ΔR∼9.5 mag Super Flare of An Ultracool Star Detected by 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. Deng, S. S. Sun, T. C. Zheng, Y. G. Yang, J. Y. Wei
In this paper, we report the detection and follow-ups of a super stellar flare GWAC\,181229A with an amplitude of ΔR∼9.5 mag on a M9 type star by SVOM/GWAC and the dedicated follow-up telescopes. The estimated bolometric energy Ebol is (5.56−9.25)×1034 ergs, which places the event to be one of the most powerful flares on ultracool stars. The magnetic strength is inferred to be (3.6-4.7) kG. Thanks to the sampling with a cadence of 15 seconds, 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. (2014). An effective temperature of 5340±40 K is measured by a blackbody shape fitting to the spectrum at 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 min after the first detection. The detection of the particular event with large amplitude, huge-emitted energy and a new component demonstrates that a high cadence sky monitoring cooperating with fast follow-up observations is very essential for understanding the violent magnetic activity.