Letter to the Editor

Evidence for magnetic activity at starbirth: a powerful X-ray flare from the Class 0 protostar HOPS 383

¹ Aix-Marseille Univ, CNRS, CNES, LAM, Marseille, France
e-mail: nicolas.grosso@lam.fr
² CRESST II and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD, USA
³ Department of Physics, University of Maryland, Baltimore County, Baltimore, MD, USA
⁴ Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA, USA
⁵ Center for Imaging Science, School of Physics & Astronomy, and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, Rochester, NY, USA

Received: 16 April 2020
Accepted: 2 May 2020

Abstract

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 (∼84 ks) 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 >  2 keV) X-ray counterpart was spatially coincident with the northwest 4 cm component of HOPS 383, which would be the base of the radio thermal jet launched by HOPS 383. The flare duration was ∼3.3 h; at the peak, the X-ray luminosity reached ∼4 × 10³¹ erg s⁻¹ in the 2−8 keV 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 ∼ 7 × 10²³ cm⁻²), and it displays a 6.4 keV emission line with an equivalent width of ∼1.1 keV, 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.