Maurice H. P. M. van Putten

Constraints on Type Ib/c Supernovae and Gamma‐Ray Burst Progenitors

Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these models, we find that single stars cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends that we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs.Although there is strong support for the collapsar engine as the power source of long-duration gamma-ray bursts (GRBs), we still do not definitively know the progenitor of these explosions. Here we review the current set of progenitor scenarios for long-duration GRBs and the observational constraints on these scenarios. Examining these, we find that single-star models cannot be the only progenitor for long-duration GRBs. Several binary progenitors can match the solid observational constraints and also have the potential to match the trends we are currently seeing in the observations. Type Ib/c supernovae are also likely to be produced primarily in binaries; we discuss the relationship between the progenitors of these explosions and those of the long-duration GRBs.

THEORY AND ASTROPHYSICAL CONSEQUENCES OF A MAGNETIZED TORUS AROUND A RAPIDLY ROTATING BLACK HOLE

We analyze the topology, lifetime, and emissions of a torus around a black hole formed in hypernovae and black hole-neutron star coalescence. The torus is ab initio uniformly magnetized, represented by two counteroriented current rings, and develops a state of suspended accretion against a magnetic wall around the black hole. Magnetic stability of the torus gives rise to a new fundamental limit /k < 0.1 for the ratio of poloidal magnetic field energy to kinetic energy, corresponding to a maximum magnetic field strength Bc (1016 G) (7 M☉/MH) (6MH/R)2 (MT/0.03MH)1/2. The lifetime of rapid spin of the black hole, effectively defined by the timescale of dissipation of spin energy Erot in the horizon, hereby satisfies T (40 s) (MH/7 M☉)(R/6MH)4(0.03MH/MT) for a black hole of mass MH surrounded by a torus of mass MT and radius R. The torus converts a major fraction Egw/Erot ~ 10% into gravitational radiation through a finite number of multipole mass moments and a smaller fraction into MeV neutrinos and baryon-rich winds. At a source distance of 100 Mpc, these emissions over N = 2 × 104 periods give rise to a characteristic strain amplitude N1/2hchar 6 × 10-21. We argue that torus winds create an open magnetic flux tube on the black hole, which carries a minor fraction Ej/Erot 10-3 in baryon-poor outflows to infinity. We conjecture that these are not high-σ outflows, owing, in part, to magnetic reconnection in surrounding current sheets. The fraction Ej/Erot ~ (MH/R)4 is standard for a universal horizon half-opening angle θH MH/R of the open flux tube. We identify this baryon-poor output of tens of seconds with gamma-ray bursts with contemporaneous and strongly correlated emissions in gravitational radiation, conceivably at multiple frequencies. Ultimately, this leaves a black hole binary surrounded by a supernova remnant.

Hyper- and Suspended-Accretion States of Rotating Black Holes and the Durations of Gamma-Ray Bursts

We analyze the temporal evolution of accretion onto rotating black holes subject to large-scale magnetic torques. Wind torques alone drive a disk toward collapse in a finite time ~tffEk/EB, where tff is the initial free-fall time and Ek/EB is the ratio of kinetic energy to poloidal magnetic energy. Additional spin-up torques from a rapidly rotating black hole can arrest the disks inflow. We associate short/long gamma-ray bursts with hyperaccretion/suspended-accretion onto slowly/rapidly spinning black holes. This model predicts afterglow emission from short bursts and may be tested by HETE-2.

Gamma-ray bursts: LIGO/VIRGO sources of gravitational radiation

Abstract The status and prospects are reviewed for the presently most favored model for the inner engine of cosmological gamma-ray bursts (GRBs): the black hole–torus model. Support for this model is derived from recent GRB-phenomenology: a cosmological origin, a bi-modal distribution in their durations, and potentially a GRB/X-ray transient connection. The black hole–torus model operates by the rotation of the central Kerr black hole, which introduces two new mechanisms: in-situ pair-creation on open field-lines along the axis of rotation and a powerful magnetic black hole-to-torus coupling. The leptonic winds serve as input to the GRB-afterglow emissions. Long/short GRBs are identified with suspended/hyper-accretion onto rapidly/slowly rotating black holes. The suspended accretion state is expected to be accompanied by baryonic winds blown off the torus; if formed in stellar collapse, these winds may account for recently detected iron line-emissions and may have contributed to the chemical abundances in X-ray transients. This implies that HETE-II will detect afterglows from all bursts, but iron-line emission only from long bursts. In long bursts, the torus is expected to radiate most of the black hole luminosity in gravitational waves. This predicts that long GRBs are potentially the most powerful burst-sources of gravitational waves in the Universe. Their emissions trace a horizontal branch in the f (f) -diagram, which can be tested by LIGO/VIRGO.

Silicon thermal anemometry: developments and applications

In this paper we present a comprehensive discussion of silicon thermal anemometry. Its possibilities and the current state of the art are discussed in detail. Based on forced convective heat transfer, it is seen how silicon technology can be used to make thermal flow sensors. The mechanism is based on development of a thermal hydrodynamic boundary layer across a heated silicon chip due to a forced flow. It is shown how this mechanism is converted into an electrical signal. Important parameters such as possible sensing elements and geometries are discussed. Different biasing modes to operate thermal sensors are presented. One of the very basic issues in silicon thermal anemometry is drift. The performance can be expressed in terms of a quality factor , where S is the desired signal, D is the drift and N is the contribution of noise. The control of this drift term plays a crucial role in the accuracy of silicon thermal flow sensors. A novel method to eliminate drift for thermal anemometry, namely the alternating direction method, is presented. In particular this method plays a crucial role when extremely low and long-term volume measurements must be performed. Examples of measurements are given. With regard to its applications, the type of packaging is a major issue. Dependent on its application, also the frequency behaviour is important. It is discussed briefly. Finally, applications and future developments of silicon thermal anemometry are discussed.

Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO

Gamma-ray bursts are believed to originate in core-collapse of massive stars. This produces an active nucleus containing a rapidly rotating Kerr black hole surrounded by a uniformly magnetized torus represented by two counter-oriented current rings. We quantify black hole spin-interactions with the torus and charged particles along open magnetic flux-tubes subtended by the event horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii) aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al. 2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating LIGO/Virgo detectors enables searches for nearby events and their spectral closure density 6e-9 around 250Hz in the stochastic background radiation in gravitational waves. At current sensitivity, LIGO-Hanford may place an upper bound around 150MSolar in GRB030329. Detection of Egw thus provides a method for identifying Kerr black holes by calorimetry.

Formation, Evolution, and Structure of Fronts Produced by Unsteady Injection of Highly Magnetized, Relativistic Flows

We study the formation, evolution, and structure of dissipative fronts produced by overtaking collisions of relativistic streams, with emphasis on strongly magnetized flows. The evolution of the system is followed using an analytical approach in the simple-wave regime and numerical simulations in the non-simple-wave regime, until a steady state is reached. The steady state structure of the front is then examined by solving the appropriate jump conditions. The conversion of magnetic energy into kinetic energy is parameterized in terms of the Alfven 4-velocity inside the front. The implications for γ-ray jets are briefly discussed.

The branching ratio of type Ib/c supernovae to gamma-ray burst supernovae

We study the centered and decentered nucleation of black holes in the core collapse of massive stars in binaries. By Bekensteins gravitational radiation recoil mechanism, a newly nucleated black hole typically leaves the central core prematurely. With low probability, the black hole remains centered and matures into a high-mass black hole that spins rapidly if the binary is compact. GRB 030329/SN 2003dh demonstrates that Type Ib/c supernovae are the parent population of long gamma-ray bursts, whose branching ratio is = (2-4) × 10-3. We identify with the low probability of centered nucleation in compact binaries. Decentered events are predicted to produce a single short burst in gravitational radiation. Centered events are predicted to produce a second, long burst in gravitational radiation powered by a luminous black hole. These signatures are of interest to the gravitational wave experiments LIGO, VIRGO, and TAMA.

Uncommon EEG burst-suppression in severe postanoxic encephalopathy

Objective In patients suffering from severe hypoxia, the EEG may show a burst-suppression pattern, characterized by low-voltage activity and the occurrence of high amplitude burst-like events. We describe the two-timescale burst phenomenology of this postanoxic condition. Methods We present EEG recordings showing remarkable burst phenomenology in two postanoxic patients and consider potential mechanisms responsible for the generation of the burst-suppression patterns. We quantify the postanoxic condition in terms of the dimension (number of degrees of freedom) of its dynamics by comparing our data with a system of three ordinary differential equations with two timescales subject to varying degrees of noise. Results EEGs displayed extreme similarity of the bursts, separated by interburst intervals up to more than 300 s. This pattern reflects a significant reduction in the number of functional brain states. This post-anoxic condition is found to have dimension 3, consisting of fast dynamics responsible for the bifurcation to bursting behavior, and a long time-scale responsible for burst termination and the interburst intervals. Conclusions Low-dimensional postanoxic brain states, as manifested by burst-similarity, appears to indicate an irreversible loss of brain function and consciousness. Significance Evidence of brain functionality in a persistent low dimensional state due to severe hypoxia is indicative of permanent loss of consciousness with essentially no chance for recovery. Quantitative evidence for such degenerate states is important for clinical decision makingOBJECTIVE In patients suffering from severe hypoxia, the EEG may show a burst-suppression pattern, characterized by low-voltage activity and the occurrence of high amplitude burst-like events. We describe the two-timescale burst phenomenology of this postanoxic condition. METHODS We present EEG recordings showing remarkable burst phenomenology in two postanoxic patients and consider potential mechanisms responsible for the generation of the burst-suppression patterns. We quantify the postanoxic condition in terms of the dimension (number of degrees of freedom) of its dynamics by comparing our data with a system of three ordinary differential equations with two timescales subject to varying degrees of noise. RESULTS EEGs displayed extreme similarity of the bursts, separated by interburst intervals up to more than 300s. This pattern reflects a significant reduction in the number of functional brain states. This post-anoxic condition is found to have dimension 3, consisting of fast dynamics responsible for the bifurcation to bursting behavior, and a long time-scale responsible for burst termination and the interburst intervals. CONCLUSIONS Low-dimensional postanoxic brain states, as manifested by burst-similarity, appears to indicate an irreversible loss of brain function and consciousness. SIGNIFICANCE Evidence of brain functionality in a persistent low dimensional state due to severe hypoxia is indicative of permanent loss of consciousness with essentially no chance for recovery. Quantitative evidence for such degenerate states is important for clinical decision making.

LIGO/VIRGO Searches for Gravitational Radiation in Hypernovae

A torus around a stellar-mass Kerr black hole can emit about 10% of the spin energy of a black hole in gravitational radiation, which is potentially associated with a gamma-ray burst (GRB). Wide tori may develop buckling modes by the Papaloizou-Pringle instability and gravitational radiation-reaction forces in the Burke-Thorne approximation. Gravitational-wave experiments may discover these emissions in a fraction of nearby supernovae. This provides a test for Kerr black holes and for GRB inner engines by a comparison with the deredshifted durations of long GRBs.