Search

We present results from a spectroscopically blind search for associated and intervening H i 21 cm and OH 18 cm absorption lines toward 88 active galactic nuclei (AGN) at 2 2. The detection rate ( 1.6(-1.4)(+3.8) %) suggests a low covering factor of the cold neutral medium (CNM; T similar to 100 K) associated with these powerful AGN. The intervening absorption line search, with a sensitivity to detect the CNM in damped Ly alpha systems (DLAs), has comoving absorption path lengths of Delta X = 130.1 and 167.7 for HI and OH, respectively. The corresponding number of absorbers per unit comoving path length are 2. Our AGN sample is optically fainter compared to the quasars used to search for DLAs in the past. In our optical spectra obtained using SALT and NOT, we detect five intervening (redshift path similar to 9.3) and two proximate DLAs. This is slightly excessive compared to the statistics based on optically selected quasars. The nondetection of H I 21 cm absorption from these DLAs suggests a small CNM covering fraction around galaxies at z > 2.

We present results from a spectroscopically blind search for associated and intervening H i 21 cm and OH 18 cm absorption lines toward 88 active galactic nuclei (AGN) at 2 2. The detection rate ( 1.6(-1.4)(+3.8) %) suggests a low covering factor of the cold neutral medium (CNM; T similar to 100 K) associated with these powerful AGN. The intervening absorption line search, with a sensitivity to detect the CNM in damped Ly alpha systems (DLAs), has comoving absorption path lengths of Delta X = 130.1 and 167.7 for HI and OH, respectively. The corresponding number of absorbers per unit comoving path length are 2. Our AGN sample is optically fainter compared to the quasars used to search for DLAs in the past. In our optical spectra obtained using SALT and NOT, we detect five intervening (redshift path similar to 9.3) and two proximate DLAs. This is slightly excessive compared to the statistics based on optically selected quasars. The nondetection of H I 21 cm absorption from these DLAs suggests a small CNM covering fraction around galaxies at z > 2.

© 2019 The Author(s). We present rapid, multiwavelength photometry of the low-mass X-ray binary Swift J1357.2-0933 during its 2017 outburst. Using several sets of quasi-simultaneous ULTRACAM/NTT (optical), NuSTAR (X-ray), XRT/Swift (X-ray), SALT (optical), and ATCA (radio) observations taken during outburst decline, we confirm the frequent optical dipping that has previously been noted both in outburst and in quiescence. We also find: (1) that the dip frequency decreases as the outburst decays, similar to what was seen in the previous outburst, (2) that the dips produce a shape similar to that in binary systems with partial disc occultations, (3) that the source becomes significantly bluer during these dips, indicating an unusual geometry compared to other LMXB dippers, and (4) that dip superposition analysis confirms the lack of an X-ray response to the optical dips. These very unusual properties appear to be unique to Swift J1357.2−0933, and are likely the result of a high binary inclination, as inferred from features such as its very low outburst X-ray luminosity. From this analysis as well as X-ray/optical timing correlations, we suggest a model with multicomponent emission/absorption features with differing colours. This could include the possible presence of a sporadically occulted jet base and a recessed disc. This source still hosts many puzzling features, with consequences for the very faint X-ray transients population.