Avishay Gal-Yam

Type IIn supernovae at redshift z ≈ 2 from archival data

Supernovae have been confirmed to redshift zu2009≈u20091.7 (refs 1, 2) for type Ia (thermonuclear detonation of a white dwarf) and to zu2009≈u20090.7 (refs 1, 3–5) for type II (collapse of the core of the star). The subclass type IIn (ref. 6) supernovae are luminous core-collapse explosions of massive stars and, unlike other types, are very bright in the ultraviolet, which should enable them to be found optically at redshifts zu2009≈u20092 and higher. In addition, the interaction of the ejecta with circumstellar material creates strong, long-lived emission lines that allow spectroscopic confirmation of many events of this type at zu2009≈u20092 for 3–5u2009years after explosion (ref. 14). Here we report three spectroscopically confirmed type IIn supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data using a method designed to exploit these properties at zu2009≈u20092. Type IIn supernovae directly probe the formation of massive stars at high redshift. The number found to date is consistent with the expectations of a locally measured stellar initial mass function, but not with an evolving initial mass function proposed to explain independent observations at low and high redshift.

Type IIn supernovae at z ~ 2 from archival data

Supernovae have been confirmed to redshift zu2009≈u20091.7 (refs 1, 2) for type Ia (thermonuclear detonation of a white dwarf) and to zu2009≈u20090.7 (refs 1, 3–5) for type II (collapse of the core of the star). The subclass type IIn (ref. 6) supernovae are luminous core-collapse explosions of massive stars and, unlike other types, are very bright in the ultraviolet, which should enable them to be found optically at redshifts zu2009≈u20092 and higher. In addition, the interaction of the ejecta with circumstellar material creates strong, long-lived emission lines that allow spectroscopic confirmation of many events of this type at zu2009≈u20092 for 3–5u2009years after explosion (ref. 14). Here we report three spectroscopically confirmed type IIn supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data using a method designed to exploit these properties at zu2009≈u20092. Type IIn supernovae directly probe the formation of massive stars at high redshift. The number found to date is consistent with the expectations of a locally measured stellar initial mass function, but not with an evolving initial mass function proposed to explain independent observations at low and high redshift.

DES14X3taz: A TYPE I SUPERLUMINOUS SUPERNOVA SHOWING A LUMINOUS, RAPIDLY COOLING INITIAL PRE-PEAK BUMP - eScholarship

We present DES14X3taz, a new hydrogen-poor superluminous supernova (SLSN-I) discovered by the Dark Energy Survey (DES) supernova program, with additional photometric data provided by the Survey Using DECam for Superluminous Supernovae. Spectra obtained using Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy on the Gran Telescopio CANARIAS show DES14X3taz is an SLSN-I at z = 0.608. Multi-color photometry reveals a double-peaked light curve: a blue and relatively bright initial peak that fades rapidly prior to the slower rise of the main light curve. Our multi-color photometry allows us, for the first time, to show that the initial peak cools from 22,000 to 8000 K over 15 rest-frame days, and is faster and brighter than any published core-collapse supernova, reaching 30% of the bolometric luminosity of the main peak. No physical 56Ni-powered model can fit this initial peak. We show that a shock-cooling model followed by a magnetar driving the second phase of the light curve can adequately explain the entire light curve of DES14X3taz. Models involving the shock-cooling of extended circumstellar material at a distance of sime400

Pair-instability and super-luminous supernova discoveries at z = 2.05, z = 2.50, and z = 3.90

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Detecting a small Kuiper Belt object using archival data of HST's Fine Guidance Sensor

are preferred over the cooling of shock-heated surface layers of a stellar envelope. We compare DES14X3taz to the few double-peaked SLSN-I events in the literature. Although the rise times and characteristics of these initial peaks differ, there exists the tantalizing possibility that they can be explained by one physical interpretation.

Type IIn supernovae at redshift z approximately 2 from archival data.

We present the discovery of three super-luminous supernovae (SLSNe) at z = 2 - 4 as part of our survey to detect ultraviolet-luminous supernova at z > 2. SLSNe are ≥10 times more luminous than normal supernova types, reaching peak luminosities of ≳10^(44) erg s^(−1). A small subset of SLSNe (type SLSN-R) exhibit a slow evolution, and thus enormous integrated energies (≳10^(51) erg), consistent with the radiative decay of several solar masses of 56 Ni. SLSN-R are believed to be the deaths of very massive stars, ∼140 - 260 M_⊙, that are theorized to result in pair-instability supernovae. Two of the high redshift SLSNe presented here are consistent with the behavior of SLSN-R out to the extent in which their light curves are sampled, with the third event being consistent with the more rapid fade of the type II-L SLSN SN 2008es at z = 0.205. SLSNe are extremely rare locally but are expected to have been more common in the early Universe and as members of the first generation of stars to form after the Big Bang, the Population III stars. The high intrinsic luminosity of SLSNe and their detectability using our image-stacking technique out to z ∼ 6 provide the first viable route to detect and study the deaths of massive Population III stars which are expected to form in pristine gas at redshifts as low as z ∼ 2.

A First Transients Survey with JWST: the FLARE project

The Kuiper Belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper Belt objects. Small, sub-kilometer-sized, Kuiper Belt objects elude direct detection, but the signature of their occultations of background stars should be detectable. Such an occultation event nlasts typically a fraction of a second, thus making it a classical high time-resolution observation. Here we report an analysis of archival data of HST’s Fine Guidance Sensors (FGS), that reveals an occultation by such a small object. The detection introduces the FGS as a valuable HTRA instrument. We discuss the statistical aspects regarding the validation of the detection claim, and its physical implications.

Explosive Transients in the Distant Universe

Supernovae have been confirmed to redshift zu2009≈u20091.7 (refs 1, 2) for type Ia (thermonuclear detonation of a white dwarf) and to zu2009≈u20090.7 (refs 1, 3–5) for type II (collapse of the core of the star). The subclass type IIn (ref. 6) supernovae are luminous core-collapse explosions of massive stars and, unlike other types, are very bright in the ultraviolet, which should enable them to be found optically at redshifts zu2009≈u20092 and higher. In addition, the interaction of the ejecta with circumstellar material creates strong, long-lived emission lines that allow spectroscopic confirmation of many events of this type at zu2009≈u20092 for 3–5u2009years after explosion (ref. 14). Here we report three spectroscopically confirmed type IIn supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data using a method designed to exploit these properties at zu2009≈u20092. Type IIn supernovae directly probe the formation of massive stars at high redshift. The number found to date is consistent with the expectations of a locally measured stellar initial mass function, but not with an evolving initial mass function proposed to explain independent observations at low and high redshift.