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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 127 records · Page 7
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NASA NTRS1979

Magnetohydrodynamic models of coronal transients in the meridional plane. II - Simulation of the coronal transient of 1973 August 21

A two-dimensional planar MHD model of solar atmospheric transient events is used to simulate the flare-associated events of August 21, 1973. This event, observed in H-alpha, He II 304 A, soft X-ray, and coronal white light, provided sufficient information (especially in the latter diagnostic) for an assessment to be made of the model's ability to simulate major features of an actual solar event. It was found that a thermodynamic input pulse based on data provided by the NASA Marshall Space Flight Center-Aerospace Corporation X-ray telescope (S-056) on Skylab was sufficient to produce the global geometry, shock and contact-surface velocities, excess mass contours, and energy budget which were, for the most part, observed by the High Altitude Observatory white-light coronagraph (S-052) on Skylab in the form of a forerunner and coronal transient.

Dryer, M.↗
NASA NTRS1984

Interpretation of microwave active region structures using SMM soft X-ray observations

A new kind of sunspot-associated microwave source was detected by Alissandrakis and Kundu (1982). The observed emission came predominantly from a ring structure with a size between that of the umbra and the penumbra. It was thought that the newly discovered structure could be the product of the low gyroresonance opacity when the angle between the magnetic field and the line of sight is close to zero. The present investigation has the objective to study the roles played by the geometrical effect of gyroresonance absorption and by the low-temperature flux tubes above the relevant sunspot, taking into account 6 cm observations made with the aid of a radio telescope and X-ray observations conducted with the X-ray Polychromator (XRPO on the Solar Maximum Mission) (SMM) satellite.

Strong, K. T.↗
NASA NTRS1977

The atmosphere of Sirius B. II - Extreme-ultraviolet observations

The letter reports an observation of Sirius in the extreme-ultraviolet (100-1000 A) band, using a grazing-incidence telescope flown aboard the Apollo-Soyuz mission. No positive flux is detected; under the arbitrary assumption of flat incident spectrum, an upper limit to the flux in the 170-620 A band is 5 billion erg/sq cm per sec. A detailed model-atmosphere analysis, when combined with the EUV limits, places severe constraints on models which attribute the previously reported soft X-ray (44-60 A) flux to thermal radiation from deep layers of the atmosphere of the white dwarf Sirius B. EUV radiation should be detectable from Sirius B just below the sensitivity threshold of the current data, or a thermal origin for the X-ray flux is untenable. If the X-ray flux is thermal, the present results provide extremely sensitive constraints on the temperature and helium abundance of Sirius B: the white dwarf has an effective temperature of 32,000 K to 32,500 K and a helium abundance (relative to hydrogen) of 0.0001 to 0.0002.

Shipman, H. L.↗
NASA NTRS1984

A Neutral Gas Jet in a Low Velocity Shock Front at the Boundary of the Draco Nebula

Twenty-one cm line observations with the Westerbork Synthesis Radio Telescope of a dust and molecular filament at the boundary of the Draco Nebula reveal a jet like neutral hydrogen feature funneling through an outlet in the low velocity shock front at the interface between the Draco Nebula and the surrounding gas. The jet like feature is apparently connected with a high velocity filament at VLSR = -180 km/sec. It is suggested that soft X-ray emission observed in the area is thermal bremsstrahlung produced by the deceleration of high velocity gas in galactic gas.

Kalberla, P. W. M.↗
NASA NTRS1971

Long term temporal variations of the hard X-ray flux from the Centaurus region

The X-ray telescope aboard the third Orbiting Solar Observatory (OSO-3) observed the Centaurus region daily from 1967 October to 1968 February, and also for five days in 1968 June. A stable minimum flux of 0.33 + or - 0.03 photons (sq cm sec)/1 between 7.7 and 38 keV from a source around l = 305 deg is derived. Several single days show enhanced fluxes, and two extensive flaring episodes, one with a soft and the other a very hard spectrum, lasting at least ten days.

