ABSTRACT Infrared dark clouds (IRDCs) represent the earliest stage of high-mass star formation and host molecular cores at different states of activity from quiet state without any IR-signature of star formation to active state with IR-signatures and pronounced maser activity. Many IRDCs show indications of shocked gas associated with protostar outflows and can contain class I methanol masers (cIMMs). The aim of this study is to probe different types of cores in IRDCs with cIMMs and thermal molecular emission and to investigate the relationship between presence of cIMMs and physical conditions in IRDCs. For a sample of 37 molecular cores, using the 20-m Onsala radio telescope, we collected molecular line data at 44, 85, and 97 GHz for more than 15 species including CH3OH, CH3CCH, and CS. Kinetic temperature of the gas and molecular column densities were obtained. Methanol emission at 44 GHz was detected in 29 sources, with 4 sources are being new discoveries. None of the cores in quiescent state show emission at 44 GHz. Our results testify that cIMM emission is a reliable marker of advanced state of molecular cores. The higher detection rate for intermediate and IR-quiet sources suggests that cIMMs most readily trace the early stages of star formation characterized by moderate IR-signatures. We found that masers with higher flux densities tend to be associated with emission in the CH3CCH lines with higher integrated intensities. Sources undetected at 44 GHz have 4 times lower integrated intensities of CH3CCH and exhibit poorer molecular spectra than the most sources with cIMMs.

The Maser Monitoring Organisation (M2O) is a research community of telescope operators, astronomy researchers and maser theoreticians pursuing a joint goal of reaching a deeper understanding of maser emission and exploring its variety of uses as tracers of astrophysical events. These proceedings detail the origin, motivations and current status of the M2O, as was introduced at the 2021 EVN symposium.

Ross A. Burns,∗ Agnieszka Kobak, Alessio Caratti o Garatti, Alexander Tolmachev, Alexandr Volvach, Alexei Alakoz, Alwyn Wootten, Anastasia Bisyarina, Andrews Dzodzomenyo, Andrey Sobolev, Anna Bartkiewicz, Artis Aberfelds, Bringfried Stecklum, Busaba Kramer, Callum Macdonald, Claudia Cyganowski, Fransisco Colomer, Cristina Garcia Miro, Crystal Brogan, Dalei Li, Derck Smits, Dieter Engels, Dmitry Ladeyschikov, Doug Johnstone, Elena Popova, Emmanuel Proven-Adzri, Fanie van den Heever, Gabor Orosz, Gabriele Surcis, Gang Wu, Gordon MacLeod, Hendrik Linz, Hiroshi Imai, Huib van Langevelde, Irina Valtts, Ivar Shmeld, James O. Chibueze, Jan Brand, Jayender Kumar, Jimi Green, Job Vorster, Jochen Eislöffel, Jungha Kim, Koichiro Sugiyama, Karl Menten, Katharina Immer, Kazuyoshi Sunada, Kee-Tae Kim, Larisa Volvach, Luca Moscadelli, Lucas Jordan, Lucero Uscanga, Malcolm Gray, Marian Szymczak, Mateusz Olech, Melvin Hoare, Michał Durjasz, Mizuho Uchiyama, Nadya Shakhvorostova, Olga Bayandina, Pawel Wolak, Sergei Gulyaev, Sergey Khaibrakhmanov, Shari Breen, Sharmila Goedhart, Silvia Casu, Simon Ellingsen, Stan Kurtz, Stuart Weston, Tanabe Yoshihiro, Tim Natusch, Todd Hunter, Tomoya Hirota, Willem BAAN, Wouter Vlemmings, Xi Chen, Yan Gong, Yoshinori Yonekura, Zsófia Marianna Szabó and Zulema Abraham The Maser Monitoring Organisation E-mail: ross.burns@nao.ac.jp

AbstractWe used the unprecedented resolution of ∼25 μas of the VLBI array formed with the RadioAstron satellite to study the structures of H2O maser spots in the star forming region W49N. We found that anisotropic diffractive scattering of the ISM dominates the images of the maser spot, but does not completely blur them. The refractive scattering floor is about 0.001 in visibility at a baseline of 8 Gλ.

