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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

RXTE Observations of LMC X-1 and LMC X-3

Of all known persistent stellar-mass black hole candidates, only LMC X-1 and LMC X-3 consistently show spectra that are dominated by a soft, thermal component. We present results from long (170 ksec) Rossi X-ray Timing Explorer (RXTE) observations of LMC X-1 and LMC X-3 made in 1996 December. The spectra can be described by a multicolor disk blackbody plus an additional high-energy power-law. Even though the spectra are very soft (Gamma approximately 2.5), RXTE detected a significant signal from LMC X-3 up to energies of 50 keV, the hardest energy at which the object was ever detected. Focusing on LMC X-3 , we present results from the first year of an ongoing monitoring campaign with RXTE which started in 1997 January. We show that the appearance of the object changes considerably over its approximately 200 d long cycle. This variability can either be explained by periodic changes in the mass transfer rate or by a precessing accretion disk analogous to Her X-1.

Wilms, J.↗
NASA NTRS1998

RXTE Observations of LMC X-1 and LMC X-3

Of all known persistent stellar-mass black hole candidates, only LMC X-1 and LMC X-3 consistently show spectra that are dominated by a soft, thermal component. We present results from long (170 ksec) Rossi X-ray Timing Explorer (RXTE) observations of LMC X-1 and LMC X-3 made in 1996 December. The spectra can be described by a multicolor disk blackbody plus an additional high-energy power-law. Even though the spectra are very soft (Gamma approximately 2.5), RXTE detected a significant signal from LMC X-3 up to energies of 50 keV, the hardest energy at which the object was ever detected. Focusing on LMC X-3, we present results from the first year of an ongoing monitoring campaign with RXTE which started in 1997 January. We show that the appearance of the object changes considerably over its approximately 200d long cycle. This variability can either be explained by periodic changes in the mass transfer rate or by a precessing accretion disk analogous to Her X-1.

Wilms, J.↗
NASA NTRS1998

RXTE Observations of LMC X-1 and LMC X-3 Spectral and Temporal Evolution

Of all known persistent stellar-mass black hole candidates, only LMC X-1 and LMC X-3 consistently show spectra that are dominated by a soft, thermal component. In the past year we have conducted a monitoring campaign with RXTE (Rossi X Ray Timing Explorer) to study the short and long term behavior of these two sources. In this poster we present results from 180 ksec of continuous RXTE observation of LMS X-1 and LMC X-3 made in December 1996. The spectra can be described by a multicolor disk blackbody plus an additional high-energy power law. In addition to the results of the long observations we also present information on the long-term spectral behavior of LMC X-3 as derived from the monitoring campaign.

Wilms, Joern↗
NASA NTRS1998

LMC X-1 and LMC X-3 as Seen by RXTE

LMC X-1 and LMC X-3 are the only two black holes that are consistently seen in the soft X-ray state. We present the results from the spectral and temporal analysis of a long (150 ksec) observation of these two objects. The spectra can be well described by a disk black body plus a high energy power-law, which extends to at least 50keV. Starting in December 1996 we have also monitored these objects with RXTE in about three to four week intervals. We present the evolution of the spectral parameters of the sources from the first twenty pointings. LMC X-1 has a very stable spectrum and does not exhibit any large scale variability. On the other hand, the appearance of LMC X-3 changes considerably over its 200d long cycle. This variability can either be explained by periodic changes in the mass transfer rate or by a precessing accretion disk analogous to Her X-1.

