The evolution of superluminous supernova LSQ14mo and its interacting host galaxy system

Abstract

We present and analyse an extensive dataset of the superluminous supernova (SLSN) LSQ14mo (z = 0.256), consisting of a multicolour lightcurve from −30 d to +70 d in the rest-frame (relative to maximum light) and a series of six spectra from PESSTO covering −7 d to +50 d. This is among the densest spectroscopic coverage, and best-constrained rising lightcurve, for a fast-declining hydrogenpoor SLSN. The bolometric lightcurve can be reproduced with a millisecond magnetar model with ∼ 4 M ejecta mass, and the temperature and velocity evolution is also suggestive of a magnetar as the power source. Spectral modelling indicates that the SN ejected ∼ 6 M of CO-rich material with a kinetic energy of ∼ 7 × 10 51 erg, and suggests a partially thermalised additional source of luminosity between −2 d and +22 d. This may be due to interaction with a shell of material originating from pre-explosion mass loss. We further present a detailed analysis of the host galaxy system of LSQ14mo. PESSTO and GROND imaging show three spatially resolved bright regions, and we used the VLT and FORS2 to obtain a deep (five-hour exposure) spectra of the SN position and the three star-forming regions, which are at a similar redshift. The FORS spectrum at +300 days shows no trace of SN emission lines and we place limits on the strength of [O i] from comparisons with other Ic supernovae. The deep spectra provides a unique chance to investigate spatial variations in the host star-formation activity and metallicity. The specific star-formation rate is similar in all three components, as is the presence of a young stellar population. However, the position of LSQ14mo exhibits a lower metallicity, with 12 + log(O/H) = 8.2 in both the R 23 and N2 scales (corresponding to ∼ 0.3 Z ). We propose that the three bright regions in the host system are interacting, which thus triggers star formation and forms young stellar populations.

The host of the Type I SLSN 2017egm

“…Rearrangement of gas in the galaxy, gas transfer, or the interaction causing metal-poor H i gas to be funneled into the galaxy could explain the occurrence of a SLSN Type I at low metallicity even in this solar-metallicity galaxy and indeed there is a small population of metal-poor stars present at the SLSN site. New SF activity due to interaction was also proposed for three other SLSN-I hosts (Cikota et al 2017;Chen et al 2017a).…”

Gas inflow and outflow in an interacting high-redshift galaxy

“…There are other examples of potentially merging systems hosting cosmic explosions, detected in absorption line profiles such as GRB 090323 (Savaglio et al 2012) and GRB 100219A (Thöne et al 2013), and in imaging of the hosts (GRB 051022;Castro-Tirado et al 2007;Rol et al 2007, and GRB060814;Perley et al 2013). Similarly, interacting systems have also been detected in the host systems of superluminous supernovae (Chen et al 2017;Perley et al 2016a). However, the detection of mergers in GRB and SN hosts could be coincidental, especially at high redshift where mergers are much more frequent (e.g.…”

One Thousand Days of SN2015bn: HST Imaging Shows a Light Curve Flattening Consistent with Magnetar Predictions

“…Thus the host and its bright neighbour appear to be a close analogue of the MW-SMC system. Chen et al (2017) found that the host of one SLSN, LSQ14mo, was in a likely interacting system with a projected separation of 15 kpc, and proposed that this could increase the likelihood of SLSNe by triggering vigorous star formation. The brightest and bluest pixels in our HST images, likely corresponding to the highest starformation rate, actually appear to be on the other side of the galaxy, though we cannot exclude comparable starformation at the position of SN 2015bn until the SLSN has completely faded.…”