SN 2016gkg

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Galaxy NGC 613 , the supernova SN 2016gkg took place on the right below the galaxy core in a spiral arm

SN 2016gkg is a Super Nova of the type SN IIb in an arm of the approximately 86 million light-years from the solar system remote spiral galaxy NGC 613 , 50  arc seconds west and 88 angular seconds south of the center of the galaxy . It was discovered by the Argentinian amateur astronomer Victor Buso on September 20, 2016, just hours after the collapse became visible on Earth. Buso immediately reported his observation to the International Astronomical Union , giving observatories around the world the opportunity to observe the early stages of the supernova.

The special meaning of SN 2016gkg is that it was discovered immediately after it lit up. The measurements of optical phenomena and the emitted electromagnetic radiation as well as the evaluation of older images of the affected region by the Hubble space telescope allow conclusions to be drawn about the size and structure of the exploded star, which are no longer possible in supernovae discovered later.

Coordinates ( equinox J2000.0 )

discovery

On September 20, 2016, the amateur astronomer Victor Buso tested a new camera in Rosario , Argentina , with his Newtonian telescope with a mirror diameter of 406 millimeters. He aimed the telescope at the 26.4  megaparsec distant spiral galaxy NGC 613 in the constellation Sculptor , as it was near the zenith . Over a period of one and a half hours, Buso took 98 pictures, the exposure time of which was only 20 seconds due to the light pollution . The first 40 images were taken over a period of 20 minutes and do not yet show any evidence of the supernova. After a break of 45 minutes, Buso took further series of 17, 20 and 21 pictures. These recordings show over 25 minutes how the supernova became visible and increased in brightness.

Because the supernova was discovered so early and the information passed on quickly, numerous more detailed observations could be made within one day by astronomical institutions such as the research satellites Swift and Gaia and other observatories around the world.

The properties of the star from which a supernova emerged can only be determined with difficulty. The electromagnetic radiation that a supernova emits within the first minutes and hours of its existence provides important information about the properties of its precursor star. Finding such early stages of supernovae is the goal of some ongoing research programs. The probability of an accidental discovery like that of SN 2016gkg is given as less than one in a million.

description

SN 2016gkg is a type IIb supernova and initially showed an extremely strong increase in brightness of around 40 magnitudes per day. The evaluation of the first recordings of the supernova and the back calculation taking into account the minimum resolution of the recording system of 19.6 magnitudes resulted in a period between 02:50 and 05:35 a.m. ( UTC ) on September 20, 2016 for the explosion of the star or for the Time at which the light cone of the explosion reached the earth. This definition of a period of less than three hours is one of the most accurate ever carried out. All data suggest that the first series of images shows the outbreak.

As early as September 21, 2016, the US astrophysicist Saurabh W. Jha from Rutgers University published an initial classification based on spectrographic images from the Southern African Large Telescope . Jha recognized SN 2016gkg as an early-stage Type II supernova. The spectral lines of SN 2016gkg largely coincided with those of SN 1993J . A few days later, this led to the classification as a type IIb supernova by a group led by the American astrophysicist Schuyler D. van Dyk .

In contrast to the previous assumptions about supernovae, the images taken in the days and weeks after the explosion show three instead of the two previously known for type IIb supernovae highlights of visible brightness: during the original eruption, during the cooling phase and during the nickel combustion. On the second day following the discovery, telescopes from the Chilean Cerro Tololo Inter-American Observatory showed a decrease in brightness of 0.7 magnitudes. The second flash was observed on September 25, 2016, which turned into a three-day plateau phase. After fading again, there was a third flash about 14 days after the explosion.

The series of the first recordings and the rapid increase in brightness that can be seen on them could not be conclusively reconciled with the later observations. Therefore, a model of the supernova was designed in two phases. The first model should represent the overall development of the supernova in accordance with the available observation data. An energy output of E = 1.2 × 10 51  erg and an ejected mass of 3.4  solar masses with 0.085 solar masses 56 nickel could be derived from this model . The extension of this model by parameters that influence the cooling phase of a type IIb supernova resulted in a radius of 320 solar radii and a mass of 0.01 solar masses for the shell of the precursor star  .

Based on the recordings of Buso and subsequent observations from various observatories, different information about the properties of the predecessor of SN 2016gkg was published in 2017. A research group led by astrophysicist Iair Arcavi from the University of California, Santa Barbara , named a radius of 40 to 150 solar radii and a mass of the shell of 2 to 40 × 10 −2  solar masses.

From September 21 to 27, 2016, SN 2016gkg was observed with the X-Ray Telescope of the Swift research satellite . Over the observation period it was found that the emitted X-rays became significantly weaker. This led to the assumption that the X-ray source is connected to SN 2016gkg.

