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"Rest, Armin"
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Expanding universe : photographs from the Hubble space telescope
On the 25th anniversary of the Hubble Telescope first being launched into low earth orbit, TASCHEN brings together some of its most breathtaking deep space images. Hubble's orbit outside the Earth's atmosphere allows it to take extremely high-resolution images with almost no background light. Its acute observations have answered some of the most compelling questions of time and space, and simultaneously revealed whole new mysteries, like the strange \"dark energy\" that sees the universe expanding at an ever-accelerated rate. With investigations into everything from black holes to exoplanets, Hubble has changed not only the face of astronomy, but also our very sense of being in the universe.
Book
Performance of NIRCam on JWST in Flight
The Near Infrared Camera for the James Webb Space Telescope (JWST) is delivering the imagery that astronomers have hoped for ever since JWST was proposed back in the 1990s. In the Commissioning Period that extended from right after launch to early 2022 July, NIRCam has been subjected to a number of performance tests and operational checks. The camera is exceeding prelaunch expectations in virtually all areas, with very few surprises discovered in flight. NIRCam also delivered the imagery needed by the Wavefront Sensing Team for use in aligning the telescope mirror segments.
Journal Article
No signature of ejecta interaction with a stellar companion in three type Ia supernovae
The explosion of a type Ia supernova could be triggered either by accretion from a companion—which should be indicated by brightening caused by interaction of supernova ejecta with the companion—or by a merger with a white dwarf or other small star; here observations by the Kepler mission of three type Ia supernovae reveal no such brightening, leading to the conclusion that they were triggered by a merger.
Type Ia supernovae are thought to be the result of a thermonuclear runaway in carbon/oxygen white dwarfs, but it is uncertain whether the explosion is triggered by accretion from a non-degenerate companion star or by a merger with another white dwarf. Observations of a supernova immediately following the explosion provide unique information on the distribution of ejected material
1
and the progenitor system. Models predict
2
that the interaction of supernova ejecta with a companion star or circumstellar debris lead to a sudden brightening lasting from hours to days. Here we present data for three supernovae that are likely to be type Ia observed during the Kepler mission
3
with a time resolution of 30 minutes. We find no signatures of the supernova ejecta interacting with nearby companions. The lack of observable interaction signatures is consistent with the idea that these three supernovae resulted from the merger of binary white dwarfs or other compact stars such as helium stars.
Journal Article
A very luminous jet from the disruption of a star by a massive black hole
Tidal disruption events (TDEs) are bursts of electromagnetic energy that are released when supermassive black holes at the centres of galaxies violently disrupt a star that passes too close
1
. TDEs provide a window through which to study accretion onto supermassive black holes; in some rare cases, this accretion leads to launching of a relativistic jet
2
–
9
, but the necessary conditions are not fully understood. The best-studied jetted TDE so far is Swift J1644+57, which was discovered in γ-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical detection of AT2022cmc, a rapidly fading source at cosmological distance (redshift
z
= 1.19325) the unique light curve of which transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-ray, submillimetre and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ‘afterglow’, probably launched by a supermassive black hole with spin greater than approximately 0.3. Using four years of Zwicky Transient Facility
10
survey data, we calculate a rate of
0.0
2
−
0.01
+
0.04
Gpc
−3
yr
−1
for on-axis jetted TDEs on the basis of the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations
11
. Correcting for the beaming angle effects, this rate confirms that approximately 1 per cent of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs.
A series of early-time, multiwavelength observations of an optical transient, AT2022cmc, indicate that it is a relativistic jet from a tidal disruption event originating from a supermassive black hole.
Journal Article
JWST detection of a supernova associated with GRB 221009A without an r-process signature
Identifying the sites of r-process nucleosynthesis, a primary mechanism of heavy element production, is a key goal of astrophysics. The discovery of the brightest gamma-ray burst (GRB) to date, GRB 221009A, presented an opportunity to spectroscopically test the idea that r-process elements are produced following the collapse of rapidly rotating massive stars. Here we present James Webb Space Telescope observations of GRB 221009A obtained +168 and +170 rest-frame days after the gamma-ray trigger, and demonstrate that they are well described by a SN 1998bw-like supernova (SN) and power-law afterglow, with no evidence for a component from r-process emission. The SN, with a nickel mass of approximately 0.09
M
⊙
, is only slightly fainter than the brightness of SN 1998bw at this phase, which indicates that the SN is not an unusual GRB-SN. This demonstrates that the GRB and SN mechanisms are decoupled and that highly energetic GRBs are not likely to produce significant quantities of r-process material, which leaves open the question of whether explosions of massive stars are key sources of r-process elements. Moreover, the host galaxy of GRB 221009A has a very low metallicity of approximately 0.12
Z
⊙
and strong H
2
emission at the explosion site, which is consistent with recent star formation, hinting that environmental factors are responsible for its extreme energetics.
