Engineering topics

Remillard, R. A.

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

At least 19 records

NASA NTRS2018

A NICER Spectrum of MAXI J1535-571: Near-Maximal Black Hole Spin and Potential Disk Warping

We report on a Neutron star Interior Composition Explorer (NICER) observation of the Galactic X-ray binary and stellar-mass black hole candidate, MAXI J1535−571. The source was likely observed in an "intermediate" or "very high" state, with important contributions from both an accretion disk and hard X-ray corona. The 2.3-10 keV spectrum shows clear hallmarks of relativistic disk reflection. Fits with a suitable model strongly indicate a nearmaximal spin parameter of a = cJ/GM(exp 2) = 0.994(2) and a disk that extends close to the innermost stable circular orbit, r/r(sub ISCO) = 1.08(8) (1σ statistical errors). In addition to the relativistic spectrum from the innermost disk, a relatively narrow Fe K emission line is also required. The resolution of NICER reveals that the narrow line may be asymmetric, indicating a specific range of emission radii. Fits with a relativistic line model suggest an inner radius of r = 144 +140/-60 GM/c(exp 2) for the putative second reflection geometry; full reflection models suggest that radii a few times larger are possible. The origin of the narrow line is uncertain, but a warp likely provides the most physically plausible explanation. We discuss our results in terms of the potential for NICER to reveal new features of the inner and intermediate accretion disk around black holes.

Miller, J. M.↗

NASA NTRS2015

High-Energy Electromagnetic Offline Follow-Up of Ligo-Virgo Gravitational-Wave Binary Coalescence Candidate Events

We present two different search methods for electromagnetic counterparts to gravitational-wave (GW) events from ground-based detectors using archival NASA high-energy data from the Fermi Gamma-ray Burst Monitor (GBM) and RXTE All-sky Monitor (ASM) instruments. To demonstrate the methods, we use a limited number of representative GW background noise events produced by a search for binary neutron star coalescence over the last two months of the LIGO-Virgo S6/VSR3 joint science run. Time and sky location provided by the GW data trigger a targeted search in the high-energy photon data. We use two custom pipelines: one to search for prompt gamma-ray counterparts in GBM, and the other to search for a variety of X-ray afterglow model signals in ASM. We measure the efficiency of the joint pipelines to weak gamma-ray burst counterparts, and a family of model X-ray afterglows. By requiring a detectable signal in either electromagnetic instrument coincident with a GW event, we are able to reject a large majority of GW candidates. This reduces the signal-to-noise ratio of the loudest surviving GW background event by around 15-20 percent.

gamma-ray burst: general↗

NASA NTRS2012

Disc-jet Coupling in the 2009 Outburst of the Black Hole Candidate H1743-322

We present an intensive radio and X-ray monitoring campaign on the 2009 outburst of the Galactic black hole candidate X-ray binary H1743-322. With the high angular resolution of the Very Long Baseline Array, we resolve the jet ejection event and measure the proper motions of the jet ejecta relative to the position of the compact core jets detected at the beginning of the outburst. This allows us to accurately couple the moment when the jet ejection event occurred with X-ray spectral and timing signatures. We find that X-ray timing signatures are the best diagnostic of the jet ejection event in this outburst, which occurred as the X-ray variability began to decrease and the Type C quasi-periodic oscillations disappeared from the X-ray power density spectrum. However, this sequence of events does not appear to be replicated in all black hole X-ray binary outbursts, even within an individual source. In our observations of H1743-322, the ejection was contemporaneous with a quenching of the radio emission, prior to the start of the major radio flare. This contradicts previous assumptions that the onset of the radio flare marks the moment of ejection. The jet speed appears to vary between outbursts with a positive correlation outburst luminosity. The compact core radio jet reactivated on transition to the hard intermediate state at the end of the outburst and not when the source reached the low hard spectral state. Comparison with the known near-infrared behaviour of the compact jets suggests a gradual evolution of the compact jet power over a few days near beginning the and end of an outburst

Miller-Jones, J. C. A.↗

NASA NTRS1999

A Multiwavelength Study of the Extreme AGN J2310-437

We present new X-ray, radio, and optical data for the unusual galaxy/cluster system J2310-437. Our results confirm the presence of an active nucleus and suggest an interpretation as an anomalous BL Lac object of bulk relativistic Doppler factor <2, with an optically deficient radio to X-ray spectrum. The radio, optical, and soft X-ray flux densities could lie along a single power-law function, lacking the curvature typical of BL Lac objects. Compared with other known sources that may have comparable multi-frequency spectra, J2310-437 is the most extreme. Its low isotropic optical/Ultraviolet (UV) radiation is consistent with the intensity of external photons governing the electron spectral break through Compton cooling; in this source the external photon density would be too low to produce a spectral break below the X-ray.