Forerunner star

Charles D. Kilpatrick of the University of California, Santa Cruz and several colleagues published the data of the most likely precursor star on September 23, 2016, based on archived images of the Wide Field / Planetary Camera 2 (WFPC2) of the Hubble Space Telescope from 2001 the position of SN 2016gkg can be seen. It is probably a blue giant with a magnitude of 24 mag. Our own observations from September 22, 2016 with an infrared camera from the Keck Observatory confirmed the evaluations of the images and also point to a blue giant as the forerunner star. The data largely agree with those of other blue giants identified as precursor stars of supernovae, but show an even greater brightness and a higher proportion of blue in the visible spectrum.

According to the supernova model, its predecessor star is a binary star system with 19.5 and 13.5 solar masses and an orbital speed of 70 days, the primary star of which has exploded in a supernova. Confirmation of this assumption is expected when the supernova has faded so far that a targeted search for the secondary star becomes possible.

Media coverage

Just a few days after its discovery, the discovery of SN 2016gkg and its research were the subject of publications in astronomical and astrophysical journals that went unnoticed by experts. It was not until February 2018 that the Argentine astrophysicist Melina C. Bersten and 20 colleagues - including Victor Buso as a member of the "Observatorio Astronómico Busoniano" in Rosario - published an article in the science magazine Nature , describing the discovery of SN 2016gkg and the results of the previous Investigations represented.

The publication in Nature was disseminated through news agencies and thus found its way into media coverage worldwide. Details about the discoverer also became known. Victor Buso, a 58-year-old locksmith from the Argentine city of Rosario , built his first telescope at the age of eleven and has been an amateur astronomer ever since. Eight years ago he sold a piece of land that he owned with his father and used the proceeds to install a Newtonian telescope with a mirror diameter of 406 millimeters on the roof of his house in an observatory .

See also

literature

  • Melina C. Bersten et al .: A surge of light at the birth of a supernova . In: Nature , February 22, 2018, No. 554, pp. 497–499 (plus 14 pages of appendix), doi : 10.1038 / nature25151 .

Web links

Individual evidence

  1. ↑ International Astronomical Union, Supernova Working Group (Ed.): Discovery Certificate for Object 2016gkg . TNS Astronomical Transient Report No. 5381 of September 21, 2016.
  2. ↑ a b c d e Melina C. Bersten et al .: A surge of light at the birth of a supernova , p. 497 and Appendix Methods .
  3. ↑ a b c d Melina C. Bersten et al .: A surge of light at the birth of a supernova , p. 498 and Appendix Methods .
  4. ↑ International Astronomical Union, Supernova Working Group (Ed.): Classification Certificate for Object 2016gkg . TNS Classification Report No. 422 of September 21, 2016.
  5. ↑ Schuyler D. Van Dyk et al .: Further Classification of SN 2016gkg as a Probable Type IIb Supernova . In: The Astronomer's Telegram No. 9573, September 30, 2016.
  6. ↑ Ping Chen et al .: An unusually fast brightness decline in optical of young type II supernova SN 2016gkg from ASAS-SN follow-up observations . In: The Astronomer's Telegram No. 9529, September 22, 2016.
  7. ↑ Leonardo Tartaglia, David J. Sand and Stefano Valenti: Possible optical re-brightening of SN2016gkg . In: The Astronomer's Telegram No. 9544, September 25, 2016.
  8. ↑ Jair Arcavi et al .: constraints on the progenitor of SN 2016gkg from its shock-cooling light curve . In: The Astrophysical Journal Letters 2017, Volume 837, Letter L2, doi : 10.3847 / 2041-8213 / aa5be1 .
  9. ↑ Raffaella Margutti et al .: X-ray detection of SN 2016gkg with Swift-XRT . In: The Astronomer's Telegram No. 9561, September 28, 2016.
  10. ^ Charles D. Kilpatrick et al .: Progenitor Candidate for SN 2016gkg in NGC 613 . In: The Astronomer's Telegram No. 9536, September 23, 2016.
  11. ^ Charles D. Kilpatrick et al .: On the progenitor of the Type IIb supernova 2016gkg . In: Monthly Notices of the Royal Astronomical Society 2017, Volume 465, No. 4, pp. 4650-4657, doi : 10.1093 / mnras / stw3082 .
  12. ↑ Thorsten Dambeck: Hobby astronomer observes star explosion live for the first time , Spiegel Online , February 22, 2018.
  13. ^ Sarah Kaplan: [A self-taught astronomer spotted something no scientist had ever seen] . The Washington Post , February 22, 2018.