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Remillard, Ronald A.

Publications and source records attributed to Remillard, Ronald A..

17 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

STROBE-X: A Probe-Class Mission for X-Ray Spectroscopy and Timing on Timescales from Microseconds to Years

We describe the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probe-class mission concept that will provide an unprecedented view of the X-ray sky, performing timing and spectroscopy over both a broad energy band (0.2-30 keV) and a wide range of timescales from microseconds to years. STROBE-X comprises two narrow-field instruments and a wide field monitor. The soft or low-energy band (0.2-12 keV) is covered by an array of lightweight optics (3-m focal length) that concentrate incident photons onto small solid-state detectors with CCD-level (85-175 eV) energy resolution, 100 ns time resolution, and low background rates. This technology has been fully developed for NICER and will be scaled up to take advantage of the longer focal length of STROBE-X. The higher-energy band (2-30 keV) is covered by large-area, collimated silicon drift detectors that were developed for the European LOFT mission concept. Each instrument will provide an order of magnitude improvement in effective area over its predecessor (NICER in the soft band and RXTE in the hard band). Finally, STROBE-X offers a sensitive wide-field monitor (WFM), both to act as a trigger for pointed observations of X-ray transients and also to provide high duty-cycle, high time-resolution, and high spectral-resolution monitoring of the variable X-ray sky. The WFM will boast approximately 20 times the sensitivity of the RXTE All-Sky Monitor, enabling multi-wavelength and multi-messenger investigations with a large instantaneous field of view. This mission concept will be presented to the 2020 Decadal Survey for consideration.

Ray, Paul S.↗
NASA NTRS2011

The Extreme Spin of the Black Hole in Cygnus X-1

The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observations. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole s accretion disk by fitting its thermal continuum spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-1 contains a near-extreme Kerr black hole with a spin parameter a* > 0.95 (3(sigma)). For a less probable (synchronous) dynamical model, we find a. > 0.92 (3 ). In our analysis, we include the uncertainties in black hole mass, orbital inclination angle, and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk s low luminosity.

Gou, Lijun↗
NASA NTRS2011

The Extreme Spin of the Black Hole Cygnus X-1

Remarkably, an astronomical black hole is completely described by the two numbers that specify its mass and its spin. Knowledge of spin is crucial for understanding how, for example, black holes produce relativistic jets. Recently, it has become possible to measure the spins of black holes by focusing on the very inner region of an accreting disk of hot gas orbiting the black hole. According to General Relativity (GR), this disk is truncated at an inner radius 1 that depends only on the mass and spin of the black hole. We measure the radius of the inner edge of this disk by fitting its continuum X-ray spectrum to a fully relativistic model. Using our measurement of this radius, we deduce that the spin of Cygnus X-1 exceeds 97% of the maximum value allowed by GR.

Gou, Lijun↗
NASA NTRS2010

AXTAR: Mission Design Concept

The Advanced X-ray Timing Array (AXTAR) is a mission concept for X-ray timing of compact objects that combines very large collecting area, broadband spectral coverage, high time resolution, highly flexible scheduling, and an ability to respond promptly to time-critical targets of opportunity. It is optimized for sub-millisecond timing of bright Galactic X-ray sources in order to study phenomena at the natural time scales of neutron star surfaces and black hole event horizons, thus probing the physics of ultra-dense matter, strongly curved spacetimes, and intense magnetic fields. AXTAR s main instrument, the Large Area Timing Array (LATA) is a collimated instrument with 2 50 keV coverage and over 3 square meters effective area. The LATA is made up of an array of super-modules that house 2-mm thick silicon pixel detectors. AXTAR will provide a significant improvement in effective area (a factor of 7 at 4 keV and a factor of 36 at 30 keV) over the RXTE PCA. AXTAR will also carry a sensitive Sky Monitor (SM) that acts as a trigger for pointed observations of X-ray transients in addition to providing high duty cycle monitoring of the X-ray sky. We review the science goals and technical concept for AXTAR and present results from a preliminary mission design study

