Engineering topics

Mushotzky, R. F.

Publications and source records attributed to Mushotzky, R. F..

At least 37 records · Page 2

NASA NTRS2002

Groups and the Entropy Floor: XMM-Newton Observations of Two Groups

Using XMM-Newton spatially resolved X-ray imaging spectroscopy we obtain the temperature, density, entropy, gas mass, and total mass profiles for two groups of galaxies out to approximately 0.3 R(sub vir)(R(sub vir), the virial radius). Our density profiles agree well with those derived previously, and the temperature data are broadly consistent with previous results but are considerably more precise. Both of these groups are at the mass scale of 2x10(exp 13) M(solar mass), but have rather different properties. Both have considerably lower gas mass fractions at r < 0.3 R(sub vir), than the rich clusters. NGC2563, one of the least luminous groups for its X-ray temperature, has a very low gas mass fraction of approximately 0.004 inside 0.1 R(sub vir), which increases with radius. NGC4325, one of the most luminous groups at the same average temperature, has a higher gas mass fraction of 0.02. The entropy profiles and the absolute values of the entropy as a function of virial radius also differ, with NGC4325 having a value of approximately 100 keV cm(exp -2) and NGC2563 a value of approximately 300 keV cm(exp -2) at r approximately 0.1 R(sub vir). For both groups the profiles rise monotonically with radius and there is no sign of an entropy 'floor'. These results are inconsistent with pre-heating scenarios that have been developed to explain a possible entropy floor in groups, but are broadly consistent with models of structure formation that include the effects of heating and/or the cooling of the gas. The total entropy in these systems provides a strong constraint on all models of galaxy and group formation, and on the poorly defined feedback process that controls the transformation of gas into stars and thus the formation of structure in the universe.

Mushotzky, R. F.↗

NASA NTRS2001

The Detection of Circumnuclear X-Ray Emission from the Seyfert Galaxy NGC 3516

We present the first high-resolution, X-ray image of the circumnuclear regions of the Seyfert 1 galaxy NGC 3516, using the Chandra X-ray Observatory (CXO). All three of the CXO observations reported were performed with one of the two grating assemblies in place, and here we restrict our analysis to undispersed photons (i.e. those detected in the zeroth-order). A previously-unknown X-ray source is detected approximately 6 arcsec (1.1h(sub 75)(exp -1) kpc) NNE of the nucleus (position angle approximately 29 degrees) which we designate CXOU 110648.1 + 723412. Its spectrum can be characterized as a power law with a photon index (Gamma) approximately 1.8 - 2.6, or as thermal emission with a temperature kT approximately 0.7 - 3 keV. Assuming a location within NGC 3516, isotropic emission implies a luminosity L approximately 2 - 8 x 10(exp 39)h(sub 75)(exp-2) erg s(exp -1) in the 0.4 - 2 keV band. If due to a single point source, the object is super-Eddington for a 1.4 solar mass neutron star. However, multiple sources or a small, extended source cannot be excluded using the current data. Large-scale extended S-ray emission is also detected out to approximately 10 arcsec (approximately 2h(sub 75)(exp -1) kpc) from the nucleus to the NE and SW, and is approximately aligned with the morphologies of the radio emission and extended narrow emission line region (ENLR). The mean luminosity of this emission is 1 - 5 x 10(exp 37)h(sub 75)(exp -2) erg s(exp -1) arcsec(exp -2), in the 0.4 - 2 keV band. Unfortunately the current data cannot usefully constrain its spectrum. These results are consistent with earlier suggestions of circumnuclear X-ray emissi in NGC 3516 based on ROSAT observations, and thus provide the first clear detection of extended X-ray emission in a Seyfert 1.0 galaxy. If the extended emission is due to scattering of the nuclear X-ray continuum, then the pressure in the X-ray emitting gas is at least two orders of magnitude too small to provide the confining medium for the ENLR clouds.

