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At least 1,369 records · Page 76
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NASA NTRS2007

The Symbiotic System SS73 17 seen with Suzaku

We observed with Suzaku the symbiotic star SS73 17, motivated by the discovery by the INTEGRAL satellite and the Swift BAT survey that it emits hard X-rays. Our observations showed a highly-absorbed X-ray spectrum with NH > loz3 emp2, equivalent to Av > 26, although the source has B magnitude 11.3 and is also bright in UV. The source also shows strong, narrow iron lines including fluorescent Fe K as well as Fe xxv and Fe XXVI. The X-ray spectrum can be fit with a thermal model including an absorption component that partially covers the source. Most of the equivalent width of the iron fluorescent line in this model can be explained as a combination of reprocessing in a dense absorber plus reflection off a white dwarf surface, but it is likely that the continuum is partially seen in reflection as well. Unlike other symbiotic systems that show hard X-ray emission (CH Cyg, RT Cru, T CrB, GX1+4), SS73 17 is not known to have shown nova-like optical variability, X-ray flashes, or pulsations, and has always shown faint soft X-ray emission. As a result, although it is likely a white dwarf, the nature of the compact object in SS73 17 is still uncertain. SS73 17 is probably an extreme example of the recently discovered and relatively small class of hard X-ray emitting symbiotic systems.

Smith, Randall K.↗
NASA NTRS2005

Discovery of a 105-ms X-ray Pulsar in Kesteven-79: On the Nature of Compact Central Objects in Supernova Remnants

We report the discovery of 105-ms X-ray pulsations from the compact central object (CCO) in the supernova remnant \snr\ using data acquired with the {\it Newton X-Ray Multi-Mirror Mission). Using two observations of the pulsar taken 6-days apart we derive an upper limit on its spin-down rate of $\dot P < 9 \times 10"{-14}$-s-~$~{-l)$,a nd find no evidence for binary orbital motion. The implied energy loss rate is $\dot E < 3 \times 10A{36)$-ergs-s$A{-1)$, polar magnetic field strength is $B-{\rm p) < 3 \times 10A{12)$-G, and spin-down age is $\tau > 18.5$-kyr. The latter exceeds the remnant's estimated age, suggesting that the pulsar was born spinning near its current period. The X-ray spectrum of \psr\ is best characterized as a blackbody of temperature $kT {BB) =, 0.43\pm0.02$ keV, radius $R-{BB) \approx 1.3$-km, and $~I{\rm bol) = 5.2 \times 10A{33)$ ergs-sSA{-1)$ at $d = 7.1$-kpc. The sinusoidal light curve is modulated with a pulsed fraction of $>45\%$, suggestive of a small hot spot on the surface of the rotating neutron star. The lack of a discernible pulsar wind nebula is consistent with an interpretation of \psr\ as a rotation-powered pulsar whose spin-down luminosity falls below the empirical threshold for generating bright wind nebulae, $\dot E-{\rm c) = 4 \times 10A{36)$-ergs-sSA{-I)$. The age discrepancy suggests that its $\dot E$ has always been below $\dot E c$, perhaps a distinguishing property of the CCOs. Alternatively, the X-ray spectrum of \psr\ suggests a low-luminosity AXP, but the weak inferred $B-{\rm p)$ field is incompatible with a magnetar theory of its X-ray luminosity. The ordinary spin parameters discovered from \psr\ highlight the inability of existing theories to explain the high luminosities and temperatures of CCO thermal X-ray spectra.

Gotthelf, E. V.↗
NASA NTRS2009

Ultrasonic Apparatus and Method to Assess Compartment Syndrome

A process and apparatus for measuring pressure buildup in a body compartment that encases muscular tissue. The method includes assessing the body compartment configuration and identifying the effect of pulsatible components on compartment dimensions and muscle tissue characteristics. This process is used in preventing tissue necrosis, and in decisions of whether to perform surgery on the body compartment for prevention of Compartment Syndrome. An apparatus is used for measuring pressure build-up in the body compartment having components for imparting ultrasonic waves such as a transducer, placing the transducer to impart the ultrasonic waves, capturing the imparted ultrasonic waves, mathematically manipulating the captured ultrasonic waves and categorizing pressure build-up in the body compartment from the mathematical manipulations.

Yost, William T.↗
NASA NTRS2010

Fast X-Ray Timing: A Window into the Strong-Field Regime

The dynamical time-scales in the vicinity of neutron star surfaces and black hole horizons are in the millisecond range. Over the past decade, timing signatures on such scales, either quasi-periodic oscillations (QPOs) and/or coherent pulsations, have been discovered and studied from both neutron stars and black holes with NASA's Rossi X-ray Timing Explorer, Although theoretical interpretations are still hotly debated, these timing properties almost certainly reflect the dynamics of matter in regions dominated by relativistic gravity. I will survey our current understanding of these timing properties, with a focus on how they might he used as probes of fundamental physics.

