EDP Sciences
Free Access
Issue
A&A
Volume 567, July 2014
Article Number A29
Number of page(s) 9
Section Stellar structure and evolution
DOI https://doi.org/10.1051/0004-6361/201423572
Published online 07 July 2014

© ESO, 2014

1. Introduction

The majority of nearby under-energetic long duration gamma-ray bursts and X-ray flashes (GRBs and XRFs1 with total isotropic energy Eiso< 1051 erg) are associated with with highly energetic supernovae (SNe; Mazzali et al. 2006a,b). The study of the SN in these cases is facilitated by the weakness of the GRB afterglow and the relatively small distance.

For z ≲ 0.3, the accuracy of optical photometric and spectroscopic monitoring is satisfactory, and individual atomic species can be identified in the SN spectrum (Galama et al. 1998; Patat et al. 2001; Hjorth et al. 2003; Stanek et al. 2003; Soderberg et al. 2004; Malesani et al. 2004; Ferrero et al. 2006; Pian et al. 2006; Sollerman et al. 2006; Mirabal et al. 2006; Bersier et al. 2006; Cano et al. 2011a; Bufano et al. 2012; Melandri et al. 2012; Schulze et al. 2014). At higher redshifts, up to z ~ 1, the presence of an associated SN is inferred from the detection of a “rebrightening” in the late afterglow light curve due to the emerging SN component (Bloom et al. 1999; Castro-Tirado Gorosabel 1999; Galama et al. 2000; Castro-Tirado et al. 2001; Lazzati et al. 2001; Masetti et al. 2003; Zeh et al. 2004; Gorosabel et al. 2005; Bersier et al. 2006; Cobb et al. 2006; Soderberg et al. 2006; Tanvir et al. 2010; Cano et al. 2011b). In a few cases, single-epoch spectra obtained close to the peak of this rebrightening show SN features similar to those exhibited by GRB-accompanying SNe at lower redshifts (Della Valle et al. 2003; Garnavich et al. 2003; Greiner et al. 2004; Soderberg et al. 2005; Berger et al. 2011; Della Valle et al. 2006a; Sparre et al. 2011; Jin et al. 2013), then confirming the association of the GRB with a SN event.

All GRBs associated with SNe at z 0.3 so far discovered show low isotropic energy, typically less than ~1050 erg, with GRB 030329/SN 2003dh (Hjorth et al. 2003; Stanek et al. 2003; Matheson et al. 2003) being the only exception. This is a relatively nearby GRB (z = 0.168) with an isotropic energy of Eγ,iso ~ 2 × 1052 erg (Vanderspek et al. 2004), which falls in the faint tail of the “cosmological” GRBs energy distribution (e.g. Amati et al. 2002; Amati et al. 2008). The long nearby GRB 130427A is exceptional and outstanding. It showed a huge isotropic energy (Eiso ~ 1054 erg; Maselli et al. 2014; Amati et al. 2013a), and at the same time the association with a SN was clear (SN 2013cq; de Ugarte Postigo et al. 2013). GRB 130427A follows the well known Amati (EpeakEiso, Amati et al. 2002) and Yonetoku (EpeakLiso, Yonetoku et al. 2004) correlations (Maselli et al. 2014). This made the study of the properties and evolution of SN 2013cq particularly interesting, since no very energetic GRB has ever been detected at relatively low redshift, so that this is the first occurrence of a connection between a SN and a GRB that has all the characteristics of a cosmological event.

In this paper we present the results of our photometric and spectroscopic campaign, covering ~1.5 months, carried out with the VLT and the TNG. Throughout the paper we assume a standard cosmology with H0 = 72 km s-1 Mpc-1, Ωm = 0.27, and ΩΛ = 0.73.