George, I. M.↗

NASA NTRS2001

Suzaku Observation of Two Ultraluminous X-Ray Sources in NGC 1313

A study was made of two ultraluminous X-ray soures (ULXs) in the nearby face-on, late-type Sb galaxy NGC 1313 using data from Suzaku, the 5th Japanese X-ray satellite. Within the 90 ks observation, both sources named X-1 and X-2 exhibited luminosity change by about 50%. The 0.4-10 keV X-ray luminosity was measured to be 2.5 x 10(exp 40) erg per second and 5.8 x 10 erg per second for X-1 and X-2, respectively, requiring a black hole of 50-200 solar mass in order not to exceed the Eddingtion limit. For X-1: the spectrum exhibited a strong power-law component with a high energy cutoff which is thought to arise from strong Comptonization by a disk corona, suggesting the source was in a very high state. Absorption line features with equivalent widths of 40-80 eV found at 7.0 keV and 7.8 keV in the X-1 spectrum support the presence of a highly ionized plasma and a high mass accretion rate on the system. Oxygen abundance of the NGC 1313 circumstellar matter toward X-1 was found to be subsolar, viz. O/H = (5.0 plus or minus 1.0) x 10(exp -4). The spectrum of X-2 in fainter phase is best represented by a multicolor disk blackbody model with T (sub in) = 1.2-1.3 keV and becomes flatter as the flux increases; the source is interpreted to be in a slim disk state.

Mizuno, T.↗

NASA NTRS2000

The Origin of the X-Ray and Ultraviolet Emission in NGC 7469

We present a spectral analysis of a approx 30 day, near-continuous observation of the Seyfert 1 galaxy NGC 7469 with RXTE. Daily integrations show strong spectral changes during the observation. Our main result is that we find the X-ray spectral index to be correlated with the UV flux. Furthermore, the broadband X-ray photon flux is also correlated with the UV continuum. These correlations point toward a model in which the X-rays originate via thermal Comptonization of UV seed photons. Furthermore, the UV is also correlated with the extrapolation of the X-ray power law into the soft X-ray/EUV region. Our data analysis therefore reopens the possibility that the UV photons and their variability arise from reprocessing, as long as the primary source of heating is photoelectric absorption in the re-processor, rather than Compton down-scattering. A coherent picture of the X-ray/UV variability can therefore be constructed whereby absorption and reprocessing of EUV/soft X-rays in a standard accretion disk produce a variable seed photon distribution, which is in turn up-scattered into the X-ray band. We also find a significant correlation between the 2-10 keV flux and the 6.4 keV iron K-alpha line, suggesting that at least some portion of the line originates within approx. 1 light day of the X-ray continuum source. Neither the power-law photon index nor the Compton reflection component are correlated with the 2-10 keV flux. The latter is not correlated with the iron K-alpha line flux either. We do find an apparent correlation between the X-ray spectral index and the strength of the Compton reflection component. In an Appendix we show, however, that this can be produced by a combination of statistical and systematic errors. We conclude that the apparent variations in the Compton reflection component may be an artifact of these effects.

Nandra, K.↗

NASA NTRS2000

X-Ray Spectroscopy of the Cluster of Galaxies Abell 1795 with XMM-Newton

The initial results from XMM-Newton observations of the rich cluster of galaxies Abell 1795 are presented. The spatially-resolved X-ray spectra taken by the European Photon Imaging Cameras (EPIC) show a temperature drop at a radius of - 200 kpc from the cluster center, indicating that the ICM is cooling. Both the EPIC and the Reflection Grating Spectrometers (RGS) spectra extracted from the cluster center can be described by an isothermal model with a temperature of approx. 4 keV. The volume emission measure of any cool component (less than 1 keV) is less than a few % of the hot component at the cluster center. A strong O VIII Lyman alpha line was detected with the RGS from the cluster core. The O abundance of the ICM is 0.2-0.5 times the solar value. The O to Fe ratio at the cluster center is 0.5 - 1.5 times the solar ratio.

Tamura, T.↗

NASA NTRS2000

X-Ray Imaging-Spectroscopy of Abell 1835

We present detailed spatially-resolved spectroscopy results of the observation of Abell 1835 using the European Photon Imaging Cameras (EPIC) and the Reflection Grating Spectrometers (RGS) on the XMM-Newton observatory. Abell 1835 is a luminous (10(exp 46)ergs/s), medium redshift (z = 0.2523), X-ray emitting cluster of galaxies. The observations support the interpretation that large amounts of cool gas are present in a multi-phase medium surrounded by a hot (kT(sub e) = 8.2 keV) outer envelope. We detect O VIII Ly(alpha) and two Fe XXIV complexes in the RGS spectrum. The emission measure of the cool gas below kT(sub e) = 2.7 keV is much lower than expected from standard cooling-flow models, suggesting either a more complicated cooling process than simple isobaric radiative cooling or differential cold absorption of the cooler gas.

