Serendipitous detection of an intense X-ray flare in the weak-line T Tauri star KM Ori with SRG/eROSITA
stars: activity; stars: flare; stars: individual (KM Ori); stars: pre-main sequence; stars: variables: T Tauri; X-rays: stars
Weak-line T Tauri stars (WTTS) exhibit X-ray flares, likely resulting from magnetic reconnection that heats the stellar plasma to very high temperatures. These flares are difficult to identify through targeted observations. Here, we report the serendipitous detection of the brightest X-ray flaring state of the WTTS KM Ori in the eROSITA DR1 survey. Observations from SRG/eROSITA, Chandra X-ray Observatory, and XMM-Newton are analysed to assess the X-ray properties of KM Ori, thereby establishing its flaring state at the eROSITA epoch. The long-term (1999-2020) X-ray light curve generated for the Chandra observations confirmed that eROSITA captured the source at its highest X-ray flaring state recorded to date. Multi-instrument observations support the X-ray flaring state of the source, with time-averaged X-ray luminosity reaching at the eROSITA epoch, marking it the brightest and possibly the longest flare observed so far. Such intense X-ray flares have been detected only in a few WTTS. The X-ray spectral analysis unveils the presence of multiple thermal plasma components at all epochs. The notably high luminosity , energy (erg), and the elevated emission measures of the thermal components in the eROSITA epoch indicate a superflare/megaflare state of KM Ori. Additionally, the H line equivalent width of from our optical spectral analysis, combined with the lack of infrared excess in the spectral energy distribution, were used to re-confirm the WTTS (thin disc/disc-less) classification of the source. The long-duration flare of KM Ori observed by eROSITA indicates the possibility of a slow-rise top-flat flare. The detection demonstrates the potential of eROSITA to uncover such rare, transient events, thereby providing new insights into the X-ray activity of WTTS. The Author(s), 2025. Published by Cambridge University Press on behalf of Astronomical Society of Australia.
Ezhikode S.H.; Anilkumar H.; Arun R.; Mathew B.; Jithesh V.; Bhattacharyya S.; Nedhath S.; Cysil T.B.; Muneer S.; Kartha S.S.; Kumar S.P.
Publications of the Astronomical Society of Australia, Vol-42
https://doi.org/10.1017/pasa.2024.98 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85215675608&doi=10.1017%2fpasa.2024.98&partnerID=40&md5=a826f08b1a166d28ce15e66ff3ee400f
Ezhikode S.H., Department of Physics and Electronics, CHRIST (Deemed to Be University), Bangalore, India, St. Francis de Sales College (Autonomous), Electronics City, Bengaluru, India; Anilkumar H., Department of Physics and Electronics, CHRIST (Deemed to Be University), Bangalore, India; Arun R., Indian Institute of Astrophysics, Koramangala, Bangalore, India; Mathew B., Department of Physics and Electronics, CHRIST (Deemed to Be University), Bangalore, India; Jithesh V., Department of Physics and Electronics, CHRIST (Deemed to Be University), Bangalore, India; Bhattacharyya S., Department of Physics and Electronics, CHRIST (Deemed to Be University), Bangalore, India, European Organisation for Astronomical Research in the Southern Hemisphere (ESO), Casilla 19001, Santiago, Chile; Nedhath S., Department of Physics and Electronics, CHRIST (Deemed to Be University), Bangalore, India, Indian Institute of Astrophysics, Koramangala, Bangalore, India; Cysil T.B., Department of Physics and Electronics, CHRIST (Deemed to Be University), Bangalore, India; Muneer S., Indian Institute of Astrophysics, Koramangala, Bangalore, India; Kartha S.S., Department of Physics and Electronics, CHRIST (Deemed to Be University), Bangalore, India; Kumar S.P., Indian Institute of Astrophysics, Koramangala, Bangalore, India