A micronova burst in the intermediate polar IGR J17014-4306

We report the detection of a short optical burst in TESS data of IGR J17014-4306, the eclipsing intermediate polar with the longest known orbital period. The burst lasts 1.56 d and shows multiple peaks, reaching (9.3 plus or minus 0.2) times 10 33 erg s-1, and releases a total energy of (3.25 plus or minus 0.01) times 10 38 erg. The burst parameters are consistent with those of a micronova eruption, currently understood as a thermonuclear runaway in the magnetically-confined accretion column. From its energy, we infer a burned column mass of about 1.6 times 10-11 M, which implies a recurrence time of about 20 d. Our search for similar events in long-term Gaia, ASAS-SN, and AAVSO light curves reveals 16 possible fast brightenings over about 11 yr, suggesting that micronova events may be frequent in IGR J17014-4306. Timing analysis of the TESS data shows that the white-dwarf spin period remains stable before and after the burst. During the burst, however, the power spectrum becomes more complex and exhibits multiple peaks. The classification of IGR J17014-4306 as a micronova brings the total number of confirmed systems to eight. Its extreme orbital period and eclipsing nature make it an ideal test-bed for further studies of magnetically confined thermonuclear burning on white dwarfs.