Simultaneous radio and X-ray observations of MXB1837+05 /Ser X-1/
Explore the source record for details and available documents.
Ulmer, M. P.↗
Engineering topics
Lewin, W. H. G.
Publications and source records attributed to Lewin, W. H. G..
Interpretation of tails of X-ray bursts
Four reasons for ruling out the Alcock and Hatchett (1978) proposal concerning the tails of X-ray bursts are advanced. This proposal suggests that the tails of X-ray bursts observed during burst decay are due to the small-angle scattering of the original pulse of X-rays on interstellar dust grains; grains with a typical size of approximately 3 microns are assumed. The arguments against this theory involve differences in burst tail sizes sometimes observed for bursts from the same source; the different kinds of bursts emitted by MXB 1730-335 (rapid burster); an indication that MXB 1730-335 bursts have tails less than 2 s long; and the lack of correlation between relative strength of burst tails and the interstellar absorption.
Van Paradijs, J.↗
A search for X-ray pulsations from the galactic center
Data from the SAS-3 satellite were used in a search for X-ray pulsations from the direction of the galactic center. No periodic X-ray behavior was detected in the frequency interval 0.6 Hz to 0.0006 Hz and energy range 2.5 - 35 keV. For periods less than 60 sec, the upper limit to the amplitude of any pulsation in the 2.5 - 10 keV band is approximately .0017 cts/sq cm/s. This corresponds to a pulsed fraction of approximately 1.3 percent of the total GCX flux. Somewhat higher limits apply for longer periods and for energies greater than 10 keV.
Cordova, F. A.↗
Discovery of optical bursts from an X-ray burst source, MXB1735-44
The optical counterpart of 4U 1735-44, X-ray burst source MXB 1735-44, was studied with the 1.5-m telescope at Cerro Tololo, and by SAS 3, during the period between June 1 and 3, 1978. Explanations for the optical activity are discussed in terms of accretion instabilities onto a neutron star, or thermonuclear flashes on the neutron star itself. Attention is given to the timing of the bursts, which indicate that the burst source probably is located in a region within 1-2 light seconds from the X-ray source. In the binary case, it is noted that the optical emission is probably removed from the X-ray heated stellar atmosphere of the possible companion.
Grindlay, J. E.↗
Optical monitoring of X-ray burst sources
Results are presented for simultaneous optical and X-ray observations of the X-ray burst sources MXB 1837+05 and 1916-05. On two occasions during these observations an X-ray burst from MXB 1837+05 was detected by SAS 3, but no accompanying optical signal was detected. The 3-sigma upper limit to the ratio of the energy in a possible optical burst to the energy in the X-ray burst is 0.0001.
Abramenko, A. N.↗
Searches for correlated X-ray and radio emission from X-ray burst sources
The NRAO Green Bank interferometer has been used to monitor MXB 1730-335 and MXB 1837+05 during periods when 68 X-ray bursts were detected by X-ray observations. No significant radio emission was detected from these objects, or from MXB 1820-30 and MXB 1906+00, which emitted no bursts throughout the simultaneous observations. The data place upper limits on radio emission from these objects in the 2695 and 8085 MHz bands.
Johnson, H. M.↗
SAS 3 observations of two X-ray transient events with precursors
SAS 3 has observed two unusual fast transient X-ray events from different sources, one lasting about 150 s and one, approximately 1500 s. Both events were preceded by precursor pulses which lasted a few seconds and which rose and fell in less than 0.4 s. The precursors were separated from the 'main' events by several seconds, during which no X-rays were detected. There are similarities between the two main events and X-ray bursts in both their temporal and spectral evolution. The spectra of the main events started out much softer than the spectra of the precursors, became harder as they approached maximum intensity, and softened as they decayed. In the 1500-s event, X-rays with energies greater than 10 keV were delayed by about 80 s compared with 1.5-6-keV X-rays. A blackbody fit to the spectral data of the main event of approximately 1500-s duration gives a maximum temperature of 29 million K and a radius for the emitting region of at least about 9 km (at a distance of 10 kpc); this is similar to the temperature and sizes found for several X-ray burst sources.
Hoffman, J. A.↗
X-ray burst sources
Current knowledge of sources of X-ray bursts, defined as having rise times of less than a few seconds, durations of a few seconds to a few minutes and a generally regular recurrence pattern, is reviewed. An examination of the galactic distribution of X-ray burst sources, which has been confirmed by SAS-3 rotating modulation collimator observations, reveals that the burst sources are spread along the galactic equator and clustered near low galactic longitudes, unlike the distribution of globular clusters. At least four X-ray burst sources have been associated with steady X-ray sources based on positional coincidence, and it has been found that the X-ray bursts are less intense but harder than steady X-ray emission from these sources. Individual burst sources, including MXB1659-29, which has not been identified with a steady X-ray source, the source in NGC6624 which has been identified with 3U1820-30, MXB1837+05, associated with Ser X-1, three burst sources near the galactic center and the rapid burster MXB1730-335 are briefly discussed.
