Very Long Baseline Interferometry (VLBI) is providing key information to the study of maser processes in the Universe, from star formation regions or circumstellar envelopes around evolved stars, to Galactic structure and cosmology, through precise astrometry. VLBI networks offer various capabilities and, most importantly, support to users, to ensure that these infrastructures are fully accesible and that the best science can emerge. In this paper we describe the advances in VLBI that enable exciting maser studies.

We have detected maser emission from the 36.2 GHz (4−1 → 30E) methanol transition towards NGC 4945. This emission has been observed in two separate epochs and is approximately five orders of magnitude more luminous than typical emission from this transition within our Galaxy. NGC 4945 is only the fourth extragalactic source observed hosting class I methanol maser emission. Extragalactic class I methanol masers do not appear to be simply highly-luminous variants of their galactic counterparts and instead appear to trace large-scale regions where low-velocity shocks are present in molecular gas.

PSR J0337+1715 is a millisecond radio pulsar in a hierarchical stellar triple system with two white dwarfs. This system is a unique and excellent laboratory in which to test the strong equivalence principle (SEP) of general relativity. An initial SEP-violation test was performed using direct 3-body numerical integration of the orbit in order to model the more than 25000 pulse times of arrival (TOAs) from three radio telescopes: Arecibo, Green Bank and Westerbork. In this work I present our efforts to quantify the effects of systematics in the TOAs and timing residuals, which limit the precision of an SEP test. In particular, we apply Fourier-based techniques to the timing residuals in order to isolate the effects of systematics that can masquerade as an SEP violation.

We present the results of sub-millimetre observations on three periodic methanol maser sources. Our results indicate that there are geometric differences between some periodic methanol masers which have different variability profiles.

Masers have been well-known phenomena for decades, but water masers at 183, 321, 325 and 658 GHz have only been detected since the 1990s. Early detections came from single-dish telescopes with follow-up observations from the PdBI and the Submillimeter Array. Detecting them at these short wavelengths has been very difficult due to water in our atmosphere, meaning that even in very good weather, one can only detect very bright masers, such as those in stellar atmospheres. In the last 7 years, a new window on submillimeter water masers, both Galactic and now extragalactic, has opened. Located at high altitude, above a large fraction of the Earth’s atmosphere, ALMA sits on the edge of the driest desert on the planet, meaning that the air that does remain above the telescope is frequently extremely low in water vapor content. Combine this with sensitive, stable receivers covering a number of masing transitions from 183-658 GHz and you have an excellent machine for detecting and characterizing submillimeter water masers. In addition, other molecules also exhibit maser emission in the ALMA observing bands, such as SiO and HCN.

Taking Rubakov-Callen effect (that nucleons may decay catalyzed by magnetic monopoles) as the energy source, we propose a unified model of supernova driven by magnetic monopoles in this paper.

We report on magnetic field measurements associated with the well-known extreme red supergiant (RSG), VY Canis Majoris (VY CMa). We measured both linear and circular polarization of the SiO v = 0, J = 1 − 0 transition using a sensitive radio interferometer. The measured magnetic field strengths are surprisingly high. A lower limit for the field strength is expected to be at least ~ 10 Gauss based on the high degree of linear polarization. Since the field strengths are very high, the magnetic field must be a key element in understanding the stellar evolution of VY CMa as well as the dynamical and chemical evolution of the complex circumstellar envelope of the star.

The MPIfR is working together with SKA-SA and the Universities of Manchester and Oxford to deploy three instruments on MeerKAT: An S-band receiver system, a dedicated beamforming cluster and a flexible pulsar search cluster. Together these instruments will provide MeerKAT with powerful tools for supporting a wide range of scientific applications and in particular will enable large-scale pulsar and fast transient surveys to be performed. In these proceedings we describe the design, implementation and deployment timeline for these instruments.

