AO Newsletter 2017 [English vol2]

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A r e c i b o

O b s e r v a t o r y

Newsletter V o l .

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FRB’S

Astronomers pinpoint radio flashes

Picture courtesy of Danielle Futselaar

Astronomers pinpoint radio flashes originating long-long ago in a galaxy far-far away 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.

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).

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.

"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."

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

"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."

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 Continue

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 Space Academy (AOSA) is a pre-college, research program for high school students in Puerto Rico. The program, which lasts a full semester and includes 10 on-site contact days at the Arecibo Observatory, aims to prepare students for careers in STEM. During the semester, students conduct research concentrated in the multidisciplinary field of Space Sciences. In this process, students are exposed to the entire “real-world” research process, from reviewing literature, proposing the research, conducting it, and presenting their findings to their peers.

This Fall 2016 semester, AOSA obtained almost 90 applications from all over Puerto Rico, from which 30 students were selected. The cohort was composed of 45% boys and 55% girls, 44% from private schools and 51% from public schools, while the rest were from homeschools. The percentage of grade between 9th to 12th are all about 25%.

This recent semester students chose from three research departments, which were: Astrophysics and Planetary Sciences, Space Science and Engineering, and Environmental Sciences. The mentors (in order of department) were Dr. Edgard Rivera-Valentin, Luisa F. Zambrano-Marin, and Betzaida Aponte-Hernández.

During the semester, students participated in different activities with the Science and Visitors Center. These included helping organizing events for the celebration of the launch of OSIRIS-REx, which launched September 10, 2016. Students mounted and demonstrated an exhibit about impact cratering. Students also created poster exhibits celebrating Puerto Rican leaders in the Space Sciences for National Hispanic Heritage Month.

For more information please visit aosa.naic.edu

Arecibo Observatory Scientists Study the Earth’s Ionosphere with New HF Facility

By Dr. Joan Schmelz Every morning, the high-energy ultraviolet light from the Sun produces some fascinating effects in the highest reaches of the Earth’s atmosphere. This sunlight causes atoms to ionize. Like a mirror reflects optical light, these charged particles form a layer – the ionosphere – that reflects high frequency (HF) radio waves between 3 and 30 MHz. Waves from radio transmitters in distant parts of the world can then bounce up and down between the ionosphere and the ground as they travel around the planet.

That is why you can listen to radio stations in Europe or Australia with a short-wave radio.

Scientists at Arecibo study a host of fascinating plasma waves that occur in the ionosphere. The experiments are even more interesting because the plasma is immersed in the magnetic field.

Arecibo’s HF facility illuminates the ionosphere and creates even more complex scientific spectacles. One of the highlights of this facility is that it is able to use of the 1000-foot dish as its antenna. The first observations were done with six transmitters feeding three crossed-dipoles at a frequency of 5 MHz. A second set of 8 MHz dipoles was added in the last year. The HF design was restricted by the fact that no additional heavy equipment could be added to the telescope’s suspended platform. So the heavy dipoles were positioned at the bottom of the main dish, firmly attached to the ground. They transmit up to a light sub reflector, down to the main dish, then up again in the form of a narrow beam to illuminate the ionosphere.

The first observing campaign with the new HF facility took place 9-15 November 2015. A dozen atmospheric scientists from around the country worked with Arecibo staff collaborators on five specialized experiments designed to take advantage of the new instrument and study the ionosphere in innovative ways. The results were everything the scientists could have hoped for and are now starting to appear in the literature (see article by Carlson et al. in this issue.)

“What beautiful data!” exclaimed Herbert Carlson, an atmospheric scientist at Utah State University and one of the participants in Arecibo’s first HF campaign. “I can’t remember the last time an experiment went so perfectly according to anticipated script.”

“We see things we’ve never seen before,” explained Paul Bernhardt, an atmospheric scientist with the Naval Research Laboratory, another participant in the campaign. “I’ve already started writing the paper!”