AbstractRecently, remarkable progress has been made in understanding the formation of high mass stars. Observations provided direct evidence that massive young stellar objects (MYSOs), analogously to low-mass ones, form via disk-mediated accretion accompanied by episodic accretion bursts, possibly caused by disk fragmentation. In the case of MYSOs, the mechanism theoretically provides a means to overcome radiation pressure, but in practice it is poorly studied - only three accretion bursts in MYSOs have been caught in action to date. A significant contribution to the development of the theory has been made with the study of masers, which have proven to be a powerful tool for locating “bursting” MYSOs. This overview focuses on the exceptional role that masers play in the search and study of accretion bursts in massive protostars.

We present results of amplitude calibration of the RadioAstron Space Radio Telescope (SRT) at wavelenghts of 1.35, 6.2,18, and 92 cm. Flux density calibrated internal noise signals and SEFDs are found to be stable within the errors at thelevel of 3–13%. We have used the flux density scale by Baars et al. (1977). The known issue of the variability of calibratorswas resolved performing comparison with two other flux density scales. We have resolved the issue by averaging SRT noisediode signals measured relative to Cassiopea A and Crab Nebula.

AbstractThe Maser Monitoring Organisation is a collection of researchers exploring the use of time-variable maser emission in the investigation of astrophysical phenomena. The forward directed aspects of research primarily involve using maser emission as a tool to investigate star formation. Simultaneously, these activities have deepened knowledge of maser emission itself in addition to uncovering previously unknown maser transitions. Thus a feedback loop is created where both the knowledge of astrophysical phenomena and the utilised tools of investigation themselves are iteratively sharpened. The project goals are open-ended and constantly evolving, however, the reliance on radio observatory maser monitoring campaigns persists as the fundamental enabler of research activities within the group.

H2O maser emission associated with the massive star formation region W49N were observed with the Space-VLBI mission RadioAstron. The procedure for processing of the maser spectral line data obtained in the RadioAstron observations is described. Ultra-fine spatial structures in the maser emission were detected on space-ground baselines of up to 9.6 Earth diameters. The correlated flux densities of these features range from 0.1% to 0.6% of the total flux density. These low values of correlated flux density are probably due to turbulence either in the maser itself or in the interstellar medium.

N. N. Shakhvorostova∗ a,b, A. M. Sobolevb, A. V. Alakoza, J. M. Moranc, H. Imaid , V. Yu. Avdeeva a Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, Moscow, Russia b Astronomical Observatory, Institute for Natural Sciences and Mathematics, Ural Federal University, Ekaterinburg, Russia c Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA d Center for General Education, Kagoshima University, Kagoshima, Japan E-mail: nadya@asc.rssi.ru

In 2017-18 the source of outstanding H2O maser bursts G25.65+1.05 have been intensively studied with a wide range of baselines - from compact array (JVLA) and ground VLBI (EVN, VLBA, KaVA) to space VLBI (RadioAstron mission supported by VLBA and EVN telescopes) - the report gives a brief summary of these observations.

Water masers are well-known to be variable on a variety of time scales, but only three Galactic H2O masers are known to flare to the level of 10(5)-10(6) Jy (T-B similar to 10(17) K): Orion KL, W49N, and the recently discovered G25.65+1.05. Recently detected flaring activity of H2O maser in the massive star-forming region G25.65+1.05 gave us a unique opportunity to study the fine structure of H2O maser emission in the bursting state with extremely high space VLBI angular resolution. Observation of the source was carried out with similar to 9 Earth diameter space-ground baseline within the framework of the RadioAstron project. H2O maser emission from two spectral features, including the bursting one, was detected in the experiment. Only similar to 1% of the bursting H2O maser emission was detected on the space-ground baselines: it indicates the presence of a very compact spatial structure with a size of 25 gas, which corresponds to 0.05 AU or solar diameters at the distance to the source of 2.08 kpc, and the brightness temperature of similar to 3 x 10(16) K. Analysis of the flux density as a function of the baseline length for the bursting H2O maser feature in the source shows that most of the emission comes from an extended "halo" structure, while the core of emission is very compact and has an extreme brightness temperature. These results are in agreement with the model of interacting maser clouds considered as the likely explanation of the nature of the burst in the source. Under the assumption of such a model, the beam size of maser emission is reduced while the brightness temperatures similar to the highest observed values are produced. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

H 2 O masers associated with the massive star formation region W49N were observed in frames of the Space-VLBI project RadioAstron.Ultra-compact structures in the masers were detected on space-ground baselines up to 9.6 Earth diameters.The flux density of ultra-compact features does not exceed a percent of the single dish flux density.Some results of the data processing for three observing sessions performed in 2014-2015 are presented.The lower limit of minimal brightness temperatures and estimates of angular sizes of the brightest features corresponding to the ultra-compact maser spots of the W49N complex are obtained.