Ray, Paul S.↗
NASA NTRS2005

The Extreme Spin of the Black Hole in Cygnus X-1

The compact primary in the X-ray binary Cygnus X-1 was the first black hole to be established via dynamical observatIOns. We have recently determined accurate values for its mass and distance, and for the orbital inclination angle of the binary. Building on these.results, which are based on our favored (asynchronous) dynamical model, we have measured the radius of the inner edge of the black hole's accretion disk by fitting its thermal continuum.spectrum to a fully relativistic model of a thin accretion disk. Assuming that the spin axis of the black hole is aligned with the orbital angular momentum vector, we have determined that Cygnus X-I contains a near-extreme Kerr black hole with a spin parameter a* > 0.95 (3(sigma)). For a less probable (synchronous) dynamIcal model, we find a* > 0.92 (3(sigma)). In our analysis, we include the uncertainties in black hole mass orbital inclination angle and distance, and we also include the uncertainty in the calibration of the absolute flux via the Crab. These four sources of uncertainty totally dominate the error budget. The uncertainties introduced by the thin-disk model we employ are particularly small in this case given the extreme spin of the black hole and the disk's low luminosity.

Gou, Lijun↗
NASA NTRS2000

Spectral and Timing Investigations of Dwarf Novae Selected in Hard X-Rays

There are 9 dwarf novae (DN) among the 43 cataclysmic variables (accreting white dwarfs in close binary systems) that were detected during the HEAO-1 all-sky X-ray survey (1977-1979). On the other hand, there are roughly one hundred dwarf novae that are closer and/or optically brighter and yet they were not detected as hard X-ray sources. Two of the HEAO-1 DN show evidence for X-ray pulsations that imply strong magnetic fields on the white dwarf surface, and magnetic CVs are known to be strong X-ray sources. However, substantial flux in hard X-rays may be caused by non-magnetic effects, such as an optically thin boundary layer near a massive white dwarf. We proposed RXTE observations to measure plasma temperatures and to search for X-ray pulsations. The observations would distinguish whether these DN belong to one of (rare) magnetic subclasses. For those that do not show pulsations, the observations support efforts to define empirical relations between X-ray temperature, the accretion rate, and the mass of the white dwarf. The latter is determined via optical studies of the dynamics of the binary constituents.

Thorstensen, John↗
NASA NTRS2000

BL-Lacs in X-Ray Outburst

We conducted a multifrequency campaign for the TeV blazar Markarian 421 in 1998 April. The campaign started from a pronounced high-amplitude flare recorded by BeppoSAX and Whipple; the Advanced Satellite for Cosmology and Astrophysics (ASCA) observation started three days later. In the X-ray data, we detected multiple flares, occurring on timescales of about one day. ASCA data clearly reveal spectral variability. The comparison of the data from ASCA, the Extreme Ultraviolet Explorer, and the Rossi X-Ray Timing Explorer indicates that the variability amplitudes in the low-energy synchrotron component are larger at higher photon energies. In TeV and gamma-rays, large intraday variations-which were correlated with the X-ray flux-were observed when results from three Cerenkov telescopes were combined. The rms variability of TeV and gamma-rays was similar to that observed in hard X-rays, above ten keV. The X-ray light curve reveals flares that are almost symmetric for most cases, implying that the dominant timescale is the light crossing time through the emitting region. The structure function analysis based on the continuous X-ray light curve of seven days indicates that the characteristic timescale is approx. 0.5 days. The analysis of ASCA light curves in various energy bands appears to show both soft (positive) and hard (negative) lags. These may not be real, as systematic effects could also produce these lags, which are all much smaller than an orbit. If the lags of both signs are real, these imply that the particle acceleration and X-ray cooling timescales are similar.

Remillard, Ronald A.↗
NASA NTRS1997

ROSAT Observations of a New X-ray Transient in the Small Magellanic Cloud

We describe ROSAT observations of a new X-ray transient and its probable optical companion in the Small Magellanic Cloud, The transient, designated RX J0117.6-7330, appeared at a position approx. 5 southeast of the X-ray pulsar, SMC X-1, in 1992 October 1-2 PSPC observations centered on the pulsar. It was detected again in a similar observation 246 days later at a counting rate diminished by a factor of 270, which corresponds to an average e-folding decay time of 44 days. No periodic pulsations have been detected. The average 1992 flux level would be produced by a source radiating isotropically with a luminosity of 1.6 x 10(exp 37) (D/50 kpc)(exp 2) ergs 1/s in the energy range 0.2-2.5 keV. The 5 radius positional error circle includes the probable optical counterpart in the form of a magnitude V = 14.2 star with the spectral characteristics of type Be.

