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"Howell, D A"
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Hydrogen-poor superluminous stellar explosions
A new class of supernovae
In all known supernovae, the radiation they emit comes from internal energy deposited in the outflowing ejecta by one or more processes: radioactive decay of freshly synthesized elements, stored heat deposited by the explosion shock in the envelope of a supergiant star, or interaction between the debris and slowly moving, hydrogen-rich circumstellar material. Quimby
et al
. report observations of a class of luminous supernovae whose properties cannot be explained by any of these processes. They are about ten times brighter than any type Ia supernova and emit significant ultraviolet flux for extended periods. They can be observed out to redshifts
z
> 4. These long-lived events, which light up their surroundings, may enable high-resolution spectroscopy to probe distant star-forming regions and primitive galaxies.
Supernovae are stellar explosions driven by gravitational or thermonuclear energy that is observed as electromagnetic radiation emitted over weeks or more
1
. In all known supernovae, this radiation comes from internal energy deposited in the outflowing ejecta by one or more of the following processes: radioactive decay of freshly synthesized elements
2
(typically
56
Ni), the explosion shock in the envelope of a supergiant star
3
, and interaction between the debris and slowly moving, hydrogen-rich circumstellar material
4
. Here we report observations of a class of luminous supernovae whose properties cannot be explained by any of these processes. The class includes four new supernovae that we have discovered and two previously unexplained events
5
,
6
(SN 2005ap and SCP 06F6) that we can now identify as members of the same class. These supernovae are all about ten times brighter than most type Ia supernova, do not show any trace of hydrogen, emit significant ultraviolet flux for extended periods of time and have late-time decay rates that are inconsistent with radioactivity. Our data require that the observed radiation be emitted by hydrogen-free material distributed over a large radius (∼10
15
centimetres) and expanding at high speeds (>10
4
kilometres per second). These long-lived, ultraviolet-luminous events can be observed out to redshifts
z
> 4.
Journal Article
An outburst from a massive star 40 days before a supernova explosion
A mass-loss event 40 days before the explosion of the type IIn supernova SN 2010mc has been detected; the outburst indicates that there is a causal relation between explosive mass-loss events seen in some massive stars before their explosion and the onset of the supernova explosion.
Energetic mass loss precedes supernova explosion
Various lines of evidence suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae. This paper reports the observation of one such event: 40 days before the explosion of the type IIn supernova SN 2010mc its progenitor underwent an energetic outburst that released 0.01 solar masses of material at velocities of around 2,000 km per second.The luminosity and velocity of the outburst are consistent with the predictions of the wave-driven pulsation model of supernova explosions.
Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae
1
,
2
,
3
,
4
, as do several models
5
,
6
,
7
. Establishing a causal connection between these mass-loss episodes and the final explosion would provide a novel way to study pre-supernova massive-star evolution. Here we report observations of a mass-loss event detected 40 days before the explosion of the type IIn supernova SN 2010mc (also known as PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6 × 10
47
erg of energy and releasing about 10
−2
solar masses of material at typical velocities of 2,000 km s
−1
. The temporal proximity of the mass-loss outburst and the supernova explosion implies a causal connection between them. Moreover, we find that the outburst luminosity and velocity are consistent with the predictions of the wave-driven pulsation model
6
, and disfavour alternative suggestions
7
.
Journal Article
Confined dense circumstellar material surrounding a regular type II supernova
With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the pre-supernova evolution of massive stars, which sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF 13dqy = SN 2013fs a mere ∼3 h after explosion. Our rapid follow-up observations, which include multiwavelength photometry and extremely early (beginning at ∼6 h post-explosion) spectra, map the distribution of material in the immediate environment (≲10
15
cm) of the exploding star and establish that it was surrounded by circumstellar material (CSM) that was ejected during the final ∼1 yr prior to explosion at a high rate, around 10
−3
solar masses per year. The complete disappearance of flash-ionized emission lines within the first several days requires that the dense CSM be confined to within ≲10
15
cm, consistent with radio non-detections at 70–100 days. The observations indicate that iPTF 13dqy was a regular type II supernova; thus, the finding that the probable red supergiant progenitor of this common explosion ejected material at a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may be common among exploding massive stars.
Type II supernova explosions are common, but our understanding of such events is not complete. Such an event was observed just three hours after the explosion started, providing important information about the early stages.
Journal Article
PTF 11kx: A Type Ia Supernova with a Symbiotic Nova Progenitor
There is a consensus that type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumstellar material are detected, and the SN ejecta are seen to interact with circumstellar material starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi.