Worrall, D. M.↗

NASA NTRS1995

A serach for 'failed clusters' of galaxies

We describe a search for a new type of object - large clouds of hot gas with no visible galaxies - which we call failed clusters of galaxies. We calculate the expected X-ray luminosity, temperature, and angular diameter of such objects as a function of total cloud mass and convert the results to expected X-ray fluxes from failed clusters at different redshifts. Using the Einstein Imaging Proportional Counter (IPC) database, we establish a strategy to search for candidate failed clusters. From this initial screening of 1435 IPC fields, 17 candidates are selected for more detailed analysis, which indicates that 10 of these are very probably extended X-ray sources. Optical follow-up on the 10 prime candidates finds eight clusters of galaxies (including six reproted for the first time in this paper), one stellar identification, and one without an obvious optical counterpart (the candidate with the weakest evidence for X-ray extent). Investigation of several candidates with less evidence for X-ray extent yields two additional new clusters of galaxies. A conservative comparison of our results with the Einstein Extended Medium Sensitivity Survey demonstrates that failed clusters are a relatively unimportant contributor to the mass density of the universe. Our inability to find failed clusters is consistent with the hierarchical clustering scenario for the formation of galaxies and clusters.

Tucker, W. H.↗

NASA NTRS1995

Ionization nebulae surrounding CAL 83 and other supersoft X-ray sources

We present the results of an optical search for ionized gaseous nebulae surrounding luminous, 'supersoft' X-ray sources in the Large and Small Magellanic Clouds. This relatively new and mysterious X-ray class has characteristic luminosities approximately 10(exp 37)-10(exp 38) ergs/s with effective temperatures in the range of 2-6 x 10(exp 5) K. The presence of a large flux of UV and soft X-ray photons from these objects has led to predictions of bright optical emission lines from the local interstellar medium. One such object, CAL 83 in the LMC, was known to have an associated nebula, and we quantify here the asymmetry and luminosity of this remarkable nebula. Deep images were made using narowband filters to isolate the emission lines of H alpha and (O III) (lambda 5007). In these emission lines, the nebula is detected out to distances as far as 25 pc from the central object, and the integrated luminositu in each line is of order approximately 100 solar luminosity. Model calculations of such nebulae for chemical abundances characteristic of the LMC indicate that approximately 1% of the X-ray luminosity of the central source is reprocessed into the nebular H-alpha and (O III) lambda 5007 emission lines, from which we conclude that the time-averaged X-ray luminosity of the central source, CAL 83, is greater than 3 x 10(exp 37) ergs/s. The bright inner nebula contains approximately 150 solar mass within 7.5 pc of CAL 83, which clearly indicates that the nebular material has its origin in the interstelar medium. In sharp contrast, there were null detections for nebulae associated with nine other luminous, supersoft X-ray sources in the LMC and SMC, with upper limits for the (O III) luminosity that are a factor of approximately 10 below that for CAL 83. For eight of these latter sources, we conclude that either their time-averaged luminosity is substantially below that of CAL 83, or that the local interstellar medium is much less dense. The latter effect may be enhanced by expansion of the ionized nebula during the last several million years.