2. GRB 130427A/SN 2013cq

GRB 130427A was a long and extremely bright GRB (T90 ~ 160 s; Barthelmy et al. 2013) that independently triggered the Fermi satellite at 07h47m0642 UT (von Kienlin 2013; Zhu et al. 2013) and the Swift satellite at 07h47m575 UT (Maselli et al. 2013), and attained the highest fluences observed in the γ-ray band for both satellites (fSwift (15150 keV) ~ 5 × 10-4 erg cm-2 and fFermi (0.0120 MeV) ~4 × 10-3 erg cm-2). The high-energy emission of GRB 130427A was also detected by several orbiting observatories, i.e. MAXI (Kawamuro et al. 2013), INTEGRAL (Pozanenko et al. 2013), Konus-Wind (Golenetskii et al. 2013), AGILE (Verrecchia et al. 2013), Suzaku (Akiyama et al. 2013), RHESSI (Smith et al. 2013), and Mars Odyssey2. This event has been the focus of several recently published studies (Ackermann et al. 2014; Preece et al. 2014; Maselli et al. 2014; Vestrand et al. 2014; Kouveliotou et al. 2013; Laskar et al. 2013; Perley et al. 2013; Panaitescu et al. 2013; Bernardini et al. 2014). The redshift was measured to be z = 0.3399 ± 0.0002 (Levan et al. 2013a; Xu et al. 2013a; Flores et al. 2013).

A bright flash in the optical band, probably due to a reverse shock component, was observed simultaneously with the high energy emission (>100 MeV) at very early times. Subsequently, the GRB afterglow emission can be described by the contribution of both reverse and forward shocks (Vestrand et al. 2014; Panaitescu et al. 2013; Maselli et al. 2014; Perley et al. 2013; Levan et al. 2013b).

GRB 130427A exploded in a relatively bright, extended host galaxy, catalogued in the Sloan Digital Sky Survey (SDSS J113232.84+274155.4), which showed the typical properties of the nearby GRB host population (Savaglio et al. 2009). Its stellar mass (M = 2.1 ± 0.7 × 109M) and mean population age (~250 Myr) indicate a blue, young and low-mass galaxy (Perley et al. 2013). The afterglow of GRB 130427A is slightly offset from the centroid of its host galaxy (~0.83′′, corresponding to ~4 kpc in projection at the redshift of the GRB) and apparently there is no strongly star-forming region underlying the GRB (Levan et al. 2013b).

Despite its relatively low redshift, which favoured the detection and follow-up of the associated SN 2013cq in the R band (Xu et al. 2013b), GRB 130427A displayed all properties of more commonly observed high-redshift bursts. The extraordinarily high observed energetics of GRB 130427A and its closeness motivated our optical multi-band search and the intensive follow-up of its associated SN.

3. Observations and data reduction

We observed the field of SN 2013cq with the ESO 8.2 m Very Large Telescope (VLT) at Paranal Observatory equipped with FORS2 (imaging in the BVRI filters and spectroscopy) and with the Italian 3.6 m Telescopio Nazionale Galileo (TNG) equipped with DOLORES (imaging in the gri filters) from 3.6 to 51.6 days after the burst. Tables 1 and 3 summarise our observations.

thumbnail Fig. 1

Observed BVRI light curves of GRB 130427A/SN 2013cq, not corrected for Galactic extinction. For clarity, R and I magnitudes have been shifted by 0.45 and 0.75 mag, respectively. Horizontal lines represent the fluxes of the host galaxy in each filter.

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3.1. Imaging

Image reduction, including de-biasing and flat-fielding, was carried out following standard procedures. Images were calibrated using a set of SDSS-catalogued stars acquired with SDSS gri filters (TNG observations) and with respect to standard fields in the BVRI filters (VLT observations). We performed differential photometry at the position of the optical afterglow, using an aperture of 2 × FWHM of individual frames, which is large enough to include also the contribution of the underlying host galaxy. Observed BVRI light curves are shown in Fig. 1.

During our campaign it was not possible to acquire a deep image of the host galaxy alone because the GRB optical counterpart dominates the emission at early epochs and may still contribute significantly at late epochs. Moreover, the offset of the SN with respect to the host galaxy is only ~0.8′′ (Levan et al. 2013b), which is always comparable to the seeing of our images (see Table 3). Therefore, we used the SDSS magnitudes of the host galaxy that are u = 22.41 ± 0.33, g = 21.98 ± 0.11, r = 21.26 ± 0.09, i = 21.19 ± 0.16 and z = 21.11 ± 0.54. We converted these magnitudes into Johnson/Cousins magnitudes using the transformation equations in Jester et al. (2005), obtaining the final values BHG = 22.2, VHG = 21.5, RHG = 21.2 and IHG = 20.5. These values are consistent with Perley et al. (2013) and shown in Fig. 1.

