J. van Paradijs

An Unusual Supernova in the Error Box of the Gamma-Ray Burst of 25 April 1998

The discovery of afterglows associated with γ-ray bursts at X-ray, optical and radio wavelengths and the measurement of the redshifts of some of these events, has established that γ-ray bursts lie at extreme distances, making them the most powerful photon-emitters known in the Universe. Here we report the discovery of transient optical emission in the error box of the γ-ray burst GRB980425, the light curve of which was very different from that of previous optical afterglows associated with γ-ray bursts. The optical transient is located in a spiral arm of the galaxy ESO184-G82, which has a redshift velocity of only 2,550 km s−1 (ref. 6). Its optical spectrum and location indicate that it is a very luminous supernova, which has been identified as SN1998bw. If this supernova and GRB980425 are indeed associated, the energy radiated in γ-rays is at least four orders of magnitude less than in other γ-ray bursts, although its appearance was otherwise unremarkable: this indicates that very different mechanisms can give rise to γ-ray bursts. But independent of this association, the supernova is itself unusual, exhibiting an unusual light curve at radio wavelengths that requires that the gas emitting the radio photons be expanding relativistically,.on April 25.90915 UT with one of the Wide Field Cameras(WFCs) and the Gamma Ray Burst Monitor (GRBM) on board BeppoSAX, and with the Burst andTransient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO).The BATSE burst profile consists of a single wide peak. The burst flux rose in ∼ 5 s to amaximum flux of (3.0± 0.3)×10

A 'hypernova' model for the supernova associated with the gamma-ray burst of 25 April 1998

The discovery of the unusual supernova SN1998bw, and its possible association with the γ-ray burst GRB 980425, provide new insights into the explosion mechanism of very massive stars and the origin of some classes of γ-ray bursts. Optical spectra indicate that SN1998bw is a type Ic supernova,, but its peak luminosity is unusually high compared with typical type Ic supernovae. Here we report our findings that the optical spectra and the light curve of SN1998bw can be well reproduced by an extremely energetic explosion of a massive star composed mainly of carbon and oxygen (having lost its hydrogen and helium envelopes). The kinetic energy of the ejecta is as large as +(2–5)× 1052 erg, more than ten times that of previously observed supernovae. This type of supernova could therefore be termed ‘hypernova’. The extremely large energy suggests the existence of a new mechanism of massive star explosion that can also produce the relativistic shocks necessary to generate the observed γ-rays.

Discovery of a magnetar associated with the soft gamma repeater SGR 1900+14

The soft gamma repeater SGR 1900+14 became active again on 1998 June after a long period of quiescence; it remained at a low state of activity until 1998 August, when it emitted a series of extraordinarily intense outbursts. We have observed the source with the Rossi X-Ray Timing Explorer twice, during the onset of each active episode. We confirm the pulsations at the 5.16 s period reported earlier from SGR 1900+14. Here we report the detection of a secular spin-down of the pulse period at an average rate of 1.1 × 10-10 s s-1. In view of the strong similarities between SGRs, we attribute the spin-down of SGR 1900+14 to magnetic dipole radiation, possibly accelerated by a quiescent flux, as in the case of SGR 1806-20. This allows an estimate of the pulsar dipolar magnetic field, which is (2–8) × 1014 G. Our results confirm that SGRs are magnetars.

The lives of the neutron stars

1. The Birth of Neutron Stars. 2. The Structure of Neutron Stars and their Thermal, Magnetic and Dynamical Evolution. 3. Radio Pulsars. 4. X-Ray Binaries. 5. ... And their Evolution. 6. Gamma-Ray Bursts. 7. Observational Prospects. Summary. Author Index. Subject Index. Object Index.

On the Accretion Instability in Soft X-Ray Transients

Dwarf nova outbursts are likely caused by a thermal-viscous instability in the accretion disk around the white dwarf, which can occur if the mass transfer rate, , is below a critical value (which depends on orbital period). Based on data for soft X-ray transients and persistent low-mass X-ray binaries with known distances and orbital periods, Porb, I show that for these systems the distributions in a (Porb, ) diagram can be understood with the dwarf nova instability criterion, if that is adapted to include X-ray heating of the disk. This supports the idea that the disk instability model applies to soft X-ray transients, and shows that X-ray heating must be included in modeling the outbursts.