Peterson, J. R.↗

NASA NTRS2000

Constraints on Cosmological Parameters From The Sunyaev-Zel'dovich Effect and Thermal Bremsstrahlung

We discuss the possibility of constraining cosmological parameters using the Sunyaev-Zel'dovich (SZ) effect and thermal bremsstrahlung caused by intra-cluster gas in clusters of galaxies. The new generation of X-ray satellites and ground based interferometers dedicated to SZ observations will enable one to reduce uncertainties in these measurements, and thus make this method potentially quite promising in the near future. The importance of this method is that, unlike most other methods, it is based on physical principles, no 'standard candles' or 'rulers' needed. We estimate the accuracy achievable in the determination of the matter density, OMEGA(sub m), the cosmological constant, OMEGA(sub LAMBDA), and the Hubble constant, h, using the redshift dependence of the angular diameter distance derived from observations in the near future. We demonstrate that constraints from the angular diameter distance are orthogonal to those from Cosmic Microwave Background (CMB) fluctuations in the parameter space defined by OMEGA(sub m), OMEGA(sub LAMBDA), and h. Assuming a statistical error of five percent in the angular diameter distance for each cluster in a sample of five hundred clusters, we show that the redshift dependence of the angular diameter distance combined with constraints from CMB fluctuations can put stringent constraints on OMEGA(sub m) (+/- 0.03), OMEGA(sub LAMBDA) (+/- 0.03) and h (+/- 0.03, 3(sigma) errors). We also show that, with as few as 50 clusters between redshifts 0.01 and 1.5 with an assumed 10% statistical error in the angular diameter distance determination, one can distinguish between models with zero cosmological constant and spatially flat models with a cosmological constant with high confidence level (independently from the supernova results) and put meaningful constraints on OMEGA(sub m) (+/- 0.01), OMEGA(sub LAMBDA) (+/- 0.01) and h (+/- 0.01, 3(sigma) errors). With the expected advances in observational technology, we will be limited by systematic errors. We discuss the sources of systematic errors and how they can be reduced.

Molnar, S. M.↗

NASA NTRS2000

X-Ray Constraints on the Warm-Hot Intergalactic Medium

Three observational constraints can be placed on a warm-hot intergalactic medium (WHIM) using ROSAT Position Sensitive Proportional Counter (PSPC) pointed and survey data, the emission strength, the energy spectrum, and the fluctuation spectrum. The upper limit to the emission strength of the WHIM is 7.5 +/- 1.0 keV/(s*sq cm*sr*keV) in the 3/4 keV band, an unknown portion of which value may be due to our own Galactic halo. The spectral stape of the WHIM emission can be described as thermal emission with logT = 6.42, although the true spectrum is more likely to come from a range of temperatures. The values of emission strength and spectral shape are in reasonable agreement with hydrodynamical cosmological models. The autocorrelation function in the 0.44 keV < E < 1.21 keV band range, w(theta), for the extragalactic soft X-ray background (SXRB) which includes both the WHIM and contributions due to point sources, is approx. < 0.002 for 10 min < 0 < 20 min in the 3/4 keV band. This value is lower than the Croft et al. (2000) cosmological model by a factor of approx. 5, but is still not inconsistent with cosmological models. It is also found that the normalization of the extragalactic power law component of the soft X-ray background spectrum must be 9.5 +/- 0.9 keV/(s*sq cm*sr*keV) to be consistent with the ROSAT All-Sky Survey.

Kuntz, K. D.↗

NASA NTRS1995

The origin of the soft X-ray excess in the Seyfert 2 galaxy NGC 2110

We present and discuss an X-ray image and a medium-resolution X-ray spectrum of the Seyfert 2 galaxy NGC 2110 obtained with the high-resolution imager (HRI) on ROSAT (0.1-2.4 keV) and Goddard's Broad Band X-ray Telescope (BBXRT; 0.3-11 keV), respectively. Spatially resolved soft X-ray emission, which peaks 4 arcsecs to the north of the nucleus and near the position of the highest excitation optical emission line gas is seen in the HRI observation. The extent has a flux of approximately 3 x 10(exp -13) ergs/sq cm/s and accounts for 11% +/- 3% of the total 0.1-2.4 keV flux. To model the BBXRT spectrum, a soft excess component is required which has a flux of approximately 3.5 x 10(exp -13) ergs/sq cm/s and accounts for approximately 14% +/- 6% of the total 0.1-2.4 keV flux. In addition, BBXRT confirms the presence of an approximately 175 eV equivalent width Fe K alpha flourescence line in NGC 2110. Because of the good agreement between their fluxes, we propose that the soft excess in NGC 2110 is due to leakage of the X-ray continuum through a patchy absorber. The temperature of the gas responsible for the soft excess is too high to be accounted for by local shock heating. In order to explain the soft excess and extent as either scattered continuum X-rays or flourescence from gas photoionized by the nuclear source, the hard X-rays must be emitted anisotropically. However, the soft excess and extent can be well modeled as thermal emission from a hot, outflowing wind, which may also be responsible for confirming at least some portion of the optical narrow line-emitting clouds.

