5 research outputs found
Exploring the canonical behaviour of long gamma-ray bursts with an intrinsic multiwavelength afterglow correlation
In this conference proceeding we examine a correlation between the afterglow luminosity (measured at restframe 200 s; logL200s) and average afterglow decay rate (measured from restframe 200 s onwards; α>200s) found in both the optical/UV and X-ray afterglows of long duration Gamma-ray Bursts (GRBs). Examining the X-ray light curves, we find the correlation does not depend on the presence of specific light curve features. We explore how the parameters in the optical/UV and X-ray bands relate to each other and to the prompt emission phase. We also use a Monte Carlo simulation to explore whether these relationships are consistent with predictions of the standard afterglow model. We conclude that the correlations are consistent with a common underlying physical mechanism producing GRBs and their afterglows regardless of their detailed temporal behaviour. However, a basic afterglow model has difficulty explaining correlations involving α>200s. We therefore briefly discuss alternative more complex models
An outflow powers the optical rise of the nearby, fast-evolving tidal disruption event AT2019qiz
At 66 Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to date, with a luminosity intermediate between the
bulk of the population and the faint-and-fast event iPTF16fnl. Its proximity allowed a very early detection and triggering of
multiwavelength and spectroscopic follow-up well before maximum light. The velocity dispersion of the host galaxy and fits
to the TDE light curve indicate a black hole mass â106 M, disrupting a star of â1 M. By analysing our comprehensive UV,
optical, and X-ray data, we show that the early optical emission is dominated by an outflow, with a luminosity evolution L â t
2,
consistent with a photosphere expanding at constant velocity (2000 km sâ1), and a line-forming region producing initially
blueshifted H and He II profiles with v = 3000â10 000 km sâ1. The fastest optical ejecta approach the velocity inferred from
radio detections (modelled in a forthcoming companion paper from K. D. Alexander et al.), thus the same outflow may be
responsible for both the fast optical rise and the radio emission â the first time this connection has been observed in a TDE.
The light-curve rise begins 29 ± 2 d before maximum light, peaking when the photosphere reaches the radius where optical
photons can escape. The photosphere then undergoes a sudden transition, first cooling at constant radius then contracting at
constant temperature. At the same time, the blueshifts disappear from the spectrum and Bowen fluorescence lines (N III) become
prominent, implying a source of far-UV photons, while the X-ray light curve peaks at â1041 erg sâ1. Assuming that these X-rays
are from prompt accretion, the size and mass of the outflow are consistent with the reprocessing layer needed to explain the
large optical to X-ray ratio in this and other optical TDEs, possibly favouring accretion-powered over collision-powered outflow
models
Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II period
Symptoms, unbearability and the nature of suffering in terminal cancer patients dying at home: a prospective primary care study
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Evidence for Late-stage Eruptive Mass Loss in the Progenitor to SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient
We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising (1.4 ± 0.1 mag hr-1) and luminous (Mg,peak = -20 mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity (Lbol âł 3 Ă 1044 erg s-1), the short rise time (trise = 3 days in g band), and the blue colors at peak (g-r ⌠-0.4) all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign, including the highest-temperature (Teff âł 40,000 K) spectra of a stripped-envelope SN. A retrospective search revealed luminous (Mg ⌠Mr â mag) emission in the days to weeks before explosion, the first definitive detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release E Îł,iso < 4.9 Ă 10 48 erg, a limit on X-ray emission LX < 1040 erg s-1, and a limit on radio emission Îœ LÎœ âČ 1037 erg s-1. Taken together, we find that the early (< 10 days) data are best explained by shock breakout in a massive shell of dense circumstellar material (0.02 Mâ) at large radii (3 Ă 1014 cm) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time (> 10 days) light curve requires an additional energy source, which could be the radioactive decay of Ni-56