The ionospheric plasma phenomena triggered by Arecibo’s HF facility were more clearly illuminated than ever before. In addition, varieties of waves were observed for the first time. These results will be a boon to the laboratory and modeling studies of plasma physics.

“We waited 17 years for the new HF,” Carlson continued. “Arecibo is the only place in the world this experiment can be done. It was worth the wait!

Gaia Weighs in on the Pleiades Distance Controversy

By Dr. Joan Schmelz

Summary of Pleiades distances from different measurements, showing 1 σ errors. The VLBI result, which uses Arecibo (red), is the most accurate determination to date and is consistent with previous ground-based measurements (black). The Hipparcos results (blue) set up the controversy, but the new measurements from Gaia (green) confirm those of Arecibo VLBI (Figure adapted from Melis et al. 2014).

Distance is one of the most challenging properties to measure in astronomy – it is bootstrapped from nearby objects like the Sun and planets all the way out to galaxies and quasars. The Pleiades, a nearby star cluster, had served as a cornerstone for astronomical distance derivations and set the scale for other clusters. Results from various ground-based techniques all agreed that the distance was about 133 parsecs, making the Pleiades a solid rung on the lower end of the “Cosmic Distance Ladder.”

This important role was called into question by results from the parallax satellite, Hipparcos, the gold standard of distance measurements. The distance measured by Hipparcos is 120.2 ± 1.5 parsecs, significantly and disturbingly different from traditional ground-based values and setting up the so-called “Pleiades distance controversy.” Although this amounts to only a 10% difference in the distance, the result propagates through the system and affects the size, age, and physics of the universe and objects in the universe. This disagreement led to significant shifts in the cosmic distance scale and controversial revisions of physical models required to obtain the Hipparcos result.

To resolve this controversy, a multi-year VLBI observing campaign using the High Sensitivity Array was conducted to derive a new independent, distance to the Pleiades. The first four parallax results derived from these measurements determined a distance to the Pleiades of 136.2 ± 1.2 pc (see Figure). This determination is in line with the original results from ground-based measurements, but incompatible with that suggested by Hipparcos (Melis et al. 2014). Now the Gaia mission, Hipparcos’s successor, has made an initial measurement of 134 ± 6 pc, consistent with the Arecibo VLBI result (Gaia Collaboration 2016).

When an observing program requires the detections of weak signals to resolve a fundamental astronomical controversy, there is no substitute for the collecting area of the Arecibo Observatory. Arecibo is an essential component of the High Sensitivity Array; its unparalleled collecting area is required to detect the weak double and triple radio star systems and decouple their proper motion from their orbital motion. The resolution of the Pleiades distance controversy would not have been possible without Arecibo.

Title: Gaia Data Release 1: Summary of the Astrometric, Photometric, and Survey Properties Authors: Gaia Collaboration Paper Reference: Astronomy & Astrophysics no. aa29512-16, Sep 2016 http://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/201629512 Title: A VLBI Resolution of the Pleiades Distance Controversy Authors: Melis, Reid, Mioduszewski, Stauffer, Bower Paper Reference: 2014, Science, 345, 1029 http://science.sciencemag.org/content/345/6200/1029

-Image of Pleiades

OSIRIS-REx Mission to Bennu On September 24, 2023, the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) spacecraft (Fig.1) will return a sample of asteroid (101955) Bennu to the Earth. The target of this mission was chosen in part because of the work at Arecibo Observatory over the course of over a decade, observing and modelling this asteroid.

In the fall of 1999, when the Arecibo Gregorian Upgrade had been complete for about a year, asteroid Bennu, then known as 1999 RQ36, was discovered by the LINEAR asteroid discovery program in New Mexico. We realized that it would make a close pass by the Earth a few weeks later and be observable at Arecibo with a high SNR. We (Lance Benner, Steve Ostro, Jean-Luc Margot, and I) arranged to observe it with the Arecibo and Goldstone planetary radar systems, and got good radar images at 15-m resolution on several days, revealing a roundish asteroid about 500m in diameter (left panel of Fig. 2). This fast response to new discoveries was a new capability, making good use of the Observatory’s 56 kbps internet connection (provided by the SETI program) to deliver radar ephemerides in real-time. Scott Hudson applied his shape modelling software to it, and derived a roundish shape, but the data were insufficient to go much farther.

