PR Contact: Suraiya Farukhi
Universities Space Research Association
Columbia, Maryland, January 4, 2017 - Astronomers have for the first time pinpointed the location of a so-called "fast radio burst" (FRB) -- a type of short-duration radio flash of enigmatic origin -- and have used this to identify its home galaxy.
Prior to this discovery, astronomers have lacked the definitive proof that FRBs come from far outside our Milky Way galaxy. This is because poor localization has prevented unique identification of their galaxies of origin. The new finding is critical because it has allowed astronomers to precisely measure the distance to the source, and hence to determine how much energy it is producing.
FRBs are visible for only a fraction of a second and have puzzled astronomers for over a decade since they were first discovered. Precise localization of an FRB requires the use of radio telescopes separated by large distances, which allows high-resolution images to be made when the data from these telescopes are combined with each other.
The FRB 121102 was originally detected at the Arecibo Observatory in Puerto Rico in November 2012. In 2014, Arecibo recorded another burst from FRB 121102, making it the only known repeating FRB.
On Aug 23, 2016, the Karl G. Jansky Very Large Array (VLA) in New Mexico was used to detect yet another burst from Arecibo's FRB and use it to determine the sky position to a fraction of an arcsecond. "This is an angle similar to that subtended by a human hair held at a distance of 200 meters," said Shami Chatterjee of Cornell University. At the same celestial position, astronomers found both steady radio and optical sources, which pointed the way to the galaxy hosting the FRB.
To zoom in even further, scientists used the European VLBI Network (EVN), which links telescopes spread across the world, to obtain a position ten times more precise than that of the VLA alone. Arecibo was a vital partner in this campaign. "With this level of precision, we could determine that the origin of the bursts lies right on top of the steady radio source seen by the VLA," noted Benito Marcote from the Joint Institute for VLBI in Europe (JIVE).
"It is the combined sensitivity of the telescopes, their large separations, and the unique capabilities of the JIVE central data processor that allow the pinpointing of events that are as short as a thousandth of a second," added Zsolt Paragi of JIVE. "That gives a positional accuracy on the sky of about 10 milliarcseconds."
"Arecibo's participation with the EVN supplies the longest baselines and the highest possible angular resolution," noted Universities Space Research Association's (USRA) Dr. Tapasi Ghosh, a VLBI astronomer at Arecibo Observatory. "We also provide unparalleled sensitivity for imaging the faint bursts."
Dr. Andrew Seymour, a USRA postdoctoral scientist at Arecibo, worked with Ghosh to set up parallel observing modes, whereby Arecibo not only acquired VLBI data, but also recorded wideband, high-time-resolution, single-dish data. "These data were used to find the exact times of the bursts," Seymour explained. "Then the VLBI imaging process could zero in on those specific times and make images of the bursts themselves."
Image: The 305-m Arecibo telescope and its suspended support platform of radio receivers is shown amid a starry night. From space, a sequence of millisecond-duration radio flashes are racing towards the dish, where they will be reflected and detected by the radio receivers. Such radio signals are called fast radio bursts. Figure Credit: Danielle Futselaar Deeper studies using one of the world's largest optical telescopes, the 8-m Gemini North on Maunakea in Hawaii, were able to confirm that the optical source was a host galaxy. Astronomers then used the optical spectrum to obtain a so-called "redshift," which places the source at a whopping distance of over 3 billion light-years. "This gives us incontrovertible confirmation that this FRB originates very deep in extragalactic space," said Cees Bassa of the Netherlands Institute for Radio Astronomy (ASTRON).
Though the mystery of this FRB's distance is now resolved, astronomers have a new puzzle on their hands. The galaxy hosting the FRB is surprisingly small -- a so-called dwarf galaxy. "These new discoveries about Arecibo's FRB give us clues to the nature of the radio bursts," noted Dr. Joan Schmelz, Director of USRA operations at Arecibo Observatory. "It is surprising that such an exotic source is hosted by such an unimpressive galaxy."
However, this might prove to be just what astronomers need to unravel the mystery. Dwarf galaxies contain gas that is relatively pristine compared to that found in the much more massive Milky Way. The conditions in this dwarf galaxy are such that it may be possible to form much more massive stars than in the Milky Way, and perhaps the source of the FRBs is from the collapsed remnant of such a star.
Alternatively, astronomers are considering a very different hypothesis in which FRBs are generated in the vicinity of a massive black hole that is swallowing the surrounding gas, a so-called active galactic nucleus.
To try and differentiate between these two scenarios, astronomers are using the world's premier radio, optical, X-ray, and gamma-ray telescopes. "For example, if we can find a periodicity to the arrival of the bursts, then we will have strong evidence that they originate from a rotating neutron star," added Seymour. "But for now there is no obvious pattern to tell us when these events will occur again."
Deciphering the origin of the FRBs will also depend on localizing more such sources, and astronomers are debating whether all FRBs detected to date are of a similar physical origin or whether there are multiple types.
These results appear on 5 January 2017 in Nature, in a paper entitled "A Direct Localization of a Fast Radio Burst and Its Host" by Chatterjee et al. 2017, and in the Astrophysical Journal Letters, in two papers, "The Host Galaxy and Redshift of the Repeating Fast Radio Burst 121102" by S. P. Tendulkar et al. and "The Repeating Fast Radio Burst 121102 as Seen on Milliarcsecond Angular Scales" by B. Marcote et al.
The findings are being presented by Dr. Jason Hessels, associate scientist at ASTRON, the Netherlands Institute for Radio Astronomy, at a press conference at the American Astronomical Society's (AAS) meeting at Grapevine, Texas, on January 4, 2017.
USRA staff members at Arecibo Observatory, Drs. A. Seymour, T. Ghosh, and C. Salter who carry out on-site observations are deeply involved in the Arecibo observations that have contributed to these discoveries. Dr. Hessels led the team that used the Arecibo telescope in Puerto Rico to locate a collection of 11 repeating bursts from the same source.
The Arecibo Observatory is a facility of the National Science Foundation (NSF) operated by SRI International in alliance with the Universities Space Research Association (USRA) and UMET under a cooperative agreement. The Arecibo Observatory Planetary Radar Program is funded through the National Aeronautics and Space Administration (NASA) Near-Earth Objects Observations program.
Formed in 1969 under the auspices of the National Academies of Science, USRA offers an avenue for government and industry to engage the expertise of the academic community together with its own technical leadership, innovative R&D, operational excellence, management of premier facilities and education programs to advance space- and aeronautics-related sciences and exploration. USRA works across disciplines including biomedicine, planetary science, astrophysics, and engineering and integrates those competencies into applications ranging from fundamental research to facility management and operations.
The 305-m Arecibo telescope and its suspended support platform of radio receivers is shown amid a starry night. From space, a sequence of millisecond-duration radio flashes are racing towards the dish, where they will be reflected and detected by the radio receivers. Such radio signals are called fast radio bursts. Figure Credit: Danielle Futselaar