2020A&A...638L...4G

Context. Class 0 protostars represent the earliest evolutionary stage of solar-type stars, during which the majority of the system mass resides in an infalling envelope of gas and dust and is not yet in the central, nascent star. Although X-rays are a key signature of magnetic activity in more evolved protostars and young stars, whether such magnetic activity is present at the Class 0 stage is still debated.
Aims. We aim to detect a bona fide Class 0 protostar in X-rays.
Methods. We observed HOPS 383 in 2017 December in X-rays with the Chandra X-ray Observatory (∼84ks) and in near-infrared imaging with the Southern Astrophysical Research telescope.
Results. HOPS 383 was detected in X-rays during a powerful flare. This hard (E>2keV) X-ray counterpart was spatially coincident with the northwest 4cm component of HOPS 383, which would be the base of the radio thermal jet launched by HOPS 383. The flare duration was ∼3.3h; at the peak, the X-ray luminosity reached ∼4x10³¹erg/s in the 2-8keV energy band, a level at least an order of magnitude larger than that of the undetected quiescent emission from HOPS 383. The X-ray flare spectrum is highly absorbed (N_H∼7x10²³cm^–2), and it displays a 6.4keV emission line with an equivalent width of ∼1.1keV, arising from neutral or low-ionization iron.
Conclusions. The detection of a powerful X-ray flare from HOPS 383 constitutes direct proof that magnetic activity can be present at the earliest formative stages of solar-type stars.