Strohmayer, Tod↗
NASA NTRS2010

High Angular Resolution Observations of Episodic Dust Emission from Long Period Variable Stars Twenty Years of Observations with the Berkeley Infrared Spatial Interferometer

Over the past twenty years the U. C. Berkeley Infrared Spatial Interferometer has observed a number of Long Period Variable stars in the mid-infrared, obtaining information on the spatial distribution of dust around these stars with resolutions of the order of a few tens of milliarcseconds. The ISI is a heterodyne interferometer operating mostly at 11.15 microns, initially with two telescopes. In the last decade, it has been taking data regularly with three telescopes, thus obtaining visibility data on three baselines and also a closure phase. Over the course of the years, the ISI has been able to measure the physical properties of the dust shells surrounding these stars, in particular the inner radii of the dust shells, as well as the temperature and density distribution. For some stars, the ISI has also made precision measurements of their diameters in the mid-infrared. Closure phase measurements have revealed asymmetries in the dust distributions around many stars. Most surprisingly the ISI data has shown evidence for substantial changes in the amount of dust on time scales of 5-10 years, rather than being directly correlated with the stellar pulsation periods, which are of the order of one year. We discuss past results and new results from the ISI that highlight the dynamic environment around these stars.

Danchi, William↗
NASA NTRS2011

Millisecond Pulsars at Gamma-Ray Energies: Fermi Detections and Implications

The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the discovery of new populations of radio quiet and millisecond gamma-ray pulsars. The Fermi Large Area Telescope has so far discovered approx.20 new gamma-ray millisecond pulsars (MSPs) by both folding at periods of known radio MSPs or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -30 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. Many of the newly discovered MSPs may be suitable for addition to the collection of very stable MSPs used for gravitational wave detection. Detection of such a large number of MSPs was surprising, given that most have relatively low spin-down luminosity and surface field strength. I will discuss their properties and the implications for pulsar particle acceleration and emission, as well as their potential contribution to gamma-ray backgrounds and Galactic cosmic rays.

Harding, Alice K.↗
NASA NTRS2010

Flow, Aurora and PI2 Associations Observed by Themis

It has been known for decades that auroral substorm onset occurs on (or at least near) the most equatorward auroral arc, which is thought to map to the near geosynchronous region. The lack of auroral signatures poleward of this arc prior to onset has been a major criticism of flow-burst driven models of sub storm onset. The combined THEMIS 5 spacecraft in-situ and ground array measurements provide an unprecedented opportunity to examine the causal relationship between midtail plasma flows, aurora, and ground magnetic signatures. I first present an event from 2008 using multi-spectral all sky imager data from Gillam and in-situ data from THEMIS. The multispectral data indicate an equatorward moving auroral form prior to sub storm onset. When this forms reaches the most equatorward arc, the arc brightens and an auroral substorm begins. The THEMIS data show fast Earthward flows prior to onset as well. I suggest that the results strongly support flow-burst driven models of magnetospheric activity. I discuss further the association of flow bursts and Pi2 pulsations, and discuss the possibility of using Pi2 waveforms to infer midtail reconnection dynamics

Kepko, E. I.↗
NASA NTRS2011

Study of the Many Fluorescent Lines and the Absorption Variability in GX 301-2 with XMM-Newton

We present an in-depth study of the High Mass X-ray Binary (HMXB) GX 301-2 during its pre-periastron flare using data from the XMM-Newton satellite. The energy spectrum shows a power law continuum absorbed by a large equivalent hydrogen column on the order of 10(exp 24)/ sq cm and a prominent Fe K-alpha fluorescent emission line. Besides the Fe K-alpha line, evidence for Fe K-Beta, Ni K-alpha, Ni K-Beta, S K-alpha, Ar K-alpha, Ca K-alpha, and Cr K-alpha fluorescent lines is found. The observed line strengths are consistent with fluorescence in a cold absorber. This is the first time that Cr K-alpha is seen in emission in the X-ray spectrum of a HMXB. In addition to the modulation by the strong pulse period of approx 685 sec the source is highly variable and shows different states of activity. We perform time-resolved as well as pulse-to-pulse resolved spectroscopy to investigate differences between these states of activity. We find that fluorescent line fluxes are strongly variable and generally follow the overall flux. The N-H value is variable by a factor of 2, but not correlated to continuum normalization. We find an interval of low flux in the light curve in which the pulsations cease almost completely, without any indication of an increasing absorption column. We investigate this dip in detail and argue that it is most likely that during the dip the accretion ceased and the afterglow of the fluorescent iron accounted for the main portion of the X-ray flux. A similar dip was found earlier in RXTE data, and we compare our findings to these results.