In 2005, we took more radar images of Bennu, and began using the combined data to build a more detailed shape model (Center panel of Fig. 2). In 2006, Bennu was proposed as a target of an asteroid sample return mission called OSIRIS in NASA’s Discovery program, and interest in it increased dramatically. We provided the team with shape model to use in planning for this mission, which was updated several times as we improved

By Dr. Michael Nolan

the shape modelling software. Finally, in 2011, OSIRIS-REx was selected in NASA’s New Frontiers program to return a sample of the surface of Bennu.

Later in 2011, we observed Bennu one last time at Arecibo. These observations were extremely challenging, occurring over the time of the Cornell / SRI management transition, while we were also replacing the main radar power supply. We only saw a dot (right panel of Fig. 2), rather than a detailed image, but that dot, which measured the distance between the observatory and the asteroid to a few hundred meters, allowed a measurement of the Yarkovsky Effect on the asteroid’s orbit, an effect of heating and cooling of the surface as the asteroid rotates.

Using the radar-derived model of Bennu, we have been able to make much more detailed plans for the mission than has been possible for other missions to small asteroids and comets, and the Observatory commonly receives requests for information about other potential spacecraft targets for mission planning.

Figure 1. Liftoff of OSIRIS-REx aboard the Atlas V 411 launch vehicle

Figure 2. Radar model and images from 1999 (left), 2005 (center), and 2011 (right). Bennu is the faint dot near the center of the circles in the 2011 images, which are at much lower resolution. Bennu is about 500m in dimeter.

The left and center panels show the derived shape model (left), the simulated radar data (center), and the actual radar data (right) for two example radar images (of approximately 700).

Arecibo Puts Limits on Gravitational Wave Models

By Emmanuel Fonseca Title: The NANOGrav Nine-year Data Set: Observations, Arrival Time Measurements, and Analysis of 37 Millisecond Pulsars Authors: NANOGrav Collaboration Paper Reference: Astrophysical Journal, 2015, 813, 65 http://iopscience.iop.org/article/10.1088/0004-637X/813/1/65/pdf

Until this year, astronomers have only been able to indirectly determine the presence of gravitational waves -- tiny, wave-like shifts of space and time -through the measurements of decaying orbits of neutron stars. In January 2016, the LIGO collaboration announced the first direct detection of gravitational waves from a system of black holes orbiting and colliding together. The discovery by LIGO has ushered in the era of gravitational-wave astronomy, showing that direct measurements of spacetime ripples are possible.

Along with experiments like LIGO, an international collaboration of students and researchers study an array of radio pulsars in order to hunt for gravitational waves with nanohertz frequencies emitted by merging supermassive black-hole binary systems. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) “pulsar timing array” collaboration relies heavily on the Arecibo Observatory for making the most precise pulsar measurements possible. While each pulsar has a unique set of properties, gravitational waves passing through the Earth will imprint the same spacetime ripples into all pulsars in the array.

These signals can be measured directly once the array has sufficient sensitivity (the more bright pulsars in the array, the greater the sensitivity). The figure shows NANOGrav's sensitivity to

gravitational waves originating from supermassive black-hole binary mergers. The data are from the NANOGrav nine-year data set and include observations, arrival time measurements, and analysis of 37 millisecond pulsars. Even though NANOGrav has not yet detected a strong gravitational wave signal, its current sensitivity can start to rule out or constrain proposed models of the supermassive black-hole binary population in the Universe. NANOGrav continues to collect high-precision data with the Arecibo telescope and will likely directly detect nanohertz-frequency gravitational waves within the next 5 to 10 years.

