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

Nicolas Grosso,Joel H. Kastner,David A. Principe,Kenji Hamaguchi

doi:10.1051/0004-6361/202038185

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 theChandraX-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 × 1031erg s−1in 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 (NH ∼ 7 × 1023cm−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.

Highlights

Low-mass objects that have evolved beyond the Class 0 stage are conspicuous X-ray emitters (Dunham et al 2014), that is, Class I protostars with remnant envelopes and massive accretion disks, and Class II and III pre-main sequence stars with and without circumstellar disks (T Tauri stars)
Starting from a model of Herschel Orion protostar survey (HOPS) 383 consisting of an infalling envelope with bipolar cavities carved by outflows and a small (5 au radius) accretion disk (Figs. 3a–c), constrained by the postoutburst spectral energy distribution (SED) using a Monte Carlo radiative transfer code (Furlan et al 2016), we computed the predicted NH toward the central protostar (Appendix E)
Our detection of an X-ray flare from HOPS 383 provides conclusive evidence that strong magnetic activity is present at this bona fide Class 0 protostar

Summary

Introduction

Low-mass objects that have evolved beyond the Class 0 stage are conspicuous X-ray emitters (Dunham et al 2014), that is, Class I protostars with remnant envelopes and massive accretion disks, and Class II and III pre-main sequence stars with and without circumstellar disks (T Tauri stars). Their high luminosities (∼1028−31 erg s−1) compared to the solar maximum (∼1027 erg s−1) and their intense flaring activity in Xrays make them appear as extremely magnetically active young suns (Feigelson & Montmerle 1999; Güdel & Nazé 2009). HOPS 383 is the first Class 0 protostar known to have undergone a mass-accretion-driven eruption (Safron et al 2015), which peaked by 2008 and ended by 2017 September (Appendix B)

Objectives

Findings

Discussion

Conclusion