We subtracted the estimated values for the host galaxy from our data, corrected for Galactic extinction (using the catalogued value of EBV, Galactic = 0.02 mag; Schlegel et al. 1998; Schlafly Finkbeiner 2011), applied k-corrections using our spectra (only B and V filters, because the spectra do not cover the redshifted R and I filters central wavelengths), and then subtracted the afterglow component. The temporal behaviour of the afterglow in each filter, where the early light curves were modelled with a forward relativistic shock into the circumstellar medium, can be described by a steepening power law with decay indices of ~0.8 and 1.5 before and after a break located at ~0.5 days (Laskar et al. 2013; Maselli et al. 2014; Perley et al. 2013; Xu et al. 2013b). Our data cover the phase after this temporal break and are consistent with the above time decay until a week after explosion, when the contribution from SN 2013cq becomes increasingly important. The afterglow model was then subtracted from the host-subtracted light curves and the residual, which is attributed to SN 2013cq alone, was corrected for intrinsic absorption following Xu et al. (2013b). These authors estimated the value E(BV), Host Galaxy = 0.05 mag from the detection of Na I D 5890 & 5896 absorption lines. The final corrected VRI light curves are reported in Fig. 2. The B-band light curve is heavily contaminated by the host galaxy and therefore not meaningful and not shown. The dereddened magnitudes have been transformed into monochromatic fluxes using the zeropoints in Fukugita et al. (1995).

3.2. Spectroscopy

Table 1

Journal of the VLT/FORS2 spectroscopic observations of SN 2013cq.

thumbnail Fig. 2

SN 2013cq rest-frame light curve for the V (magenta squares), R (blue circles), and I (red diamonds) bands. We also show the k-corrected R band light curves of SN 1998bw (dashed line) and SN 2010bh (dotted line). Solid coloured lines are the k-corrected light curves of SN 1998bw transformed by stretch and luminosity factors and represent the best fit to the SN 2013cq VRI light curves.

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VLT/FORS2 spectroscopy was carried out using the 300V grism, covering the range 44509500 Å (corresponding to 33207090 Å in the GRB rest-frame). For two epochs we also used the 300I grism, covering the range 600011 000 Å (44788210 Å rest-frame). In all cases we used a 1′′ slit, resulting in an effective resolution R = 440 at the central wavelengths λ300V = 5900 Å and λ300I = 8600 Å, respectively. The spectra were extracted using standard procedures within the packages ESO-MIDAS3 and IRAF4. A He-Ar lamp and spectrophotometric stars were used to calibrate the spectra in wavelength and flux, respectively. We accounted for slit losses by matching the flux-calibrated spectra to our simultaneous multi-band photometry.

After subtracting the contribution of the host galaxy using a spline interpolation to the SDSS magnitudes, we corrected the residual for Galactic extinction (with the extinction curve of Cardelli et al. 1989). We also applied the correction for the intrinsic reddening following Xu et al. (2013b) as in Sect. 3.1. We model the afterglow spectrum with a single power law as (1)where we fixed λnorm to the rest-frame flux at 6588 Å (corresponding to the R band), N is the power law normalisation and the spectral index βλ = 1.5 (Maselli et al. 2014; Perley et al. 2013). Telluric absorption features and the noisier parts of the spectra (λRF< 3400 Å and λRF> 6800 Å for the 300V grism and λRF< 4600 Å for the 300I grism) have been omitted. A clearly spurious feature has been deleted from the spectrum acquired at + 11.68 rest-frame days.

4. Results

4.1. Optical light curves

Inspection of Fig. 1 shows a rebrightening at ~20 days, more pronounced in the redder filters, that is the tell-tale signature of an underlying SN, first identified by Xu et al. (2013a) and named SN 2013cq (de Ugarte Postigo et al. 2013). In Fig. 2 we show the final VRI light curves of SN 2013cq.

Also plotted in Fig. 2 are the k-corrected, R band light curves of SN 1998bw and SN 2010bh, which were associated with GRB 980425 (Galama et al. 1998) and XRF 100316D (Starling et al. 2011; Cano et al. 2011a; Bufano et al. 2012; Olivares et al. 2011), respectively, as they would appear if they occurred at a redshift of z = 0.3399. To determine the rest-frame peak times in each filter, we adopted the formalism of Cano (2013), by which the optical light curves of the well observed type Ic SN 1998bw are used as templates to describe SNe with less well sampled light curves. The solid lines in Fig. 2 are the k-corrected light curves of SN 1998bw in the relevant bands, stretched in time and flux to match SN 2013cq. The scaling factors were obtained with a best fit to the data of SN 2013cq, following Cano (2013). The peaks of these template light curves represent our best estimates of the light maxima of SN 2013cq: Tpeak,V~ 9.6 ± 0.7, Tpeak,R~ 13.8 ± 0.9, and Tpeak,I ~ 17.9 ± 1.4 days after the burst. We note that the errors are formal uncertainties returned by the fit and are likely to underestimate the real uncertainties by about a factor of 2. Our best-fit R band maximum flux and time agree with those determined by Xu et al. (2013b) within the error bars. The SN 2013cq flux maximum in the R band is found to be slightly fainter (~0.2 mag) than SN 1998bw.