W49 A is a star-forming region (SFR) found in the constellation of Aquila. It contains 3 active regions: W49 North (W49 N), W49 South West (W49 SW) and W49 South (W49 S). We present preliminary results from two epochs (e-)MERLIN observations of all ground-state OH masers towards the star-forming region (SFR) complex W49 A. The first epoch of observations was done in full-polarization mode with MERLIN in 2005 while the second epoch was obtained only in dual circular polarization during the test observations of the upgraded e-MERLIN in 2013. The overall maser spatial distributions in both epochs are in good agreement. We found several new high velocity maser features up to +34 km s−1 and −28 km s−1. The magnetic field strengths are between 1.1 to 10.8 mG. All three sources show evidence of magnetic field reversal.

A wind nebula generating extended X-ray emission was recently detected surrounding Swift 1834.9-0846. This is the first magnetar for which such a (pulsar) wind nebula (PWN) was found. I demonstrate that Swift 1834.9-0846’s nebula can be rotationally-powered if it is being compressed by the environment. The physical reason behind this is the dominance of adiabatic heating over all other cooling and escape processes. This effect can happen only for pulsars of relatively low spin-down power and can make for very efficient nebulae. This contribution is based on previous work published in ApJ 835, article id. 54, 13 pp. (2017).

We present a case study of a single high-mass protostar associated with an infrared quiet massive clump selected from the ATLASGAL survey. The thermal dust emission reveals a single collapsing object associated with a prominent molecular outflow. We detect bright emission from a torsionally excited state transition of CH3OH offset from the protostar that is well explained by shocks at the transition from the infalling envelope onto an accretion disk.

New simultaneous X-ray and radio observations of the archetypal mode-switching pulsar PSR B0943+10 have been carried out with XMM-Newton and the LOFAR, LWA and Arecibo radio telescopes in November 2014. They allowed us to better constrain the X-ray spectral and variability properties of this pulsar and to detect, for the first time, the X-ray pulsations also during the X-ray-fainter mode. The combined timing and spectral analysis indicates that unpulsed non-thermal emission, likely of magnetospheric origin, and pulsed thermal emission from a small polar cap are present during both radio modes and vary in a correlated way.

We have observed a young stellar object, IRAS 18360-0537, with a far-infrared luminosity of 1.2 × 105 L⊙. It is perhaps the most promising candidate of a high-mass protostar associated with a Keplerian disk and a jet/outflow system in the regime of L > 105L⊙. We are conducting the SMA, VLA, and VLBA studies to provide a comprehensive understanding of this interesting high mass star formation scenario.

We report astrometric results for seven 6.7 GHz CH3OH and one 22 GHz H2O masers in the Perseus arm with VLBA and VERA observations. Among the eight sources, we succeeded in obtaining trigonometric parallaxes for all sources, except G098.03+1.44 at 6.7 GHz band. By combining our results with previous astrometry results (Choi et al. 2014), we determined an arm width of 0.41 kpc and a pitch angle of 8.2 ± 2.5 deg for the Perseus arm. By using a large sample of the Perseus arm (26 sources), we examined the three-dimensional, non-circular motions (defined as U, V and W) of sources in the Perseus arm as a function of the distance (D) perpendicular to the arm. Interestingly, we found a weighted mean of <U > = 12.7 ± 1.2 km s−1 for 14 sources with D < 0 kpc (i.e. sources on the interior side of the arm) and <U > = −0.3 ± 1.5 km s−1 for 12 sources with D > 0 kpc (i.e. sources exterior to the arm). These findings might be the first observational indication of the ”damping phase of a spiral arm” suggested by the non-steady spiral arm model of Baba et al. (2013). The small pitch angle of the Perseus arm (< 10 deg) also supports the damping phase, based on ”pitch angle vs. arm amplitude” relation shown in Grøsbol et al. (2004).

The first long-term maser (mainly methanol) monitoring program is under way with the radio telescopes of Ventspils International Radio Astronomy Center. The first activity of this program was to develop an observations methodology and data registration and reduction software for the Ventspils telescopes. The developed routines are to be used for maser variability monitoring, investigating short bursts of intensity and a search for new, previously unknown, maser sources. Currently the program consists of 41 methanol masers observed at 6.7 GHz, while new ones are periodically added. The maser sources are observed at 3 – 5 day intervals. It was found that most the sources display a significant level of variability with time, ranging from a few days, up to several months and, perhaps, years. In addition to non-varying masers, several types of maser variability behavior were observed, including: monotonic increases or decreases, un-periodical, quasi-periodic and periodic variations.