Schwartz, D. A.↗
DOE OSTI2025

Directly imaging the cooling flow in the Phoenix cluster

In the centres of many galaxy clusters, the hot (approximately 10 7 kelvin) intracluster medium can become dense enough that it should cool on short timescales. However, the low measured star formation rates in massive central galaxies and the absence of soft X-ray lines from the cooling gas suggest that most of this gas never cools. This is known as the cooling flow problem. The latest observations suggest that black hole jets are maintaining the vast majority of gas at high temperatures. A cooling flow has yet to be fully mapped through all the gas phases in any galaxy cluster. Here we present observations of the Phoenix cluster using the James Webb Space Telescope to map the [Ne vi] λ 7.652-μm emission line, enabling us to probe the gas at 10 5.5 kelvin on large scales. These data show extended [Ne vi] emission that is cospatial with the cooling peak in the intracluster medium, the coolest gas phases and the sites of active star formation. Taken together, these imply a recent episode of rapid cooling, causing a short-lived spike in the cooling rate, which we estimate to be 5,000–23,000 solar masses per year. As a result, these data provide a large-scale map of gas at temperatures between 10 5 kelvin and 10 6 kelvin in a cluster core, and highlight the critical role that black hole feedback has in not only regulating cooling but also promoting it.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Long-term temporal variations of the hard X-ray flux from the Centaurus region.

An X-ray telescope aboard OSO 3 observed the Centaurus region daily from October 1967 to February 1968, and also for five days in June 1968. For this period, we derive a stable minimum flux of 0.33 plus or minus 0.33 photons per sq cm per sec between 7.7 and 38 keV from a persistent hard X-ray source around 305 deg longitude. Several single days show enhanced fluxes; and two extensive flaring episodes, one with a soft and the other with a very hard spectrum, last at least 10 days.

Schwartz, D. A.↗
DOE OSTI2025

Chandra Discovery of a Candidate Hyperluminous X-Ray Source in MCG+11-11-032

We present a multiwavelength analysis of MCG+11-11-032, a nearby active galactic nucleus (AGN), with a unique classification as being both a binary and a dual AGN candidate. With new Chandra observations, we aim to resolve any dual AGN system via imaging data and search for signs of a binary AGN via analysis of the X-ray spectrum. Analyzing the Chandra spectrum, we find no evidence of the previously suggested double-peaked Fe Kα lines; the spectrum is instead best fit by an absorbed power law with a single Fe Kα line, as well as an additional line centered at ≈7.5 keV. The Chandra observation reveals faint, soft, and extended X-ray emission, possibly linked to low-level nuclear outflows. Further analysis shows evidence for a compact hard source—MCG+11-11-032 X2—located 3.″3 from the primary AGN. Modeling MCG+11-11-032 X2 as a compact source, we find that it is relatively luminous (L2–10 keV=1.5−0.5+0.9×1041erg s$^{−1}$), and the location is coincident with a compact and off-nuclear source resolved in Hubble Space Telescope infrared (F105W) and optical (F621M, F547M) bands. Pairing our X-ray results with a 144 MHz radio detection at the host galaxy location, we observe X-ray and radio properties similar to those of ESO 243-49 HLX-1, suggesting that MCG+11-11-032 X2 may be a hyperluminous X-ray source. This detection with Chandra highlights the importance of a high-resolution X-ray imager as well as how previous binary AGN candidates detected with large-aperture instruments can benefit from high-resolution follow-up. Future spatially resolved optical spectra, and deeper X-ray observations, can better constrain the origin of MCG+11-11-032 X2.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

Design of the Extreme Ultraviolet Explorer long-wavelength grazing incidence telescope optics

Designing optics for photometry in the long-wavelength portion of the EUV spectrum (400-900) A) poses different problems from those arising for optics, operating shortward of 400 A. The available filter materials which transmit radiation longward of 400 A are also highly transparent at wavelengths shortward of 100 A. Conventional EUV optics, with grazing engles of less than about 10 deg, have very high throughput in the EUV, which persists to wavelengths shortward of 100 A. Use of such optics with the longer-wavelength EUV filters thus results in an unacceptably large soft X-ray leak. This problem is overcome by developing a mirror design with larger graze angles of not less than 20 deg, which has high throughput at wavelengths longer than 400 A but at the same time very little throughput shortward of 100 A.

