Some gamma-ray bursts (GRBs) have a tera–electron volt (TeV) afterglow, but the early onset of this has not been observed. We report observations with the Large High Altitude Air Shower Observatory of the bright GRB 221009A, which serendipitously occurred within the instrument field of view. More than 64,000 photons >0.2 TeV were detected within the first 3000 seconds. The TeV flux began several minutes after the GRB trigger, then rose to a peak about 10 seconds later. This was followed by a decay phase, which became more rapid ~650 seconds after the peak. We interpret the emission using a model of a relativistic jet with half-opening angle ~0.8°. This is consistent with the core of a structured jet and could explain the high isotropic energy of this GRB.

The frequency dependence of pulse width is studied for 150 normal pulsars, mostly selected from the European Pulsar Network, for which the multifrequency 10% pulse widths can be well fit with the Thorsett relationship W 10 = Aν µ + W 10,min . The relative fraction of pulse width change between 0.4 GHz and 4.85 GHz, η = (W 4.85 − W 0.4 )/W 0.4 , is calculated in terms of the best-fit relationship for each pulsar. It is found that 81 pulsars (54%) have η < −10% (group A), showing considerable profile narrowing at high frequencies, 40 pulsars (27%) have −10%≤ η ≤ 10% (group B), meaning a marginal change in pulse width, and 29 pulsars (19%) have η > 10% (group C), showing a remarkable profile broadening at high frequencies.The fractions of the group-A and group-C pulsars suggest that the profile narrowing phenomenon at high frequencies is more common than the profile broadening phenomenon, but a large fraction of the group-B and group-C pulsars (a total of 46%) is also revealed. The group-C pulsars, together with a portion of group-B pulsars with a slight pulse broadening, can hardly be explained using the conventional radius-to-frequency mapping, which only applies to the profile narrowing phenomenon. Based on a recent version of the fan beam model, a type of broadband emission model, we propose that the diverse frequency dependence of pulse width is a consequence of different types of distribution of emission spectra across the emission region. The geometrical effect predicting a link between the emission beam shrinkage and the spectrum steepening is tested but disfavored.

To shed light onto the circumnuclear environment of 22 GHz (λ ∼ 1.3 cm) H 2 O maser galaxies, we have analyzed some of their multi-wavelength properties, including the far infrared luminosity (FIR), the luminosity of the [O III]λ5007 emission line, the nuclear X-ray luminosity, and the equivalent width of the neutral iron Kα emission line (EW (K α )). Our statistical analysis includes a total of 85 sources, most of them harboring an active galactic nucleus (AGN). There are strong anti-correlations between EW (K α ) and two "optical thickness parameters", i.e. the ratios of the X-ray luminosity versus the presumably more isotropically radiated [O III] and far infrared (FIR) luminosities. Based on these anticorrelations, a set of quantitative criteria, EW (K α )>300 eV, L 2−10 keV <2 L [O III] and L FIR >600 L 2−10 keV can be established for Compton-thick nuclear regions. 18 H 2 O maser galaxies belong to this category. There are no obvious correlations between the EW (K α ), the [O III] luminosity and the isotropic H 2 O maser luminosity. When comparing samples of Seyfert 2s with and without detected H 2 O maser lines, there seem to exist differences in EW (K α ) and the fraction of Compton-thick nuclei. This should be studied further. For AGN masers alone, there is no obvious correlation between FIR and H 2 O maser luminosities. However, including masers associated with star forming regions, a linear correlation is revealed. Overall, the extragalactic FIR-H 2 O data agree with the corresponding relation for Galactic maser sources, extrapolated by several orders of magnitude to higher luminosities.