The Spectroscopic Classification and Explosion Properties of SN2009nz Associated with GRB091127 at z=0.490

📝 Abstract

We present spectroscopic observations of GRB091127 (z=0.490) at the peak of the putative associated supernova, SN2009nz. Subtracting a late-time spectrum of the host galaxy, we isolate the contribution of SN2009nz and uncover broad features typical of nearby GRB-SNe. This establishes unambiguously that GRB091127 was accompanied by a broad-lined Type Ic SN, and links a cosmological long burst with a standard energy release (E_gamma,iso ~ 1.1e52 erg) to a massive star progenitor. The spectrum of SN2009nz closely resembles that of SN2006aj, with SN2003dh also providing an acceptable match, but has significantly narrower features than SNe 1998bw and 2010bh, indicative of a lower expansion velocity. The photospheric velocity inferred from the SiII 6355 absorption feature, v_ph ~ 17,000 km/s, is indeed closer to that of SNe 2006aj and 2003dh than to the other GRB-SNe. Combining the measured velocity with the light curve peak brightness and width, we estimate the following explosion parameters: M_Ni ~ 0.35 M_sun, E_K ~ 2.3e51 erg, and M_ej ~ 1.4 M_sun, similar to those of SN2006aj. These properties indicate that SN2009nz follows a trend of lower M_Ni for GRB-SNe with lower E_K and M_ej. Equally important, since GRB091127 is a typical cosmological burst, the similarity of SN2009nz to SN2006aj either casts doubt on the claim that XRF060218/SN2006aj was powered by a neutron star, or indicates that the nature of the central engine is encoded in the SN properties but not in the prompt emission. Future spectra of GRB-SNe at z > 0.3, including proper subtraction of the host galaxy contribution, will shed light on the full dispersion of SN properties for standard long GRBs, on the relation between SNe associated with sub-energetic and standard GRBs, and on a potential dispersion in the associated SN types.

💡 Analysis

We present spectroscopic observations of GRB091127 (z=0.490) at the peak of the putative associated supernova, SN2009nz. Subtracting a late-time spectrum of the host galaxy, we isolate the contribution of SN2009nz and uncover broad features typical of nearby GRB-SNe. This establishes unambiguously that GRB091127 was accompanied by a broad-lined Type Ic SN, and links a cosmological long burst with a standard energy release (E_gamma,iso ~ 1.1e52 erg) to a massive star progenitor. The spectrum of SN2009nz closely resembles that of SN2006aj, with SN2003dh also providing an acceptable match, but has significantly narrower features than SNe 1998bw and 2010bh, indicative of a lower expansion velocity. The photospheric velocity inferred from the SiII 6355 absorption feature, v_ph ~ 17,000 km/s, is indeed closer to that of SNe 2006aj and 2003dh than to the other GRB-SNe. Combining the measured velocity with the light curve peak brightness and width, we estimate the following explosion parameters: M_Ni ~ 0.35 M_sun, E_K ~ 2.3e51 erg, and M_ej ~ 1.4 M_sun, similar to those of SN2006aj. These properties indicate that SN2009nz follows a trend of lower M_Ni for GRB-SNe with lower E_K and M_ej. Equally important, since GRB091127 is a typical cosmological burst, the similarity of SN2009nz to SN2006aj either casts doubt on the claim that XRF060218/SN2006aj was powered by a neutron star, or indicates that the nature of the central engine is encoded in the SN properties but not in the prompt emission. Future spectra of GRB-SNe at z > 0.3, including proper subtraction of the host galaxy contribution, will shed light on the full dispersion of SN properties for standard long GRBs, on the relation between SNe associated with sub-energetic and standard GRBs, and on a potential dispersion in the associated SN types.

