The Late‐Time Light Curve of SN 1998bw Associated with GRB 980425

Abstract

We report 139 photometric observations through the B, V, and I filters of the supernova SN 1998bw, an object which is associated with the Gamma-Ray Burst GRB 980425. Detailed light curves of this unique supernova can be compared to theoretical models, so we report here our light curve for 123 days between 27 June 1998 and 28 October 1998. The light curve of SN 1988bw is consistent with those of the Type Ic class. We find that the magnitude-versus-time relation for this supernova is linear to within 0.05 mags in all colors over the entire duration of our study. Our measured uniform decline rates are 0.0141 ± 0.0002, 0.0184 ± 0.0003, and 0.0181 ± 0.0003 magnitudes per day in the B, V, and I bands. The linear decline and the rate of that decline suggest that the late time light curve is powered by the radioactive decay of cobalt with some leakage of the gamma rays.

Evidence for Magnetar Formation in Broad-lined Type Ic Supernovae1998bw and 2002ap

“…Thanks to its proximity, only 9.4 Mpc in distance, high quality observational data were acquired until 580 days after explosion, which is prerequisite for the identification of late excess over the exponential 56 Co decay. SN 1998bw (Galama et al 1998;McKenzie & Schaefer 1999;Sollerman et al 2000;Patat et al 2001;Clocchiatti et al 2011), on the other hand, is the nearest SN associated with a GRB (Cano et al 2016). Although at a distance greater than SN 2002ap, its brighter luminosity qualifies SN 1998bw as an ideal observational target and its light curve was measured to ∼ 1000 days post explosion (Sollerman et al 2002).…”

Optical and Near-IR Observations of SN 1998bw

“…The broad-band photometric observations by McKenzie & Schaefer [16] taken during the intermediate phases revealed that the object settled on an exponential decay similar to that observed in other type Ic SNe. McKenzie & Schaefer first suggested that even in this case the light curve was powered by the radioactive decay of 56 Co with some leakage of γ-rays.…”

“…Starting with the Nature papers by Galama et al [7] and Iwamoto et al [11], a number of authors have presented the results of their observational campaigns: McKenzie & Schaefer [16], Galama et al [8], Stathakis et al [23], Fynbo et al [5], Sollerman et al [21], Patat et al [18] and Sollerman et al [22].…”

GRB 091127/SN 2009nz and the VLT/X-shooter spectroscopy of its host galaxy: probing the faint end of the mass-metallicity relation

“…In both cases, the effects of extinction by dust and absorption by gas in the Galaxy had been previously removed. For the optical data fit, we used a broken power-law with the addition of a late-time constant component, the host galaxy, and a SN component modelled following SN 1998bw (Galama et al 1998;McKenzie & Schaefer 1999;Sollerman et al 2000;Patat et al 2001;Sollerman et al 2002), i.e. the same as that used by Cobb et al (2010).…”