Bohdan Paczyński

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It is proposed that gamma-ray bursts are created in the mergers of double neutron star binaries and black hole neutron star binaries at cosmological distances. Bursts with complex profiles and relatively long durations are the result of magnetic flares generated by the Parker instability in a post-merger differentially-rotating disk. Some bursts may also be(More)
The optical afterglow of the gamma-ray burst GRB 970508 (z = 0.835) was a few hundred times more luminous than any supernova. Therefore, a name ‘hypernova’ is proposed for the whole GRB/afterglow event. There is tentative evidence that the GRBs: 970228, 970508, and 970828 were close to star forming regions. If this case is strengthened with future(More)
The status of searches for gravitational microlensing events of the stars in our galaxy and in other galaxies of the Local Group, the interpretation of the results, some theory, and prospects for the future are reviewed. The searches have already unveiled ∼ 100 events, at least two of them caused by binaries, and have already proven to be useful for studies(More)
Mergers of neutron stars (NS+NS) or neutron stars and stellar mass black holes (NS+BH) eject a small fraction of matter with a sub-relativistic velocity. Upon rapid decompression nuclear density medium condenses into neutron rich nuclei, most of them radioactive. Radioactivity provides a long term heat source for the expanding envelope. A brief transient(More)
A few percent of all stars are variable, yet over 90% of variables brighter than 12 magnitude have not been discovered yet. There is a need for an all sky search and for the early detection of any unexpected events: optical flashes from gamma-ray bursts, novae, dwarf novae, supernovae, ‘killer asteroids’. The ongoing projects like ROTSE, ASAS, TASS, and(More)
There is growing evidence that long and hard gamma-ray bursts (GRBs), discovered at redshifts between 0.4 and 3.4, are related to some type of supernova (SN) explosions. The GRB ejecta are ultra-relativistic, and possibly beamed. There is a possibility that some SN ejecta are also beamed and/or relativistic. Prospects for farther advances guided by expected(More)
We use masses, radii, and luminosities of the detached eclipsing binary OGLEGC17 derived from photometric and spectroscopic observations to calculate the age and distance of the globular cluster ω Cen. Age versus turnoff mass and age versus luminosity relations from Girardi et al. (2000) yield two independent estimates of the age, 9.1 < t < 16.7 Gyr and(More)
The class of type Ic supernovae have drawn increasing attention since 1998 owing to their sparse association (only four so far) with long duration gamma-ray bursts (GRBs). Although both phenomena originate from the core collapse of a massive star, supernovae emit mostly at optical wavelengths, whereas GRBs emit mostly in soft gamma-rays or hard X-rays.(More)