Diversity of GRB energetics vs. SN homogeneity: supernova 2013cq
  associated with the gamma-ray burst 130427A
  Long-duration gamma-ray bursts (GRBs) have been found to be associated with
broad-lined type-Ic supernovae (SNe), but only a handful of cases have been
studied in detail. Prompted by the discovery of the exceptionally bright,
nearby GRB130427A (redshift z=0.3399), we aim at characterising the properties
of its associated SN2013cq. This is the first opportunity to test directly the
progenitors of high-luminosity GRBs. We monitored the field of the Swift long
duration GRB130427A using the 3.6-m TNG and the 8.2-m VLT during the time
interval between 3.6 and 51.6 days after the burst. Photometric and
spectroscopic observations revealed the presence of the type Ic SN2013cq.
Spectroscopic analysis suggests that SN2013cq resembles two previous GRB-SNe,
SN1998bw and SN2010bh associated with GRB980425 and XRF100316D, respectively.
The bolometric light curve of SN2013cq, which is significantly affected by the
host galaxy contribution, is systematically more luminous than that of SN2010bh
($\sim$ 2 mag at peak), but is consistent with SN1998bw. The comparison with
the light curve model of another GRB-connected SN2003dh, indicates that
SN2013cq is consistent with the model when brightened by 20%. This suggests a
synthesised radioactive $^{56}$Ni mass of $\sim 0.4 M_\odot$.
GRB130427A/SN2013cq is the first case of low-z GRB-SN connection where the GRB
energetics are extreme ($E_{\rm \gamma, iso} \sim 10^{54}$ erg). We show that
the maximum luminosities attained by SNe associated with GRBs span a very
narrow range, but those associated with XRFs are significantly less luminous.
On the other hand the isotropic energies of the accompanying GRBs span 6 orders
of magnitude (10$^{48}$ erg $< E_{\rm \gamma, iso} <$ 10$^{54}$ erg), although
this range is reduced when corrected for jet collimation. The GRB total
radiated energy is in fact a small fraction of the SN energy budget.