Remillard, R. A.↗

NASA NTRS1995

Ionization Nebulae Surrounding CAL 83 and Other Supersoft X-ray Sources

We present the results of an optical search for ionized gaseous nebulae surrounding luminous, "supersoft" X-ray sources in the Large and Small Magellanic Clouds. This relatively new and mysterious X-ray class has characteristic luminosities approximately 10(exp 37) - 10(exp 38) ergs/s with effective temperatures in the range of 2 - 6 x 10(exp 5) K. The presence of a large flux of UV and soft X-ray photons from these objects has led to predictions of bright optical emission lines from the local interstellar medium. One such object, CAL 83 in the LMC, was known to have an associated nebula, and we quantify here the asymmetry and luminosity of this remarkable nebula. Deep images were made using narrowband filters to isolate the emission lines of H.alpha and [O III] (lamda5007). In these emission lines, the nebula is detected out to distances as far as 25 pc from the central object, and the integrated luminosity in each line is of order approximately 100 solar luminosity. Model calculations of such nebulae for chemical abundances characteristic of the LMC indicate that approximately 1% of the X-ray luminosity of the central source is reprocessed into the nebular H.alpha and [O III] lamda5007 emission lines, from which we conclude that the time-averaged X-ray luminosity of the central source, CAL 83, is greater than 3 x 10(exp 37) ergs/s. The bright inner nebula contains approximately 150 solar mass within 7.5 pc of CAL 83, which clearly indicates that the nebular material has its origin in the interstellar medium. In sharp contrast, there were null detections for nebulae associated with nine other luminous, supersoft X-ray sources in the LMC and SMC, with upper limits for the [O III] luminosity that are a factor of approximately 10 below that for CAL 83. For eight of these latter sources, we conclude that either their time-averaged luminosity is substantially below that of CAL 83, or that the local interstellar medium is much less dense. The latter effect may be enhanced by expansion of the ionized nebula during the last several million years.

Remillard, R. A.↗

NASA NTRS1994

The X-ray selected cataclysmic variables H0459 + 246 and H0857 - 242

We report the discovery of two cataclysmic variables located with the assistance of X-ray positions from the HEAO 1 Modulation Collimator and the Large-Area Sky Survey. Each case is distinguished by evidence of two periodic modulations that appear to represent the orbital period and the spin period of the white dwarf, respectively. The first case, H0459 + 246, has been observed optically during faint states (V approximately 16), in which there are spectral features of both an accretion disk and a K star. The light curves in the V and I bands are consistent with ellipsoidal variations in the secondary stars with a binary period of 9.952 hr. X-ray observations with EXOSAT reveal a strong pulsation with a period approximately 62 minutes. This result confirms an 'intermediate polar' classification for H0459 + 246. The pulsation is observed at 63.2 minutes in the optical I band. The long orbital period opens the possibility that H0459 + 246 is a relatively young intermediate polar that might evolve into a polar. The second case, H0857--242, shows radial velocity modulations at 1.78 hr along with photometric variations at a period approximately 49 minutes. The latter are observed only during the decay phase of dwarf nova outbursts (13 less than V less than 17), which apparently recur frequently. Given the lack of X-ray monitoring observations and the absence of proof that the 49 minute periodicity is coherent over long time-scales, we regard H0857--242 as a candidate intermediate polar. Photographic records from th e Harvard Observatory Plate Library further reveal superoutbursts for H0857--242 (V approximately 11). A bright X-ray source that is both an intermediate polar and a continually cycling dwarf nova may provide an effective means of measuring the time delay for the arrival of accreting matter at the white dwarf surface, relative to the onset of optical brightening.

Remillard, R. A.↗

NASA NTRS1994

1ES 1113+432: Luminous, soft X-ray outburst from a nearby cataclysmic variable (AR Ursae Majoris)

A remarkable X-ray transient from the Einstein Slew Survey, 1 ES 1113+432, is identified with a nearby, short-period cataclysmic variable. Wenzel (1993) has confirmed that the optical counterpart is the variable star, AR UMa (cataloged as 'semiregular'), erroneously reported 5.7 min southeast of the true position. One of the Einstein slew observations recorded a flux of 43 IPC counts/s, which is an order of magnitude above the flux observed from the brightest cataclysmic variables in other X-ray surveys. The outburst spectrum is extremely 'soft,' with an implied blackbody temperature of approximately 22 eV. The optical counterpart (V = 16.5) exhibits a strong UV component, TiO bands from an M star, and broadened Balmer emission lines. Optical states as bright as V approx. 13 were found on photographs from the Harvard Plate Library, confirming outburst behavior in the optical counterpart. The historical photographic record suggests that 1ES 1113+432 remains in a low-accretion state most of the time. Both of the soft X-ray spectrum and the transitions between high and low-accretion states are suggestive of the AM Her (magnetic) subclass. Photometric observations in the I band show 0.18 mag modulations at a period of 0.966 hr. These are interpreted as ellipsiodal variations in the secondary star for a binary period of 1.932 hr, which is near the lower boundary of the 'period gap' in the histogram, of orbital periods of accreting white dwarfs. Thus 1ES 1113+432 provides the rare opportunity to study a secondary star in a cataclysmic binary that has evolved through the period gap. The optical spectral features from the secondary imply a spectral type of approximately M6 and a distance of approximately 88 pc. The peak luminosity in the soft X-ray component (unabsorbed) is then estimated to be 3 X 10(exp 33) ergs/s, assuming emission from a blackbody slab with a temperature of 22 eV. While this luminosity is higher than previous measures of the soft X-ray component, it does not exceed the amount of radiation that could be emitted from the accretion-heated surface of a white dwarf.

