Detected Maser Emission Research Articles

The Effelsberg survey of FU Orionis and EX Lupi objects

Context. FU Orionis (FUor) and EX Lupi (EXor) type objects are two groups of peculiar and rare pre-main sequence low-mass stars that are undergoing powerful accretion outbursts during their early stellar evolution. Although water masers are widespread in star-forming regions and serve as powerful probes of mass accretion and ejection on small scales, little is known about the prevalence of water masers toward FUors and EXors. Aims. We aim to perform the first systematic search for the 22.2 GHz water maser line in FUors and EXors in order to determine its overall incidence in these eruptive variables and to facilitate high angular-resolution follow-up observations. Methods. We used the Effelsberg 100-m radio telescope to observe the H2O (616 – 523) transition at 22.2GHz toward a sample of 51 eruptive young stellar objects. Results. We detected a total of five water masers in our survey; three are associated with eruptive stars, equivalent to a detection rate of ~6% for our sample of eruptive sources. These detections include one EXor, V512 Per (also known as SVS 13 or SVS 13A), and two FUors, Z CMa, and HH 354 IRS. This is the first reported detection of water maser emission towards HH 354 IRS. We also detected water maser emission in our pointing towards the FUor binary RNO 1B/1C, which most likely originates from the nearby deeply embedded source IRAS 00338+6312 (~4″ from RNO 1B/1C). Emission was also detected from H2O(B), (also known as SVS 13C), a Class 0 source ~30″ from the EXor V512 Per. The peak flux density of H2O(B) in our observations, 498.7 Jy, is the highest observed to date, indicating that we have serendipitously detected a water maser flare in this source. In addition to the two non-eruptive Class 0 sources (IRAS 00338+6312 and H2O(B)/SVS 13C), we detected maser emission towards one Class 0/I (HH 354 IRS) and two Class I (V512 Per/SVS 13A and Z CMa) eruptive stars. Conclusions. Despite the low detection rate, we demonstrate the presence of 22.2 GHz water maser emission in both FUor and EXor systems, paving the way to radio interferometric observations to study the environments of these eruptive stars on small scales. Comparisons of our data with historical observations spanning several decades suggest that multiple water maser flares have occurred in both V512 Per and H2O(B).

An unusually powerful and long-lasting water maser flare phenomenon in IRAS 16293-2422

Aims. Our goal is to obtain new detailed observational data on the water maser flare phenomenon, unprecedented in power and duration, that occurred in IRAS 16293-2422 and determine the physical characteristics of the individual flares. Methods. We used the ground-based 22 m radio telescope to conduct long-term observations of the water maser features near – 1.5 km s−1 in IRAS 16293-2422. The movement of the radio telescope, collection of observational data, and processing were performed automatically. We used spectral-temporal data analysis to identify water maser flares in a complex flare phenomenon and determine their physical parameters. Results. The detected maser emission came from the largest structure of maser spots, the high density of which resulted in their partial overlap in time. There were a total of ten individual powerful flares in the phenomenon. The existence of such a complex configuration of emitting maser spots with very similar radial velocities has been confirmed for the first time. We were able to determine that masers of the powerful flares were in an unsaturated state due to a cascade pumping of radiation from several masers located in the observer’s line of sight. We obtained new important physical parameters of maser flares: the detailed shape of flares, the state of the water maser during flares, the H2O kinetic temperature, the density of the medium, the degree of ionization, and the velocities of the maser spots responsible for the flares.

Radio continuum properties of OH megamaser galaxies

ABSTRACT We present a study of the radio continuum properties of two luminous/ultraluminous infrared galaxy samples: the OH megamaser (OHM) sample (74 objects) and the control sample (128 objects) without detected maser emission. We carried out pilot observations for 140 objects with the radio telescope RATAN-600 at 1.2, 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2019–2021. The OHM sample has two times more flat-spectrum sources (32 per cent) than the control sample. Steep radio spectra prevail in both samples. The median spectral index at 4.7 GHz α4.7 = −0.59 for the OHM sample, and α4.7 = −0.71 for the non-OHM galaxies. We confirm a tight correlation of the far-infrared (FIR) and radio luminosities for the OHM sample. We found correlations between isotropic OH line luminosity LOH and the spectral index α4.7 (ρ = 0.26, p-val. = 0.04) and between LOH and radio luminosity P1.4 (ρ = 0.35, p-val. = 0.005). Reviewing subsamples of masers powered by active galactic nuclei (AGNs) and star formation revealed insignificant differences for their FIR and radio properties. None the less, AGN-powered galaxies exhibit larger scatter in a range of parameters and their standard deviations. The similarities in the radio and FIR properties in the two samples are presumably caused by the presence of a significant amount of AGN sources in both samples (47 and 30 per cent in the OHM and control samples) and/or possibly by the presence of undetected OH emission sources in the control sample.

