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First detections of methanol maser lines from a rare transition family

Bradley R. Johnson, Simon P. Ellingsen, Shari L. Breen, Maxim A. Voronkov, Tiege P. McCarthy, Lucas J. Hyland

Abstract

We report the first observations in a rare family of class II methanol maser transitions in both CH$_3$OH and $^{13}$CH$_3$OH toward three southern high-mass star formation regions, along with the first maser detected in the $^{13}$CH$_3$OH line. The $8_2 \rightarrow 9_1 A^{-}$ methanol transition was observed in both CH$_3$OH and $^{13}$CH$_3$OH (at 28.9 GHz and 41.9 GHz respectively) toward three sources; G358.93-0.03, NGC6334I and G345.01+1.79, all of which are star formation regions with recent maser flaring events. We report the first maser detection of the 41.9 GHz line in $^{13}$CH$_3$OH toward G358.93-0.03 and the first confirmed maser detection of the 28.9 GHz line in CH$_3$OH toward NGC6334I. Additionally we report a maser detection of the 28.9 GHz line in CH$_3$OH toward G358.93-0.03, meaning that with our detection of the 41.9 GHz line, this is the first isotopic detection of these lines toward G358.93-0.03. The newly detected maser transitions are associated with the primary millimetre continuum sources (MM1) in both G358.93-0.03 and NGC6334I, within the varying positional uncertainties.

First detections of methanol maser lines from a rare transition family

Abstract

We report the first observations in a rare family of class II methanol maser transitions in both CHOH and CHOH toward three southern high-mass star formation regions, along with the first maser detected in the CHOH line. The methanol transition was observed in both CHOH and CHOH (at 28.9 GHz and 41.9 GHz respectively) toward three sources; G358.93-0.03, NGC6334I and G345.01+1.79, all of which are star formation regions with recent maser flaring events. We report the first maser detection of the 41.9 GHz line in CHOH toward G358.93-0.03 and the first confirmed maser detection of the 28.9 GHz line in CHOH toward NGC6334I. Additionally we report a maser detection of the 28.9 GHz line in CHOH toward G358.93-0.03, meaning that with our detection of the 41.9 GHz line, this is the first isotopic detection of these lines toward G358.93-0.03. The newly detected maser transitions are associated with the primary millimetre continuum sources (MM1) in both G358.93-0.03 and NGC6334I, within the varying positional uncertainties.

Paper Structure

This paper contains 20 sections, 2 figures, 3 tables.

Table of Contents

  1. INTRODUCTION
  2. G358.93-0.03 2019 Flare Event
  3. Observed Methanol Transitions
  4. Additional Observations (NGC6334I & G345.01+1.79)
  5. Previous Isotopic Methanol Maser Detections
  6. OBSERVATIONS AND METHODS
  7. RESULTS
  8. G358.93-0.03
  9. NGC6334I
  10. G345.01+1.79
  11. DISCUSSION
  12. G358.93-0.03
  13. NGC6334I
  14. G345.01+1.79
  15. Comparison of G358.93-0.03 Results to Miao:2022
  16. ...and 5 more sections

Figures (2)

  • Figure 1: G358.93-0.03 Spectra Comparison; The signal in black indicates the 28.9 GHz line detected on 2019 April 30 with a peak of 10.5 Jy, while the magenta line indicates the 41.9 GHz line detected on 2019 April 26 with a peak of 0.4 Jy. Note the difference in the scale of the respective axes; the 28.9 GHz line is $\sim$26 times stronger than the 41.9 GHz line. The similarity in signal-to-noise despite the different scales is due to the longer integration time and the better bandpass in the 41.9 GHz observations
  • Figure 2: NGC6334I Spectra Comparison; The signal in black indicates the 28.9 GHz line detected on 2019 April 30. Due to the difficulty in calibration of this transition, the amplitude of this signal has been scaled based on the RMS noise compared to the same transition observed at the same time toward G358.93‑0.03 (see Section \ref{['sec:ngc6334 results']}). We estimate this gives an uncertainty of a factor of $\sim$2. The peak based on this calculation is $\sim$6 Jy. The signal in magenta is the 41.9 GHz line detected on 2019 April 26 with a peak of 0.2 Jy. The shape of this signal shows the characteristics of a thermal line and closely resembles the thermal detection toward this source in Wu:2023. Note the difference in the scale of the respective axes; the 28.9 GHz line, as scaled by the procedure described in Section \ref{['sec:ngc6334 results']}, is $\sim$30 times stronger than the 41.9 GHz line. The similarity in signal-to-noise despite the different scales is due to the longer integration time and the better bandpass in the 41.9 GHz observations