The Burst Alert Telescope aboard the Neil Gehrels Swift Observatory continuously scans the sky producing one of the most sensitive all-sky surveys in the hard X-rays. The survey is especially useful at finding nearby active galaxies, even those obscured at other wavelengths by gas and dust. Using high resolution IR observations of active galaxies detetected with BAT, a team of astronomers found a surprising number of galaxies in the final stages of merging together into single, larger galaxies. Peering through thick walls of gas and dust surrounding the merging galaxies' messy cores, the research team captured pairs of supermassive black holes drawing closer together before they coalescence into one giant black hole. It is not easy to find galactic nuclei so close together. Most prior observations of merging galaxies have caught the coalescing black holes at earlier stages, when they were about 10 times farther away. When the black holes finally do collide, they will unleash enormous energy in the form of gravitational waves.
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About a year ago, astronomers excitedly reported the first detection of electromagnetic waves, or light, from a gravitational wave source. Now, a year later, researchers are announcing the existence of a cosmic relative to that historic event. GRB150101B was a gamma-ray burst that lasted less than a second, localized by the NASA's Neil Gehrels Swift Observatory in an old elliptical galaxy 1.7 billion years away. The apparent match between GRB 150101B and GW170817 is striking: both produced an unusually faint and short-lived gamma ray burst, and both were a source of bright, blue optical light lasting a few days, and X-ray emission lasted much longer. The host galaxies are also remarkably similar. Both are bright elliptical galaxies with a population of stars a few billion years old and displaying no evidence for new stars forming. A paper reporting the results was published today in Nature Communications.
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The Ultraviolet/Optical Telescope (UVOT) aboard the Neil Gehrels Swift Observatory captured its millionth image on May 13, 2018. It took an image of an active galaxy called 2MASX J16110570+0234002, which scientists think exhibited some unusual behavior. A mosaic, created using images UVOT has taken since Swift launched in 2004, celebrates this major milestone for the mission.
Using data from NASA's Neil Gehrels Swift Observatory and ESA's XMM-Newton, researchers found evidence of an unusual long decay of X-ray emission coming from the active galaxy GSN 069. The X-ray signal was first seen in July 2010 by XMM-Newton. These observations showed that the source became at least 240 times brighter in X-rays. Since this initial detection, Swift and XMM-Newton observed GSN 069 multiple times and caught the long decay behavior of this outburst spanning about a decade. The X-ray data also indicate that the X-ray spectra are ultra-soft, i.e. steeply decreasing towards higher energies. All these properties point to a rare long-lived tidal disruption event (TDE). A few dozen of these events are known, but are mostly short-lived. The unusual long decay of the X-ray signal in GSN 069 suggests that either this was a late stage of evolution from a typical TDE, or the rare case where a long sustained TDE was caught in a galaxy with a pre-existing AGN. A paper describing these results was published in the journal Astrophysical Journal Letters.
As a star passes too close to a black hole, the black hole’s gravitational pull generates tidal forces on the star, similar to the way in which the moon stirs up tides on Earth. However, a black hole’s gravitational forces are so immense that they can disrupt the star, stretching and flattening it like a pancake and eventually shredding the star to pieces. In the aftermath, a shower of stellar debris rains down and gets caught up in an accretion disk — a swirl of cosmic material that eventually funnels into and feeds the black hole. This entire tidal disruption process generates colossal bursts of energy across the electromagnetic spectrum.
Scientists from MIT and Johns Hopkins University used Swift's X-ray Telescope (XRT) to monitor the X-ray emission arising from ASASSN-14li, a tidal disruption event 300 million light years away discovered in 2014 by the global telescope network ASASSN (All-sky Automated Survey for Supernovae). They noticed that the same fluctuations observed in the X-ray signal appeared 13 days later in the radio band. These radio “echoes,” which are more than 90 percent similar to the event’s X-ray light, are more than a passing coincidence. Instead, they appear to be evidence of a giant jet of highly energetic particles streaming out from the black hole as stellar material is falling in. The highly similar patterns between the X-ray and radio signals suggest that the power of the jet shooting out from the black hole is somehow controlled by the rate at which the black hole is feeding on the obliterated star.
While waiting for new gamma-ray bursts, Swift's Burst Alert Telescope (BAT) continuously scans the hard X-ray sky and accumulates data in survey mode covering a fraction between 50 and 80% of the sky every day. The data collected during the first 105 months of the Swift mission were published in the new Swift BAT 105-month catalog. This catalog is a uniform hard X-ray all-sky survey with a sensitivity of 8.40 x 10-12 erg s-1 cm-2 over 90% of the sky in the 14–195 keV band, and provides 422 new hard X-ray sources identified as Seyfert active galactic nuclei (AGN) in nearby galaxies (34%), X-ray binaries (7%) and blazars/BL Lac objects (10%). A large fraction of these sources remains unidentified. As part of this new edition of the Swift BAT catalog, the eight-channel spectra and monthly sampled light curves for each object are released on the Swift-BAT 105-month website.
Swift Cycle 14 Recommended Targets and Proposals have been posted.
Observations by NASA's Swift spacecraft, now renamed the Neil Gehrels Swift Observatory after the spacecraft's late principal investigator, have captured an unprecedented change in the rotation of a comet. Images taken in May 2017 reveal that comet 41P/Tuttle-Giacobini-Kresák - 41P for short - was spinning three times slower than it was in March, when it was observed by the Discovery Channel Telescope at Lowell Observatory in Arizona.
In honor of Neil Gehrels, who helped develop Swift and served as its principal investigator until his death on Feb. 6, 2017, the Swift Gamma-Ray Burst Explorer has officially been renamed the Neil Gehrels Swift Observatory.
Today the advanced LIGO and Virgo gravitational wave observatories announced the discovery of a new type of gravitational wave signal, likely caused by the collision of two neutron stars. The gravitational wave event occurred on 2017 August 17th, and was accompanied by a gamma-ray burst of short duration. Astronomers across the world began searching for the precise location of this event, quickly tracking it down to the nearby galaxy NGC 4993. Once pin-pointed, the Swift satellite quickly maneuvered to look at the object with its X-ray and UV/optical telescopes. The spacecraft saw no X-rays - a surprise for an event that produced higher-energy gamma rays. Instead, it found a bright and quickly fading flash of ultraviolet (UV) light. This bright UV signal was unexpected and revealed unprecedented details about the aftermath of the collision. The short-lived UV pulse likely came from material blown away by the short-lived disk of debris that powered the gamma-ray burst. The rapid fading of the UV signal suggests that this outflow was expanding with a velocity close to a tenth of the speed of light. The results of the Swift observations were published today on the journal Science. The discovery of this powerful wind was only possible using light, which is why combining gravitational waves and light in what we call 'multi-messenger astronomy' is so important.
KIC 8462852, also known as Boyajian's Star, or Tabby's Star, is one of the most mysterious stellar objects. The star has experienced unusual dips in brightness, up to 20 percent over a matter of days, and undergoes much subtler but longer-term enigmatic dimming trends. None of this behavior is expected for a normal star slightly more massive than the Sun. Speculations have included the idea that the star swallowed a planet and that it is unstable. A more imaginative theory involves an advanced civilization, which could be harvesting energy from the star and causing its brightness to decrease. A new study by Huan Meng and collaborators using NASA's Swift and Spitzer missions reveals less dimming in the infrared light from the star than in its ultraviolet light, suggesting that the cause of the dimming over long periods is likely an uneven dust cloud moving around the star.