Weaver, K. A.↗

NASA NTRS1995

Joint ROSAT-Compton GRO observations of the X-ray bright Seyfert galaxy IC 4329A

We report a simultaneous ROSAT and Gamma Ray Observatory (GRO) observation of the X-ray-bright Seyfert galaxy IC 4329A. For the GRO Oriented Scintillation Spectrometer Experiment (OSSE) detector, we also present the sum of the data for this and earlier observations. The overall spectrum is very well described as a power law with an energy spectral index of approximately 1 absorbed at low energies plus a strong Compton reflection component, typical for Seyfert 1 galaxies. The low energy absorption can be well described by a sum of a neutral column density of approximately 3 x 10(exp 21)sq cm, most of which is associated with the edge-on galactic disk of IC 4329A, plus an edgelike feature at approximately 700 eV; this feature implies either complex absorption (due to additional ionized material, or due to a partial covering), or a soft excess. The data only weakly constrain the presence of a high-energy cutoff in the underlying power law; they are compatible with an exponential cutoff at any energy E(sub c) approximately greater than 100 keV. The relative steepness of the OSSE data, with the power-law energy index of 1.6 +/- 0.2, can be accounted for entirely by the contribution of the high-energy tail of the reflection component when E(sub c) approaches infinity. (We find that the definite cutoff at an energy E(sub c)approximately 130 keV suggested in the recently published analysis of the OSSE data for this subject is due to a data reduction error.) Including nonsimultaneous Ginga observations with 2 keV fluxes matching well that of ROSAT gives us likely broad-band X-ray/gamma-ray spectra of the object from approximately 0.1 keV up to several hundred keV. We also report the ROSAT spectrum of the companion object to the Seyfert galaxy, the elliptical galaxy IC 4329.

Madejski, G. M.↗

NASA NTRS1995

Calibrating the broad band X-ray telescope

This paper describes the calibration of the two solid-state Si(Li) X-ray detectors and the X-ray telescopes that flew as part of Goddard Space Flight Center's Broad Band X-Ray Telescope (BBXRT) experiment on board the space shuttle Columbia in 1990 December. During the 9 day shuttle mission, BBXRT performed approximately 150 observations of 82 celestial sources. The content of the archive is summarized here. Although BBXRT had a relatively short life, it stands as a milestone in X-ray astronomy as being the first instrument to offer moderate spectral resolution over a wide bandpass (0.3-12.0 keV). Among other things, this paper discusses the effective area calibration of the instrument, the flux calibration and flux corrections for off-axis observations, the detector background, and optimal background subtraction techniques. The on-axis effective area calibration for the central detector elements was performed using data from the Crab Nebula, while other carefully selected targets were used for calibration of the outer detector elements. The remaining systematic uncertainties in the effective area calibration for point sources observed both on and off axis are generally less than 5%-10%. The energy scale is known to better than 0.5% at 6.0 keV for both detectors. The results presented here have an impact on the calibration of other medium resolution X-ray experiments such as the CCDs on board ASCA (Astro-D) as well as the Advanced X-Ray Astrophysics Facility detectors.

Weaver, K. A.↗

NASA NTRS1995

Granularity of the Diffuse Background Observed

First results are reported from a program for measuring the field-to-field fluctuation level of the cosmic diffuse background by using differences between the two background positions of each deep exposure with the High Energy X-ray Timing Experiment (HEXTE) instrument on the Remote X Ray Timing Explorer (RXTE). With 8 million live seconds accumulated to date a fluctuation level on the 15-25 keV band is observed which is consistent with extrapolations from the High Energy Astrophysical Observatory-1 (HEAO-1) measurements. Positive results are expected eventually at higher energies. Models of (active galactic nuclei) AGN origin will eventually be constrained by this program.

Gruber, D. E.↗

NASA NTRS1994

New X-ray spectral observations of NGC 4151 with ASCA

We present new X-ray spectral data for the well-studied Seyfert galaxy NGC 4151, which was observed twice for about 20 ks each during the ASCA performance verification phase, once on 1993 May 25 and again on 1993 November 5. The source underwent complex spectral variability, and the observed 2-10 keV flux increased by a factor of 2 while the intrinsic 2-10 keV flux increased by no more than 20%. The data can be modeled with either a dual cold absorber plus a soft X-ray excess consisting of scattered continuum flux and an additional 'ultrasoft' X-ray excess component, or a warm absorber plus scattered continuum flux. There is evidence for variability at less than 1 keV energies that is unrelated to the 2-10 keV continuum. For an ionized-absorber description of NGC 4151, changes in the ionization state of the absorber appear to be unrelated to changes in the ionizing continuum.

