The complex circumstellar environment of supernova 2023ixf

The early evolution of a supernova (SN) can reveal information about the environment and the progenitor star. When a star explodes in vacuum, the first photons to escape from its surface appear as a brief, hours-long shock-breakout flare1,2, followed by a cooling phase of emission. However, for stars exploding within a distribution of dense, optically thick circumstellar material (CSM), the first photons escape from the material beyond the stellar edge and the duration of the initial flare can extend to several days, during which the escaping emission indicates photospheric heating3. Early serendipitous observations2,4 that lacked ultraviolet (UV) data were unable to determine whether the early emission is heating or cooling and hence the nature of the early explosion event. Here we report UV spectra of the nearby SN 2023ixf in the galaxy Messier 101 (M101). Using the UV data as well as a comprehensive set of further multiwavelength observations, we temporally resolve the emergence of the explosion shock from a thick medium heated by the SN emission. We derive a reliable bolometric light curve that indicates that the shock breaks out from a dense layer with a radius substantially larger than typical supergiants.

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

The final fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are open questions in astrophysics. Many massive stars are stripped of their outer hydrogen envelopes as they evolve. Such Wolf-Rayet stars¹ emit strong and rapidly expanding winds with speeds greater than 1,000 kilometres per second. A fraction of this population is also helium-depleted, with spectra dominated by highly ionized emission lines of carbon and oxygen (types WC/WO). Evidence indicates that the most commonly observed supernova explosions that lack hydrogen and helium (types Ib/Ic) cannot result from massive WC/WO stars^2,3, leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosion⁴. Here we report observations of SN 2019hgp, beginning about a day after the explosion. Its short rise time and rapid decline place it among an emerging population of rapidly evolving transients^5-8. Spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen and neon. Narrow absorption features show that this material is expanding at high velocities (greater than 1,500 kilometres per second), requiring a compact progenitor. Our observations are consistent with an explosion of a massive WC/WO star, and suggest that massive Wolf-Rayet stars may be the progenitors of some rapidly evolving transients.

A surge of light at the birth of a supernova

It is difficult to establish the properties of massive stars that explode as supernovae. The electromagnetic emission during the first minutes to hours after the emergence of the shock from the stellar surface conveys important information about the final evolution and structure of the exploding star. However, the unpredictable nature of supernova events hinders the detection of this brief initial phase. Here we report the serendipitous discovery of a newly born, normal type IIb supernova (SN 2016gkg), which reveals a rapid brightening at optical wavelengths of about 40 magnitudes per day. The very frequent sampling of the observations allowed us to study in detail the outermost structure of the progenitor of the supernova and the physics of the emergence of the shock. We develop hydrodynamical models of the explosion that naturally account for the complete evolution of the supernova over distinct phases regulated by different physical processes. This result suggests that it is appropriate to decouple the treatment of the shock propagation from the unknown mechanism that triggers the explosion.

USE OF VIBRIO CHOLERAE SURFACE STRUCTURES FOR SPECIFIC PROPHY- LAXIS AND DIAGNOSTICS OF CHOLERA

The need for efficient and cost-effective cholera vaccine hasn't lost its actuality in view of the emergence of new strains leading to severe clinical forms of cholera and capable to replace strains of the seventh.cholera pandemic, and in connection with the threat of cholera spreading beyond the borders of endemic countries. In this review data from literature sources are presented about the use of outer membrane proteins, vesicles, cell ghosts of the cholera causative agent in specific prophylaxis and diagnostics of the disease.

[SOME ASPECTS OF NON-SPECIFIC PROPHYLAXIS AND THERAPY OF ESPECIALLY DANGEROUS INFECTIONS]

Recently, due to spread of dangerous and especially dangerous infections much attention is given to development of complex approaches to their prophylaxis and therapy. Data on use of immune modulators, cytokines, probiotics, preparations of plant origin for non-specific prophylaxis of especially dangerous infections are analyzed in the review, and expediency of their combined use with specific and emergency prophlaxis of these diseases is evaluated.

