Postflare Сhanges in Spectrums of Water Maser Emissions for 1.35 cm Wavelength in Sources W49N and G43.8-0.1 from 2024.95 to 2025.25

A. V. Ipatov, I. A. Rahimov, S. A. Grenkov, T. S. Andreeva

Transactions of IAA RAS, issue 73, 40–46 (2025)

DOI: 10.32876/ApplAstron.73.40-46

Keywords: masers, spectral line observations, water maser flares, maser monitoring, W49N, G43.8-0.1, polarization, magnetic fields

Abstract

Regular spectral monitoring of water maser emission at 1.35 cm (22 GHz) from selected sources has being conducted under the Ru-OH program using the radio telescopes of the “Kvazar-KVO” very-long-baseline interferometry (VLBI) complex. The primary goal of these observations is to study both short-term and long-term variability in water maser emission. The sources W49N and G43.8-0.1, included in the Ru-OH target list, attracted significant attention from the radio astronomy community in late 2024 due to powerful maser flares detected in these regions. Post-flare spectral variations of water maser emission were monitored from late November 2024 through March 2025. W49N, one of the richest water maser sources with spectral features spanning ±150 km/s in radial velocity, exhibits frequent flaring activity. Monitoring revealed synchronized flares in velocity components at –71.6 km/s and –59.4 km/s. The –71.6 km/s feature showed an intensity increase of over 10 times (from 2.4 kJy to more than 26 kJy) before beginning to decay on November 27, 2024 while the –59.4 km/s component exhibited a 16.6-fold amplification (from ~ 600 Jy to 9.96 kJy). G43.8-0.1, like most water masers, displays spectral variability across its components, except for a stable emission peak at +40 to +42 km/s. This source typically undergoes flares of varying strength approximately every three years. The 2024 flare in the +39.2 km/s component, which was already at about 1.5 kJy when monitoring began, gradually increased to 2.2 kJy and peaked at 2.8 kJy on February 6, 2025. This event was accompanied by nearly synchronous variations in neighboring components at +40.8 km/s and +35.7 km/s. The methodology section describes the use of an FFT spectrometer with high frequency resolution (488 Hz) and flux calibration performed using standard radio sources. Analysis revealed asymmetric flare profiles with different rise and decay timescales, suggesting nonlinear energy dissipation mechanisms. This study underscores the importance of systematic single-dish monitoring combined with follow-up interferometric observations for understanding maser flare dynamics and their connection to star formation processes.

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