Accurate OH Maser Positions from the SPLASH Survey. III. The Final 96 deg2

Abstract We present high spatial resolution observations of ground-state OH masers achieved with the Australia Telescope Compact Array (ATCA). These observations targeted 253 pointing centers containing OH maser candidates at all four ground-state OH transitions identified in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH) across 96 deg2 of the southern Galactic plane (332° < l < 334° and −2° < b < +2°, 344° < l < 355° and −2° < b < +2°, 358° < l < 4° and +2° < b < +6°, 5° < l < 10° and −2° < b < +2°). We detect maser emission toward 236 fields and suggest that 7 out of 17 nondetections are due to the slightly lower sensitivity of the ATCA observations, combined with some temporal variability. The superior resolution provided by the ATCA data has allowed us to identify 362 OH maser sites in the 236 target fields. Almost half (160 of 362) of these masers have been detected for the first time. Comparison between these 362 maser sites and information presented in the literature allowed us to categorize 238 sites as evolved star sites (66%), 63 as star formation (17%), 8 as supernova remnants, and 53 as unknown maser sites (15%). We present an analysis of the OH masers across the full SPLASH survey range (176 deg2) and find that the detection rate of 1.7 GHz radio continuum sources (18%) is lower than that previously found at 8.2 and 9.2 GHz (38%). We also find that the velocity separations of evolved star sites with symmetric 1612 MHz maser profiles are generally smaller than those with asymmetric profiles.

Accurate OH Maser Positions. II. The Galactic Center Region

Abstract We present high spatial resolution observations of ground-state OH masers achieved using the Australia Telescope Compact Array (ATCA). These observations were conducted toward 171 pointing centers where OH maser candidates were identified previously in the Southern Parkes Large-Area Survey in Hydroxyl toward the Galactic center region between Galactic longitudes of 355◦ and 5◦ and Galactic latitudes of −2° and +2°. We detect maser emission toward 162 target fields and suggest that six out of nine nondetections are due to intrinsic variability. Due to the superior spatial resolution of the follow-up ATCA observations, we have identified 356 OH maser sites in the 162 target fields with maser detections. Almost half (161 of 356) of these maser sites have been detected for the first time in these observations. After comparing the positions of these 356 maser sites to the literature, we find that 269 (76%) sites are associated with evolved stars (two of which are PNe), 31 (9%) are associated with star formation, and four are associated with supernova remnants; we were unable to determine the origin of the remaining 52 (15%) sites. Unlike the pilot region, the infrared colors of evolved star sites with symmetric maser profiles in the 1612 MHz transition do not show obvious differences compared with those of evolved star sites with asymmetric maser profiles.

Class I Methanol Maser Emission in NGC 4945

AbstractWe 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.

A systematic observational study of radio properties of H2O megamaser Seyfert-2 galaxies

A systematic study is performed on radio properties of H$_{2}$O megamaser host Seyfert 2 galaxies, through multi-band radio continuum observations (at 11cm, 6.0 cm, 3.6 cm, 2.0 cm and 1.3 cm) with the Effelsberg 100-m radio telescope within a total time duration of four days. For comparison, a control Seyfert 2 galaxy sample without detected maser emission was also observed. Spectral indices were determined for those sources for which measurements exist at two adjacent bands assuming a power-law dependence S$_\nu \propto \nu^{-\alpha}$, where S is the flux density and $\nu$ is the frequency. Comparisons of the radio continuum properties between megamaser and non-masing Seyfert 2s show no difference in spectral indices. However, a difference in radio luminosity is statistically significant, i.e. the maser galaxies tend to have higher radio luminosities by a factor of 2 to 3 than the non-masing ones, commonly reaching values above a critical threshold of 10$^{29}$ ergs$^{-1}$Hz$^{-1}$. This result confirms an earlier conclusion by Zhang et al. (2012), but is based on superior data with respect to the time interval within which the data were obtained, with respect to the observational facility (only one telescope used), the number of frequency bands.

