Comparison Between the First and Second Mass Eruptions From
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Astronomy & Astrophysics manuscript no. main ©ESO 2021 February 23, 2021 Comparison between the first and second mass eruptions from progenitors of Type IIn supernovae Naoto Kuriyama1; 2 and Toshikazu Shigeyama1; 2 1 Research Center for the Early Universe, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan 2 Department of Astronomy, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan Received 11 June 2020 / Accepted 16 December 2020 ABSTRACT Context. Some massive stars experience episodic and intense mass loss phases with fluctuations in the luminosity. Ejected material forms circumstellar matter around the star, and the subsequent core collapse results in a Type IIn supernova that is characterized by interaction between supernova ejecta and circumstellar matter. The energy source that triggers these mass eruptions and dynamics of the outflow have not been clearly explained. Moreover, the mass eruption itself can alter the density structure of the envelope and affect the dynamics of the subsequent mass eruption if these events are repeated. A large amount of observational evidence suggests multiple mass eruptions prior to core collapse. Aims. We investigate the density structure of the envelope altered by the first mass eruption and the nature of the subsequent second mass eruption event in comparison with the first event. Methods. We deposited extra energy at the bottom of the hydrogen envelope of 15M stars twice and calculated the time evolution by radiation hydrodynamical simulation code. We did not deal with the origin of the energy source, but focused on the dynamics of repeated mass eruptions from a single massive star. Results. There are significant differences between the first and second mass eruptions in terms of the luminosity, color, and amount of produced circumstellar matter. The second eruption leads to a redder burst event in which the associated brightening phase lasts longer than the first. The amount of ejected matter is different even with the same deposited energy in the first and second event, but the difference depends on the density structure of the star. Conclusions. Upcoming high cadence and deep transient surveys will provide us a lot of pre-supernova activities, and some of which might show multi-peaked light curves. These should be interpreted taking the effect of density structure altered by the preceding outburst events into consideration. Key words. stars: massive - stars: mass-loss - supernovae: general 1. Introduction a few decades before the core collapse. For example, SN 2018cnf (Pastorello et al. 2019b), SN 2016bdu (Pastorello et al. 2018), Growing observational evidence suggests that massive stars SN 2013gc (Reguitti et al. 2019), PTF12cxj (Ofek et al. 2014), sometimes experience episodic and intense mass loss accompa- and SN 2011ht (Fraser et al. 2013b) were reported to exhibit nied by temporal brightening. Eta Carinae is one of the most such brightening. Since the peak luminosity exceeds the Edding- well-studied and well-known objects that experienced such an ton luminosity of a massive star, this brightening must lead to an event (e.g., Davidson & Humphreys 1997). This intense mass eruptive mass loss. The sparsely observed light curves prior to loss or brightening event has been considered to be related with these SNe show that the brightening phase typically lasted for the activity of luminous blue variables (LBVs), which were in- several years and indicate that the progenitors repeated episodic troduced by Conti (1984). On the other hand, some recent ob- mass loss events during this period. SN 2009ip is one of the servations suggest that Wolf-Rayet stars (WR stars) may also most famous SNe IIn whose progenitor star experienced multi- experience such events (Foley et al. 2007; Pastorello et al. 2008; ple brightening phases likely associated with episodic mass loss Smith et al. 2020). events. The progenitor star of SN 2009ip in a brightening phase These mass loss events could affect the observational fea- was first detected in 2009, and repeatedly exhibited brighten- tures of subsequent core-collapse supernovae (SN). After a mas- arXiv:2006.06389v2 [astro-ph.SR] 21 Feb 2021 ing with short intervals less than 50 days in 2011 (Pastorello sive star abruptly loses a significant portion of the envelope, et al. 2013). Eventually this object experienced the most lumi- dense circumstellar matter (CSM) is formed around the star. If nous outburst "2012b" in 2012. While some authors have ar- a core-collapse SN (CCSN) takes place in this dense CSM, the gued that it was a genuine CCSN (e.g., Mauerhan et al. 2013; ejecta collide with the CSM. Then the kinetic energy of the ejecta Smith et al. 2014; Graham et al. 2017), some have suggested is dissipated at shocks and becomes the main energy source (e.g., other scenarios (e.g., merger-burst event (Soker & Kashi 2013), Chugai 1992; Smith 2017). These kinds of SNe are classified as pulsational pair-instability event (Pastorello et al. 2013)). The Type IIn supernovae (SNe IIn) in case of hydrogen-rich CSM progenitor mass of SN 2009ip is estimated as 50 − 80 M (Smith (Schlegel 1990) or Type Ibn supernovae (SNe Ibn) in case of et al. 2010b). helium-rich CSM (Pastorello et al. 2007). Recent observations have revealed that some progenitors of The mass loss rates from progenitors of SNe IIn are es- −1 −4 SNe IIn experienced temporary brightening phase a few years or timated at 0:026 − 0:12M yr (Kiewe et al. 2012), 10 − Article number, page 1 of 11 A&A proofs: manuscript no. main −2 −1 −3 10 M yr (Taddia et al. 2013), or more than 10 M (Moriya 12 et al. 2014). These values are so high that they cannot be rec- onciled with a steady wind mass loss model (Vink et al. 2001; ) 11 sun van Loon et al. 2005; Smith 2014). In addition, some SNe IIn show bumps in their light curves that are thought to be related 10 to bumpy density structures of CSM (Reguitti et al. 2019; Ny- 9 holm et al. 2017; Stritzinger et al. 2012). Although these bumps seem to be rare cases among SNe IIn (Nyholm et al. 2019), 8 this bumpy CSM structure also implies not steady but episodic 7 mass loss events from the progenitor star. Therefore, a dynami- Nuclear luminosity log(L/L model RSG cal phenomenon, which is not included in most of current stellar model BSG evolution models, would occur during the temporary brightening 6 phase. 100 10 1 0.1 Time to core-collapse [yr] However, the extra energy sources that trigger these mass loss events and dynamical mechanism of the mass eruption re- Fig. 1. Evolution of the energy generation rate by nuclear burning for producing observational features have not been fully understood. each model indicated by labels. The rate becomes higher toward the core collapse. There are some local peaks for each model around ten There are several works that investigate the dynamics of the years, five years, and one year before core collapse. We adopted the stellar envelope of massive stars into which an extra energy peaks at 11.2 years before core collapse (model RSG) and at 7.2 years is deposited (Quataert et al. 2016; Fuller 2017; Fuller & Ro before core collapse (BSG) as initial models for our calculations. These 2018; Ouchi & Maeda 2019; Dessart et al. 2010; Owocki et al. peaks correspond to the core neon burning phase. 2019; Kuriyama & Shigeyama 2020). In Kuriyama & Shigeyama (2020), we investigated the observational properties of mass 108 eruption from the progenitors of SNe IIn/Ibn assuming an ex- model RSG 106 tra energy is supplied into the envelope of single massive stars. model BSG 104 We deposited energy into the bottom of the stellar envelope with 2 ] 10 a short timescale and calculated the dynamics of the subsequent -1 100 mass eruption using 1-D radiation hydrodynamical simulation -2 code. 10 10-4 Although energy is deposited only once and the correspond- Density [g cc 10-6 ing single dynamical eruption event is discussed in these stud- 10-8 ies including Kuriyama & Shigeyama (2020), an intense mass 10-10 loss event is often repeated in real situations, as discussed above, 10-12 and this could become a key factor for understanding the mass 0 2 4 6 8 10 12 14 16 loss mechanism. Once a dynamical eruption takes place, the ex- Mass Coordinate [Msun] panding envelope keeps its altered density profile for the thermal timescale. If another eruption event occurs again before the en- Fig. 2. Density distribution of each progenitor model. Model RSG has a velope returns to a hydrostatic equilibrium state, the property of more extended envelope than model BSG because of higher metallicity the second eruption may be completely different because of a (Table 1) and opacity. In addition to that, model RSG has experienced different density profile of the envelope. stronger mass loss due to higher metallicity and thus has a lower total mass. To deal with this problem, in this work we study the dynam- ics of eruptive mass loss that is repeated twice, as a supplemental work of Kuriyama & Shigeyama (2020). Of course eruption can 2. Setup and methods repeat more than twice, but we just focus on a comparison be- 2.1. Progenitor models tween eruptions from the original (hydrostatic) envelope and the expanding envelope. We assume that eruptive mass loss is re- Although it has been often considered that eruptive mass loss and lated to the local peak of the energy generation rate of nuclear SNe IIn are related to activities of LBVs (e.g., Kotak & Vink burning shown in Figure 1, although the specific mechanism of 2006; Gal-Yam et al. 2007; Langer 2012) as described in Sect energy transportation from the burning region to the envelope is 1, observations suggest that red supergiants (RSGs) may also be not assumed as was the case in Kuriyama & Shigeyama (2020).