CALCIUM-RICH GAP TRANSIENTS IN THE REMOTE OUTSKIRTS OF GALAXIES

By M. Kasliwal, Shrinivas R. Kulkarni, A. Gal-yam, P. Nugent, M. Sullivan, L. Bildsten, O. Yaron, H. Perets, I. Arcavi, S. Ben-Ami and 18 more. 2011

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From the first two seasons of the Palomar Transient Factory, we identify three peculiar transients (PTF 09dav, PTF 10iuv, and PTF 11bij) with five distinguishing characteristics: peak luminosity in the gap between novae and supernovae (MR ≈ −15.5 to −16.5 mag), rapid photometric evolution (trise ≈ 12–15 days), large photospheric velocities (≈6000–11,000 km s−1), early spectroscopic evolution into nebular phase (≈1–3 months), and peculiar nebular spectra dominated by calcium. We also culled the extensive decade-long Lick Observatory Supernova Search database and identified an additional member of this group, SN 2007ke. Our choice of photometric and spectroscopic properties was motivated by SN 2005E (Perets et al.). To our surprise, as in the case of SN 2005E, all four members of this group are also clearly offset from the bulk of their host galaxy. Given the well-sampled early- and late-time light curves, we derive ejecta masses in the range of 0.4–0.7 M☉. Spectroscopically, we find that there may be a diversity in the photospheric phase, but the commonality is in the unusual nebular spectra. Our extensive follow-up observations rule out standard thermonuclear and standard core-collapse explosions for this class of “calcium-rich gap” transients. If the progenitor is a white dwarf, we are likely seeing a detonation of the white dwarf core and perhaps even shock-front interaction with a previously ejected nova shell. If the progenitor is a massive star, a nonstandard channel specific to a low-metallicity environment needs to be invoked (e.g., ejecta fallback leading to black hole formation). Detection (or the lack thereof) of a faint underlying host (dwarf galaxy and cluster) will provide a crucial and decisive diagnostic to choose between these alternatives.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/b3c1668ef987381eddb7754685d501da9626f29d

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Citations in the corpus

• IDENTIFYING ELUSIVE ELECTROMAGNETIC COUNTERPARTS TO GRAVITATIONAL WAVE MERGERS: AN END-TO-END SIMULATION (2012, methodology): “We can easily search 10 times the size of the galaxy to accommodate large kicks of the order of hundred kiloparsec (e.g., Fong et al. 2010; Kasliwal et al. 2012) in NS-NS mergers and still gain a factor of 25 in terms of reduction of false positives.”
• TYPE Iax SUPERNOVAE: A NEW CLASS OF STELLAR EXPLOSION (2012, background): “However, both SN 2005E and PTF 09dav appear to come from old stellar populations (although PTF 09dav had hydrogen in its late-time spectrum; Kasliwal et al. 2012).”
• OPACITIES AND SPECTRA OF THE r-PROCESS EJECTA FROM NEUTRON STAR MERGERS (2013, background): “…that produce low mass ejections of radioactive material (e.g., Bildsten et al. 2007; Moriya et al. 2010), and an increasing number of fast, faint transients have been observed at optical wavelengths (e.g., Kasliwal et al. 2010; Perets et al. 2010; Kasliwal et al. 2012; Foley et al. 2012).”
• Dawes Review 6: The Impact of Companions on Stellar Evolution (2016, background): “Current (small) samples place them in the outskirts of galaxies (Kasliwal et al., 2012).”
• Sub-Chandrasekhar-mass White Dwarf Detonations Revisited (2017, background): “Note that we only consider comparisons to “normal” SNe Ia, ranging from SN 1991bg-likes to SN 1991T-likes, and not to the peculiar classes of Carich transients (e.g., Kasliwal et al. 2012) and SNe Iax (e.g., Foley et al. 2013).”
• RAPIDLY EVOLVING AND LUMINOUS TRANSIENTS FROM PAN-STARRS1 (2014, background): “…circles/squares: type Ia SN (Nugent et al. 2002; Taubenberger et al. 2008; Scalzo et al. 2012), type Iax & “calcium-rich” Ia (Foley et al. 2013; Kasliwal et al. 2012; Perets et al. 2010), type Ib/Ic (Drout et al. 2011; Valenti et al. 2008; Campana et al. 2006; Taubenberger et al. 2006;…”
• Observational and Physical Classification of Supernovae (2016, unknown): “…of these events, and focussed on the unusual remote galactic locations they seemed to preferntially occur in. Ca-rich events have similar expansion velocities to those of regular SNe Ib, and fainter peaks magnitudes by ∼ 2 mag, as well as more rapidly declining light curves (Kasliwal et al. 2012).”