We present an approach to testing the gravitational redshift effect using the RadioAstron satellite. The experiment is based on a modification of the Gravity Probe A scheme of nonrelativistic Doppler compensation and benefits from the highly eccentric orbit and ultra-stable atomic hydrogen maser frequency standard of the RadioAstron satellite. Using the presented techniques we expect to reach an accuracy of the gravitational redshift test of order 10−5, a magnitude better than that of Gravity Probe A. Data processing is ongoing, our preliminary results agree with the validity of the Einstein Equivalence Principle.

Results of systematic observations of a sample of bright H2O maser sources with fluxes, on average, exceeding 200 Jy in their main spectral feature during April–September 2017 (G25.65+1.05, G25.825−0.178, G27.184−0.082, G34.403+0.233, G35.20−0.74, G43.8−0.13, G107.30+5.64) are presented. These observations were carried out in preparation for Very Long Baseline Interferometry observations with an array including the Crimean Astrophysical Observatory 22-m radio telescope. All these sources display fairly strong variability during the time interval considered, encompassing fluxes from ∼40 to ∼2300 Jy. A flare reaching ∼17 000 Jy was detected at a velocity of 42.8 km/s in G25.65+1.05 on September 7, 2017, which subsequently grew to 60 000 Jy at the end of September 2017. This suggests the presence of compact maser structures. The velocities covered by various spectral components range from 5 to 20 km/s. In three sources (G25.65+1.05,G25.825−0.178,G35.20−0.74), a general growth in the fluxes of all the spectral features is observed, which may indicate variations in the conditions for pumping by an external source, for example, variations in the infrared flux from a central source or the passage of a shock. Possible evidence for the presence of bipolar outflows or disk structures in G25.65+1.05 is discussed.

We present the first VLBI observations of a Galactic water maser (in Cepheus. A) made with a very long baseline interferometric array involving the RadioAstron Earth-orbiting satellite station as one of its elements. We detected two distinct components at -16.9 and 0.6 km s(-1) with a fringe spacing of 66 mu as. In total power, the 0.6 km s(-1) component appears to be a single Gaussian component of strength 580 Jy and width of 0.7 km s(-1). Single-telescope monitoring showed that its lifetime was only eight. months. The absence of a Zeeman pattern implies the longitudinal magnetic field component is weaker than 120 mG. The space-Earth cross power spectrum shows two unresolved components smaller than 15 mu as, corresponding to a linear scale of 1.6 x 10(11) cm, about the diameter of the Sun, for a distance of 700 pc, separated by 0.54 km s(-1) in velocity and by 160 +/- 35 mu as in angle. This is the smallest angular structure ever observed in a Galactic maser. The brightness temperatures are greater than 2 x 10(14) K, and the line widths are 0.5 km s(-1). Most of the flux (about 87%) is contained in a halo of angular size of 400 +/- 150 mu as. This structure is associated with the compact HII region HW3diii. We have probably picked up the most prominent peaks in the angular size range of our interferometer. We discuss three dynamical models: (1) Keplerian motion around a central object, (2) two chance overlapping clouds, and (3) vortices caused by flow around an obstacle (i.e., von Karman vortex street) with a Strouhal number of about. 0.3.

AbstractThe RadioAstron space-VLBI mission has successfully detected extragalactic H2O MegaMaser emission regions at very long Earth to space baselines ranging between 1.4 and 26.7 Earth Diameters (ED). The preliminary results for two galaxies, NGC 3079 and NGC 4258, at baselines longer than one ED indicate masering environments and excitation conditions in these galaxies that are distinctly different. Further observations of NGC 4258 at even longer baselines are expected to reveal more of the physics of individual emission regions.