The Detection Rate of Early Uv Emission From Supernovae: A Dedicated Galex/PTF Survey and Calibrated Theoretical Estimates

Abstract

The radius and surface composition of an exploding massive star, as well as the explosion energy per unit mass, can be measured using early UV observations of core-collapse supernovae (SNe). We present the first results from a simultaneous GALEX/PTF search for early ultraviolet (UV) emission from SNe. Six SNe II and one Type II superluminous SN (SLSN-II) are clearly detected in the GALEX near-UV (NUV) data. We compare our detection rate with theoretical estimates based on early, shock-cooling UV light curves calculated from models that fit existing Swift and GALEX observations well, combined with volumetric SN rates. We find that our observations are in good agreement with calculated rates assuming that red supergiants (RSGs) explode with fiducial radii of 500 R e , explosion energies of 10 51 erg, and ejecta masses of 10 M e . Exploding blue supergiants and Wolf-Rayet stars are poorly constrained. We describe how such observations can be used to derive the progenitor radius, surface composition, and explosion energy per unit mass of such SN events, and we demonstrate why UV observations are critical for such measurements. We use the fiducial RSG parameters to estimate the detection rate of SNe during the shock-cooling phase (<1 day after explosion) for several ground-based surveys (PTF, ZTF, and LSST). We show that the proposed wide-field UV explorer ULTRASAT mission is expected to find >85 SNe per year (∼0.5 SN per deg 2 ), independent of host galaxy extinction, down to an NUV detection limit of 21.5 mag AB. Our pilot GALEX/PTF project thus convincingly demonstrates that a dedicated, systematic SN survey at the NUV band is a compelling method to study how massive stars end their life.

The First Hours of the GW170817 Kilonova and the Importance of Early Optical and Ultraviolet Observations for Constraining Emission Models

“…Such observations should therefore be possible for future events. Future events could also benefit from space-based wide-field ultraviolet imagers, such as the proposed ULTRASAT mission (Ganot et al 2016).…”

A WC/WO star exploding within an expanding carbon–oxygen–neon nebula

“…Shock breakout in a wind: The first electromagnetic signature arriving to a distant observer from an exploding star is a flare of radiation emitted when the explosion shock breaks out from the stellar surface (the shock-breakout flare 142 ). For a compact star as we consider here, the shock breakout emission peaks at high energy and would be too weak to be observed in visible light by ZTF 143 . However, if the star is embedded in a thick wind, as may be the case here, the breakout occurs in the wind, at a radius much larger than that of the progenitor.…”

UV/Optical Emission from the Expanding Envelopes of Type II Supernovae

“…For the planar breakout phase, their estimates of L and T exceed those of the exact solutions (Sapir et al 2011;Katz et al 2012;Sapir et al 2013) by factors of a few (leading to an overestimate of the optical/UV flux, which is in the Rayleight-Jeans regime at this time, by 1-2 orders of magnitude, e.g. Ganot et al 2016). For the spherical post-breakout cooling phase, the NS10 estimate of L(t) is similar to that of RW11 (similar functional dependence on parameters with normalization lower[higher] by 10[40]% compared to the exact self-similar solution of eq.…”