It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron star’s rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales

Using the Australia Telescope Compact Array (ATCA), we conducted a survey of CO J = 1 − 0 and J = 2 − 1 line emission towards strongly lensed high-redshift dusty star forming galaxies (DSFGs) previously discovered with the South Pole Telescope (SPT). Our sample comprises 17 sources that had CO-based spectroscopic redshifts obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder Experiment (APEX). We detect all sources with known redshifts in either CO J = 1 − 0 or J = 2 − 1. Twelve sources are detected in the 7-mm continuum. The derived CO luminosities imply gas masses in the range (0.5 − 11) × 10 10 M ⊙ and gas depletion timescales t dep < 200 Myr, using a CO to gas mass conversion factor α CO = 0.8 M ⊙ (K km s −1 pc 2 ) −1 . Combining the CO luminosities and dust masses, along with a fixed gas-to-dust ratio, we derive α CO factors in the range 0.4 − 1.8 M ⊙ (K km s −1 pc 2 ) −1 , similar to what is found in other starbursting systems. We find small scatter in α CO values within the sample, even though inherent variations in the spatial distribution of dust and gas in individual cases could bias the dust-based α CO estimates. We find that lensing magnification factors based on the CO linewidth to luminosity relation (µ CO ) are highly unreliable, but particularly when µ < 5. Finally, comparison of the gas and dynamical masses suggest that the average molecular gas fraction stays relatively constant at z = 2 − 5 in the SPT DSFG sample.

We present new observations of 34 Young Stellar Object (YSO) candidates in the Small Magellanic Cloud (SMC). The photometric selection required sources to be bright at 24 and 70 µm (to exclude evolved stars and galaxies). The anchor of the analysis is a set of Spitzer-IRS spectra, supplemented by groundbased 3−5 µm spectra, Spitzer IRAC and MIPS photometry, near-IR imaging and photometry, optical spectroscopy and radio data. The sources' spectral energy distributions (SEDs) and spectral indices are consistent with embedded YSOs; prominent silicate absorption is observed in the spectra of at least ten sources, silicate emission is observed towards four sources. Polycyclic Aromatic Hydrocarbon (PAH) emission is detected towards all but two sources. Based on band ratios (in particular the strength of the 11.3-µm and the weakness of the 8.6-µm bands) PAH emission towards SMC YSOs is dominated by predominantly small neutral grains. Ice absorption is observed towards fourteen sources in the SMC. The comparison of H 2 O and CO 2 ice column densities for SMC, Large Magellanic Cloud (LMC) and Galactic samples suggests that there is a significant H 2 O column density threshold for the detection of CO 2 ice. This supports the scenario proposed by Oliveira et al. (2011), where the reduced shielding in metal-poor environments depletes the H 2 O column density in the outer regions of the YSO envelopes. No CO ice is detected towards the SMC sources. Emission due to pure-rotational 0 − 0 transitions of molecular hydrogen is detected towards the majority of SMC sources, allowing us to estimate rotational temperatures and H 2 column densities. All but one source are spectroscopically confirmed as SMC YSOs. Based on the presence of ice absorption, silicate emission or absorption, and PAH emission, the sources are classified and placed in an evolutionary sequence. Of the 33 YSOs identified in the SMC, 30 sources populate different stages of massive stellar evolution. The presence of ice-and/or silicate-absorption features indicates sources in the early embedded stages; as a source evolves, a compact H II region starts to emerge, and at the later stages the source's IR spectrum is completely dominated by PAH and fine-structure emission. The remaining three sources are classified as intermediate-mass YSOs with a thick dusty disc and a tenuous envelope still present. We propose one of the SMC sources is a D-type symbiotic system, based on the presence of Raman, H and He emission lines in the optical spectrum, and silicate emission in the IRS-spectrum. This would be the first dust-rich symbiotic system identified in the SMC.