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The GRB redshift distribution promises to be a unique probe of the cosmic history of massive star formation. Such effort has been hampered by observational biases in the redshift sample. This has motivated work on understanding the origin of the dominant selection effects that have polluted this data. Our recent work has revealed a previously overlooked observational bias that may influence the selection of GRB redshifts. The bias results from a combination of the transient nature of GRB optical afterglows and the efficiency of ground‐based telescopes to acquire redshifts. This bias is related to ground‐based telescope response times. From Swift data it is found that different response times can affect the average redshift. This has implications for studies of the formation rate of GRBs.

Conditions for the existence and stability of the currents which would be required to support an intergalactic magnetic field are examined to see what upper limit could be obtained for the photon rest mass if the existence of such a field is established.

Mestel, Wang and Westfold (1984; ‘MWW’) have recently introduced a pulsar magnetosphere model in which electrons leave the star with non-negligible, but not highly-relativistic, speeds, and flow with moderate acceleration along magnetic field lines before reaching a limiting surface, near which rapid acceleration occurs. Such moderately accelerated flows are analysed here. A second class of flows, which do not encounter a region of rapid acceleration, is found.

The effect of a photon rest mass on the dissipation of magnetic fields in the Galaxy is discussed and an upper limit on the rest mass is obtained: an earlier treatment is corrected and refined.

Following an idea of Goldhaber and Nieto, conditions for the existence and stability of the currents which are required to support the observed galactic magnetic field are used to obtain an upper limit for the photon rest mass.

SEVERAL people have investigated the absorption of electromagnetic and neutrino waves in cosmological models and discussed the self-consistency or otherwise, in the Wheeler–Feynman absorber theory of radiation, of retarded and advanced fields; a solution of the field equations is self-consistent if the absorption tends to completeness as the field propagates. Cosmological absorption of gravitational waves has been treated briefly by Hawking1. Here, the completeness or otherwise of the absorption of retarded and advanced gravitational waves will be investigated using a technique introduced, in the case of electromagnetic absorption, by Davies2; the technique applies to the Robertson–Walker cosmologies of arbitrary spatial curvature.

Tn the axisymmetric pulsar magnetosphere model of Mestel et al. (1985), electrons, following injection with non-negligible speeds from the stellar surface, flow with moderate acceleration, and with poloidal motion that is closely tied to poloidal magnetic field lines, before reaching a limiting surface, near which rapid acceleration occurs. The present paper continues an analysis of flows which either encounter the limiting surface beyond the light cylinder (between the cones of zero axial magnetic field), or do not meet it at all. The formalism introduced by Mestel et aL for the description of the outflow is applied in an extended version which fully incorporates Yo, the emission Lorentz factor of the particles. This treatment removes the singularity of Yo at the stellar poles that occurred in the earlier work: because of a nonuniformity in taking the limit of nonrelativistic injection, full incorporation of Yo acts to keep it finite.

A formalism introduced by Mestel, Robertson, Wang and Westfold for the description of electron outflow in axisymmetric pulsar magnetospheres, following injection with non-negligible speeds from the stellar surface, is extended here to incorporate emission with relativistic speeds. The formalism is then used to study the possible kinds of outflow. They are organized into five types, corresponding to differences in the emission speed and its variation with latitude, and into two classes according to whether or not they reach a region of rapid acceleration.

MAXWELL'S equations are well established for phenomena on laboratory and terrestrial scales, but there are other electrodynamic theories, as yet indistinguishable on such scales from Maxwell's theory, that have significantly different consequences for phenomena on an astronomical scale. For example, extensive magnetic fields are possible in the Universe1 because of the general absence of magnetic monopoles. Parker1 considered the abundance of magnetic monopoles that would neutralise or dissipate the magnetic fields of the Earth, Sun and the Galaxy, and deduced for the number density of free magnetic monopoles upper limits that are more stringent than those deduced from laboratory and terrestrial data.