A. M. Tolmachev

Time variation of the water maser in ON2

Context. The results of monitoring of the water-vapour maser in the 1.35-cm line toward ON2 in 1995-2004 are reported. Aims. The main goal was to study variations of the H 2 O maser emission on a long (10 years) time interval, in particular, velocity drifts and correlation between fluxes in various spectral features. Methods. The observations were carried out on the RT-22 radio telescope of Pushchino Radio Astronomy Observatory. Results. The emission of the northern component (ON2 N) took place in a broad interval of radial velocities, from -12 to 9 km s -1 . The total H 2 O emission has two variability components: slow and flaring. The period of the former component is most likely between 25 and 30 years. The flaring component has a cyclic character with a period from 1.1 to 2.6 years. The alternation of the activity cycles was accompanied by changes in the velocity structure of the H 2 O spectra. There is good correlation between the variations in the integrated flux and velocity centroid, as well as between the emissions in various segments of the H 2 O spectrum. We suggest that long-term variations and oscillations of the water-maser emission can be related to the non-stationarity and anisotropy of bipolar molecular outflow from the B-type star in the ultracompact H II region.

An H2O maser in the infrared source IRAS 20126+4104

Results of monitoring of H2O maser in the infrared source IRAS 20126+4104, which is associated with a cool molecular cloud, are presented. The observations were carried out on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory (Russia) between June 1991 and January 2006. The spectrum of the H2O maser emission extends from − 16.7 to 4.8 km/s and splits into separate groups of emission features. Cyclic variations of the integrated maser flux with a period from 3.4 to 5.5 years were detected, together with strong flares of up to 220 Jy in individual emission features. It is shown that large linewidths in periods of high maser activity are due to small-scale turbulent motions of the material. An expanding envelope around a young star is accepted as a model for the source. The protostar has a small peculiar velocity with respect to the molecular cloud (∼2 km/s). Individual emission features form organized structures, including multi-link chains.

Superflares of H 2 O Maser Emission Toward the Protostellar Object G25.65+1.05 (IRAS 18316−0602)

The results of a study of the maser source IRAS 18316−0602 in the H2O line at λ = 1.35 cm are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) from June 2002 until March 2017. Three superflares were detected, in 2002, 2010, and 2016, with peak flux densities of >3400, 19 000, and 46 000 Jy, respectively. An analysis of these superflares is presented. The flares took place during periods of high maser activity in a narrow interval of radial velocities (40.5–42.5 km/s), and could be associated with the passage of a strong shock. The emission of three groups of features at radial velocities of about 41, 42, and 43 km/s dominated during themonitoring. The flare in 2016 was accompanied by a considerable increase in the flux densities of several features with velocities of 35–56 km/s.

Results of a long-term monitoring of the 1.35-cm water-vapor maser source ON 1 (1981–2013)

We present the results of our long-term monitoring of the 1.35-cm water-vapor maser source ON 1 performed at the 22-m radio telescope of the Pushchino Radio Astronomy Observatory from 1981 to 2013. Maser emissionwas observed in a wide range of radial velocities, from −60 to +60 km s−1. Variability of the integrated flux with a period of ∼9 years was detected. We show that the stable emission at radial velocities of 10.3, 14.7, and 16.5 km s−1 belongs to compact structures that are composed of maser spots with close radial velocities and that are members of two water-maser clusters, WMC 1 and WMC 2. The detected short-lived emission features in the velocity ranges from −30 to 0 and from 35 to 40 km s−1 as well as the high-velocity ones are most likely associated with a bipolar molecular outflow observed in the CO line.

Flares of the H2O maser in W31(2)

We analyze our monitoring data for the water-vapor maser in the source W31(2), associated with a region of vigorous star formation, a cluster of OB stars. The monitoring was performed with the 22-m radio telescope at Pushchino Radio Astronomy Observatory during 1981–2004. The variability of the H2O maser in W31(2) was found to be cyclic, with a mean period of 1.9 yr. Two flares were most intense (superflares): in 1985–1986 and 1998–1999. In each activity cycle, we observed up to several short flares, subpeaks. The fluxes of many emission features during the flares were correlated. We also observed successive activation of individual emission features in order of increasing or decreasing radial velocity, suggesting an ordered structure and, hence, a radial-velocity gradient of the medium. There is a clear correlation of the emission peaks of the main components in the spectra at radial velocities of −1.7, −1.3, 0.5, and 1.3 km s−1 with activity cycles and of the emission at VLSR < −8 km s−1 with short flares. During the superflares, the emission in the low-velocity part of the H2O spectrum and a number of other phenomena related to coherent maser-emission properties were suppressed. The maser spots are assumed to form a compact structure, to have a common pumping source, and to be associated with an accretion flow onto the cluster of OB stars.