Finley, David S.↗
NASA NTRS1988

The scattered solar X-ray background in low earth orbit

In order to interpret X-ray observations of the sun-lit earth obtained with the IPC, a detailed model is developed that treats the radiative transfer of solar X-rays in single scattering approximation and employs the relevant scattering processes (elastic Thomson scattering and inelastic fluorescent scattering). The X-ray-bright earth, one of the strongest soft X-ray sources seen by the IPC, can then be understood in terms of solar X-rays scattered in the upper atmosphere. Using the CIRA 1972 Reference Atmosphere, it is possible to account for the observed 'bright earth' X-ray light curves under a variety of different viewing geometries. It is argued that the observed changes in hardness ratio of the scattered radiation can be interpreted as an indication of a change in the ratio of Thomson and fluorescently scattered photons as a function of zenith angle. The relevance of bright earth X-ray observations is further discussed in the context of operating X-ray telescopes in low-earth orbit, as well as in a broader astrophysical context.

Fink, H. H.↗
NASA NTRS1975

Interstellar absorption lines toward gamma Arae

The available data on interstellar absorption lines in the spectrum of gamma Ara observed from the ground and with the Copernicus telescope have been analyzed to give column densities of various ion stages of H, C, N, O, Na, Mg, Si, P, S, Ar, Ca, Mn, and Fe. The element abundances with respect to H nuclei in H I regions are similar to the values for zeta Oph, with depletions relative to the sun tending to increase with increasing condensation temperature. For example, toward gamma Ara, Fe is depleted by a factor of 50; Mg, Si, and Mn by about 10; and S, P, and N little or none. Interstellar Si IV and probably S IV appear stronger than in most other stars, but still their low ratios to Si III and S III suggest that soft X-rays and low-energy cosmic rays are not important sources of ionization. The width of the O VI lines and the absence of N V have been interpreted as evidence for a collisionally ionized region with a temperature between 300,000 and 700,000 K containing at least 0.0004 of the total interstellar column density.

Morton, D. C.↗
NASA NTRS1981

The Einstein Observatory and future X-ray telescopes

A history of the events leading to the development and flight of the Einstein Observatory is given. The advantages of using grazing-incidence telescopes for solar and extrasolar X-ray astronomy is first discussed and followed by a description of the HEAO program. The Einstein Observatory marks a departure from the manner in which X-ray investigations are carried out, from individual experiments to the shared use of large facilities. The Observatory has achieved a sensitivity to point sources of 10 to the -14th erg/sq cm-sec in the 1-3 keV band, a flux 500 times smaller than previously detected and about 10 million times smaller than that of the first extrasolar source detected in 1962. The design philosophy of the Observatory entails three principles: (1) the unified scientific approach, (2) the establishment of spacecraft requirements at lowest acceptable levels that still allow operating flexibility, and (3) the idea of 'soft' rather than 'hard' failure. The mirror design, including the high resolution imager, the imaging proportional counter, and the solid-state and focal plane crystal spectrometers, is also given. An account of the struggle to gain acceptance by the scientific community and the funding agencies of the need for the Einstein Observatory mission is discussed. Finally, results of observations made by the Observatory are presented in detail, along with plans for future observation experiments.

Giacconi, R.↗
DOE OSTI2025

Delving into the depths of NGC 3783 with XRISM

The 2024 X-ray/UV observation campaign of NGC 3783, led by XRISM, revealed the launch of an ultrafast outflow (UFO) with a radial velocity of 0.19c (57 000 km s −1 ). This event is synchronized with the sharp decay, within less than half a day, of a prominent soft X-ray/UV flare. Accounting for the look-elsewhere effect, the XRISM Resolve data alone indicate a low probability of 2 × 10 −5 that this UFO detection is due to random chance. The UFO features narrow H-like and He-like Fe lines with a velocity dispersion of ∼1000 km s −1 , suggesting that it originates from a dense clump. Beyond this primary detection, there are hints of weaker outflow signatures throughout the rise and fall phases of the soft flare. Their velocities increase from 0.05c to 0.3c over approximately three days, and they may be associated with a larger stream in which the clump is embedded. The radiation pressure is insufficient to drive the acceleration of this rapidly evolving outflow. The observed evolution of the outflow kinematics instead closely resembles that of solar coronal mass ejections, implying magnetic driving and, conceivably, reconnection near the accretion disk as the likely mechanisms behind both the UFO launch and the associated soft flare.