It is commonly observed in SNe of all types, including nearby Ic SNe and GRB/XRF SNe (Richmond et al. 1996; Foley et al. 2003; Mazzali et al. 2002, 2007; Valenti et al. 2008; Galama et al. 1998; Soderberg et al. 2004, 2006; Bufano et al. 2012), that the light maximum is reached later in redder bands. In SN 2013cq, this temporal evolution is particularly fast, so that the rise in the V band is rapid and resembles the one of XRF SNe (Pian et al. 2006; Ferrero et al. 2006; Mirabal et al. 2006; Bufano et al. 2012; Olivares et al. 2011), while in R and I bands the rise is more like to that of SNe associated with low-z under-luminous GRBs and classical GRBs at higher redshifts (Galama et al. 1998; Patat et al. 2001; Garnavich et al. 2003; Malesani et al. 2004; Della Valle et al. 2006b; Clocchiatti et al. 2011; Melandri et al. 2012).

4.2. Optical spectra

thumbnail Fig. 3

Spectral evolution of SN 2013cq. Each panel shows the signal obtained with VLT-300V grism from SN 2013cq (black) and the comparison with SN 2010bh (green) and SN 1998bw (red) at comparable rest frame phases. We superimpose, when available, the signal obtained with the VLT-300I grism (gray). All spectra have been smoothed with a boxcar of 15 Å.

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In Fig. 3 we show the FORS2 spectra acquired between ~5.0 and ~23.6 rest-frame days after the burst event. The quality of our spectra is not sufficient for accurately measuring of individual absorption features and for estimating photospheric velocities, but only for a general comparison with the spectra of high kinetic energy Type Ic SNe. Among these we have selected some with good S/N and/or spectral coverage: the GRB SNe 1998bw (Patat et al. 2001) and 2003dh (Hjorth et al. 2003; Mazzali et al. 2002), XRF SNe 2006aj (Pian et al. 2006), 2010bh (Bufano et al. 2012), and the broad-lined Ic SN2010ah (Mazzali et al. 2013). A similarity is found with SN 2010bh (see also Xu et al. 2013b) and with SN 1998bw, and for clarity we only show the comparison with these two SNe in Fig. 3. The spectra of SN 2010bh are a good match to those of SN 2013cq, although those of SN 1998bw are a better representation in the blue, especially at phases +12.44, +21.40, and +22.88 days, suggesting strong line-blocking from high-velocity material.

4.3. Bolometric light curve

We have constructed a bolometric light curve in the range 300010 000 Å using the available photometry. For each epoch we followed the reduction procedure described in Sect. 3. Then we fitted with a spline function the residual monochromatic light curves, which represent the SN component, and integrated the broad-band flux at each photometric observation epoch. The flux was linearly extrapolated blueward of the V-band flux down to 3000 Å and redward of the I-band flux to 10 000 Å. The result is reported in Fig. 4. The errors associated with our photometry, galaxy measurement, afterglow fit and intrinsic absorption were propagated and summed in quadrature. These are extremely large at the earlier epochs, so that the points have been omitted in the figure. For comparison and as a consistency check, we report the bolometric point obtained from the HST measurements of May 20, 2013 (Levan et al. 2013b). We also compare the bolometric light curve of SN 2013cq with those of SN 1998bw (Patat et al. 2001), SN 2006aj (Pian et al. 2006) and with the models for SN 2003dh (Mazzali et al. 2003) and SN 2012bz (Melandri et al. 2012). The bolometric light curve of SN 1998bw was constructed in the same rest-frame band (300010 000 Å) and using a Galactic extinction of EBV = 0.052 mag as recently reported by Schlafly & Finkbeiner (2011). It does not differ significantly from the one reported in Pian et al. (2006), which was corrected for a lower estimate of Galactic extinction and included a ~15% flux correction for NIR contribution. The model of the light curve of SN 2003dh (Mazzali et al. 2003) was rescaled by 20% to match the HST point, which is very accurate. The rescaled model also fits the rest of the light curve well, within the large errors. This suggests that the 56Ni mass synthesized by SN 2013cq is ~20% higher than that of SN 2003dh, which leads to an estimate of ~0.4 M (Mazzali et al. 2006a).

