[vsnet-grb-info 13683] GRB 130702A: TNG spectroscopic observations of the emerging supernova

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15000
SUBJECT: GRB 130702A: TNG spectroscopic observations of the emerging supernova
DATE:    13/07/10 13:35:24 GMT
FROM:    Valerio D'Elia at ASDC  <delia at asdc.asi.it>

V. D'Elia (ASI/ASDC, INAF-OAR), P. D'Avanzo (INAF-OAB), A. Melandri (INAF-OAB), M. Della Valle (INAF-OAC), G. Tagliaferri (INAF-OAB), D. Malesani (DARK/NBI), E. Pian (SNS), L. A. Antonelli, S. Piranomonte (INAF-OAR), A. Harutyunyan, D. Carosati (INAF/TNG) report on behalf of the CIBO collaboration:

We continued monitoring the optical counterpart of the Fermi GRB 130702A (Singer et al., GCN 14967, Cheung et al. GCN 14971; Collazzi et al. GCN 14972) with the Italian 3.6m TNG telescope located in the Canary Islands, equipped with the DOLoRes camera.

In addition to what reported in D'Avanzo et al. (GCN 14977, GCN 14984), further observations were carried out during the nights of Jul 5 and Jul 9 (4 and 8 days after the Fermi GBM trigger).

At a mean t-t0=7.92 days we detect the optical counterpart in the SDSS r band with a magnitude of 19.91 (calibrated against nearby SDSS stars). This value is consistent with our previous epoch obtained 4 days before, confirming the flattening of the optical light curve reported by (Perley et al. GCN 14981, Butler et al. GCN 14993, Schulze et al. GCN 14994, Pozanenko et al. GCN 14996).

We also obtained a 2000 seconds spectrum with the LR-B grism, starting at t-t0=7.92 days, covering the wavelength range 3900-8200 AA with a resolution of R~600. With respect to our previous epoch  observation which featured a blue, featureless continuum (D'Avanzo et al. GCN 14984), the spectrum is now considerably redder, and shows a number of broad features similar to GRB-associated supernovae. In particular, the shape of the continuum closely resembles the spectrum of SN 1998bw observed at a similar epoch, despite a prominent feature at 4300 AA rest frame, reminiscent of what seen in SN 2006aj (Pian et al. 2006, Nature, 442, 1011). This confirms the emerging of the supernova already reported by Schulze et al. (GCN 14994) and Cenko et al. (GCN 14998).

We acknowledge support from the TNG visiting astronomer K. Biazzo.