Neutron monitors (NMs) are ground-based detectors of cosmic-ray showers that are widely used for high-precision monitoring of changes in the Galactic cosmic-ray (GCR) flux due to solar storms and solar wind variations. In the present work, we show that a single neutron monitor station can also monitor short-term changes in the GCR spectrum, avoiding the systematic uncertainties in comparing data from different stations, by means of NM time-delay histograms. Using data for 2007–2014 from the Princess Sirindhorn Neutron Monitor, a station at Doi Inthanon, Thailand, with the world’s highest vertical geomagnetic cutoff rigidity of 16.8 GV, we have developed an analysis of time-delay histograms that removes the chance coincidences that can dominate conventional measures of multiplicity. We infer the “leader fraction” L of neutron counts that do not follow a previous neutron count in the same counter from the same atmospheric secondary, which is inversely related to the actual multiplicity and increases for increasing GCR spectral index. After correction for atmospheric pressure and water vapor, we find that L indicates substantial short-term GCR spectral hardening during some but not all Forbush decreases in GCR flux due to solar storms. Such spectral data from Doi Inthanon provide information about cosmic-ray energies beyond the Earth’s maximum geomagnetic cutoff, extending the reach of the worldwide NM network and opening a new avenue in the study of short-term GCR decreases.

Multi Element Radio Linked Interferometer Network (MERLIN) measurements of 1.6‐GHz hydroxyl (OH) masers associated with Orion‐Becklin–Neugebauer/Kleinmann–Low (Orion‐BN/KL) are presented, and the data are compared with data on other masers, molecular lines, compact radio continuum sources and infrared sources in the region. OH masers are detected over an area of 30 arcsec in diameter, with the majority lying along an approximately E–W structure that extends for ∼18 arcsec, encompassing the infrared sources IRc2, IRc6 and IRc7. Radial velocities range from −13 to +42 km s−1. The system of OH masers shows a velocity gradient together with non‐circular motions. The kinematics are modelled in terms of an expanding and rotating disc or torus. The rotation axis is found to be in the same direction as the molecular outflow. There is an inner cavity of radius ∼1300 au with no OH masers. The inner cavity, like the H2O ‘shell’ masers and SiO masers, is centred on radio source I. Some of the OH masers occur in velocity‐coherent strings or arcs that are longer than 5 arcsec (2250 au). One such feature, Stream A, is a linear structure at position angle ∼45°, lying between IRc2 and BN. We suggest that these masers trace shock fronts, and have appeared, like a vapour trail, 200 yr after the passage of the runaway star BN. The radio proper motions of BN, source I and source n project back to a region near the base of Stream A that is largely devoid of OH masers. The 1612‐MHz masers are kinematically distinct from the other OH masers. They are also more widely distributed and appear to be associated with the outflow as traced by H2O masers and by the 2.12‐μm emission from shocked H2. The magnetic field traced by the OH masers ranges from 1.8 to 16.3 mG, with a possible reversal. No OH masers were found associated with even the most prominent proplyds within 10 arcsec of θ1 Ori C.

Multi‐Element Radio‐Linked Interferometer Network polarization measurements of the OH 18‐cm masers in ON1 are presented. OH maser emission is detected in all four ground state lines. The bulk of the masers lie in an elongated distribution covering 2 arcsec at position angle 130°, near the southern edge of the ultracompact H ii region. The maser distribution is orthogonal to the bipolar outflow seen in HCO+ at position angle (PA) 44°. An isolated group of 1720‐MHz masers is also seen 6 arcsec to the east. The magnetic field deduced from Zeeman splitting of the OH maser lines shows a large‐scale order, with field values ranging from −0.4 to −4.6 mG.

MERLIN maps of OH 1665-and 1667-MHz masers in the source G34.3+0.2 are presented. The majority of the OH masers lie in a parabolic arc along the eastern edge of the cometary H II region G34.3+0.2C, possibly tracing a bow shock. The OH masers lie systematically closer to the cometary H II region than the H 2 O masers, suggesting that OH is formed by dissociation of H 2 O in the shock. The remaining OH masers cluster around the ultracompact H II region G34.3+0.2B. Zeeman splitting indicates a magnetic field strength of typically −5 mG (directed towards us). A complex magnetic field structure is inferred from the maser polarization. Linear polarization is detected in half of the masers, at levels up to 85 per cent. The linear polarization vectors suggest that the magnetic field in some regions near the cometary H II region is perpendicular to the curved edge of the bow shock.

In this paper, the frequency allocation reserved for radio astronomy in the L band set by the International Telecommuni-