Journal Article
Light echoes reveal an unexpectedly cool η Carinae during its nineteenth-century Great Eruption
Light echoes from the massive binary star η Carinae reveal it to have been much cooler than models suggest during its Great Eruption in 1840 but the cause of the eruption remains unknown.
Echoes from a nineteenth-century stellar explosion
η Carinae became the second-brightest star in the sky during its mid-nineteenth-century 'great eruption', but then faded from view. Remarkably, light echoes from that event are still reaching us, and analyses of their spectra reveal unexpected features that place important constrains on the eruption mechanism. No emission lines are present, only blueshifted absorption lines. The spectra resemble those of G2-to-G5 supergiants, which have effective temperatures of about 5,000 K, which is significantly cooler than expected.
η Carinae is one of the most massive binary stars in the Milky Way
1
,
2
. It became the second-brightest star in our sky during its mid-nineteenth-century ‘Great Eruption’, but then faded from view (with only naked-eye estimates of brightness
3
,
4
). Its eruption is unique in that it exceeded the Eddington luminosity limit for ten years. Because it is only 2.3 kiloparsecs away, spatially resolved studies of the nebula have constrained the ejected mass and velocity, indicating that during its nineteenth-century eruption, η Car ejected more than ten solar masses in an event that released ten per cent of the energy of a typical core-collapse supernova
5
,
6
, without destroying the star. Here we report observations of light echoes of η Carinae from the 1838–1858 Great Eruption. Spectra of these light echoes show only absorption lines, which are blueshifted by −210 km s
−1
, in good agreement with predicted expansion speeds
6
. The light-echo spectra correlate best with those of G2-to-G5 supergiants, which have effective temperatures of around 5,000 kelvin. In contrast to the class of extragalactic outbursts assumed to be analogues of the Great Eruption of η Carinae
7
,
8
,
9
,
10
,
11
,
12
, the effective temperature of its outburst is significantly lower than that allowed by standard opaque wind models
13
. This indicates that other physical mechanisms such as an energetic blast wave may have triggered and influenced the eruption.
Journal Article
Low-redshift Type Ia Supernova from the LSQ/LCO Collaboration
This paper is the data release of a new sample of 140 type Ia supernovae (SNe Ia) from the LaSilla-QUEST/Las Cumbres Observatory (LCO) collaboration. The discovery of the supernovae came from the LaSilla-QUEST variability survey, the ASASSN survey, as well as smaller low redshift supernova surveys. All of the supernovae in this sample were spectroscopically identified as SNe Ia using spectra from the PESSTO survey using the 3.5 m NTT telescope at LaSilla and spectra from the LCO 2 m Faulkes telescopes. The light-curves were obtained from a rapid cadence photometric follow up of the supernovae with the 9 LCO 1 m telescopes located at various observatories around the globe. Reference images of the host galaxies were taken approximately a year after the supernova have faded to allow precise galaxy background subtraction from the supernova magnitudes. The supernovae in this sample were discovered over a seven year period from 2012 October to 2019 June, and the last galaxy reference images were taken before 2020 June.
Journal Article
Preferred and actual place of death in haematological malignancy
Home is considered the preferred place of death for many, but patients with haematological malignancies (leukaemias, lymphomas and myeloma) die in hospital more often than those with other cancers and the reasons for this are not wholly understood. We examined preferred and actual place of death among people with these diseases.
The study is embedded within an established population-based cohort of patients with haematological malignancies. All patients diagnosed at two of the largest hospitals in the study area between May 2005 and April 2008 with acute myeloid leukaemia, diffuse large B-cell lymphoma or myeloma, who died before May 2010 were included. Data were obtained from medical records and routine linkage to national death records.
323 deceased patients were included. A total of 142 (44%) had discussed their preferred place of death; 45.8% wanted to die at home, 28.2% in hospital, 16.9% in a hospice, 5.6% in a nursing home and 3.5% were undecided; 63.4% of these died in their preferred place. Compared to patients with evidence of a discussion, those without were twice as likely to have died within a month of diagnosis (14.8% vs 29.8%). Overall, 240 patients died in hospital; those without a discussion were significantly more likely to die in hospital than those who had (p≤0.0001). Of those dying in hospital, 90% and 75.8% received haematology clinical input in the 30 and 7 days before death, respectively, and 40.8% died in haematology areas.
Many patients discussed their preferred place of death, but a substantial proportion did not and hospital deaths were common in this latter group. There is scope to improve practice, particularly among those dying soon after diagnosis. We found evidence that some people opted to die in hospital; the extent to which this compares with other cancers is of interest.
Journal Article