PSR B0943+10 is an old non-recycled pulsar which for decades has been mostly known for its rapid and spontaneous radio mode switching. Recently, Hermsen et al. (2013) discovered correlated changes in the thermal X-ray emission from the polar cap, thus demonstrating that radio modes are not just a product of the local changes in the radio emission region, but a sign of some global magnetospheric transformation. At about the same time, owing to the commissioning of the new generation of low-frequency radio arrays, the broadband observations at the lowest edge of ionospheric transparency window became available. At these radio frequencies profile morphology and the single-pulse properties of PSR B0943+10’s emission become very dynamic, providing details not only about the emission itself, but also about the conditions in the polar gap. Here, I will present the recent results of the LOFAR observations of PSR B0943+10 and discuss their contribution to the multiwavelength picture.

Imaging the inner few 1000 AU around massive forming stars, at typical distances of several kpc, requires angular resolutions of better than 0″.1. Very Long Baseline Interferometry (VLBI) observations of interstellar molecular masers probe scales as small as a few AU, whereas (new-generation) centimeter and millimeter interferometers allow us to map scales of the order of a few 100 AU. Combining these informations all together, it presently provides the most powerful technique to trace the complex gas motions in the proto-stellar environment. In this work, we review a few compelling examples of this technique and summarize our findings.

The Australia Telescope Compact Array (ATCA) participated in a number of survey programs to search for and image common class I methanol masers (at 36 and 44 GHz) with high angular resolution. In this paper, we discuss spatial and velocity distributions revealed by these surveys. In particular, the number of maser regions is found to fall off exponentially with the linear distance from the associated young stellar object traced by the 6.7-GHz maser, and the scale of this distribution is 263±15 milliparsec. Although this relationship still needs to be understood in the context of the broader field, it can be utilised to estimate the distance using methanol masers only. This new technique has been analysed to understand its limitations and future potential. It turned out, it can be very successful to resolve the ambiguity in kinematic distances, but, in the current form, is much less accurate (than the kinematic method) if used on its own.

G22 is a hub-filament system composed of four supercritical filaments. Velocity gradients are detected along three filaments. A total mass infall rate of 700 M⊙ Myr−1 would double the hub mass in about three free-fall times. The most massive clump C1 would be in global collapse with an infall velocity of 0.26 km s−1 and a mass infall rate of 5 × 10−4 M⊙ yr−1, which is supported by the prevalent HCO+ (3-2) and 13CO (3-2) blue profiles. A hot molecular core (SMA1) was revealed in C1. At the SMA1 center, there is a massive protostar (MIR1) driving multipolar outflows which are associated with clusters of class I methanol masers. MIR1 may be still growing with an accretion rate of 7 × 10−5 M⊙ yr−1. Filamentary flows, clump-scale collapse, core-scale accretion coexist in G22, suggesting that high-mass starless cores may not be prerequisite to form high-mass stars. In the high-mass star formation process, the central protostar, the core, and the clump can grow in mass simultaneously.

In this proceeding, we summarize the key science goals and reference design for a next-generation Very Large Array (ngVLA) that is envisaged to operate in the 2030s. The ngVLA is an interferometric array with more than 10 times the sensitivity and spatial resolution of the current VLA and ALMA, that will operate at frequencies spanning ~1.2 – 116 GHz, thus lending itself to be highly complementary to ALMA and the SKA1. As such, the ngVLA will tackle a broad range of outstanding questions in modern astronomy by simultaneously delivering the capability to: unveil the formation of Solar System analogues; probe the initial conditions for planetary systems and life with astrochemistry; characterize the assembly, structure, and evolution of galaxies from the first billion years to the present; use pulsars in the Galactic center as fundamental tests of gravity; and understand the formation and evolution of stellar and supermassive blackholes in the era of multi-messenger astronomy.