Professor Stephen Smartt CBE FRS MRIA

Abstract:

On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. Preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope (ENGRAVE) collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical/near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS and VINROUGE projects also carried out a search on this event. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN) possibly generated by this NS-BH merger, and for the strategy of future searches. Altogether, our observations allow us to exclude a KN with large ejecta mass M> 0.1Msolar to a high (>90%) confidence, and we can exclude much smaller masses in a subsample of our observations. This disfavours the tidal disruption of the neutron star during the merger. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundreds Mpc will be detected only by large facilities with both high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event

Abstract:

Core-collapse supernovae (CCSNe) are the bright explosions of massive stars. During the explosion heavy elements are produced by nuclear burning. One of these products is 56Ni that radioactively decays into 56Co. The explosion energy and the produced 56Ni and its product 56Co are what powers the light curves of classical supernovae (SNe). Stripped envelope (SE) SNe have lost their hydrogen (H) and in some cases, helium (He) envelopes through mass loss at some point in their lives. These SE SNe are known to produce SNe of types IIb (weak H), Ib (He-rich), Ic (He-poor), and Ic-BL (He-poor broad lines). Type IIn SNe, on the other hand, are SNe that interact with circumstellar medium (CSM) around the progenitor. The CSM is thought to be caused by the progenitor’s mass loss. The mechanism of the mass loss for these can happen in a variety of ways. All stars have mass loss through stellar winds, but in some cases, it is not enough to produce interaction that would produce a type IIn. The mass loss can also happen because of pair instability pulsations, eruptions, or binary effects. The mass loss can be studied by analysing the observational properties of a SN and understanding the mass loss might shed light on what kind of progenitor produced the SN. In this thesis, photometric and spectroscopic data of SN 2017dio are analysed. The photometric data are used to study the explosion epoch, light curves, and color curves of SN 2017dio and it is compared with four other SNe. The spectroscopic data are used to verify the classification of SN 2017dio, to study the spectral evolution, and to discuss the possible CSM properties and progenitor scenario. The findings indicate that SN 2017dio is a SN of type Ic-BL interacting with H-rich CSM. Both spectroscopic and photometric analysis support the theory of the CSM not being close to the explosion site and the calculated mass loss rate 0.04M⊙/year indicates that the progenitor must have experienced massive mass loss periods in the decade before its explosion