Clark, George W.↗
NASA NTRS1997

ROSAT Observations of a New X-ray Transient in the Small Magellanic Cloud

We describe ROSAT observations of a new X-ray transient and its probable optical companion in the Small Magellanic Cloud. The transient, designated RX J0117.6-7330, appeared at a position approximately 5 min southeast of the X-ray pulsar, SMC X-1, in 1992 October 1-2 PSPC observations centered on the pulsar. It was detected again in a similar observation 246 days later at a counting rate diminished by a factor of 270, which corresponds to an average epsilon-folding decay time of 44 days. No periodic pulsations have been detected. The average 1992 flux level would be produced by a source radiating isotropically with a luminosity of 1.6 X 10(exp 37)(D/50 kpc)(exp 2) ergs/s in the energy range 0.2-2.5 keV. The 5 sec radius positional error circle includes the probable optical counterpart in the form of a magnitude V = 14.2 star with the spectral characteristics of type Be.

Clark, George W.↗
NASA NTRS1995

The dim inner accretion disk of the quiescent black hole A0620-00

We observed the X-ray nova A0620-00 with the Hubble Space Telescope (HST) Faint object Spectrograph 16 yr after its 1975 outburst. We present a single spectrum (1250-4750 A), which is approximately an average over a full 7.8 hr orbital cycle of the source. The continuum can be fitted approximately by a blackbody model with T = 9000 K and a small projected source area, which is approximately 1 % of the expected area of the accretion disk. AS0620-00 is faint in the far-UV band; its luminosity is comparable to the luminosity of the quiescent dwarf-nova accretion disk (i.e., excluding the white dwarf). By analogy with dwarf novae, the optical luminosity of the disk (M(sub nu) approximately = 7) and the orbital period of A0620-00 imply that the rate of mass transfer onto the outer disk in M(sub d) approximately 10(exp -10) solar mass/yr. We also observed A0620-00 with the ROSAT PSPC X-ray detector for 3 x 10(exp 4) s and detected a faint source (5 sigma) at the location of the X-ray nova. For an assumed blackbody spectrum the source temperature and luminosity are approximately 0.16 keV and 6 x 10(exp 30) ergs/s, respectively (d = 1 kpc). This luminosity implies that the rate of mass transfer into the black hole is extraordinarily small: M(sub BH) less than 5 x 10(exp -15) solar mass/yr. The much larger mass transfer rate onto the outer disk, and the UV/X-ray faintness of the inner disk confirm key predictions of the disk instability model for the nova outburst of A0620-00 published by Huang and Wheeler and by Mineshige and Wheeler.

Mcclintock, Jeffrey E.↗
NASA NTRS1995

Observations of the X-ray Nova GRO J0422+32. 1: Outburst and the decay to quiescence

We present optical photometry and spectroscopy and Burst and Transient Source Experiment (BATSE) observations of the X-ray nova GRO J0422+32, obtained during outburst and its subsequent decay to quiescence. Although the X-ray and optical properties of GRO J0422+32 are broadly similar to those of other X-ray novae, it is unique in several respects. The unusually protracted decay to quiescence of the optical light curve has been punctuated by at least two minioutbursts of approximately 4 mag. The BATSE and optical outbursts are each separated by approximately 120 days. We find that the optical luminosity of GRO J0422+32 during the primary outburst is dominated by reprocessing of E greater than 10 keV X-rays. In contrast, the optical minioutbursts are most likely generated by an intrinsically bright disk rather than X-ray reprocessing: they do not appear to have any X-ray counterparts. Extremely broad (up to 6000 km/s FWZI) absorption lines have also been observed during both primary outbursts and minioutbursts. During the second minioutburst, H-alpha and H-beta emission was observed superposed on redshifted absorption features. We find that the interoutburst light curve of GRO J0422+32 may be inconsistent with an accretion disk instability as the origin of the minioutbursts. Finally, a transient 5.1/10.2 hr modulation, which may be related to the orbital period, has been observed during roughly half of our observations. However, confirmation of the orbital period must await observations in quiescence.