Fuerst, F.↗
NASA NTRS2009

The Nature of the X-Ray Binary IGR J19294+1816 from INTEGRAL, RXTE, and Swift Observations

We report the results of a high-energy multi-instrumental campaign with INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR J19294+ 1816. The Swift/XRT data allow us to refine the position of the source to R.A. (J2000) = 19h 29m 55.9s, Decl. (J2000) = +18 deg 18 feet 38 inches . 4 (+/- 3 inches .5), which in turn permits us to identify a candidate infrared counterpart. The Swift and RXTE spectra are well fitted with absorbed power laws with hard (Gamma approx 1) photon indices. During the longest Swift observation, we obtained evidence of absorption in true excess to the Galactic value, which may indicate some intrinsic absorption in this source. We detected a strong (P = 40%) pulsations at 12.43781 (+/- 0.00003) s that we interpret as the spin period of a pulsar. All these results, coupled with the possible 117 day orbital period, point to IGR J19294+ 1816 being an high-mass X-ray binary (HMXB) with a Be companion star. However, while the long-term INTEGRAL/IBIS/ISGRI 18-40 keV light curve shows that the source spends most of its time in an undetectable state, we detect occurrences of short (2000-3000 s) and intense flares that are more typical of supergiant fast X-ray transients. We therefore cannot make firm conclusions on the type of system, and we discuss the possible implication of IGR J19294+1816 being an Supergiant Fast X-ray Transient (SFXT).

Rodriquez, J.↗
NASA NTRS2012

PSR J0007+7303 in the CTA1I Supenova Remnant: New Gamma-Ray Results from Two Years of Fermi Large Area Telescope Observations

One of the main results of the Fermi Gamma-Ray Space Telescope is the discovery of -ray selected pulsars. The high magnetic field pulsar, PSR J0007+7303 in CTA1, was the first ever to be discovered through its -ray pulsations. Based on analysis of two years of Large Area Telescope (LAT) survey data, we report on the discovery of -ray emission in the off-pulse phase interval at the 6 level. The emission appears to be extended at the 2 level with a disk of extension 0.6. level. The flux from this emission in the energy range E 100 MeV is F 100 = (1.73 0.40stat 0.18sys) 108photonscm2 s1 and is best fitted by a power law with a photon index of = 2.54 0.14stat 0.05sys. The pulsed -ray flux in the same energy range is F 100 = (3.95 0.07stat 0.30sys) 107photonscm2 s1 and is best fitted by an exponentially cutoff power-law spectrum with a photon index of = 1.41 0.23stat 0.03sys and a cutoff energy Ec = 4.04 0.20stat 0.67sysGeV. We find no flux variability either at the 2009 May glitch or in the long-term behavior. We model the -ray light curve with two high-altitude emission models, the outer gap and slot gap, and find that the preferred model depends strongly on the assumed origin of the off-pulse emission. Both models favor a large angle between the magnetic axis and observer line of sight, consistent with the nondetection of radio emission being a geometrical effect. Finally, we discuss how the LAT results bear on the understanding of the cooling of this neutron star.

Abdo, A.↗
NASA NTRS2011

PSR J0007+7303 in the CTA1 SNR: New Gamma-ray Results from Two Years of Fermi-LAT Observations

One of the main results of the Fermi Gamma-Ray Space Telescope is the discovery of gamma-ray selected pulsars. The high magnetic field pulsar, PSR J0007+7303 in CTA1, was the first ever to be discovered through its gamma-ray pulsations. Based on analysis of 2 years of LAT survey data, we report on the discovery of I-ray emission in the off-pulse phase interval at the approx. 6sigma level. The flux from this emission in the energy range E > or =::: 100 MeV is F(sub 100) = (1.73+/-0.40) x 10(exp -8) photons/sq cm/s and is best fitted by a power law with a photon index of Gamma = 2.54+/-0.14. The pulsed gamma-ray flux in the same energy range is F(sub 100) = (3.95+/-0.07) x 10(exp -7) photons/sq cm/s and is best fitted by an exponentially-cutoff power-law spectrum with a photon index of Gamma = 1.41+/-0.23 and a cutoff energy E(sub c) = 4.04+/-0.20 GeV. We find no flux variability neither at the 2009 May glitch nor in the long term behavior. We model the gamma-ray light curve with two high-altitude emission models, the outer gap and slot gap, and find that the model that best fits the data depends strongly on the assumed origin of the off-pulse emission. Both models favor a large angle between the magnetic axis and observer line of sight, consistent with the nondetection of radio emission being a geometrical effect. Finally we discuss how the LAT results bear on the understanding of the cooling of this neutron star.