Catalogue of high-mass X-ray binaries in the Galaxy (4th edition)

We present a new edition of the catalogue of high-mass X-ray binaries in the Galaxy. The catalogue contains source name(s), coordinates, finding chart, X-ray luminosity, system parameters, and stellar parameters of the components and other characteristic properties of 114 high-mass X-ray binaries, together with a comprehensive selection of the relevant literature. The aim of this catalogue is to provide the reader with some basic information on the X-ray sources and their counterparts in other wavelength ranges (gamma-rays, UV, optical, IR, radio). About 60% of the high-mass X-ray binary candidates are known or suspected Be/X-ray binaries, while 32% are supergiant/X-ray binaries. Some sources, however, are only tentatively identified as high-mass X-ray binaries on the basis of their X-ray properties similar to the known high-mass X-ray binaries. Further identification in other wavelength bands is needed to finally determine the nature of these sources. In cases where there is some doubt about the high-mass nature of the X-ray binary this is mentioned. Literature published before 1 October 2005 has, as far as possible, been taken into account.

A catalogue of low-mass X-ray binaries in the Galaxy, LMC, and SMC (Fourth edition)

We present a new edition of the catalogue of the low-mass X-ray binaries in the Galaxy and the Magellanic Clouds. The catalogue contains source name(s), coordinates, finding chart, X-ray luminosity, system parameters, and stellar parameters of the components and other characteristic properties of 187 low-mass X-ray binaries, together with a comprehensive selection of the relevant literature. The aim of this catalogue is to provide the reader with some basic information on the X-ray sources and their counterparts in other wavelength ranges (gamma-rays, UV, optical, IR, and radio). Some sources, however, are only tentatively identified as low-mass X-ray binaries on the basis of their X-ray properties similar to the known low-mass X-ray binaries. Further identification in other wavelength bands is needed to finally determine the nature of these sources. In cases where there is some doubt about the low-mass nature of the X-ray binary this is mentioned. Literature published before 1 October 2006 has, as far as possible, been taken into account.

An Unstable Central Disk in the Superluminal Black Hole X-Ray Binary GRS 1915+105

We have analyzed the X-ray spectra of the microquasar GRS 1915+105, as observed with the Proportional Counter Array (PCA) on the Rossi X-Ray Timing Explorer, during periods of stable weak emission, outbursts, and rapid flaring. We find that the complicated X-ray intensity curve of this source can be described by the rapid removal and replenishment of matter forming the inner part of an optically thick accretion disk, probably caused by a thermal-viscous instability analogous to that operating in dwarf novae, but here driven by the Lightman-Eardley instability. We find that the mass accretion rate in quiescence is about 10-6 M☉ yr-1. Only a small fraction of the energy liberated by accretion is emitted as radiation. We suggest that most of this energy is advected into the black hole in the high-viscosity state of the outburst cycle.

A unified model for the spectral variability in grs 1915+105

We have analyzed the spectral variations of the superluminal black hole X-ray binary GRS 1915+105 by using data obtained with the PCA on the Rossi XTE. We find that, despite the marked differences in the structure and the timescale of variability, all spectral changes can be attributed to the rapid disappearing of the inner region of an accretion disk, followed by a slower refilling of the emptied region. The timescale for each event is determined by the extent of the missing part of the disk. The observed relation between the duration of an event and the radius of the disappearing region matches remarkably well the expected radius dependence of the viscous timescale for the radiation-pressure-dominated region of an accretion disk.

Discovery of submillisecond quasi-periodic oscillations in the x-ray flux of scorpius X-1

We report the discovery, with NASAs Rossi X-Ray Timing Explorer (RXTE), of the first submillisecond oscillations found in a celestial X-ray source. The quasi-periodic oscillations (QPOs) come from Sco X-1 and have a frequency of ~1100 Hz and amplitudes of 0.6%-1.2% (rms) and are relatively coherent, with Q up to ~102. The frequency of the QPOs increases with accretion rate, rising from 1050 to 1130 Hz when the source moves from top to bottom along the normal branch in the X-ray color-color diagram, and shows a strong, approximately linear correlation with the frequency of the well-known 6-20 Hz normal/flaring-branch QPOs. We also report the discovery of QPOs with a frequency near 800 Hz that occur, simultaneously with the 1100 Hz QPOs, in the upper normal branch. We discuss several possible interpretations, one involving a millisecond X-ray pulsar whose pulses we see reflected off accretion flow inhomogeneities. Finally, we report the discovery of ~45 Hz QPOs, most prominent in the middle of the normal branch, which might be magnetospheric beat-frequency QPOs.