Callanan, Paul J.↗
NASA NTRS1994

Quiescent accretion disks in black hole X-ray novae

We present detailed time-resolved spectroscopy of the Balmer emission lines from two black hole binary systems in quiescence, A0620-00 and Nova Muscae 1991. We find extraordinary similarities between the two systems. There are 30-40 km/s velocity variations of the emission lines over the orbital period, the phases of which are not aligned with the expected phase of the motion of the compact primary. Detailed modeling of both systems is complicated by variable hot spot components, regions of optical thickness, and intermittent excess emission in the blue line wings of the H-alpha lines. Both sources also display low velocities at the outer edge of the accretion disk, implying a large primary Roche lobe and extreme mass ratios. These complications suggest that although simple optically thin, Keplerian alpha-disk models provide a useful parameterization of emission lines from these systems, the straightforward physical models they imply should be treated with great caution.

Orosz, Jerome A.↗
NASA NTRS1994

1H 1752 + 081: An eclipsing cataclysmic variable with a small accretion disk

We announce the discovery of an eclipsing nova-like cataclysmic variable (CV) as the optical counterpart to the HEAO 1 X-ray source 1H1752 + 081. This CV has an orbital period of 1.882801 hr, a high equivalent width of H-beta, and an average m(sub v) of 16.4 out of the eclipse. A geometric model is constructed from observations of the eclipse ingress and egress in many optical bandpasses. The broad-band emission originates primarily in two regions; the disk/accretion stream 'hot spot' and a compact central component, which may be a spot on the white dwarf surface, the entire white dwarf surface or the boundary layer between the accretion disk and the white dwarf surface. Based on the durations and offsets of the two eclipses we determined the mass ratio q = 2.5 +/- 0.6 and the angle of inclination i = 77 deg +/- 2 deg. If the central component is the entire white dwarf surface the masses of the stars are M(sub 1) = 0.80 +/- 0.06 solar masses and M(sub 2) = 0.32 +/- 0.06 solar masses. The disk is faint and small (R(sub D) = 0.25 +/- 0.05 r(sub L1), where r(sub L1) is the distance from the primary to the L(sub 1) point), compared to other eclipsing CVs. The small disk may result from the removal of angular momentum from the accretion disk by the magnetic field of the white dwarf; this CV may be a DQ Her type with a slowly rotating white dwarf. The emission-line velocities do not show the 'Z-wave' expected from the eclipse of a Keplerian accretion disk, nor do they have the correct phasing to originate near the white dwarf. The most likely origin of the line emission is the hot spot. The secondary star is visible at wavelengths greater than or equal to 6000 A during eclipse. We estimate a spectral type approximately M6 which, together with the observed m(sub 1) = 16.94 during eclipse, results in a distance estimate of 150 +/- 27 pc.

Silber, Andrew D.↗
NASA NTRS1992

Evidence for a black hole in the X-ray binary Nova Muscae 1991

Optical photometry and spectroscopy of the X-ray Nova Muscae 1991 in quiescence reveal an orbital period of 10.398 +/- 0.014 hr and an absorption-line velocity curve consistent with a sinusoidal modulation at a half-amplitude of 409 +/- 18 km/s. The spectral type of the secondary star is in the range K0 V to K4 V. The value of the mass function, 3.1 +/- 0.4 solar mass, is a conservative lower limit on the mass of the compact primary and suggests that the primary is a black hole. Further considerations of the binary inclination angle and the mass of the secondary strengthen the black hole model. The folded light curves in the I band and the B + V band resemble ellipsoidal variations, with an additional brightening near one of the maxima in the B + V band. The orbital period is 1.4 percent shorter than the photometric period observed during outburst, as expected if the outburst modulations are analogs of 'superhumps' in dwarf novae. In quiescence, the optical properties of the X-ray binary Nova Muscae 1991 bear a striking resemblance to the black hole binary A0620-00, which extends the basis of similarity that was demonstrated during outburst at X-ray and optical wavelengths.

Remillard, Ronald A.↗
NASA NTRS1991

The X-ray cooling flow in the cluster of galaxies around PKS 2354-35

The identification of the bright, hard X-ray source 4U 0009-33 = 3A 2356-341 = 1H 2355-350 is presently confirmed on the basis of Exosat CMA detector measurements of position and spatial extent. On the basis of these X-ray observations, a strong accretion flow is deduced; the luminosity and core radius imply a central density of at least 0.008/cu cm. The central cooling time is not greater than 5 billion yr, and the mass accretion rate is about 320 solar masses/yr.

Schwartz, Daniel A.↗