Table 2

GRBs–SNe properties.

thumbnail Fig. 4

Bolometric light curve of SN 2013cq (red filled circles) compared with those of SN 1998bw (orange filled circles), SN 2006aj (blue filled triangles), SN 2010bh (green filled squares), and with the models for SN 2003dh (dotted line) and SN 2012bz (dashed line). We also show the best fit model for SN 2013cq (solid line). As a consistency check, we report the bolometric point (black filled circle) obtained from the HST measurements of May 20, 2013. The error on this point is within the size of the symbol.

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4.4. GRBs–SNe properties and correlations

GRB 130427A is the brightest GRB detected by Swift/BAT, one of the most energetic ever (Eγ,iso ~ 1054 erg, Eγ,peak ~ 1.2 − 1.3 × 103 keV), and the most energetic GeV emitting GRB (~125 GeV in rest frame; Ackermann et al. 2014). GRB 130427A is located in a still unexplored region of the Eγ,isoEγ,peak plane for low-z GRBs associated with SNe, yet it follows the Amati and Yonetoku correlations very well (see Fig. S6 in Maselli et al. 2014). Prior to SN 2013cq only one nearby SN was associated with a GRB having energetics similar to cosmological gamma-ray bursts, i.e. GRB 030329 (Eγ,iso ~ 2 × 1052 erg, Eγ,peak = 82 ± 3 keV; Vanderspek et al. 2004). However, the properties of the GRB 030329 were less extreme than those observed for GRB 130427A.

A striking result when comparing GRB and SN properties (see Table 2) is that, while the values of Eiso of the GRB span nearly six orders of magnitude (~3 after correcting for collimation effects) the SNe maximum luminosities (Mbol), which trace the mass of radioactive 56Ni and correlate (like the SN kinetic energies) with the progenitor masses (Mazzali et al. 2013), are distributed in a narrow range (~0.5 mag) and can be considered roughly constant. On the other hand, nearby XRFs have total isotropic-equivalent energies similar to those of the less energetic GRBs, but their SNe have lower luminosities (Fig. 5).

thumbnail Fig. 5

GRB Eγ,iso versus the peak magnitude of the bolometric light curve of the corresponding SN: the lack of correlation is apparent, where the SN brightness is nearly constant, while the GRB energy spans several orders of magnitude.

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5. Conclusion

The R band light curve reported by Xu et al. (2013b, see also Perley et al. 2013) is ~0.2 mag fainter than that of SN 1998bw at maximum (Patat et al. 2001). Our analysis seems to confirm this (Fig. 2). However, the bolometric light curve (Fig. 4), and especially the accurate HST measurement (Levan et al. 2013b), suggest that SN 2013cq is marginally brighter than SN 1998bw and significantly more luminous (~1.5 mag) than SN 2010bh. This points to the need to refer to bolometric rather than monochromatic information in the comparison of SN physical quantities.

Although the S/N of the spectra is very limited, we note a some similarity with SN 2010bh (see also Xu et al. 2013b) and with SN 1998bw. In either case, this points to a classification of SN 2013cq as a broad line type Ic SN, as seen so far for all GRB/XRF SNe, and in turn to a massive, highly envelope-stripped progenitor.

This is in line with the finding that SNe associated with GRBs – both underluminous and highly energetic – have all comparable luminosities and are more luminous than the two known low-z spectroscopically identified XRF/SNe 2006aj and 2010bh (Melandri et al. 2012). The extended host galaxy of GRB 130427A/SN 2013cq is similar to the host galaxies of GRB 100316D/SN 2010bh and GRB 980425/SN 1998bw. The other ones known at low redshift are instead associated with smaller galaxies (Starling et al. 2011). However, there is no apparent correlation between the brightness of the GRB, the associated SNe, and their host galaxies (Levesque et al. 2010).