JWST observations of GRB 221009A reveal the associated supernova, confirming that the GRB resulted from the collapse of a rapidly rotating massive star. The lack of r-process emission suggests that these extreme events are not key sources of the heaviest elements.
Journal Article
Publisher Correction
In the version of this article initially published, there was in an error in the third-to-last sentence of the abstract, now reading, in part, “we calculate a rate of 0.02–0.01 +0.04 Gpc–3 yr–1”, where Gpc was spelled out as gigapascals, not gigaparsecs. Also, the scale label (2″) was missing in the lower-left corner of Fig. 1b. The errors have been corrected in the HTML and PDF versions of the article.
Journal Article
Light Echoes of Transients and Variables
Tycho Brahe's observations of a supernova in 1572 challenged the contemporaneous European view of the cosmos that the celestial realm was unchanging. 439 years later we have once again seen the light that Tycho saw, as some of the light from the 1572 supernova is reflected off dust and is only now reaching Earth. These light echoes, as well as ones detected from other transients and variables, give us a very rare opportunity in astronomy: direct observation of the cause (the supernova explosion) and the effect (the supernova remnant) of the same astronomical event. Furthermore, in some cases we can compare light echoes at different angles around a supernova remnant, and thus investigate possible asymmetry in the supernova explosion. In addition, in cases where the scattering dust is favorably positioned, the geometric distance to the SN remnant can be determined using polarization measurements. These techniques have been successfully applied to various transients in the last decade, and the talk gave an overview of the scientific results and techniques, with a particular focus on the challenges we will face in the current and upcoming wide-field time-domain surveys.
Journal Article
Performance of NIRCam on JWST in Flight
The Near Infrared Camera for the James Webb Space Telescope (JWST) is delivering the imagery that astronomers have hoped for ever since JWST was proposed back in the 1990s. In the Commissioning Period that extended from right after launch to early 2022 July, NIRCam has been subjected to a number of performance tests and operational checks. The camera is exceeding prelaunch expectations in virtually all areas, with very few surprises discovered in flight. NIRCam also delivered the imagery needed by the Wavefront Sensing Team for use in aligning the telescope mirror segments.
Journal Article
Light echoes from ancient supernovae in the Large Magellanic Cloud
Catch up with Kepler
We may soon be able to see the slight seen by Tycho and Kepler, but 400 years later. In 1940 Fritz Zwicky, the man who coined the term ‘supernova’ for massive star explosions, suggested that it should be possible to see echo light from historical supernovae centuries after the event. Data from the SuperMACHO survey, which is monitoring the millions of stars in the Large Magellanic Cloud for the brightening associated with gravitational microlensing, show that Zwicky was spot on. Echoes have now been traced back to three positions where young supernova remnants appear, and ages have been estimated for two of them, at 610 and 410 years. This discovery opens up the prospect of finding echoes from the supernovae in our own Galaxy that were observed by Tycho and Kepler. Light from the echoes can be observed spectroscopically to determine what type of supernova exploded.
The light from historical supernovae could in principle still be visible as scattered-light echoes centuries after the explosion
1
,
2
,
3
,
4
,
5
,
6
. The detection of light echoes could allow us to pinpoint the supernova event both in position and age and, most importantly, permit the acquisition of spectra to determine the ‘type’ of the supernova centuries after the direct light from the explosion first reached Earth. Although echoes have been discovered around some nearby extragalactic supernovae
7
,
8
,
9
,
10
,
11
,
12
,
13
, targeted searches have not found any echoes in the regions of historical Galactic supernovae
14
,
15
,
16
. Here we report three faint variable-surface-brightness complexes with high apparent proper motions pointing back to three of the six smallest (and probably youngest) previously catalogued supernova remnants in the Large Magellanic Cloud, which are believed to have been thermonuclear (type Ia) supernovae
17
. Using the distance and apparent proper motions of these echo arcs, we estimate ages of 610 and 410 years for two of them.
Journal Article