A Near-infrared Search for Helium in the Superluminous Supernova SN 2024ahr

Abstract

We present a detailed study of SN 2024ahr, a hydrogen-poor superluminous supernova (SLSN-I), for which we determine a redshift of z = 0.0861. SN 2024ahr has a peak absolute magnitude of M _g ≈ M _r ≈ −21 mag, rest-frame rise and decline times (50% of peak) of about 40 and 80 days, respectively, and typical spectroscopic evolution in the optical band. Similarly, modeling of the UV/optical light curves with a magnetar spin-down engine leads to typical parameters: an initial spin period of ≈3.3 ms, a magnetic field strength of ≈6 × 10 ^13 G, and an ejecta mass of ≈9.5 M _⊙ . Due to its relatively low redshift, we obtained a high signal-to-noise ratio near-IR (NIR) spectrum about 43 rest-frame days postpeak to search for the presence of helium. We do not detect any significant feature at the location of the He i λ 2.058 μ m feature and place a conservative upper limit of ∼0.05 M _⊙ on the mass of helium in the outer ejecta. We detect broad features of Mg i λ 1.575 μ m and Mg ii λ 2.136 μ m, which are typical of Type Ic SNe, but with higher velocities. Examining the sample of SLSNe-I with NIR spectroscopy, we find that, unlike SN 2024ahr, these events are generally peculiar. This highlights the need for a large sample of prototypical SLSNe-I with NIR spectroscopy to constrain the fraction of progenitors with helium (Ib-like) and without helium (Ic-like) at the time of explosion, and hence the evolutionary path(s) leading to the rare outcome of SLSNe-I.

Keywords

• Time domain astronomy
• Transient sources
• Near infrared astronomy
• Spectroscopy
• Supernovae
• Type Ic supernovae