Wilms, J.↗
NASA NTRS1985

Soft X-ray maps of the Large Magellanic Cloud (LMC)

Soft X-ray maps of the Large Magellanic Cloud (LMC) were obtained from scanning-observations with the HEAO-1 low energy detectors. Comparison of the 1/4 keV X-ray observations with the neutral hydrogen column densities in the LMC obtained from a 21 cm line survey, shows no evidence for absorption effects in the 1/4 keV X-ray flux from the LMC due to the neutral matter in the LMC. Instead, faint X-ray emission is detected from the LMC. The extent of this emission is smaller than the size of the halo or the disk of the LMC. Assuming this 1/4 keV emission to be diffuse, it is identified with a supergiant shell of optical nebulosity known as Shapley III, and the bar of the LMC. The X-ray luminosities of the regions are estimated to be 9 times 10 to the 38th power ergs/sec and 1.8 times 10 to the 39th power ergs/sec for the Shapley III region and the bar of the LMC respectively. Shapley III could be an X-ray superbubble.

Singh, K. P.↗
NASA NTRS2017

Unusual Black Hole Binary LMC X-3: A Transient High-Mass X-Ray Binary That Is Almost Always On?

We have analyzed a rich, multimission, multiwavelength data set from the black hole X-ray binary (BHXB) LMC X-3, covering a new anomalous low state (ALS), during which the source flux falls to an unprecedentedly low and barely detectable level, and a more normal low state. Simultaneous X-ray and UV/optical monitoring data from Swift are combined with pointed observations from the Rossi X-ray Timing Explorer (RXTE) and X-ray Multi- Mirror Mission (XMM-Newton) and light curves from the Monitor of All-Sky X-ray Image (MAXI) instrument to compare the source characteristics during the ALS with those seen during the normal low state. An XMM-Newton spectrum obtained during the ALS can be modeled using an absorbed power law with Gamma = 1.41‚+/- 0.65 and a luminosity of 7.97 x 10(exp 33) erg/s (0.6-5 keV). The Swift X-ray and UV light curves indicate an X-ray lag of approx. 8 days as LMC X-3 abruptly exits the ALS, suggesting that changes in the mass accretion rate from the donor drive the X-ray lag. The normal low state displays an asymmetric profile in which the exit occurs more quickly than the entry, with minimum X-ray flux a factor of approx. 4300 brighter than during the ALS. The UV brightness of LMC X-3 in the ALS is also fainter and less variable than during normal low states. The existence of repeated ALSs in LMC X-3, as well as a comparison with other BHXBs, implies that it is very close to the transient/persistent X-ray source dividing line. We conclude that LMC X-3 is a transient source that is almost always "on."

Simultaneous X-ray and UV/optical monitoring dat↗
NASA NTRS1983

X-ray observations of LMC X-3 with the monitor proportional counter aboard the HEAO 2 Einstein observatory - A comparison with Cygnus X-1

A comparison is presented of the black hole candidates LMC X-3 and Cygnus X-1 based on Einstein observations of LMC X-3 with the monitor proportional counter. A spectral analysis shows LMC X-3 to be more like the typical bright galactic X-ray source than Cygnus X-1. A search for periodic pulsations over a period range from 0.2 ms to over 1000 s set upper limits at the 90 percent confidence level of the order of 10 percent. An analysis of the aperiodic variability of LMC X-3 shows none of the shot noise behavior characteristic of Cygnus X-1. The absence of distinctive X-ray properties common to both sources suggests that the identification of black hole candidates on the basis of X-ray properties similar to Cygnus X-1 (or LMC X-3) is not reliable.

Weisskopf, M. C.↗
NASA NTRS1990

Infrared analysis of LMC superbubbles

Researchers are analyzing three superbubbles in the Large Magellanic Cloud (LMC), cataloged by Meaburn (1980) as LMC-1, LMC-4 (a.k.a. Shapley Constellation III), and LMC-5. Superbubbles are the largest infrared sources in the disks of external galaxies. Their expansion requires multiple supernovae from successive generations of star formation. In LMC superbubbles, the grains swept up by shocks and winds represent an interstellar medium (ISM) whose abundances are quite different from the Galaxy. By applying the Dwek (1986) grain model, we can derive the composition and size spectrum of the grains. The inputs to this model are the dust emission in the four Infrared Astronomy Satellite (IRAS) bands and the interstellar radiation field (ISRF) that provides the heating. The first step in the project is to derive the ISRF for star-forming regions on the periphery of superbubbles. Researchers are doing this by combining observations at several wavelengths to determine the energy budget of the region. They will use a UV image to trace the ionizing stellar radiation that escapes, an H alpha image to trace the ionizing stellar radiation that is absorbed by gas, and the four IRAS images to trace the stellar radiation, both ionizing and non-ionizing, that is absorbed by dust. This multi-wavelength approach has the advantages that we do not have to assume the shape of the IMF or the extinction of the source.