Remillard, R. A.↗

NASA NTRS1993

Twenty-two emission-line AGNs from the HEAO-1 X-ray survey

We report 22 emission-line AGN as bright, hard X-ray sources. All of them appear to be new classifications with the exception of one peculiar IRAS source which is a known quasar and has no published spectrum. This sample exhibits a rich diversity in optical spectral properties and luminosities, ranging from a powerful broad-absorption-line quasar to a weak nucleus embedded in a nearby NGC galaxy. Two cases confer X-ray luminosities in excess of 10 exp 47 erg/s. However, there is a degree of uncertainty in the X-ray identification for the AGN fainter than V about 16.5. Optically, several AGN exhibit very strong Fe II emission. One Seyfert galaxy with substantial radio flux is an exception to the common association of strong Fe II emission and radio-quiet AGN. The previously recognized IRAS quasar shows extreme velocities in the profiles of the forbidden lines; the 0 III pair is broadened to the point that the lines are blended. Several of these AGN show evidence of intrinsic obscuration, illustrating the effectiveness of hard X-ray surveys in locating AGN through high column density.

Remillard, R. A.↗

NASA NTRS1992

EC 19314 - 5915 - A bright, eclipsing cataclysmic variable from the Edinburgh-Cape Blue Object Survey

A deeply eclipsing cataclysmic variable, with an orbital period of 4.75 hr, has been discovered in the southern Edinburgh-Cape Blue Object Survey. The star, EC 19314 - 5915, lies close to the positional constraints of a previously unidentified HEAO-1 hard X-ray source, 1H1930 - 5989. Its optical spectrum is unusual in that it shows, apart from the emission lines characteristic of a novalike, or dwarf nova cataclysmic variable (Balmer, He I and He II), metallic absorption lines typical of a late-G star. The individual time-resolved spectra, with the tertiary absorption lines removed, show absorption reversals in the Balmer emission lines, increasing in strength for the higher series. The Balmer emission radial velocities are therefore severely distorted in comparison to the He II 4686-A emission and He I 4471-A absorption radial velocity curves. An independent distance estimate of about 600 pc is derived for EC19314 - 5915, from the spectroscopic parallax of the third star.

Buckley, D. A. H.↗

NASA NTRS1992

S-154 in the Large Magellanic Cloud - Spectral evolution from a luminous Fe II variable to a symbiotic-like star

The evolution of the emission-line Star S-154, between February and December 1988, from a low-excitation 'Fe II star' into a high-excitation state that resembles symbiotic stars, is traced. It is inferred that the spectral type of central stars do not always dominate the physical conditions in the circumstellar material and thereby determine the nebular classification. The membership of S-154 in the LMC was confirmed with a radial velocity measurement of +274 km/s. The historical light curve (1880-1990) obtained from 346 photograph plates of the Harvard Plate Library exhibits about 4 mag of variations, with an MB range of -6 to -2. No evidence was found for coherent modulations that would represent the orbital period of a symbiotic binary.

Remillard, R. A.↗

NASA NTRS1992

H0538 + 608 (= BY Camelopardalis) - An asynchronously rotating AM Herculis binary?

Evidence from a concurrent X-ray/optical observing program is presented which indicates that the orbital period of the anomalous AM Her-type cataclysmic variable H0538 + 608 (BY Cam) differs from the rotational period by 1.3 +/- 0.1 percent. This finding would explain much of the unusual behavior previously exhibited in optical photometry and polarimetry. The model proposed by Ishida et al. (1991) is developed further using observations of accretion and the primary characteristics of optical and X-ray light curves and radial velocity measures of H-alpha. An optical QPO with a period of about 30 min was seen on two nights and possible causes of it are discussed.