The H2O maser toward IRAS 06308+0402

We present the monitoring results for the H2O maser toward the infrared source IRAS 06308+0402 associated with a dense cold molecular cloud. The observations were carried out with the 22-m radio telescope at the Pushchino Radio Astronomy Observatory (Russia) during 1992–2003. The H2O maser was discovered in May 1992 (Pashchenko 1992) during a survey of IRAS sources associated with dense cold clouds with bipolar molecular outflows. The H2O spectrum contains many emission features, suggesting the fragmentation of the envelope around a young star. The star has a low peculiar velocity relative to the CO molecular cloud (∼2.2 km s−1). We found a cyclic variability of the total maser flux with a period from 1.8 to 3.1 yr.

Long-Term Monitoring and Interpretation of Flares in the H2O Maser Emission of IRAS 16293–2422

The results of a study of the H2O and OH maser emission from the cool IR source IRAS 16293−2422 are presented. The observations analyzed were obtained in H2O lines with the 22-m telescope of the Pushchino Radio Astronomy Observatory during 1999–2015 and in OH lines with the Nanc¸ ay radio telescope (France). A large number of very strong flares of the H2O maser were detected, reaching fluxes of tens of thousands of Jansky. Individual features can form organized structures resembling chains ∼2 AU in length with a radial-velocity gradient along them. The observed drift of the H2O emission (2003–2004) in space and velocity (from 4.3 to 5.3 km/s) is not due solely to proper motion of the features. The other origin of the drift is a drift of the emission maximum during a flare as the shock consecutively excites spatially separated features in the structure in the form of a chain. The OH-line observations at 18 cm show that the emission remains unpolarized and thermal, with a line width of 0.7 km/s, which corresponds to a cloud temperature of ∼30 K.

H2O and OH masers associated with cold infrared sources

We present the results of our monitoring of four maser sources associated with cold infrared sources. The observations were performed in the water-vapor line at 1.35 cm with the 22-m radio telescope at the Pushchino Radio Astronomy Observatory and in the hydroxyl lines at 18 cm with the Nançay radio telescope. Cyclic variability of the H2O maser emission was detected in all four sources. The durations of the cycles are different and lie within the range 1.8–5.5 yr. In each source, the cycles differed by a factor from 1.5 to 2.25. A fairly periodic pattern of variability was observed in IRAS 20126+4104 on a time scale from 3.6 to 5.3 yr. Models of the maser sources are discussed. In IRAS 20126+4104, we detected strong variability of the maser emission in the main OH 1665 and 1667 MHz lines. We calculated the magnetic field strength for two maser features from the Zeeman splitting of the OH line: in IRAS 18265-1517 (1.3 mG at epoch 2008) and IRAS 20126+4104 (10 mG at epoch 2014). Variability of the magnetic field was detected in the second feature. In the same sources, we detected maser emission in the 1667 MHz OH line. The presence of emission in both main OH 1665 and 1667 MHz lines is consistent with the existing model calculations and will allow the gas density in the masing regions to be refined.

The results of ultra‐rapid flux fluctuations monitoring in 2002–2009 for galactic sources of water‐vapor maser emission at a wavelength of 1.35 cm

Results of a search for ultra rapid flux fluctuations of galactic sources of maser emission in the water‐vapor line at a wavelength of 1.35 cm. An observational technique of a search for ultra rapid flux fluctuations has been developed. From 2002 to 2009 a number of observational sessions for about 40 maser sources have been carried out. Several of them have demonstrated such a variability. Possible mechanisms of the variability are discussed, among them internal processes within the sources themselves as well as external ones, including the theoretical possibility of a resonant effect of gravitational waves from galactic objects on the maser region. Clear evidence for the presence of such a variability has been found in several sources (Cep A, W43M3, W49N, W33B). This variability appears not permanently, but only certain states of particular H2O masers. In some sources (Ori A, W3 OH, W49N) demonstrated any variations by linear polarization of signal.

Maser emission toward the very young massive star GH2O 092.67+03.07 (IRAS 21078+5211)

Results of monitoring of the H2O maser observed toward the infrared source IRAS 21078+5211 in the giant molecular cloud Cygnus OB7 are presented. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) from April 1992 to March 2006. Five cycles of maser activity at various levels were observed. In the periods of highest activity, the spectrum of the H2O maser emission extended from −43 to 12 km/s. During strong flares, the flux densities in some emission features reached nearly 600 Jy. The protostar has a small peculiar velocity with respect to the CO molecular cloud (∼2 km/s). Based on the character of the radial-velocity variations and the tendency for the linewidth to increase with the flux, it is concluded that the medium is strongly fragmented and that there is a small-scale turbulent outflow of ga in the H2O maser region, which may impede the formation of an HII region. The asymmetric distribution of the maser components in VLSR, the difference in the average linewidths of the central and lateral clusters of components, and the fairly high radial velocities relative to the molecular cloud (especially during periods of the highest maser activity) suggest that the maser spots belong to different clusters and different structures of the source: a disk and bipolar outflow.