Abdo, A. A.↗
NASA NTRS2011

Fermi Detection of a Luminous gamma-ray Pulsar in a Globular Cluster

We report the Fermi Large Area Telescope detection of gamma -ray (>100 mega-electron volts) pulsations from pulsar J1823--3021A in the globular cluster NGC 6624 with high significance (approx 7 sigma). Its gamma-ray luminosity L (sub 3) = (8:4 +/- 1:6) X 10(exp 34) ergs per second, is the highest observed for any millisecond pulsar (MSP) to date, and it accounts for most of the cluster emission. The non-detection of the cluster in the off-pulse phase implies that its contains < 32 gamma-ray MSPs, not approx 100 as previously estimated. The gamma -ray luminosity indicates that the unusually large rate of change of its period is caused by its intrinsic spin-down. This implies that J1823--3021A has the largest magnetic field and is the youngest MSP ever detected, and that such anomalous objects might be forming at rates comparable to those of the more normal MSPs.

Freire, P. C. C.↗
NASA NTRS2011

Observations of Energetic High Magnetic Field Pulsars with the Fermi Large Area Telescope

We report the detection of gamma-ray pulsations from the high-magnetic-field rotation-powered pulsar PSR J1119.6127 using data from the Fermi Large Area Telescope. The gamma-ray light curve of PSR J1119.6127 shows a single, wide peak offset from the radio peak by 0.43 +/- 0.02 in phase. Spectral analysis suggests a power law of index 1.0 +/- 0.3(+0.4 -0.2) with an energy cut-off at 0.8 +/- 0.2(+2.0 -0.5) GeV. The first uncertainty is statistical and the second is systematic. We discuss the emission models of PSR J1119.6127 and demonstrate that despite the object's high surface magnetic field--near that of magnetars -- the field strength and structure in the gamma-ray emitting zone are apparently similar to those of typical young pulsars. Additionally, we present upper limits on the gamma-ray pulsed emission for the magnetically active PSR J1846.0258 in the supernova remnant Kesteven 75 and two other energetic high-Beta pulsars, PSRs J1718.3718 and J1734.3333. We explore possible explanations for the non-detection of these three objects, including peculiarities in their emission geometry.

Parent, D.↗
NASA NTRS2011

Neutron Star Spin Measurements and Dense Matter with LOFT

Observations over the last decade with RXTE have begun to reveal the X-ray binary progenitors of the fastest spinning neutron stars presently known. Detection and study of the spin rates of binary neutron stars has important implications for constraining the nature of dense matter present in neutron star interiors, as both the maximum spin rate and mass for neutron stars is set by the equation of state. Precision pulse timing of accreting neutron star binaries can enable mass constraints. Particularly promIsing is the combination of the pulse and eclipse timing, as for example, in systems like Swift 11749.4-2807. With its greater sensitivity, LOFT will enable deeper searches for the spin periods of the neutron stars, both during persistent outburst intervals and thermonuclear X-ray bursts, and enable more precise modeling of detected pulsations. I will explore the anticipated impact of LOFT on spin measurements and its potential for constraining dense matter in neutron stars

Strohmayer, Tod↗
NASA NTRS2011

Discovery of Nine Gamma-Ray Pulsars in Fermi-Lat Data Using a New Blind Search Method

We report the discovery of nine previously unknown gamma-ray pulsars in a blind search of data from the Fermi Large Area Telescope (LAT). The pulsars were found with a novel hierarchical search method originally developed for detecting continuous gravitational waves from rapidly rotating neutron stars. Designed to find isolated pulsars spinning at up to kHz frequencies, the new method is computationally efficient, and incorporates several advances, including a metric-based gridding of the search parameter space (frequency, frequency derivative and sky location) and the use of photon probability weights. The nine pulsars have spin frequencies between 3 and 12 Hz, and characteristic ages ranging from 17 kyr to 3 Myr. Two of them, PSRs Jl803-2149 and J2111+4606, are young and energetic Galactic-plane pulsars (spin-down power above 6 x 10(exp 35) ergs per second and ages below 100 kyr). The seven remaining pulsars, PSRs J0106+4855, J010622+3749, Jl620-4927, Jl746-3239, J2028+3332,J2030+4415, J2139+4716, are older and less energetic; two of them are located at higher Galactic latitudes (|b| greater than 10 degrees). PSR J0106+4855 has the largest characteristic age (3 Myr) and the smallest surface magnetic field (2x 10(exp 11)G) of all LAT blind-search pulsars. PSR J2139+4716 has the lowest spin-down power (3 x l0(exp 33) erg per second) among all non-recycled gamma-ray pulsars ever found. Despite extensive multi-frequency observations, only PSR J0106+4855 has detectable pulsations in the radio band. The other eight pulsars belong to the increasing population of radio-quiet gamma-ray pulsars.