Silber, A.↗

NASA NTRS1991

A large radio galaxy behind the supernova remnant HB9

HB9 is a 2-deg-diameter radio shell with X-ray emission from a broad diffuse band in the interior. Within this band, a weak unresolved X-ray source coincides with the radio source 4C 46.09. To identify this source CCD I and V band pictures and a spectrum were obtained. The source is a galaxy at redshift 0.195, and is therefore only accidentally aligned with HB9. The galaxy is large and bright and has the characteristics of a cD galaxy, often found at the center of clusters. If the galaxy is centered in a cluster, some of the surrounding diffuse X-rays may also be extragalactic.

Seward, F. D.↗

NASA NTRS1991

Discovery of a long-term periodic variation in LMC X-3

The highly variable X-ray luminosity of LMC X-3 is found to be strongly modulated with a period of about 198 (or possibly about 99) days. Observations from satellites show this periodic variation. For energies of less than 13 keV, the X-ray intensity and hardness are positively correlated; for higher energies, there appears to be no correlation. Available optical photometry indicates the mean V brightness also varies by more than 1 mag with this same long-term period. The regularity of this 'clock' in LMC X-3 suggests that it may be related to an accretion-disk precession, similar to that seen in LMC X-4, Her X-1, SS 433, or possibly periodic variations in the mass-transfer rate.

Cowley, A. P.↗

NASA NTRS1991

The eclipsing AM Herculis variable H1907 + 690

The discovery is reported of an eclipsing cataclysmic variable that exhibits up to 10 percent circular polarization at optical wavelengths, securing its classification as an AM Herculis type binary. The object, H1907 + 609, was located with the guidance of X-ray positions from the HEAO 1 survey. Optical CCD photometry exhibits deep eclipses, from which is derived a precise orbital period of 1.743750 hr. The eclipse duration suggests an inclination angle about 80 deg for a main-sequence secondary star. The optical flux has been persistently faint during observations spanning 1987-1990, while the X-ray measurements suggest long-term X-ray variability. The polarization and photometric light curves can be interpreted with a geometric model in which most of the accretion is directed toward a single magnetic pole, with an accretion spot displaced about 17 deg in longitude from the projection of the secondary star on the white dwarf surface.

Remillard, R. A.↗

NASA NTRS1991

A rapid energetic X-ray flare in the quasar PKS0558 - 504

A recent observation from the Ginga satellite of the quasar PKS0558 - 504 is reported during which the X-ray flux increased by 67 percent in the space of only three minutes. There was no significant change in the spectrum. Comprehensive analysis of the data strongly indicates that this was a genuine X-ray flare originating in the quasar. The implied rate of change in luminosity in the 2-10 keV range, assuming a Hubble constant of 70 km/s/Mpc, and a cosmological deceleration parameter q0 = 0.5, is 3.2 x 10 to the 42nd erg/sq s, the highest value measured for a quasar. When photon scattering is considered, this is about 16 times greater than could be produced, with a three-minute rise time, in an isotropically emitting plasma. It is argued that the apparent luminosity must be enhanced by relativistic beaming. This is the first indication of beaming in an 'ordinary' unpolarized quasar.

Remillard, R. A.↗

NASA NTRS1991

Ginga observation of an AM Herculis type source H0538 + 608

Results from a Ginga observation of the AM Her type object H0538 + 608 are presented. During the first half of the observation (pulsing state) the source showed periodic modulations caused by the white dwarf rotation, and the modulation profile was characterized by a flat top and a flat bottom. During the second half, the source was in a remarkable flaring state and the periodic modulation disappeared. The dramatic change of the X-ray light curve is interpreted in terms of a change of accretion pattern between an eclipsing spot and a noneclipsing spot. The spectrum is well described throughout by a thin thermal model including an iron K-line with equivalent width of some hundred eV, supporting the standard model for the hard X-ray emission region. The temperature in the pulsing state was found to change with the spin phase of the white dwarf. In the flaring state, the temperature showed a positive correlation with the source luminosity.

Ishida, M.↗