An FUor-like Outbursting Class I Protostar in NGC 7538

TL;DR

This paper reports the discovery of an FUor-like eruptive event in a Class I protostar in NGC 7538, characterized by a significant luminosity burst and distinct phases of variability, emphasizing the importance of IR monitoring.

Contribution

First identification of an FUor-like outburst in a deeply embedded Class I protostar using long-term infrared data.

Findings

The protostar experienced a $ riangle K_s ext{~} hicksim 5$ luminosity increase.

The event lasted at least five years with a three-phase evolution.

Infrared variability aligns with an episodic accretion event at an early stage.

Abstract

We report on the discovery of an FUor-like Class I protostar in NGC~7538. The source, named NGC~7538~MIR, exhibited a giant luminosity burst ($\Delta K_s\sim5$) and a prolonged high-luminosity state lasting at least five years. Its mid-infrared (mid-IR) light curves, constructed from WISE/NEOWISE multiepoch data, presented a rapid rise and slight fading after the peak, placing this event among long-duration eruptive phenomena observed in protostars, for example, FUor-type events. The evolution of W1/W2 luminosity and $W1-W2$ color can be naturally split into three phases, pre-burst, burst and post-burst, suggesting that different physical processes may dominate in the three phases. The evolution of NGC~7538~MIR is consistent with a transition from variability influenced by circumstellar extinction (pre-burst) to a phase with greatly enhanced accretion luminosity (burst), and followed by a gradual relaxation of the circumstellar environment (post-burst). Overall, the observed IR variability of NGC~7538~MIR is consistent with an FUor-like accretion event occurred at an early evolutionary stage, highlighting the importance of long-term IR monitoring for identifying episodic accretion events in deeply embedded protostars.