Celik-Tinmaz, Ozlem↗
NASA NTRS2011

Upstream Structures and Their Effects on the Magnetosphere

Kinetic processes within the Earth's foreshock generate a profusion of plasma and magnetic field structures with sizes and durations ranging from the microscale (e.g. SLAMs, solitons, and density holes) to the mesoscale (e.g. foreshock cavities or boundaries, hot flow anomalies, and bubbles). Swept into the bow shock by the solar wind flow, the perturbations associated with these features batter the magnetosphere, driving a wide variety of magnetospheric effects, including large amplitude magnetopause motion, bursty reconnection and the generation of flux transfer events, enhanced pulsation activity within the magnetosphere, diffusion and energization of radiation belt particles, enhanced particle precipitation resulting in dayside aurora and riometer absorption, and the generation of field-aligned currents and magnetic impulse events in high-latitude ground magnetometers. This talk reviews the ever growing menagery of structures observed upstream from the bow shock, examines their possible interrelationships, and considers their magnetospheric consequences.

Sibeck, D. G.↗
NASA NTRS2011

The Origin and Shape of Diffuse Auroral Patches

Patchy pulsating aurora occurs commonly in the post-midnight sector. Recent studies have moved us significantly closer to understanding the mechanisms responsible for pitch angle scattering of the Central Plasma Sheet (CPS) electrons that produce these aurora. However, there is not yet an adequate explanation of what physical process gives rise to the patchy nature of the aurora. These patches last for minutes up to tens of minutes, with sizes that do not change significantly over their life time, and remain more or less stationary relative to the ground. In this paper, we use THEMIS and NORSTAR ASI observations of these auroral features to explore the shape of these patches. Based on our results, we conclude that the patches are the ionospheric counterpart of structures in cold plasma near the magnetospheric equator.

Rae, Kyle↗
NASA NTRS2012

Discovery of an Energetic Pulsar Associated with SNR G76.9+1.0

We report the discovery of PSR J2022-<-3842, a 24 ms radio and X-ray pulsar in the supernova remnant G76.9+i.0, in observations with the Chandra X-ray telescope, the Robert C. Byrd Green Bank Radio Telescope, and the Rossi X-ray Timing Explorer (RXTE). The pulsar's spin-down rate implies a rotation-powered luminosity E = 1.2 X 10(exp 38) erg/s, a surface dipole magnetic field strength B(sub S), = 1.0 X 10(exp 12) G, and a characteristic age of 8.9 kyr. PSR J2022+3842 is thus the second-most energetic Galactic pulsar known, after the Crab, as well as the most rapidly-rotating young, radio-bright pulsar known. The radio pulsations are highly dispersed and broadened by interstellar scattering, and we find that a large (delta f/f approximates 1.9 x 10(exp -6)) spin glitch must have occurred between our discovery and confirmation observations. The X-ray pulses are narrow (0.06 cycles FWHM) and visible up to 20 keV, consistent with magnetospheric emission from a rotation-powered pulsar. The Chandra X-ray image identifies the pulsar with a hard, unresolved source at the midpoint of the double-lobed radio morphology of G76.9+ 1.0 and embedded within faint, compact X-ray nebulosity. The spatial relationship of the X-ray and radio emissions is remarkably similar to extended structure seen around the Vela pulsar. The combined Chandra and RXTE pulsar spectrum is well-fitted by an absorbed power-law model with column density N(sub H) = (1.7 +/- 0.3) x 10(exp 22) / sq cm and photon index Gamma = 1.0 +/- 0.2; it implies that the Chandra point-source flux is virtually 100% pulsed. For a distance of 10 kpc, the X-ray luminosity of PSR J2022+3842 is L(sub x){2-1O keV) = 7.0 x 10(exp 33) erg/s. Despite being extraordinarily energetic, PSR J2022+3842 lacks a bright X-ray wind nebula and has an unusually low conversion efficiency of spin-down power to X-ray luminosity, Lx/E = 5.9 X 10(exp-5).

Arzoumanian, Zaven↗