hole binary in outburst

Under this program, Rossi X-ray timing explorer (RXTE) made observations of the Galactic black hole X-ray binary GX 339-4. These observations were timed to be simultaneous with Chandra observations of the same source. Supporting multi-wavelength observations were also obtained using optical and radio telescopes. The RXTE data have been partially analyzed, and will be published in a paper summarizing both the Chandra and RXTE spectral results. The RXTE spectra are instrumental in defining the continuum spectrum in the Chandra data. Moreover, the timing properties measured with RXTE are essential to diagnosing the "state" of the black hole when it was observed by the array of telescopes organized for this effort.

Swank, Jean↗
NASA NTRS2005

RXTE timing and spectroscopy of a black hole X-ray binary in outburst

Under this program, RXTE observed the Galactic black hole candidate X-ray binary H1743-322. Observations were made simultaneously in the X-ray and radio bands with Chandra and the VLA, respectively. First results from this multi-wavelength study have been reported in two papers published in refereed journals, one focusing on timing results and the other focusing on spectroscopy. The timing studies revealed high frequency QPOs at approximately 180 Hz and 240 Hz, likely in a 2:3 frequency ratio as predicted by some models. The RXTE spectra were remarkable in that they showed no evidence of disk reflection or line emission, both of which are expected in black holes.

Miller, Jon↗
NASA NTRS2011

The July 2010 Outburst of the NLS1 PMN J0948+0022

We report about the multiwavelength campaign on the Narrow-Line Seyfert 1 (NLS1) Galaxy PMN J0948+0022 (z = 0.5846) performed in 2010 July-September and triggered by high activity as measured by Fermi/LAT. The peak luminosity in the 0.1 - 100 GeV energy band exceeded, for the first time in this type of source, the value of 1048 erg/s, a level comparable to the most powerful blazars. The comparison of the spectral energy distribution of the NLS1 PMN J0948+0022 with that of a typical blazar like 3C 273 shows that the power emitted at gamma rays is extreme.

Foschini, L.↗
NASA NTRS2013

Star-jet Interactions and Gamma-ray Outbursts from 3C454.3

We propose a model to explain the ultra-bright GeV gamma-ray flares observed from the blazar 3C454.3. The model is based on the concept of a relativistic jet interacting with compact gas condensations produced when a star (a red giant) crosses the jet close to the central black hole. The study includes an analytical treatment of the evolution of the envelope lost by the star within the jet, and calculations of the related high-energy radiation. The model readily explains the day-long that varies on timescales of hours, GeV gamma-ray flare from 3C454.3, observed during 2010 November on top of a plateau lasting weeks. In the proposed scenario, the plateau state is caused by a strong wind generated by the heating of the stellar atmosphere due to nonthermal particles accelerated at the jet-star interaction region. The flare itself could be produced by a few clouds of matter lost by the red giant after the initial impact of the jet. In the framework of the proposed scenario, the observations constrain the key model parameters of the source, including the mass of the central black hole: Blackhole Mass is approx. equal to 10(exp 9) Solar Mass, the total jet power: L(j) is approx. equal to 10(exp 48) erg s(exp −1), and the Doppler factor of the gamma-ray emitting clouds: Delta is approx. equal to 20. Whereas we do not specify the particle acceleration mechanisms, the potential gamma-ray production processes are discussed and compared in the context of the proposed model.We argue that synchrotron radiation of protons has certain advantages compared to other radiation channels of directlyaccelerated electrons. An injected proton distribution varies as E(exp −1) or harder below the relevant energies would be favored to alleviate the tight energetic constraints and to avoid the violation of the observational low-energy constraints.

radiation mechanisms↗
NASA NTRS2016

Very High Energy Outburst of Markarian 501 in May 2009

The very high energy (VHE; E great than 100 GeV) blazar Markarian 501 was observed between April 17 and May 5 (MJD 5493854956), 2009, as part of an extensive multi-wavelength campaign from radio to VHE. Strong VHE -ray activity was detected on May 1st with Whipple and VERITAS, when the flux (E greater than 400 GeV) increased to 10 times the pre-flare baseline flux (3.9 x 10(exp -11 ph cm(exp -2 S(exp -1), reaching five times the flux of the Crab Nebula. This coincided with a decrease in the optical polarization and a rotation of the polarization angle by 15deg. This VHE flare showed a fast flux variation with an increase of a factor approximately 4 in 25 min, and a falling time of approximately 50 min. We present the observations of the quiescent state previous to the flare and of the high state after the flare, focusing on the flux and spectral variability from Whipple, VERITAS, Fermi-LAT, RXTE, and Swift combined with optical and radio data.

BL Lacertae objects: individual: Mrk 501 / gamma r↗