Massive stars end their life as core-collapse supernovae, amongst which some extremes are Type Ic broad-lined supernovae associated with long-duration gamma-ray bursts (LGRBs) having powerful relativistic jets. Their less-extreme brethren make unsuccessful jets that are choked inside the stars, appearing as X-ray flashes or low-luminosity GRBs. On the other hand, there exists a population of...
There is now an amalgam of observational evidence that massive stars undergo enhanced and/or eruptive mass-loss in their final years before explosion. In this talk, I will present multi-wavelength observations of >40 type II SNe whose very early-time ("flash") spectra showed transient, narrow emission lines from shock interaction with confined circumstellar material (CSM) around their red...
TBD
The rare and mysterious class of events sometimes known as luminous fast blue optical transients (LFBOTs), typefied by the event AT2018cow, has provided a steady stream of surprises over the past seven years. LFBOTs radiate primarily in the UV, are extremely radio-luminous, are highly X-ray variable, and at least in some cases they produce ultra-fast optical flares for months and leave behind...
Despite great advances in our understanding of transients over the ~20 years of Swift operations, it remains extremely challenging to link a transient to a progenitor with certain properties and to constrain the final phases of its life. Very early follow-up of supernovae (SNe), however, can provide critical insights into the progenitor: flash spectroscopy can reveal short-lived CSM...
We present the results of our multi-wavelength (X-ray to radio) follow-up campaign of the Einstein Probe transient EP240408a. The initial 10 s trigger displayed bright soft X-ray (0.5-4 keV) radiation with a peak luminosity of 1e49 (1e50) erg/s for an assumed redshift of z=0.5 (2.0). The Neil Gehrels Swift Observatory and Neutron star Interior Composition ExploreR discovered a fading X-ray...
Extragalactic Fast X-ray Transients (eFXTs) are defined as short flares in X ray with cosmological origins. But the nature of eFXT is still uncertain due to the lack of timely follow up observations. The possible physical mechanisms include the shock breakout of a supernova, the fireball phase of a nova, the magnetar powered X-ray emission after the mergers of binary neutron stars, off-axis...