📄 Content

arXiv:1106.3073v1 [astro-ph.HE] 15 Jun 2011 DRAFT VERSION NOVEMBER 20, 2021 Preprint typeset using LATEX style emulateapj v. 03/07/07 THE SPECTROSCOPIC CLASSIFICATION AND EXPLOSION PROPERTIES OF SN 2009NZ ASSOCIATED WITH GRB 091127 AT z = 0.490 E. BERGER1, R. CHORNOCK1, T. R. HOLMES1, R. J. FOLEY1,2, A. CUCCHIARA3,4, C. WOLF5, PH. PODSIADLOWSKI5, D. B. FOX6, AND K. C. ROTH7 Draft version November 20, 2021 ABSTRACT We present spectroscopic observations of GRB 091127 (z = 0.490) at the peak of the putative associated supernova SN 2009nz. Subtracting a late-time spectrum of the host galaxy, we isolate the contribution of SN 2009nz and uncover broad features typical of nearby GRB-SNe. This establishes unambiguously that GRB 091127 was accompanied by a broad-lined Type Ic SN, and links a cosmological long burst with a standard energy release (Eγ,iso ≈1.1 × 1052 erg) to a massive star progenitor. The spectrum of SN 2009nz closely resembles that of SN 2006aj, with SN 2003dh also providing an acceptable match, but has significantly narrower features than SNe 1998bw and 2010bh, indicative of a lower expansion velocity. The photospheric velocity inferred from the Si IIλ6355 absorption feature, vph ≈17,000 km s−1, is indeed closer to that of SNe 2006aj and 2003dh than to the other GRB-SNe. Combining the measured velocity with the light curve peak brightness and width, we estimate the following explosion parameters: MNi ∼0.35 M⊙, EK ∼2.3 × 1051 erg, and Mej ∼1.4 M⊙, similar to those of SN 2006aj. These properties indicate that SN 2009nz follows a trend of lower MNi for GRB-SNe with lower EK and Mej. Equally important, since GRB 091127 is a typical cosmologi- cal burst, the similarity of SN 2009nz to SN 2006aj either casts doubt on the claim that XRF 060218/SN2006aj was powered by a neutron star, or indicates that the nature of the central engine is encoded in the SN properties but not in the prompt emission. Future spectra of GRB-SNe at z ≳0.3, including proper subtraction of the host galaxy contribution, will shed light on the full dispersion of SN properties for standard long GRBs, on the relation between SNe associated with sub-energetic and standard GRBs, and on a potential dispersion in the associated SN types. Subject headings: gamma-rays:bursts

1. INTRODUCTION The association of long-duration gamma-ray bursts (GRBs) with Type Ic supernovae (SNe) provides the most direct ev- idence for massive stripped-envelope (Wolf-Rayet) stars as the progenitors of long GRBs (e.g., Woosley & Bloom 2006). This connection was first intimated by the dis- covery of the unusually luminous and broad-lined Type Ic SN 1998bw (d = 40 Mpc) in spatial and temporal co- incidence with GRB 980425 (Galama et al. 1998). It was further supported by the detection of late-time photometric “bumps” in the optical light curves of several GRBs at z ≲1 that resembled the optical light curve of SN 1998bw (e.g., Bloom et al. 1999; Lazzati et al. 2001; Bloom et al. 2002; Soderberg et al. 2005, 2006b), although alternative explana- tions for these bumps have been proposed (Esin & Blandford 2000; Waxman & Draine 2000). Subsequently, unambiguous spectroscopic identifications were obtained for four nearby GRBs: GRB 030329/SN2003dh (z = 0.169; Hjorth et al. 2003; Stanek et al. 2003), GRB 031203/SN2003lw (z = 0.105; Malesani et al. 2004), XRF 060218/SN2006aj 1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cam- bridge, MA 02138 2 Clay Fellow 3 Lawrence Berkeley National Laboratory, M.S. 50-F, 1 Cyclotron Road, Berkeley, CA 94720 4 Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720-3411 5 Department of Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford OX1 3RH 6 Department of Astronomy and Astrophysics, Pennsylvania State Univer- sity, 525 Davey Laboratory, University Park, PA 16802 7 Gemini Observatory, 670 N. Aohoku Place Hilo, HI 96720 (z = 0.033; Modjaz et al. 2006; Pian et al. 2006), and GRB 100316D/SN2010bh (z = 0.059; Chornock et al. 2010). All four events are broad-lined Type Ic SNe, similar to SN 1998bw. However, only GRB 030329 is typical of the cosmological long GRB population in terms of its energy scale (Berger et al. 2003), while the remaining three events are all sub-energetic in γ-rays, have no clear optical after- glows, exhibit only mildly relativistic velocities, and appear to be quasi-spherical (the so-called sub-energetic GRBs; Soderberg et al. 2004, 2006a). As a result, there is a clear impetus to obtain spectroscopic observations of GRB-SNe at z ≳0.3 to bolster the GRB-SN connection for the cosmological population, as well as to map the range of GRB-SN properties (i.e., velocity, kinetic en- ergy, ejecta mass, 56Ni mass), and to compare the properties of the SNe associated with standard and sub-energetic GRBs. The challenge of obtaining such spectroscopic observations is twofold. First, the associated SNe are faint, with a peak op- tical apparent brightnes

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