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An Unusually Powerful Water-Maser Flare in the Galactic Source W49N

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Abstract

The most powerful flare ever registered in the Galactic water-maser source W49N has been detected in long-term monitoring data in the 616–523 transition with line frequency f = 22.235 GHz carried out on the 22-m Simeiz, 32-m Toruń, 100-m Effelsberg, and 32-m Medicina radio telescopes, beginning in September 2017 and continuing in 2018. Some stages of the flare were monitored daily. Detailed variations of the source spectral flux density with time have been obtained. At the flare maximum, the flux exceeded P ≈ 8 × 104 Jy, and this was record highest flux registered over the entire history of observations of this source. Important conclusions related to details of the mechanism for the H2O line emission have been drawn. An exponential increase in the flare flux density was detected during both the rise and decline of the flare. The data obtained indicate that the maser is unsaturated, and remained in this state up to the maximum observed flux densities. Additional support for the idea that the maser is unsaturated is the shape of the dependence of the line width on the flux. The characteristics of the variations of the spectral flux density are probably associated with a sharp increase in the density of the medium and the photon flux that led to an increase in the temperature from an initial level of 10–40 K to hundreds of Kelvins. Interferometric maps of the object during the increase in the spectral flux density of the flare have been obtained. A possible mechanism for the primary energy release in W49N is considered.

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Authors and Affiliations

  1. Department of Radio Astronomy and Geodynamics, Crimean Astrophysical Observatory, Katsivelli, Russia

    L. N. Volvach & A. E. Volvach

  2. Institute of Applied Astronomy, Russian Academy of Sciences, St. Petersburg, 191187, Russia

    A. E. Volvach, A. V. Ipatov, D. V. Ivanov, A. G. Mikhailov & A. Mel’nikov

  3. Astro Space Center, P. N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow, 117997, Russia

    M. G. Larionov

  4. Torun Centre for Astronomy, Nicolaus Copernicus University, Piwnice, PL-87-148, Lysomice, Poland

    P. Wolak

  5. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121, Bonn (Endenich), Germany

    B. Kramer, K. Menten & A. Kraus

  6. INAF—Istituto di Radioastronomia, 40129, Bologna, Italy

    J. Brand, A. Zanichelli & S. Rigini

  7. Italian ALMA Regional Centre, Bologna, Italy

    J. Brand

  8. INAF—Osservatorio Astronomico di Cagliari, 09047, Selargius (CA), Italy

    S. Poppi

Authors
  1. L. N. Volvach
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  2. A. E. Volvach
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  3. M. G. Larionov
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  4. P. Wolak
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  5. B. Kramer
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  6. K. Menten
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  7. A. Kraus
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  8. J. Brand
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  9. A. Zanichelli
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  10. S. Poppi
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  11. S. Rigini
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  12. A. V. Ipatov
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  13. D. V. Ivanov
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  14. A. G. Mikhailov
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  15. A. Mel’nikov
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Corresponding author

Correspondence to L. N. Volvach.

Additional information

Russian Text © The Author(s), 2019, published in Astronomicheskii Zhurnal, 2019, Vol. 96, No. 8, pp. 638–652.

Funding

This work was supported by the Polish National Science Center (grant 2016/21/B/ST9/01455) and partially supported by Program 12 of the Presidium of the Russian Academy of Sciences and the Russian Foundation for Basic Research (grant 19-52-4014). The study is partially based on observations with the 100-m telescope of the Max Planck Institute for Radio Astronomy.

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Volvach, L.N., Volvach, A.E., Larionov, M.G. et al. An Unusually Powerful Water-Maser Flare in the Galactic Source W49N. Astron. Rep. 63, 652–665 (2019). https://doi.org/10.1134/S1063772919080067

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  • DOI: https://doi.org/10.1134/S1063772919080067

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