Formation and evolution of the water maser outflow event in AFGL 2591 VLA 3-N

In this paper we analyze multi-epoch Very Long Baseline Interferometry (VLBI) water maser observations carried out with the Very Long Baseline Array (VLBA) toward the high-mass star-forming region AFGL 2591. We detected maser emission associated with the radio continuum sources VLA 2 and VLA 3. In addition, a water maser cluster, VLA 3-N, was detected ~ 0.5" north of VLA 3. We concentrate the discussion of this paper on the spatio-kinematical distribution of the water masers towards VLA 3-N. The water maser emission toward the region VLA 3-N shows two bow shock-like structures, Northern and Southern, separated from each other by ~ 100 mas (~ 330 AU). The spatial distribution and kinematics of the water masers in this cluster have persisted over a time span of seven years. The Northern bow shock has a somewhat irregular morphology, while the Southern one has a remarkably smooth morphology. We measured the proper motions of 33 water maser features, which have an average proper motion velocity of ~ 1.3 mas/yr (~ 20 km/s). The morphology and the proper motions of this cluster of water masers show systematic expanding motions that could imply one or two different centers of star formation activity. We made a detailed model for the Southern structure, proposing two different kinematic models to explain the 3-dimensional spatio-kinematical distribution of the water masers: (1) a static central source driving the two bow-shock structures; (2) two independent driving sources, one of them exciting the Northern bow-shock structure, and the other one, a young runaway star moving in the local molecular medium exciting and molding the remarkably smoother Southern bow-shock structure. Future observations will be necessary to discriminate between the two scenarios, in particular by identifying the still unseen driving source(s).

An evolutionary sequence for high-mass star formation

AbstractDetermining an evolutionary clock for high-mass star formation is an important step towards realizing a unified theory of star formation, as it will enable qualitative studies of the associated high-mass stars to be executed. Our recent studies have shown that masers have great potential to accurately trace the evolution of these regions. We have investigated the relative evolutionary phases associated with the presence of combinations of water, methanol and hydroxyl masers. Comparison between the characteristics of coincident sources has revealed strong evidence for an evolutionary sequence for the different maser species, a result that we now aim to corroborate through comparisons with chemical clocks.Using our new, large samples of methanol masers at 6.7 GHz (MMB survey; Green et al. (2009)) and 12.2 GHz (Breen et al. 2012), 22 GHz water masers (Breen & Ellingsen 2012), OH masers together with complementary data, we find strong evidence that it is not only the presence or absence of the different maser species that indicates the evolutionary stage of the associated high-mass star formation region (see e.g. Breen et al. (2010)), but that the properties of those masers can give even finer evolutionary details. Most notably, the intensity and velocity range of detected maser emission increases as the star forming region evolves (Breen et al. 2011).Subsequent work we have undertaken (Ellingsen et al. 2011) has shown that the presence of rare 37.7 GHz methanol masers may signal the end of the methanol maser phase. They show that 37.7 GHz methanol masers are associated only with the most luminous 6.7 and 12.2 GHz methanol masers, which combined with the rarity of these objects is consistent with them being a short lived phase towards the end of the 6.7 GHz methanol maser lifetime.An independent confirmation of our maser evolutionary timeline can be gained through comparisons with chemical clocks. MALT90 is a legacy survey of 1000s of dense star forming cores at 90GHz, simultaneously observing 16 molecular lines with the Mopra radio telescope (see e.g. Foster et al. 2011). It provides the perfect dataset to test the maser evolutionary timeline due to the targeted lines and the fact that at least one-quarter of the MALT90 sources correspond to maser sites, providing a large enough sample for meaningful analysis. From our preliminary analysis, we find that star formation regions showing similar maser properties also show similar thermal line properties; as would be expected if our evolutionary scenario were accurate.

EVLA imaging of the water masers in the massive protostellar cluster NGC6334I

AbstractWe have used the recently-upgraded Karl G. Jansky Very Large Array (VLA) in A-configuration to observe the water masers in the massive protostellar cluster NGC6334I with broad bandwidth and high spectral resolution. Four groups of maser spots are found. The two groups with the broadest velocity span (40 km/s) are towards the UCHII region and the hot core SMA1. The spatial kinematics of the SMA1 masers are consistent in sense and orientation with the large-scale CO outflow and appear to trace the base of the outflow from a protostar at the dust peak of SMA1. Additional masers at the southern end of SMA1 provide evidence for a second protostar. The highest intensity maser lies about 2″ north of SMA1. Interestingly, no water masers are seen on the equally impressive hot core SMA2. Finally, we have detected maser emission toward the enigmatic source SMA4, which shows no millimeter molecular lines despite having strong, compact submillimeter continuum and may trace another protostar.