Verter, Fran↗
NASA NTRS1998

A Survey of the 30.5 Day Cycle in LMC X-4

LMC X-1 is a high mass X-ray binary system with a 13.5 sec period accreting pulsar n in a 1.4 day orbit. The system displays a super-orbital cycle of X-ray intensity variations repeating every 30.5 days consisting of alternating high and low X-ray flux state . This phenomenon is believed to be caused by a tilted , precessing accretion disk similar to that in Her X-1. We present results of a study of the 30.5 day "long" cycle of LMC X-4 using RXTE observations. The 30.5 day cycle was surveyed with a series of RXTE pointings. We present the resulting lightcurve and compare it to the average lightcurve obtained from the RXTE All SKY Monitor. We show color - color and color-intensity plots as well as representative spectra. The pulse profile evolution across the single High state of LMC X-4 is shown . there is no evidence for a second weaker high state in LMC X-4 unlike that in Her X-1. We compare the properties of the long cycle in LMC X-4 with those in Her X-1.

Scott, Matthew↗
NASA NTRS2016

A Dark Energy Camera Search for Missing Supergiants in the LMC After the Advanced LIGO Gravitational-Wave Event GW150914

The collapse of a stellar core is expected to produce gravitational waves (GWs), neutrinos, and in most cases a luminous supernova. Sometimes, however, the optical event could be significantly less luminous than a supernova and a direct collapse to a black hole, where the star just disappears, is possible. The GW event GW150914 was detected by the LIGO Virgo Collaboration via a burst analysis that gave localization contours enclosing the Large Magellanic Cloud (LMC). Shortly thereafter, we used DECam to observe 102 deg(exp.2) of the localization area,including 38 deg(exp. 2) on the LMC for a missing supergiant search. We construct a complete catalog of LMC luminous red supergiants, the best candidates to undergo invisible core collapse, and collected catalogs of other candidates:less luminous red supergiants, yellow supergiants, blue supergiants, luminous blue variable stars, and Wolf-Rayet stars. Of the objects in the imaging region, all are recovered in the images. The timescale for stellar disappearance is set by the free-fall time, which is a function of the stellar radius. Our observations at 4 and 13 days after the event result in a search sensitive to objects of up to about 200 solar radii. We conclude that it is unlikely that GW150914 was caused by the core collapse of a relatively compact supergiant in the LMC, consistent with the LIGO Collaboration analyses of the gravitational waveform as best interpreted as a high mass binary black hole merger. We discuss how to generalize this search for future very nearby core-collapse candidates.

galaxies: individual (LMC) – gravitational waves↗
DOE OSTI2025

Exploring the interaction between the MW and LMC with a large sample of blue horizontal branch stars from the DESI survey

The Large Magellanic Cloud (LMC) is a Milky Way (MW) satellite that is massive enough to gravitationally attract the MW disc and inner halo, causing significant motion of the inner MW with respect to the outer halo. In this work, we probe this interaction by constructing a sample of 9866 blue horizontal branch (BHB) stars with radial velocities from the DESI spectroscopic survey out to 120 kpc from the Galactic centre. This is the largest spectroscopic set of BHB stars in the literature to date, and it contains four times more stars with Galactocentric distances beyond 50 kpc than previous BHB catalogues. Using the DESI BHB sample combined with SDSS BHBs, we measure the bulk radial velocity of stars in the outer halo and observe that the velocity in the Southern Galactic hemisphere is different by 3.7σ from the North. Modelling the projected velocity field shows that its dipole component is directed at a point 22 deg away from the LMC along its orbit, which we interpret as the travel direction of the inner MW. The velocity field includes a monopole term that is –24 km s –1 ⁠, which we refer to as compression velocity. This velocity is significantly larger than predicted by the current models of the MW and LMC interaction. This work uses DESI data from its first 2 yr of observations, but we expect that with upcoming DESI data releases, the sample of BHB stars will increase and our ability to measure the MW–LMC interaction will improve significantly.