An outburst from a massive star 40 days before a supernova explosion

Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae, as do several models. 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, and disfavour alternative suggestions.

An unusually brilliant transient in the galaxy M85

Historically, variable and transient sources have both surprised astronomers and provided new views of the heavens. Here we report the discovery of an optical transient in the outskirts of the lenticular galaxy Messier 85 in the Virgo cluster. With a peak absolute R magnitude of -12, this event is distinctly brighter than novae, but fainter than type Ia supernovae (which are expected in a population of old stars in lenticular galaxies). Archival images of the field do not show a luminous star at that position with an upper limit in the g filter of about -4.1 mag, so it is unlikely to be a giant eruption from a luminous blue variable star. Over a two-month period, the transient source emitted radiation energy of almost 10(47) erg and subsequently faded in the optical sky. It is similar to, but six times more luminous at peak than, an enigmatic transient in the galaxy M31 (ref. 1). A possible origin of M85 OT2006-1 is a stellar merger. If so, searches for similar events in nearby galaxies will not only allow study of the physics of hyper-Eddington sources, but also probe an important phase in the evolution of stellar binary systems.

An optical supernova associated with the X-ray flash XRF 060218

Long-duration gamma-ray bursts (GRBs) are associated with type Ic supernovae that are more luminous than average and that eject material at very high velocities. Less-luminous supernovae were not hitherto known to be associated with GRBs, and therefore GRB-supernovae were thought to be rare events. Whether X-ray flashes--analogues of GRBs, but with lower luminosities and fewer gamma-rays--can also be associated with supernovae, and whether they are intrinsically 'weak' events or typical GRBs viewed off the axis of the burst, is unclear. Here we report the optical discovery and follow-up observations of the type Ic supernova SN 2006aj associated with X-ray flash XRF 060218. Supernova 2006aj is intrinsically less luminous than the GRB-supernovae, but more luminous than many supernovae not accompanied by a GRB. The ejecta velocities derived from our spectra are intermediate between these two groups, which is consistent with the weakness of both the GRB output and the supernova radio flux. Our data, combined with radio and X-ray observations, suggest that XRF 060218 is an intrinsically weak and soft event, rather than a classical GRB observed off-axis. This extends the GRB-supernova connection to X-ray flashes and fainter supernovae, implying a common origin. Events such as XRF 060218 are probably more numerous than GRB-supernovae.

Evidence for a Black Hole and Accretion Disk in the LINER NGC 4203

We present spectroscopic observations from the Hubble Space Telescope that reveal for the first time the presence of a broad pedestal of Balmer line emission in the LINER galaxy NGC 4203. The emission-line profile is suggestive of a relativistic accretion disk and is reminiscent of double-peaked transient Balmer emission observed in a handful of other LINERs. The very broad line emission thus constitutes clear qualitative evidence for a black hole, and spatially resolved narrow-line emission in NGC 4203 can be used to constrain its mass, MBH</=6x106 M middle dot in circle, at 99.7% confidence. This value implies a ratio of black hole mass to bulge mass of less, similar7x10-4 in NGC 4203, which is less by a factor of approximately 3-9 than the mean ratio obtained for other galaxies. The availability of an independent constraint on central black hole mass makes NGC 4203 an important testbed for probing the physics of weak active galactic nuclei. Assuming MBH near the detection limit, the ratio of the observed luminosity to the Eddington luminosity is approximately 10-4. This value is consistent with advection-dominated accretion and hence with scenarios in which an ion torus irradiates an outer accretion disk that produces the observed double-peaked line emission. Follow-up observations will make it possible to improve the black hole mass estimate and study variability in the nuclear emission.

Black holes in the milky way galaxy

Extremely strong observational evidence has recently been found for the presence of black holes orbiting a few relatively normal stars in our Milky Way Galaxy and also at the centers of some galaxies. The former generally have masses of 4-16 times the mass of the sun, whereas the latter are "supermassive black holes" with millions to billions of solar masses. The evidence for a supermassive black hole in the center of our galaxy is especially strong.