SN 2020bvc: A Broad-line Type Ic Supernova with a Double-peaked Optical Light Curve and a Luminous X-Ray and Radio Counterpart

Abstract

We present optical, radio, and X-ray observations of SN 2020bvc (=ASASSN-20bs, ZTF 20aalxlis), a nearby (= z 0.0252; d=114 Mpc) broad-line (BL) Type Ic supernova (SN) and the first double-peaked Ic-BL discovered without a gamma-ray burst (GRB) trigger. Our observations show that SN 2020bvc shares several properties in common with the Ic-BL SN 2006aj, which was associated with the low-luminosity gamma-ray burst (LLGRB) 060218. First, the 10 GHz radio luminosity (»-L 10 erg s radio 37 1) is brighter than ordinary core-collapse SNe but fainter than LLGRB SNe such as SN 1998bw (associated with LLGRB 980425). We model our VLA observations (spanning 13-43 days) as synchrotron emission from a mildly relativistic (v  0.3c) forward shock. Second, with Swift and Chandra, we detect X-ray emission (L X ≈10 41 ergs 1) that is not naturally explained as inverse Compton emission or part of the same synchrotron spectrum as the radio emission. Third, high-cadence (6× night-1) data from the Zwicky Transient Facility (ZTF) show a double-peaked optical light curve, the first peak from shock cooling of extended low-mass material (mass <-M M 10 e 2  at radius R e >10 12 cm) and the second peak from the radioactive decay of Ni 56. SN 2020bvc is the first double-peaked Ic-BL SN discovered without a GRB trigger, so it is noteworthy that it shows X-ray and radio emission similar to LLGRB SNe. For four of the five other nearby (z0.05) Ic-BL SNe with ZTF high-cadence data, we rule out a first peak like that seen in SN 2006aj and SN 2020bvc, i.e., that lasts ≈1 dayand reaches a peak luminosity M≈−18. Follow-up X-ray and radio observations of Ic-BL SNe with well-sampled early optical light curves will establish whether double-peaked optical light curves are indeed predictive of LLGRB-like X-ray and radio emission. Unified Astronomy Thesaurus concepts: Radio transient sources (2008); High energy astrophysics (739); Transient sources (1851); Core-collapse supernovae (304); Supernovae (1668); Type Ic supernovae (1730); X-ray transient sources (1852); Gamma-ray bursts (629) Supporting material: data behind figure, machine-readable table

Near-infrared and Optical Observations of Type Ic SN 2020oi and Broad-lined Type Ic SN 2020bvc: Carbon Monoxide, Dust, and High-velocity Supernova Ejecta

“…The extinctions we derive from marginal dips in SN 2020oi are consistent with the techniques described in Poznanski et al (2012). The estimated extinction of SN 2020oi is comparable to those of Izzo et al (2020) and Ho et al (2020c), and that of SN 2020bvc is comparable to that of Horesh et al (2020).…”

“…The change in velocity between days 1 and 20 is ∼34,000 km s −1 , while from day 20 to 73 it is ∼10,000 km s −1 . Such high expansion velocities in SN 2020bvc have also been reported by Izzo et al (2020) and Ho et al (2020c), using the Ca II triplet absorption feature in the same FLOYDS spectrum (available in TNS) on day 1. Significant velocity changes in eight optical spectra taken during the pre-max stage are also shown by Ho et al (2020c), who report the change of 32,000 km s −1 in expansion velocity between days 0.76 and 12.5.…”

“…The high velocities of SN 2020bvc are in better agreement with those SNe Ic-BL associated with GRBs than those with Type Ic-BL without associated GRBs. If SNe Ic-BL without associated GRBs are off-axis GRBs, our results indicate that the on-axisunobserved GRB scenario is more appropriate for SN 2020bvc, which is supported by the work by Ho et al (2020a). In contrast, Izzo et al (2020) suggest an off-axis GRB for SN 2020bvc because of the lack of early X-ray detection.…”

“…It has been suggested by Izzo et al (2020) that the lack of a counterpart GRB is due to it being an off-axis GRB or having a choked jet. Ho et al (2020c) present double-peaked light curves of SN 2020bvc. NIR 0.8-2.5 μm spectra of SN 2020oi and SN 2020bvc were obtained by the Gemini Near-Infrared Spectrograph (GNIRS) on the 8.1 m Frederick C. Gillett Gemini-North telescope, for program GN-2020A-Q-211.…”

“…Figure 4 shows optical light curves of SN 2020bvc with LCO, Konkoly, and ZTF photometry. We use 2020 February 3.67 (MJD = 58,882.67) from Ho et al (2020c) as day 0, which is based on the time of the ATLAS nondetection. The maximum in the V-band light curve occurred on 2020 February 20 (MJD Vmax = 58,899 ± 0.12) at V max = 16.36 ± 0.02 mag.…”