A Δr ∼ 9.5 mag Superflare of an Ultracool Star Detected by the SVOM/GWAC System

L. P. Xin, H. L. Li, J. Wang, X. H. Han, Y. Xu, X. M. Meng, H. B. Cai, L. Huang, X. M. Lu, Y. L. Qiu, X. G. Wang, E. W. Liang, Z. G. Dai, X. Y. Wang, C. Wu, J. B. Zhang, G. W. Li, D. Turpin, Q. C. Feng, J. S. DengS. S. Sun, T. C. Zheng, Y. G. Yang, J. Y. Wei

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1 Scopus citations


We report the detection and follow-up of a superstellar flare GWAC 181229A with an amplitude of ΔR ∼ 9.5 mag on an M9-type star by SVOM/GWAC and the dedicated follow-up telescopes. The estimated bolometric energy E bol is (5.56-9.25) 1034 erg, which makes the event one of the most powerful flares seen on ultracool stars. The magnetic strength is inferred to be 3.6-4.7 kG. Thanks to sampling with a cadence of 15 s, a new component near the peak time with a very steep decay is detected in the R-band light curve, followed by the two-component flare template given by Davenport et al. An effective temperature of 5340 40 K is measured by fitting a blackbody shape to the spectrum in the shallower phase during the flare. The filling factors of the flare are estimated to be ∼30% and 19% at the peak time and at 54 minutes after the first detection. The detection of this particular event with large amplitude, huge emitted energy, and a new component demonstrates that high-cadence sky monitoring cooperation with fast follow-up observations is very important for understanding the violent magnetic activity.

Original languageEnglish (US)
Article number106
JournalAstrophysical Journal
Issue number2
StatePublished - Mar 10 2021
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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