37 GHz METHANOL MASERS : HORSEMEN OF THE APOCALYPSE FOR THE CLASS II METHANOL MASER PHASE?

We report the results of a search for class II methanol masers at 37.7, 38.3 and 38.5 GHz towards a sample of 70 high-mass star formation regions. We primarily searched towards regions known to show emission either from the 107 GHz class II methanol maser transition, or from the 6.035 GHz excited OH transition. We detected maser emission from 13 sources in the 37.7 GHz transition, eight of these being new detections. We detected maser emission from three sources in the 38 GHz transitions, one of which is a new detection. We find that 37.7 GHz methanol masers are only associated with the most luminous 6.7 and 12.2 GHz methanol maser sources, which in turn are hypothesised to be the oldest class II methanol sources. We suggest that the 37.7 GHz methanol masers are associated with a brief evolutionary phase (of 1000-4000 years) prior to the cessation of class II methanol maser activity in the associated high-mass star formation region.

Narrow-line Seyfert 1 galaxies: an amasing class of AGN

[Abridged] Narrow-line Seyfert 1 (NLS1) galaxies are a class of active galactic nuclei (AGN) that have all the properties of type 1 Seyfert galaxies but show peculiar characteristics, including the narrowest Balmer lines, strongest Fe II emission, and extreme properties in the X-rays. Line and continuum radio observations provide an optimal tool to access the (often) optically obscured innermost regions of AGN and reveal the kinematics of the gas around their central engines. We investigate the interplay between the peculiar NLS1 class of AGN and the maser phenomenon, to help us understand the nature of the maser emission in some NLS1s where water maser emission has been detected. We observed a sample of NLS1 galaxies with the Green Bank Telescope in a search for water maser emission at 22 GHz. We also reduced and analysed archival Green Bank Telescope and Very Large Array data and produced 22-GHz spectra for the five NLS1 galaxies with detected maser emission. In particular, we imaged the maser and nuclear radio continuum of NGC5506 at subarcsec scales with the Very Large Array. We discovered maser emission in two NLS1 galaxies: IGRJ16385-2057, and IRAS03450+0055. In addition to the three previously known maser detections in the NLS1s Mrk766, NGC4051, and NGC5506, this yields a water maser detection rate in NLS1 galaxies of ~7% (5/71). This value rises significantly to ~21% (5/24) when considering only NLS1 galaxies at recessional velocities less than 10000 km/s. For NGC4051 and NGC5506, we find that the water maser emission is located within 5 and 12 pc, respectively, of nuclear radio continuum knots, which are interpreted as core-jet structures.

SIMULTANEOUS OBSERVATIONS OF SiO AND H2O MASERS TOWARD SYMBIOTIC STARS

We present the results of simultaneous observations of SiO v = 1, 2, J = 1–0, 29SiO v = 0, J = 1–0, and H2O 616–523 maser lines performed with the KVN Yonsei 21 m radio telescope from 2009 November to 2010 January. We searched for these masers in 47 symbiotic stars and detected maser emission from 21 stars, giving the first time detection from 19 stars. Both SiO and H2O masers were detected from seven stars of which six were D-type symbiotic stars and one was an S-type star, WRAY 15-1470. In the SiO maser emission, the 28SiO v = 1 maser was detected from 10 stars, while the v = 2 maser was detected from 15 stars. In particular, the 28SiO v = 2 maser emission without the v = 1 maser detection was detected from nine stars with a detection rate of 60%, which is much higher than that of isolated Miras/red giants. The 29SiO v = 0 maser emission was also detected from two stars, H 2-38 and BF Cyg, together with the 28SiO v = 2 maser. We conclude that these different observational results between isolated Miras/red giants and symbiotic stars may be related with the presence of hot companions in a symbiotic binary system.

PROPER MOTIONS OF H2O MASERS IN THE WATER FOUNTAIN SOURCE IRAS 19190+1102

We report on the results of two epochs of Very Long Baseline Array (VLBA) observations of the 22 GHz water masers toward IRAS 19190+1102. The water maser emission from this object shows two main arc-shaped formations perpendicular to their NE-SW separation axis. The arcs are separated by ~280 mas in position, and are expanding outwards at an angular rate of 2.35 mas/yr. We detect maser emission at velocities between -53.3 km/s to +78.0 km/s and there is a distinct velocity pattern where the NE masers are blueshifted and the SW masers are redshifted. The outflow has a three-dimensional outflow velocity of 99.8 km/s and a dynamical age of about 59 yr. A group of blueshifted masers not located along the arcs shows a change in velocity of more than 35 km/s between epochs, and may be indicative of the formation of a new lobe. These observations show that IRAS 19190+1102 is a member of the class of "water fountain"' pre-planetary nebulae displaying bipolar structure