Galaxy: evolution↗
NASA NTRS1978

LMC X-1, X-2, and X-3 - Precise positions from the HEAO 1 modulation collimator

Precise (to about 20 arcsec) positions are reported for the Large Magellanic Cloud X-ray sources LMC X-1, X-2, and X-3, determined with the HEAO 1 scanning modulation collimator. The error regions for LMC X-1 and X-3 contain, respectively, the B5 supergiant R148 and a possibly variable B III-IV star. Spectra taken of the latter confirm the spectral type and show that it is a member of the LMC. A search for a previously reported extended component of LMC X-1 yields upper limits which exclude it.

Johnston, M. D.↗
NASA NTRS1984

Ultraviolet studies of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330 and the Galactic cluster NGC 6530

High-resolution and low-resolution IUE spectra of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330, and the young Galactic cluster NGC 6530 are investigated. Temperatures and luminosities are determined. In the LMC and SMC clusters, the most luminous stars are evolved stars on the horizontal supergiant branch, while in NGC 6530 the stars are all still on the main sequence. Extinction laws were determined. They confirm the known differences between LMC and Galactic extinctions. No mass loss was detected for the evolved B stars in the LMC and SMC clusters, while the high-luminosity stars in NGC 6530 show P Cygni profiles.

Boehm-Vitense, E.↗
NASA NTRS1989

Sanduleak's Star (LMC Anonymous) - Its similarity in the far-ultraviolet with the luminous object Eta Carinae and SN 1987A

Low-resolution IUE SWP spectra of the peculiar object LMC Anonymous (Sanduleak's Star) indicates strong evidence for CNO-processed nebula in the vicinity of the star. The far-UV spectrum of LMC Anonymous closely resembles that of the S Condensation of Eta Carinae. The similarity between LMC Anonymous and the S Condensation is apparent from the absolute intensity of the N V, semiforbidden N IV, and semiforbidden N III emission lines compared with the reduced strength of C IV or semiforbidden C III emission. IUE spectra of the S Condensation and SN 1987A may provide important clues concerning the nature of LMC Anonymous, which indicates departures from normal cosmic abundances of nitrogen relative to carbon that are extreme. This may suggest that carbon envelope burning and dredge-up occurred simultaneously during the helium-burning stage.

Michalitsianos, A. G.↗
NASA NTRS1994

A new ejecta shell surrounding a Wolf-Rayet star in the LMC

We have obtained CCD spectra of newly discovered shell-like nebulae around the WN4 star Breysacher 13 and the WN1 star Breysacher 2 in the Large Magellanic Cloud (LMC). The shell around Br 13 shows definite signs of enrichment in both nitrogen and helium, having much stronger (N II) and He I emission lines than are seen in typical LMC H II regions. From the measured electron temperature of about 17,000 K in the shell, we derive He/H and N/O abundance ratios which are factors of 2 and more than 10 higher, respectively, than the average LMC interstellar values. The derived oxygen abundance in the Br 13 shell is down by a factor of 8 compared to the local LMC interstellar medium (ISM); however, the derived electron temperature is affected by the presence of an incomplete shock arising from the interaction of the stellar wind with photoionized material. This uncertainty does not affect the basic conclusion that the Br 13 shell is enriched by processed material from the Wolf-Rayet star. In contrast, the shell around Br 2 shows no clear evidence of enrichment. The nebular spectrum is characterized by extremely strong (O III) and He II emission and very weak (N II). We derive normal He, O, and N abundances from our spectrum. This object therefore appears to be simply a wind-blown structure associated with a relatively dense cloud near the Wolf-Rayet star, although the very high-ionization state of the gas is unusual for a nebula associated with a Wolf-Rayet star.