Lewin, W. H. G.↗
Observations of the X-ray burst source MXB 1636-53
X-ray bursts have been observed from MXB 1636-53, almost certainly associated with the strong steady X-ray source 2S 1636-536 (Norma X-1, 3U 1636-53). The steady source was observed in January 1977 at roughly half the intensity reported in the 3U catalog and showed about 15% variability on a time scale of hours. The spectra of the X-ray bursts are well fitted by blackbody radiation whose temperature rises rapidly to a maximum of approximately 28 million K and then cools slowly. If the source is at a distance of 10 kpc, the radius of the projected burst emission region is about 10 km, similar to the size of a neutron star.
Hoffman, J. A.↗
Further observations of recurrent X-ray bursts from the globular cluster NGC 6624
Explore the source record for details and available documents.
Clark, G. W.↗
Some further information on the rapid burster MXB 1730-335
Further analysis of SAS-3 data on the rapid burster MXB 1730-335 show the existence of anomalous bursts. They have approximately 3-s rise times and low peak intensities; they also violate the energy vs. interburst-interval relationship for normal bursts. The short normal bursts of about 4-s duration do not show a long tail such as observed in the long normal bursts. Evidence for time structure in normal bursts down to a time scale of 50 ms is presented. No periodic variations in the total X-ray flux were found in the 1-500-Hz range.
Ulmer, M. P.↗
Galactic distribution of X-ray burst sources
Data on X-ray bursts recorded by the OSO-8 and SAS-3 satellites and criteria (rise time, duration, recurrence) for X-ray bursts are examined in a study of possible correlation between the galactic longitude distribution of X-ray burst sources and globular clusters. Correlations are weak, with only two X-ray bursts sources (NGC6624 and the rapid burster) coinciding with globular clusters, another seven possibly coinciding, most not correlated. Ad hoc explanations (globular clusters obscured by dust clouds, bursts associated with remnants of disrupted globular clusters evolved into supermassive black holes) are considered briefly.
Lewin, W. H. G.↗
Further observations of the burst source MXB 1728-34
MXB 1728-34 has been observed by the SAS 3 observatory on eight occasions. It was bursting 95-100 per cent of the time, with burst intervals from 4 to 8 hr. The burst intervals were not correlated with the burst intensities. Seven relatively hard bursts occurring in July 1976 were all observed at energies up to about 30 keV. Following each of these bursts, enhanced X-ray emission was observed for several minutes, with a much softer spectrum than that of the bursts themselves. No periodic pulsations were observed from the associated steady source.
Hoffman, J. A.↗
X-ray burst sources
Available information on 12 well-observed and three poorly observed X-ray burst sources is reviewed. Specific attention is given to source positions, associated 'steady' X-ray emission, intervals between bursts, energy fluxes, spectral hardening and softening during bursts, as well as burst-active and inactive states. Differences and similarities between X-ray and gamma-ray bursts are discussed, the possibility is considered that the gradual decay of bursts results from scattering of an initial short pulse by a surrounding cloud or atmosphere, and it is suggested that most burst sources are not located in globular clusters. The proposed association of X-ray bursts with supermassive black holes is considered to be almost certainly incorrect.
Lewin, W. H. G.↗
X-ray bursts from MXB 1837+05
Results are reported for SAS 3 observations of 22 bursts from the X-ray source designated MXB 1837+05. Assuming that all the bursts come from one source, the source position is determined to be right ascension (1950) 18 hr 37.9 min, declination (1950) 5 deg 4.2 min. Integrated burst intensities are listed along with ratios of counts in different energy channels, and it is found that there are significant variations in these ratios from burst to burst. The bursts are also shown to exhibit a variety of temporal structures (including double peaks) and changes in spectral hardness. No regularity was detected in the burst occurrence times during one observing period, but four bursts during another period seemed to recur at regular intervals of about 6.3 hr. It is concluded that an intensity-interval correlation similar to that for a rapid burster does not exist for MXB 1837+05 and that this source is probably identical with the relatively strong and steady source Ser X.1.
Li, F. K.↗
Transient structure in the high-energy X-ray light curve of NP 0532
The paper reports the observation of pulsed fractions in the primary and secondary peaks, as well as in the interpulse region, of the high-energy X-ray light curve of NP 0532. A statistical analysis of light-curve data is performed, and a similar analysis is carried out using simulated data. It is concluded that a previously reported third peak in the light curve was transient in nature.
Ryckman, S. G.↗
Intense X-ray flares from Aquila X-1 and Circinus X-1
Explore the source record for details and available documents.
Buff, J.↗
Discovery of X-ray bursts from several sources near the galactic centre
Three X-ray burst sources have been discovered within approximately 0.5 deg of the Galactic center. All bursts from this region show a low-energy cutoff near 3 keV. The bursts from MXB 1743-29 show distinct double and triple peaks; the time interval between bursts from this source was about 1.46 day. The intervals between bursts from MXB 1742-29 and MXB 1743-28 were approximately 0.55 day and 10 min respectively. Steady emission from this collection of burst sources could account for most of the flux from the apparently extended X-ray source GCX (3U 1743-29).
Lewin, W. H. G.↗