Astronomy and AstroPhysics↗
DOE OSTI2025

Initial in-orbit operation of the soft X-ray spectrometer Resolve onboard the X-ray imaging and spectroscopy mission satellite

The X-Ray Imaging and Spectroscopy Mission satellite was launched on September 6, 2023 (UT). Its Resolve instrument is a high-resolution X-ray spectrometer enabled by a microcalorimeter array thermally anchored to a 50-mK heat sink. Many sensitive, critical sub-systems comprise Resolve, including a multistage cryogenic cooling system, thin-film aperture filters, low-noise electronics, on-board signal processing, and several sources of X-rays for calibration. We summarize the initial on-orbit power-on and checkout of Resolve that commenced immediately after launch. Soon after launch, the cryocoolers were activated, and their operation was successfully established. On October 9, 2023, the first cycle of the adiabatic demagnetization refrigerator was carried out, bringing the sensors to their steady-state operational temperatures. Following this, the energy resolution at 5.9 keV was successfully measured. The energy scale of the system is highly sensitive to the thermal environment surrounding both the sensors and their analog electronics. Gain correction was performed using reference X-ray lines from onboard calibration sources. To optimize cooler frequency settings, noise spectra were collected across a range of frequencies, and the most suitable frequency pair was selected based on the in-orbit environment. During the final phase of the checkout, an attempt was made to open the gate valve, which is designed to protect the Dewar’s interior from external pressure during ground operations and launch. Unfortunately, this attempt was unsuccessful. As a result, the checkout process was temporarily paused, and a stable operational strategy was subsequently developed to enable Resolve to function effectively with the gate valve remaining closed.

X-ray micro-calorimeter↗
DOE OSTI2025

GRB 221009A: The B.O.A.T. Burst that Shines in Gamma Rays

We present a complete analysis of Fermi Large Area Telescope (LAT) data of GRB 221009A, the brightest gamma-ray burst (GRB) ever detected. The burst emission above 30 MeV detected by the LAT preceded, by 1 s, the low-energy (<10 MeV) pulse that triggered the Fermi Gamma-Ray Burst Monitor (GBM), as has been observed in other GRBs. The prompt phase of GRB 221009A lasted a few hundred seconds. It was so bright that we identify a bad time interval of 64 s caused by the extremely high flux of hard X-rays and soft gamma rays, during which the event reconstruction efficiency was poor and the dead time fraction quite high. The late-time emission decayed as a power law, but the extrapolation of the late-time emission during the first 450 s suggests that the afterglow started during the prompt emission. We also found that high-energy events observed by the LAT are incompatible with synchrotron origin, and, during the prompt emission, are more likely related to an extra component identified as synchrotron self-Compton (SSC). A remarkable 400 GeV photon, detected by the LAT 33 ks after the GBM trigger and directionally consistent with the location of GRB 221009A, is hard to explain as a product of SSC or TeV electromagnetic cascades, and the process responsible for its origin is uncertain. Because of its proximity and energetic nature, GRB 221009A is an extremely rare event.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Rocket spectrogram of a solar flare in the 10-100 A region

The soft (10-100 A) X-ray spectrum of an M-class solar flare was observed with a high-resolution (0.02 A) rocket-borne spectrograph on 1982 July 13. The spectrum samples an area of 600/sq arcsec on the sun, centered on or near the brightest X-ray feature of the flare. Several hundred emission lines characteristic of temperatures from about 0.5 to 7 x 10 to the 6th K have been photographically recorded. All but three of the stronger lines have been identified. It is argued that previous identification of the line at 17.62 A as iron Ly-alpha is incorrect. Spectral lines from nickel, iron, chromium, calcium, sulphur, silicon, aluminium, magnesium, neon, oxygen, nitrogen, and carbon are tabulated and discussed with extensive reference to earlier work. Absolute line intensities are given and the calibration of the telescope-spectrograph is discussed.

Acton, L. W.↗