Garnett, Donald R.↗
NASA NTRS2001

X-Ray and UV Orbital Phase Dependence in LMC X-3

The black-hole binary LMC X-3 is known to be variable on time scales of days to years. We investigated X-ray and ultraviolet variability in the system as a function of the 1.7 d binary orbit using a 6.4 day observation with the Rossi X-ray Timing Explorer (RXTE) in 1998 December. An abrupt 14 % flux decrease lasting nearly an entire orbit was followed by a return to previous flux levels. This behavior occurred twice at nearly the same binary phase, but is not present in consecutive orbits. When the X-ray flux is at lower intensity, a periodic amplitude modulation of 7 % is evident in data folded modulo the orbital period. The higher intensity data show weaker correlation with phase. This is the first report of X-ray variability at the orbital period of LMC X-3. Archival RXTE observations of LMC X-3 during a high flux state in 1996 December show similar phase dependence. An ultraviolet light curve obtained with the High Speed Photometer (HSP) on the Hubble Space Telescope (HST) shows a phase dependent variability consistent with that observed in the visible, ascribed to the ellipsoidal variation of the visible star. The X-ray spectrum of LMC X-3 is acceptably represented by a phenomenological disk black-body plus a power law. Changes in the spectrum of LMX X-3 during our observations are compatible with earlier observations during which variations in the 2-10 keV flux are closely correlated with the disk geometry spectral model parameter.

Dolan, Joseph F.↗
NASA NTRS2002

Timing and Spectral Study of LMC X-4

Specialized programs for an uses or RXTE data to achieve the purposes of this study were developed with the support from this contract. These programs have been employed in the analysis and publication of an RXTE observation of 4U 1538-52 that revealed a surprisingly large eccentricity of the orbit and evidence of orbital decay ("The orbit of the binary X-ray purser 4U 1538-52 from ROSSI X-RAY TIMING EXPLORER observations", G. W. Clark 2000, ApJ 542, L133). Meanwhile two studies of LMC X-4 based on RXTE and Beppo-Sax observations have been published covering almost completely the objectives of our proposed study ("Orbital decay in LMC X-4", A. L. Levine, S. A. Rappaport, & G. Zojcheski 2000, Adopt, 541, 194; "The 0.1 - 100 key spectrum of LMC X-4. in the high state: evidence for a high-energy cyclotron absorption line", A. LaBarbera et al. 2001, ApJ 553, 375). Both are based on more extensive observations than were obtained for our proposed study and present more comprehensive and accurate results than can be derived from our data. The effort to complete our proposed RXTE study of LMC X-4 has therefore been abandoned in favor of other research which can take better advantage of the specialized programs mentioned above.

Source record↗
NASA NTRS2003

The Complete Z-diagram of LMC X-2

We present results from four Rossi X-ray Timing Explorer (RXTE) observations of the bright low mass X-ray binary LMC X-2. During these observations, which span a year and include over 160 hrs of data, the source exhibits clear evolution through three branches on its hardness-intensity and color-color diagrams, consistent with the flaring, normal, and horizontal branches (FB, NB, HB) of a Z-source, and remarkably similar to Z-tracks derived for GX 17+2, Sco X-1 and GX 349+2. LMC X-2 was observed in the FB, NB, and HB for roughly 30%, 40%, and 30% respectively of the total time covered. The source traces out the full extent of the Z in approximately 1 day, and the Z-track shows evidence for secular shifts on a timescale in excess of a few days. Although the count rate of LMC X-2 is low compared with the other known 2-sources due to its greater distance, the power density spectra selected by branch show very-low-frequency noise characteristics at least consistent with those from other Z-sources. We thus confirm the identification of LMC X-2 as a Z-source, the first identified outside our Galaxy.

White, Nicholas E.↗