Can massive Be/Oe stars be progenitors of long gamma ray bursts?

Abstract

Context. The identification of long-gamma-ray-bursts (LGRBs) is still uncertain, although the collapsar engine of fast-rotating massive stars is gaining a strong consensus. Aims. We propose that low-metallicity Be and Oe stars, which are massive fast rotators, as potential LGRBs progenitors. Methods. We checked this hypothesis by 1) testing the global specific angular momentum of Oe/Be stars in the ZAMS with the SMC metallicity; 2) comparing the ZAMS (Ω/Ω c , M/M ) parameters of these stars with the area predicted theoretically for progenitors with metallicity Z = 0.002; and 3) calculating the expected rate of LGRBs/year/galaxy and comparing them with the observed ones. To this end, we determined the ZAMS linear and angular rotational velocities for SMC Be and Oe stars using the observed V sin i parameters, corrected from the underestimation induced by the gravitational darkening effect. Results. The angular velocities of SMC Oe/Be stars are on average Ω/Ω c = 0.95 in the ZAMS. These velocities are in the area theoretically predicted for the LGRBs progenitors. We estimated the yearly rate per galaxy of LGRBs and the number of LGRBs produced in the local Universe up to z = 0.2. We have considered that the mass range of LGRB progenitors corresponds to stars hotter than spectral types B0-B1 and used individual beaming angles from 5 to 15• . We thus obtain R predLGRB ∼ 10 −7 to ∼10 −6LGRBs/year/galaxy, which represents on average 2 to 14 LGRB predicted events in the local Universe during the past 11 years. The predicted rates could widely surpass the observed ones [(0.2−3) × 10 −7LGRBs/year/galaxy; 8LGRBs observed in the local Universe during the last 11 years] if the stellar counts were made from the spectral type B1-B2, in accordance with the expected apparent spectral types of the appropriate massive fast rotators. Conclusions. We conclude that the massive Be/Oe stars with SMC metallicity could be LGRBs progenitors. Nevertheless, other SMC O/B stars without emission lines, which have high enough specific angular momentum, can enhance the predicted R LGRB rate.

The longγ-ray burst rate and the correlation with host galaxy properties

“…However, there is a range of possible lower range masses (Nomoto et al 2010) and also secondary mechanisms for BHs to generate a LGRB, for example SN-fallback (for a review see Fryer et al 2007). There are also different types of progenitor systems (other than a WR) that are thought to be possible to generate a LGRB, e.g., NS-white dwarf binaries ), Helium-Helium binaries (Fryer & Heger 2005), Quark stars (Ouyed et al 2005), Be/Oe stars (Martayan et al 2010;Eldridge et al 2011), blue-stragglers (Woosley & Heger 2006) and red-giants (Eldridge et al 2011). Different mechanisms have been investigated before, but not in combination with the parameters of this paper (see Young & Fryer 2007).…”

The MiMeS survey of Magnetism in Massive Stars: magnetic analysis of the O-type stars

“…Low-metallicity Oetype stars have also been associated with the origin of longsoft gamma-ray bursts (e.g. Martayan et al 2010).…”

The long gamma-ray burst rate and the correlation with host galaxy properties

“…However, there is a range of possible lower range masses (Nomoto et al 2010) and also secondary mechanisms for BHs to generate a LGRB, for example SN-fallback (for a review see Fryer et al 2007). There are also different types of progenitor systems (other than a WR) that are thought to be possible to generate a LGRB, e.g., NS-White Dwarf binaries (Thompson et al 2009), Helium-Helium binaries (Fryer & Heger 2005), Quark stars (Ouyed et al 2005), Be/Oe stars (Martayan et al 2010;Eldridge et al 2011), blue-stragglers (Woosley & Heger 2006) and red-giants (Eldridge et al 2011). Different mechanisms have been investigated before, but not in combination with the parameters of this paper (see Young & Fryer 2007).…”