| 1. |
- Pastorello, A., et al.
(author)
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A luminous stellar outburst during a long-lasting eruptive phase first, and then SN IIn 2018cnf
- 2019
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 628
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Journal article (peer-reviewed)abstract
- We present the results of the monitoring campaign of the Type IIn supernova (SN) 2018cnf (a.k.a. ASASSN-18mr). It was discovered about ten days before the maximum light (on MJD = 58 293.4 +/- 5.7 in the V band, with M-V = -18.13 +/- 0.15 mag). The multiband light curves show an immediate post-peak decline with some minor luminosity fluctuations, followed by a flattening starting about 40 days after maximum. The early spectra are relatively blue and show narrow Balmer lines with P Cygni profiles. Additionally, Fe II, O I, He I, and Ca II are detected. The spectra show little evolution with time and with intermediate-width features becoming progressively more prominent, indicating stronger interaction of the SN ejecta with the circumstellar medium. The inspection of archival images from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey has revealed a variable source at the SN position with a brightest detection in December 2015 at M-r = -14.66 +/- 0.17 mag. This was likely an eruptive phase from the massive progenitor star that started from at least mid-2011, and that produced the circumstellar environment within which the star exploded as a Type IIn SN. The overall properties of SN 2018cnf closely resemble those of transients such as SN 2009ip. This similarity favours a massive hypergiant, perhaps a luminous blue variable, as progenitor for SN 2018cnf.
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| 2. |
- Pastorello, A., et al.
(author)
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The evolution of luminous red nova AT 2017jfs in NGC 4470
- 2019
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In: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 625
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Journal article (peer-reviewed)abstract
- We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of M-g = 15.46 +/- 0.15 mag and a bolometric luminosity of 5.5 x 10(41) erg s(-1). Its light curve has the double-peak shape typical of luminous red novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer-lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappears in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC4490-2011OT1.
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| 3. |
- Cano, Z., et al.
(author)
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GRB 161219B/SN 2016jca : A low-redshift gamma-ray burst supernova powered by radioactive heating
- 2017
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 605
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Journal article (peer-reviewed)abstract
- Since the first discovery of a broad-lined type Ic supernova (SN) with a long-duration gamma-ray burst (GRB) in 1998, fewer than fifty GRB-supernovae (SNe) have been discovered. The intermediate-luminosity Swift GRB 161219B and its associated supernova SN 2016jca, which occurred at a redshift of z = 0.1475, represents only the seventh GRB-SN to have been discovered within 1 Gpc, and hence provides an excellent opportunity to investigate the observational and physical properties of these very elusive and rare type of SN. As such, we present optical to near-infrared photometry and optical spectroscopy of GRB 161219B and SN 2016jca, spanning the first three months since its discovery. GRB 161219B exploded in the disk of an edge-on spiral galaxy at a projected distance of 3.4 kpc from the galactic centre. GRB 161219B itself is an outlier in the E-p,E-i - E-gamma,E-iso plane, while SN 2016jca had a rest-frame, peak absolute V-band magnitude of M-V = -19.0 +/- 0.1, which it reached after 12.3 +/- 0.7 rest-frame days. We find that the bolometric properties of SN 2016jca are inconsistent with being powered solely by a magnetar central engine, and demonstrate that it was likely powered exclusively by energy deposited by the radioactive decay of nickel and cobalt into their daughter products, which were nucleosynthesised when its progenitor underwent core collapse. We find that 0.22 +/- 0.08 M-circle dot of nickel is required to reproduce the peak luminosity of SN 2016jca, and we constrain an ejecta mass of 5.8 +/- 0.3 M-circle dot and a kinetic energy of 5.1 +/- 0.8 x 10(52) erg. Finally, we report on a chromatic, pre-maximum bump in the g-band light curve, and discuss its possible origin.
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| 4. |
- Schulze, S., et al.
(author)
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GRB 120422A/SN 2012bz : Bridging the gap between low- and high-luminosity gamma-ray bursts
- 2014
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 566
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Journal article (peer-reviewed)abstract
- Context. At low redshift, a handful of gamma-ray bursts (GRBs) have been discovered with luminosities that are substantially lower (L-iso less than or similar to 10(48.5) erg s(-1)) than the average of more distant ones (L-iso greater than or similar to 10(49.5) erg s(-1)). It has been suggested that the properties of several low-luminosity (low-L) GRBs are due to shock break-out, as opposed to the emission from ultrarelativistic jets. This has led to much debate about how the populations are connected. Aims. The burst at redshift z = 0.283 from 2012 April 22 is one of the very few examples of intermediate-L GRBs with a gamma-ray luminosity of L-iso similar to 10(49.6-49.9) erg s(-1) that have been detected up to now. With the robust detection of its accompanying supernova SN 2012bz, it has the potential to answer important questions on the origin of low-and high-L GRBs and the GRB-SN connection. Methods. We carried out a spectroscopy campaign using medium-and low-resolution spectrographs with 6-10-m class telescopes, which covered a time span of 37.3 days, and a multi-wavelength imaging campaign, which ranged from radio to X-ray energies over a duration of similar to 270 days. Furthermore, we used a tuneable filter that is centred at H alpha to map star-formation in the host and the surrounding galaxies. We used these data to extract and model the properties of different radiation components and fitted the spectral energy distribution to extract the properties of the host galaxy. Results. Modelling the light curve and spectral energy distribution from the radio to the X-rays revealed that the blast wave expanded with an initial Lorentz factor of Gamma(0) similar to 50, which is a low value in comparison to high-L GRBs, and that the afterglow had an exceptionally low peak luminosity density of less than or similar to 2 x 10(30) erg s(-1) Hz(-1) in the sub-mm. Because of the weak afterglow component, we were able to recover the signature of a shock break-out in an event that was not a genuine low-L GRB for the first time. At 1.4 hr after the burst, the stellar envelope had a blackbody temperature of k(B)T similar to 16 eV and a radius of similar to 7 x 10(13) cm (both in the observer frame). The accompanying SN 2012bz reached a peak luminosity of M-V = -19.7 mag, which is 0.3 mag more luminous than SN 1998bw. The synthesised nickel mass of 0.58 M-circle dot, ejecta mass of 5.87 M-circle dot, and kinetic energy of 4.10x10(52) erg were among the highest for GRB-SNe, which makes it the most luminous spectroscopically confirmed SN to date. Nebular emission lines at the GRB location were visible, which extend from the galaxy nucleus to the explosion site. The host and the explosion site had close-to-solar metallicity. The burst occurred in an isolated star-forming region with an SFR that is 1/10 of that in the galaxy's nucleus. Conclusions. While the prompt gamma-ray emission points to a high-L GRB, the weak afterglow and the low Gamma(0) were very atypical for such a burst. Moreover, the detection of the shock break-out signature is a new quality for high-L GRBs. So far, shock break-outs were exclusively detected for low-L GRBs, while GRB 120422A had an intermediate L-iso of similar to 10(49.6-49.9) erg s(-1). Therefore, we conclude that GRB 120422A was a transition object between low-and high-L GRBs, which supports the failed-jet model that connects low-L GRBs that are driven by shock break-outs and high-L GRBs that are powered by ultra-relativistic jets.
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