SN 2019gsc: a faint type Iax supernova discovered by ATLAS S. Srivastav1, G. Leloudas2, S. J. Smartt1, J. Gillanders1, D. B. Malesani3, J. Hjorth3, M. Huber4, K. C. Chambers4 et al. 1Astrophysics Research Centre, Queen's University Belfast, BT7 1NN, United Kingdom 2DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark 3DARK, Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen, Denmark 4Institute for Astronomy, University of Hawai‘i, 2680 Woodland Drive, Honolulu, HI 96822, USA krishnamurthy@mps.mpg.de; lagg@mps.mpg.de; solanki@mps.mpg.de; castellanos@mps.mpg.de Summary TARDIS Fits Spectral Evolution Introduction SNe Iax are a subclass of the thermonuclear supernova family with the following distinctive characteristics: • Early spectra blue and hot, with weak Si II and prominent Fe III features, akin to the 1991T-like subclass (Foley+ 2013). • Expansion velocities considerably lower (# km s# ) than those for the rest of the SN Ia family (# km s# ). • Lower rise times and post-maximum decline rates on the higher side relative to normal SNe Ia (Stritzinger+ 2015). • Lower peak luminosities relative to normal SNe Ia, although there’s a large scatter (# ), eg. Magee+ (2017). • Generally found in star-forming, late-type host environments, akin to SNe IIP and 1991T/1999aa-like SNe Ia (Jha 2017). ∼2000 −7000 −1 ∼10000 −1 −19 ≲MV ≲−14 Light Curves and Colour Curves • Disc. 2019-06-2.36 UT • Disc. mag: # (ATLAS cyan band) • # • # • # • # • # 19.7 ± 0.2 Mpeak* g ≈−13.6 ± 0.2 Mpeak* r ≈−13.8 ± 0.2 Δm15(g) = 1.65 ± 0.25 Δm15(r) = 0.91 ± 0.11 Δm15(i) = 0.80 ± 0.07 *for negligible host reddening Fig 1: Pan-STARRS1 target, reference, diﬀerence and colour composite images Of the ﬁeld for SN 2019gsc. Fig 2: Pan-STARRS1 # light curves of SN 2019gsc along with ZTF # and # -band magnitudes and upper limits. grizy g r Fig 3: Light curve (# ) and colour curve (# ) comparison between SN 2019gsc and faint Iax SNe 2010ae (Stritzinger+ 2014) and 2008ha (Foley+ 2009). # was assumed for SN 2010ae. gri g −r E(B −V)host = 0.3 Bolometric Light Curve • Host reddening was assumed to be negligible for SN 2019gsc. • # was assumed for SN 2010ae. SN 2019gsc parameters: • # • # • # erg • # days • # • # erg E(B −V)host = 0.3 MNi ≈1.2 −2.1 × 10−3 M⊙ Mej ≈0.1 −0.3 M⊙ E51 ≈0.01 −0.02 trise ≈10 mpeak bol ≈−13.3 ± 0.2 Lpeak bol ≈6.3 × 1040 Fig 4: Quasi-bolometric (# ) and blackbody ﬁt (# ) bolometric light curves of SN 2019gsc, along with those of SNe 2010ae and 2008ha. Also plotted is the best-ﬁtting Arnett-Valenti model (Valenti+ 2008) for each of the events. SuperBol (Nicholl 2018) was used to construct the bolometric light curves. grizy 1000 −25000 Å Fig 5: Early spectral evolution of SN 2019gsc, compared with spectra of SNe 2010ae and 2008ha at similar epochs. SN 2019gsc features show expansion velocities between # km s# , intermediate to SNe 2010ae and 2008ha. 3000 −4000 −1 Fig 6: The NOT spectral time series of SN 2019gsc, ﬁt with a self-consistent ejecta model computed using the 1D Monte Carlo radiative transfer code TARDIS (Kerzendorf & Sim 2014). An exponential density proﬁle was assumed, with uniform chemical abundance throughout the ejecta. Only the time- dependent parameters were tweaked for each individual epoch, following Barna+ 2018. The density proﬁle of the ejecta model has a low exponent, requiring signiﬁcant amounts of material at higher velocities. • At # , SN 2019gsc is among, and potentially the faintest thermonuclear supernova yet observed. • The # yield is a very modest # . • Ejected mass # , consistent with a sub-# progenitor or a WD deﬂagration leaving a bound remnant. • Photospheric spectra show a host of narrow P-Cygni features, with velocities between # km s# . Mpeak g ≈−13.6 ± 0.2 56Ni 0.001 −0.002 M⊙ Mej ≈0.1 −0.3 M⊙ MCh 3000 −4000 −1