Owing to the limited S/N of the spectra of SN 2013cq, it is difficult to evaluate the photospheric velocity evolution of this SN and therefore its kinetic energy. Xu et al. (2013b) estimate ~6 × 1052 erg, i.e. similar to SN 1998bw, which is plausible, considering the similarity of spectra and bolometric light curve. The data reported by Maselli et al. (2013b, their Fig. 2) show a break in the afterglow light curve, which they interpret as a jet break. If this is the case (jet collimation-correction can be complex, Campana et al. 2007; Perley et al. 2013), after correcting for the corresponding jet opening angle of about 3°, the total energy of GRB 130427A decreases to 3 × 1050 erg, which is less than 1% of the kinetic energy associated with its SN. A similar finding has been reported for other GRB-SN associations (Woosley Bloom 2006, Amati et al. 2007). Therefore it is very plausible that the SN may drive the GRB jet. The monitoring of nearby energetic GRBs is a critical test bed for confirming SN-driven GRB models or opening more exotic (and more energetic) scenarios based on black hole formation.


1

XRFs are a softer version of GRBs, with integrated spectra peaking around 510 keV instead of 1001000 keV.

Acknowledgments

We thank the anonymous referee for valuable comments and suggestions that improved the paper. We thank the TNG staff, in particular G. Andreuzzi, L. Di Fabrizio, and M. Pedani, for their valuable support with TNG observations, and the Paranal Science Operations Team, in particular H. Boffin, S. Brillant, C. Cid, O. Gonzales, V. D. Ivanov, D. Jones, J. Pritchard, M. Rodrigues, L. Schmidtobreick, F. J. Selman, J. Smoker, and S. Vega. The Dark Cosmology Centre is funded by the Danish National Research Foundation. F.B. acknowledges support from FONDECYT through Postdoctoral grant 3120227 and from Project IC120009 “Millennium Institute of Astrophysics (MAS)” of the Iniciativa Científica Milenio del Ministerio de Economía, Fomento y Turismo de Chile. A.J.C.T. thanks the Spanish Ministry’s Research Project AYA 2012-39727-C03-01. R.L.C.S. is supported by a Royal Society fellowship. D.M. acknowledges the Instrument Center for Danish Astrophysics (IDA) for support. This research was partially supported by contracts ASI INAF I/004/11/1, ASI INAF I/088/06/0, INAF PRIN 2011, and PRIN MIUR 2010/2011.

References

Online material

Table 3

Observation log.

All Tables

Table 1

Journal of the VLT/FORS2 spectroscopic observations of SN 2013cq.

Table 2

GRBs–SNe properties.

Table 3

Observation log.

All Figures

thumbnail Fig. 1

Observed BVRI light curves of GRB 130427A/SN 2013cq, not corrected for Galactic extinction. For clarity, R and I magnitudes have been shifted by 0.45 and 0.75 mag, respectively. Horizontal lines represent the fluxes of the host galaxy in each filter.

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In the text
thumbnail Fig. 2

SN 2013cq rest-frame light curve for the V (magenta squares), R (blue circles), and I (red diamonds) bands. We also show the k-corrected R band light curves of SN 1998bw (dashed line) and SN 2010bh (dotted line). Solid coloured lines are the k-corrected light curves of SN 1998bw transformed by stretch and luminosity factors and represent the best fit to the SN 2013cq VRI light curves.

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In the text
thumbnail Fig. 3

Spectral evolution of SN 2013cq. Each panel shows the signal obtained with VLT-300V grism from SN 2013cq (black) and the comparison with SN 2010bh (green) and SN 1998bw (red) at comparable rest frame phases. We superimpose, when available, the signal obtained with the VLT-300I grism (gray). All spectra have been smoothed with a boxcar of 15 Å.

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In the text
thumbnail Fig. 4

Bolometric light curve of SN 2013cq (red filled circles) compared with those of SN 1998bw (orange filled circles), SN 2006aj (blue filled triangles), SN 2010bh (green filled squares), and with the models for SN 2003dh (dotted line) and SN 2012bz (dashed line). We also show the best fit model for SN 2013cq (solid line). As a consistency check, we report the bolometric point (black filled circle) obtained from the HST measurements of May 20, 2013. The error on this point is within the size of the symbol.

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In the text
thumbnail Fig. 5

GRB Eγ,iso versus the peak magnitude of the bolometric light curve of the corresponding SN: the lack of correlation is apparent, where the SN brightness is nearly constant, while the GRB energy spans several orders of magnitude.

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In the text

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