Weaver, K. A.↗

NASA NTRS1994

Detections of hard X-ray emissions from bright early-type galaxies with ASCA

Five bright elliptical galaxies in the Virgo Cluster, NGC 4365, NGC 4374 (M84), NGC 4406 (M86), NGC 4472 (M49), and NGC 4636, were observed with ASCA. In addition to the extended thermal X-ray emission of temperature kT approximately 1 keV, harder X-rays with color temperature kT greater than or equal to 2 keV were detected from all of them. The 2-10 keV luminosities of this hard component for the five galaxies, integrated within 5 min, are distributed within a relatively narrow range of (1-4) x 10(exp 40) ergs/s. The hard X-ray component is primarily attributed to the integrated emission from discrete X-ray sources. In NGC 4406 and NGC 4374 the data indicate that the hard component is contributed additionally by foreground/background emission from the hot intracluster medium (ICM) of the Virgo Cluster. The hard component of NGC 4472 seems also contributed by the Virgo ICM emission, but in this case there is evidence that the ICM brightness is locally enhanced within approximately 10 min of NGC 4472.

Matsushita, K.↗

NASA NTRS1994

Temperature and iron abundance variation of the gas in the Perseus cluster

We present the first two-dimensional map of the temperature and iron abundance in the Perseus cluster. Analysis of spectra obtained using the Gas Imaging Spectrometer on ASCA shows nonaxisymmetric variations in both the temperature and iron abundance. Traveling west from the cluster center, the temperature increases to 9 keV at 20 min and then decreases rapidly to 5 keV at 40 min. There is a hot (greater than 10 keV) region to the northwest of the cluster center. The abundance is approximately constant over much of the surveyed region, but there is evidence for an increased abundance in the northwest hot area and a gradual decrease in a westerly direction.

Arnaud, K. A.↗

NASA NTRS1994

Discovery and implications of very low metal abundances in NGC 1404 and NGC 4374

We present our analysis of ASCA PV phase observations of the elliptical galaxies NGC 1404 and NGC 4374 (M84). The average metallicities in the hot gas derived from the SIS spectra are exceptionally low, Z approximately 0.15 solar, while the temperatures are 'typical,' kT approximately 0.75 keV. We also place upper limits on intrinsic column densities. The low abundances lend support to the theory of Fe enrichment of intracluster media by protogalactic Type II supernova-driven winds and raise the possibility of a fundamental connection between baryon fraction, dissipation, and abundances in elliptical galaxies.

Loewenstein, M.↗

NASA NTRS1994

ASCA observation of NGC 4636: Dark matter and metallicity gradient

We present our analysis of ASCA PV phase observation of the elliptical galaxy NGC 4636. Solid state imaging spectrometer (SIS) spectra in six concentric annuli centered on NGC 4636 are used to derive temperature, metallicity, and column density profiles for the hot interstellar medium. Outside of the central 3 min the temperature is roughly constant at approximately 0.85 keV, while the metallicity decreases from greater than 0.36 solar at the center to less than 0.12 solar at R approximately 9 min. The implications of this gradient for elliptical galaxy formation and the enrichment of intracluster gas are discussed. We derive a detailed mass profile consistent with the stellar velocity dispersion and with ROSAT position sensitive proportional counter (PSPC) and ASCA SIS X-ray temperature profiles. We find that NGC 4636 becomes dark matter dominated at roughly the de Vaucouleurs radius, and, at r approximately 100 kpc, the ratio of dark to luminous matter density is approximately 80 and solar mass/solar luminosity approximately equal to 150. Evidence for the presence of a cooling flow is also discussed.

Mushotzky, R. F.↗

NASA NTRS1994

A broad-band X-ray telescope observation of the black hole candidate LMC X-1

We present the spectrum of the black hole candidate LMC X-1 as observed by the Broad-Band X-ray Telescope (BBXRT). The spectrum cannot be fitted by a simple model, but it requires a soft disk blackbody component and a power-law tail, confirming earlier studies. The blackbody disk component is essentially unchanged since the Ginga measurement in 1987. The implied mass of the compact object is approximately 4.7 (square root of cosine i) solar mass from the soft component fit. We report a 95% confidence detection of weak emission features at approximately 5.1 keV and approximately 7.3 keV. If the 5.1 keV feature is attributed to Fe I K-alpha at 6.39 keV, then the redshift is approximately 0.19. No quasi-periodic behavior is found in the data at this epoch.

Schlegel, Eric M.↗