Class I methanol masers in the outflow of IRAS 16 547-4247

The Australia Telescope Compact Array (ATCA) has been used to image class I methanol masers at 9.9, 25 (a series from J = 2 to 9), 84, 95 and 104 GHz located in the vicinity of IRAS 16 547-4247 (G343.12-0.06), a luminous young stellar object known to harbour a radio jet. The detected maser emission consists of a cluster of six spots spread over an area of 30 arcsec. Five spots were detected in only the 84- and 95-GHz transitions (for two spots the 84-GHz detection is marginal), while the sixth spot shows activity in all 12 observed transitions. We report the first interferometric observations of the rare 9.9- and 104-GHz masers. It is shown that the spectra contain a very narrow spike (< 0.03 km s -1) and the brightness temperature in these two transitions exceeds 5.3 × 10 7 and 2.0 × 10 4K, respectively. The three most southern maser spots show a clear association with the shocked gas traced by the H 2 2.12-μm emission associated with the radio jet and their velocities are close to that of the molecular core within which the jet is embedded. This fact supports the idea that the class I masers reside in the interface regions of outflows. Comparison with OH masers and infrared data reveals a potential discrepancy in the expected evolutionary state. The presence of the OH masers usually means that the source is evolved, but the infrared data suggest otherwise. The lack of any class II methanol maser emission at 6.7 GHz in the source raises an additional question, Is this source too young or too old to have a 6.7-GHz maser? We argue that both cases are possible and suggest that the evolutionary stage where the class I masers are active, may last longer and start earlier than when the class II masers are active. However, it is currently not possible to reveal the exact evolutionary status of IRAS 16 547-4247. © 2006 RAS.

VLBI Observations of the Water Masers near LkHα 234 and BD +40 4124

I present observations made with the National Radio Astronomy Observatory's Very Large Array and Very Long Baseline Array of the water masers near the candidate Herbig Ae/Be star V1318 Cygni S (V1318S) in the vicinity of the Herbig Ae/Be star BD +40 4124 and near the Herbig Ae/Be star LkHα 234. The water masers are not found to be associated with either of the Herbig Ae/Be stars dominant in the optical but with other embedded sources. The masers appear to form in the outflows from these sources, some of which have been detected in radio continuum by other authors. The water masers near BD +40 4124 are found to be associated with the star V1318S, itself a candidate Herbig Ae/Be star. The water masers imaged with very long baseline interferometry resolutions near LkHα 234 are found to be associated with the continuum sources LkHα 234–VLA 2 and LkHα 234–VLA 3B. I do not detect maser emission from LkHα 234–VLA1. It is likely that the water maser emission originally thought to be associated with Herbig Ae/Be stars is in fact hosted by embedded young stellar objects, is linked to their outflowing jets, and is not found in their disks.

A search for extragalactic H2O maser emission towards IRAS galaxies

We report the result of an on-going survey for 22 GHz H2O maser emission towards infrared luminous galaxies. The observed galaxies were selected primarily from the IRAS bright galaxy sample. The survey has resulted in the detection of one new maser. The new maser was discovered towards the [U]LIRG/merger galaxy NGC 6240, which contains a LINER nucleus. This is the first detection of an H2Omaser towards this class of galaxy, they are traditionally associated with OH megamaser sources. The detected maser emission is highly redshifted (~260–300 km s-1) with respect to the adopted systemic velocity of the galaxy, and we identified no other significant emission at velocities ±500 km s relative to the systemic velocity. The presence of high-velocity maser emission implies the possible existence of a rotating maser disk formed in the merging process. The large maser luminosity (~40 ) suggests that an active galactic nucleus could be the energy source that gives rise to the water emission. Alternatively, the maser emission could be associated with the previously observed double radio source in the centre of the galaxy. Interferometric observations with high angular resolution will be able to clarify the origin of the new maser.

Water-vapour maser emission from galactic nuclei

We report here the progress of a survey of galactic nuclei for water-vapour maser emission at 22.235 GHz. We observed 29 late-type galaxies in November 1982, January 1983, and September 1983 using the 40-m radio telescope of the Owens Valley Radio Observatory (OVRO) equipped with a travelling-wave maser receiver1. We have detected maser emission from four nuclei: NGC4258 (M106), NGC1068 (M77), NGC3034 (M82), and NGC6946. The masers in NGC4258 and NGC1068 are extremely luminous; NGC1068 has the most luminous water-vapour maser yet reported—350 L⊙ assuming isotropic emission. We suggest that the extremely bright nuclear masers indicate an ongoing burst of star formation, and therefore provide a useful probe of the physical conditions of the starburst phenomenon.