No supernovae associated with two long-duration γ-ray bursts

Abstract

3It is now accepted that long duration γ-ray bursts (GRBs) are produced during the collapse of a massive star 1,2 . 11,12 . GRB 060505 was a faint burst with a duration of 4 s. GRB 060614 had a duration of 102 s and a pronounced hard to soft evolution. Both were rapidly localised by Swift's X-ray telescope (XRT). Subsequent follow-up of these bursts led to the discovery of their optical afterglows, locating them in galaxies at low redshift: GRB 060505 at z = 0.089 13 and GRB 060614 at z = 0.125 14,15 . The relative proximity of these bursts engendered an expectation that a bright SN would be discovered a few days after the bursts, as had been found just a few months before in 4 another low-redshift Swift burst, GRB 060218 (z = 0.033) 9 , and in all previous wellobserved nearby bursts 1,5-8 .We monitored the afterglows of GRB 060505 and 060614 using a range of telescopes (see supplementary material for details). These led to early detections of the afterglows. We continued the monitoring campaign and obtained stringent upper limits on any re-brightening at the position of the optical afterglows up to 12 and 5 weeks after the bursts, respectively. The light-curves obtained based on this monitoring are shown in Fig. 1. For GRB 060505 we detected the optical afterglow at a single epoch. All subsequent observations resulted in deep upper limits. For GRB 060614 we followed the decay of the optical afterglow in the R-band up to four nights after the burst. In later observations no source was detected to deep limits (see also 14,15 for independent studies of this event). As seen in Fig. 1, the upper limits are far below the level seen in previous SNe, in particular previous SNe associated with long-duration GRBs 5-9 . For both GRBs A concern in any attempt to uncover a SN associated with a GRB is the presence of a poorly quantified level of extinction along the line of sight. In these cases however,we are fortunate that the levels of Galactic extinction in both directions are very low,. In the case of GRB 060505, our spatially resolved spectroscopy of the host galaxy allows us to use the Balmer emission line ratios to limit the dust obscuration 5 at the location of the burst. The Balmer line ratio is consistent with no internal reddening. In the case of GRB 060614, the detection of the early afterglow in many bands, including the Swift UV bands UVW1 and UVW2 17 , rules out significant obscuration of the source in the host galaxy and we conclude that there is no significant dust obscuration in either case (see also 15 ).Both GRBs were located in star-forming galaxies. The host galaxy of GRB 060505 has an absolute magnitude of about M B = -19.6 and the spectrum displays the prominent emission lines typically seen in star-forming galaxies. The 2-dimensional spectrum shows that the host galaxy emission seen at the position of the afterglow is due to a compact H II region in a spiral arm of the host (see the supplementary material for details). We estimate a star-formation rate of 1 M  yr −1 and a specific rate of about 4T...

GRB 080517: a local, low-luminosity gamma-ray burst in a dusty galaxy at z = 0.09

“…Only a handful of such low luminosity events have been identified in the past decade, all of which have been relatively local (given the difficulty in observing low luminosity bursts beyond z ∼ 0.1). These include the well studied GRBsupernova pairs GRB 980425/SN 1998bw (Galama et al 1998), GRB 031203/SN 2003lw (Malesani et al 2004;Soderberg et al 2004), GRB 060218/SN 2006aj (Pian et al 2006) and GRB 100316D/SN 2010bh (Starling et al 2011;Cano et al 2011), and the enigmatic GRBs 060505 and 060614, where associated SNe have been ruled out to deep limits, and whose origin remains mysterious (Fynbo et al 2006;Della Valle et al 2006). They may be low luminosity events akin to those above, but where the SNe is absent (e.g.…”

“…Watson et al 2011;Starling et al 2011). Low redshift bursts include several which are sub-luminous, such as GRBs 090825 and 031203 (Galama et al 1998;Malesani et al 2004;Soderberg et al 2004), and others such as GRBs 060505 and 060614 that were long bursts without associated supernovae (Fynbo et al 2006;Della Valle et al 2006). Cross-correlation with local galaxy surveys (at z < 0.037) has suggested that some low redshift GRBs in the existing burst catalogues have yet to be identified as such (Chapman et al 2007) and hence opportunities to study their properties in detail have been missed.…”

The supernova–gamma-ray burst–jet connection

“…As shown in figure 1, the constraints on GRB 060505 and GRB 060614 are about as constraining as the those related to the short gamma-ray bursts discussed earlier. These puzzling systems may be related to non-56 Ni-producing supernovae or they may be merger gamma-ray bursts with longer durations than usually found [41][42][43][44][45].…”

The Connection between Gamma-Ray Bursts and Extremely Metal-Poor Stars as Nucleosynthetic Probes of the Early Universe

“…In contrast, "non-SN GRBs" (or dark HNe) have also been discovered (GRBs 060605 and 060614) (Fynbo et al 2006, Gal-Yam et al 2006, Della Valle et al 2006, Gehrels et al 2006. Upper limits to brightness of the possible SNe are about 100 times fainter than SN 1998bw.…”