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For almost a quarter of a century 1 , the origin of γ-ray bursts— brief, energetic bursts of high-energy photons—has remained unknown. The detection of a counterpart at another wavelength has long been thought to be a key to understanding the nature of these bursts (see, for example, ref. 2), but intensive searches have not revealed such a counterpart. The distribution and properties of the bursts 3 are explained naturally if they lie at cosmological distances (a few Gpc) 4 , but there is a countervailing view that they are relatively local objects 5 , perhaps distributed in a very large halo around our Galaxy. Here we report the detection of a transient and fading optical source in the error box associated with the burst GRB970228, less than 21 hours after the burst 6,7 . The optical transient appears to be associated with a faint galaxy 7,8 , suggesting that the burst occurred in that galaxy and thus that γ-ray bursts in general lie at cosmological distance.

An intensive radio frequency interference (RFI) monitoring campaign has been carried out at several proposed Square Kilometer Array (SKA) sites in China, based on the RFI measurement protocol for SKA candidate sites (hereafter RFI protocol), over a period of at least one year. In this paper we summarize the RFI equipment, data handling, and presentation. The results, measured in both modes 1 and 2 of the RFI protocol, demonstrate that the radio-quiet spectrum around Dawodang in Guizhou province makes it an exceptional location for a radio observatory.

A variety of anomalous geomorphological features on Mars can be explained by a conceptual scheme involving episodic ocean and ice-sheet formation. The formation of valley networks early in Mars' history is evidence for a long-term hydrological cycle, which may have been associated with the existence of a persistent ocean. Cataclysmic flooding, triggered by extensive Tharsis volcanism, subsequently led to repeated ocean formation and then dissipation on the northern plains, and associated glaciation in the southern highlands until relatively late in Martian history.

The origin of γ-ray bursts has been one of the great unsolved mysteries in high-energy astrophysics for almost 30 years. The recent discovery of fading sources at X-ray 1 and optical 2,3 wavelengths coincident with the location of the γ-ray burst GRB970228 therefore provides an unprecedented opportunity to probe the nature of these high-energy events. The optical counterpart appears to be a transient point source embedded in a region of extended nebulosity 3–6 , the latter having been tentatively identified as a high-redshift galaxy 3 . This would seem to favour models that place γ-ray bursts at cosmological distances, although a range of mechanisms for producing the bursts is still allowed. A crucial piece of information for distinguishing between such models is how the brightness of the optical counterpart evolves with time. Here we re-evaluate the existing photometry of the optical counterpart of GRB970228 to construct an optical light curve for the transient event. We find that between 21 hours and six days after the burst, the R-band brightness decreased by a factor of ∼40, with any subsequent decrease in brightness occurring at a much slower rate. As the point source faded, it also became redder. The initial behaviour of the source appears to be consistent with the 'fireball' model 7 , but the subsequent decrease in the rate of fading may prove harder to explain.

Variable x-ray and γ-ray emission is characteristic of the most extreme physical processes in the universe. We present multiwavelength observations of a unique γ-ray—selected transient detected by the Swift satellite, accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z = 0.3534. Its high-energy emission has lasted much longer than any γ-ray burst, whereas its peak luminosity was ∼100 times higher than bright active galactic nuclei. The association of the outburst with the center of its host galaxy suggests that this phenomenon has its origin in a rare mechanism involving the massive black hole in the nucleus of that galaxy.

Long-duration γ-ray bursts (GRBs) release copious amounts of energy across the entire electromagnetic spectrum, and so provide a window into the process of black hole formation from the collapse of massive stars. Previous early optical observations of even the most exceptional GRBs (990123 and 030329) lacked both the temporal resolution to probe the optical flash in detail and the accuracy needed to trace the transition from the prompt emission within the outflow to external shocks caused by interaction with the progenitor environment. Here we report observations of the extraordinarily bright prompt optical and γ-ray emission of GRB 080319B that provide diagnostics within seconds of its formation, followed by broadband observations of the afterglow decay that continued for weeks. We show that the prompt emission stems from a single physical region, implying an extremely relativistic outflow that propagates within the narrow inner core of a two-component jet. GRB 080319B: fit to burst The γ-ray burst GRB 080319B, the result of the violent collapse of a massive star to form a black hole, is the most luminous optical flash so far observed in the 40-year history of γ-ray astronomy. Discovered by the Swift satellite on 19 March 2008 and briefly visible to the naked eye, it produces energy across the entire electromagnetic spectrum. Now a reanalysis of the extraordinarily bright emissions of GRB 080319B within a few seconds of its formation, together with broadband observations of its decay over the following few weeks, provide the clearest picture yet of one of these events. The data clearly establish that the prompt optical flash was produced in the same physical region as the γ-ray burst itself. The afterglow properties cannot be explained by the standard simple models, but rather imply a multi-component jet interpretation. Long duration γ-ray bursts (GRBs) release copious amounts of energy across the entire electromagnetic spectrum, and provide a window into the process of black hole formation from the collapse of massive stars. Observations of the extraordinarily bright prompt optical and γ-ray emission of GRB 080319B shows that the prompt emission stems from a single physical region, implying an extremely relativistic outflow that propagates within the narrow inner core of a two-component jet.

Insights into the history of the inner solar system can be derived from the impact cratering record of the Moon, Mars, Venus, and Mercury and from the size distributions of asteroid populations. Old craters from a unique period of heavy bombardment that ended [approximately]3.8 billion years ago were made by asteroids that were dynamically ejected from the main asteroid belt, possibly due to the orbital migration of the giant planets. The impactors of the past [approximately]3.8 billion years have a size distribution quite different from that of the main belt asteroids but very similar to that of near-Earth asteroids.

We show that at wavelengths comparable to the length of the shower produced by an Ultra-High Energy cosmic ray or neutrino, radio signals are an extremely efficient way to detect these particles. Through an example it is shown that this new approach offers, for the first time, the realistic possibility of measuring UHE neutrino fluxes below the Waxman-Bahcall limit. It is shown that in only one month of observing with the upcoming LOFAR radio telescope, cosmic-ray events can be measured beyond the GZK-limit, at a sensitivity level of two orders of magnitude below the extrapolated values.

The discovery of afterglows associated with γ-ray bursts at X-ray 1 , optical 2 and radio 3 wavelengths and the measurement of the redshifts of some of these events 4 , 5 has established that γ-ray bursts lie at extreme distances, making them the most powerful photon-emitters known in the Universe. Here we report the discovery of transient optical emission in the error box of the γ-ray burst GRB980425, the light curve of which was very different from that of previous optical afterglows associated with γ-ray bursts. The optical transient is located in a spiral arm of the galaxy ESO184-G82, which has a redshift velocity of only 2,550 km s −1 ( ref. 6 ). Its optical spectrum and location indicate that it is a very luminous supernova 7 , which has been identified as SN1998bw. If this supernova and GRB980425 are indeed associated, the energy radiated in γ-rays is at least four orders of magnitude less than in other γ-ray bursts, although its appearance was otherwise unremarkable: this indicates that very different mechanisms can give rise to γ-ray bursts. But independent of this association, the supernova is itself unusual, exhibiting an unusual light curve at radio wavelengths that requires that the gas emitting the radio photons be expanding relativistically 8 , 9 .

Research suggests a generic connection between the inner and the outer radio structures of a radio source associated with Cygnus X-3, and implies that the (poor) collimation evident in the large-scale double source originates near the binary system.