GRB 100418A: a Long GRB without a Bright Supernova in a High-Metallicity Host Galaxy

TL;DR

This study investigates the absence of a bright supernova associated with GRB 100418A, finding no supernova features and setting an upper brightness limit, suggesting some long GRBs may lack bright supernovae especially in high-metallicity environments.

Contribution

It provides the first detailed observational constraints on the supernova component of GRB 100418A, highlighting the possibility of long GRBs without bright supernovae in high-metallicity host galaxies.

Findings

No supernova rebrightening detected in optical afterglow.

Set an upper limit on supernova brightness at MIc,obs > -17.2.

Host galaxy is relatively massive with high metallicity.

Abstract

We present results of a search for a supernova (SN) component associated with GRB 100418A at the redshift of 0.624. The field of GRB 100418A was observed with FOCAS on Subaru 8.2m telescope under a photometric condition (seeing 0.3"-0.4") on 2010 May 14 (UT). The date corresponds to 25.6 days after the burst trigger (15.8 days in the restframe). We did imaging observations in V, Rc, and Ic bands, and two hours of spectrophotometric observations. We got the resolved host galaxy image which elongated 1.6" (= 11 kpc) from north to south. No point source was detected on the host galaxy. The time variation of Rc-band magnitude shows that the afterglow of GRB 100418A has faded to Rc \sim > 24 without SN like rebrightening, when we compare our measurement to the reports in GCN circulars. We could not identify any SN feature such as broad emission-lines or bumps in our spectrum. Assuming the SN is fainter than the 3{\sigma} noise spectrum of our observation, we estimate the upper limit on the SN absolute magnitude MIc,obs > -17.2 in observer frame Ic-band. This magnitude is comparable to the faintest type Ic SNe. We also estimate host galaxy properties from the spectrum. The host galaxy of GRB 100418A is relatively massive (log M_{star}/M_{sun} = 9.54) compared to typical long GRB host galaxies, and has 12+log(O/H) = 8.75.