A superflare of BP Tau simultaneously caught by EP X-ray and TESS optical observations
13 affiliations
- 1Polar Research Institute of China
- 2Key Laboratory for Polar Science, MNR, Polar Research Institute of China
- 3National Astronomical Observatories, Chinese Academy of Sciences
- 4Kavli Institute for Astronomy and Astrophysics, Peking University
- 5Department of Astronomy, Peking University
- 6Hamburger Sternwarte
- 7Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel
- 8INAF–Osservatorio Astronomico di Palermo
- 9Department of Physics, Imperial College London
- 10School of Astronomy and Space Science, University of Chinese Academy of Sciences, Chinese Academy of Sciences
- 11Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University
- 12Department of Physics, the University of Hong Kong
- 13Key Laboratory for Research in Galaxies and Cosmology of Chinese Academy of Sciences, Department of Astronomy, University of Science and Technology of China
Abstract
Multiwavelength observations of stellar flares trace the activity of different components of the stars’ outer atmosphere, providing insight into their interactions. In the present paper, we report a superflare from BP Tau, simultaneously observed with the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) satellite and TESS. While we attribute the X-ray flux increase to a magnetically powered flare, the optical light curve likely results from the superposition of the flare and an accretion burst. The X-ray flare has a mean flux of (1.5 −0.04 +0.3 ) × 10 ⁻¹¹ erg cm ⁻² s ⁻¹ in the WXT energy band (0.5−4.0 keV), with e-folding times of 1.7 ± 1.0 ks and 14 ± 5 ks for the rise and decay phase, respectively. The corresponding time-integrated flare energy is (1.0 ± 0.2)×10 ³⁶ erg. The optical flare has an e-folding time of 0.33 ± 0.04 ks for the rise phase, but the data do not constrain the decay timescale. Assuming a decay phase equal to the rise phase, the resulting optical flare energy is (2.8 ± 0.4)×10 ³⁴ erg in the TESS band (∼6000 − ∼10 000 Å), corresponding to a bolometric energy of (1.9 ± 0.3)×10 ³⁵ erg (assuming a blackbody at 11 000 K). The Follow-up X-ray Telescope (FXT) on EP triggered an observation ∼1.5 day after the flare, with a flux of (4.6 −0.5 +0.2 ) × 10 ⁻¹³ erg cm ⁻² s ⁻¹ (0.5−10.0 keV), indicating that BP Tau had returned to quiescence. This work demonstrates the potential of jointly analyzing EP and TESS data for superflares. WXT is expected to detect ∼800 superflares per year, with FXT capable of slewing to the flaring star within ∼3 − 5 minutes. The large field of view of both missions offers us the opportunity to study multiwavelength variability during energetic flares.
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BibTeX
@article{zhou2026superflare,
title = {{A superflare of BP Tau simultaneously caught by EP X-ray and TESS optical observations}},
author = {Xingyu Zhou and Mingjun Liu and Gregory J. Herczeg and P. Christian Schneider and Fabio Favata and Chenwei Yang and Chichuan Jin and Dongyue Li and Xuan Mao and Yi-Han Iris Yin and Minghao Zhang and Weimin Yuan and Hongyan Zhou},
journal = {Astronomy \& Astrophysics},
year = {2026},
month = oct,
doi = {10.1051/0004-6361/202557686},
url = {https://www.aanda.org/10.1051/0004-6361/202557686},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - A superflare of BP Tau simultaneously caught by EP X-ray and TESS optical observations
AU - Xingyu Zhou
AU - Mingjun Liu
AU - Gregory J. Herczeg
AU - P. Christian Schneider
AU - Fabio Favata
AU - Chenwei Yang
AU - Chichuan Jin
AU - Dongyue Li
AU - Xuan Mao
AU - Yi-Han Iris Yin
AU - Minghao Zhang
AU - Weimin Yuan
AU - Hongyan Zhou
PY - 2026
DA - 2026/10/02
JO - Astronomy & Astrophysics
DO - 10.1051/0004-6361/202557686
UR - https://www.aanda.org/10.1051/0004-6361/202557686
AB - Multiwavelength observations of stellar flares trace the activity of different components of the stars’ outer atmosphere, providing insight into their interactions. In the present paper, we report a superflare from BP Tau, simultaneously observed with the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) satellite and TESS. While we attribute the X-ray flux increase to a magnetically powered flare, the optical light curve likely results from the superposition of the flare and an accretion burst. The X-ray flare has a mean flux of (1.5 −0.04 +0.3 ) × 10 ⁻¹¹ erg cm ⁻² s ⁻¹ in the WXT energy band (0.5−4.0 keV), with e-folding times of 1.7 ± 1.0 ks and 14 ± 5 ks for the rise and decay phase, respectively. The corresponding time-integrated flare energy is (1.0 ± 0.2)×10 ³⁶ erg. The optical flare has an e-folding time of 0.33 ± 0.04 ks for the rise phase, but the data do not constrain the decay timescale. Assuming a decay phase equal to the rise phase, the resulting optical flare energy is (2.8 ± 0.4)×10 ³⁴ erg in the TESS band (∼6000 − ∼10 000 Å), corresponding to a bolometric energy of (1.9 ± 0.3)×10 ³⁵ erg (assuming a blackbody at 11 000 K). The Follow-up X-ray Telescope (FXT) on EP triggered an observation ∼1.5 day after the flare, with a flux of (4.6 −0.5 +0.2 ) × 10 ⁻¹³ erg cm ⁻² s ⁻¹ (0.5−10.0 keV), indicating that BP Tau had returned to quiescence. This work demonstrates the potential of jointly analyzing EP and TESS data for superflares. WXT is expected to detect ∼800 superflares per year, with FXT capable of slewing to the flaring star within ∼3 − 5 minutes. The large field of view of both missions offers us the opportunity to study multiwavelength variability during energetic flares.
SN - 0004-6361
SN - 1432-0746
ER -