We present and analyse an extensive dataset of the superluminous supernova ( SLSN ) LSQ14mo ( z = 0.256 ) , consisting of a multi-colour 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 hydrogen-poor SLSN .
The bolometric lightcurve can be reproduced with a millisecond magnetar model with \sim 4 M _ { \odot } 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 \sim 6 M _ { \odot } of CO-rich material with a kinetic energy of \sim 7 \times 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 \sim 0.3 Z _ { \odot } ) .
We propose that the three bright regions in the host system are interacting , which thus triggers star formation and forms young stellar populations .