The Arecibo Observatory and pulsar astronomy share an important history in gravitational wave science. Indeed, the first evidence for the existence of gravitational waves came from long-term Arecibo observations of a pulsar in a decaying orbit with another neutron star, where the rate of orbital shrinkage matched the rate expected from the loss of energy carried away by emitted gravitational waves. The NANOGrav effort, along with the international pulsar-timing-array community, will soon allow us to directly see gravitational waves from distant black-hole pairs. The Arecibo Observatory therefore continues to play a decisive role in gravitational wave astronomy.

The expected gravitational wave spectrum at nanohertz frequencies from various supermassive black-hole merger models (color) along with upper limits of the spectrum measured from the NANOGrav nine-year data set (black).

The black-dashed line represents the experimental upper limit of the gravitational wave strength when assuming that the signal is entirely due to super massive black hole binary mergers (i.e., power-law); the solid line represents the upper limit when allowing for the derived spectrum to have any shape. The colored areas correspond predictions of three different models. At large frequencies, the free-shape spectrum is dominated by white-noise (i.e. non-astrophysical) signals due to pulsars with small data sets.

First Results from the Arecibo HF Ionospheric Modification Facility

By H. C. Carlson, F. T. Djuth, and L. D. Zhang Title: Creating Space Plasma from the Ground Paper Reference: J. Geophys. Res., 2016JA023366, in press

We report the first experimental results of the new Arecibo HF heating facility. Earth is enveloped in a shell of ionization, the ionosphere, with peak electron density typically in the vicinity of 250 km. Solar UV and EUV radiation breaks electrons loose from neutral particles leaving ions to produce the ionosphere. A 1993 measurement made at Arecibo predicted that high-power HF transmitters could produce ionospheric ionization from the ground, similar to that produced by the Sun. The responsible physical process was electron acceleration by wave-particle interaction with the Arecibo HF heater radio waves. This prediction was confirmed in 2009 at two high-latitude facilities, but through electron-acceleration processes that could not operate at mid latitudes without violating the known laws of physics.

This experiment was designed to see if the old Arecibo measurement was repeatable. The observation with the new HF facility measured a ~10% energy conversion efficiency for HF radio wave-to-electron acceleration based on plasma wave intensity measurements (see figure). This confirms that HF radio waves can create space plasmas at both mid and high latitudes. This was the first direct comparison of ionization production rates by Sun vs. by HF accelerated electrons. The physical process at Arecibo is dominated by the Langmuir decay instability operating near the height of HF reflection. This is in contrast to the high-latitude results, which are dominated by four entirely different physical processes.

These processes combine to yield a similar ~10% efficiency of wave-to-particle energy conversion, but at an altitude a few km below that which dominates the Arecibo mid-latitude environment. These results strongly suggest that the contribution of electron Arecibo Observations acceleration to the of incoherent scatter space-plasma energy radar echo intensity from the “plasma line” distribution is more component, which here is important than currently a measure of the wave recognized. amplitude excited by electrons of energy adequate to impact-ionize atoms in the upper atmosphere. The upper profile [19:28-19:29 AST] shows strong intensity only above ~320 km, an intensity due to ~25 eV photoelectrons produced by the Sun. The lower profile from 2 minutes later [19:30-19:31 AST] is significantly brighter below 320 km because of extra ~25 eV electrons generated by the HF transmitter having been turned on.

Equal brightness under these observing conditions indicates equal ionizing-electron fluxes produced by the Sun and by the HF-excited instabilities.

This field of research has attracted interest in the past because electron acceleration in a simple electric field potential drop has an upper limit set by the dielectric breakdown in the media, e.g., particle accelerators require acceleration over limited scales to reach high energies. In contrast, for a plasma it is its mechanical properties and turbulence that sets the upper limit, which can generally be orders of a larger magnitude.

Pictured are Luis Quintero, head of electronics, Dana Whitlow , and Joan Schmelz, Director of USRA operations at AO

After many years at the observatory, Dana Whitlow has decided to retire.

AO staff gathered in December to honor Dana’s service and accomplishments.

Thank you Dana, you'll certainly be missed!

The Arecibo Observatory

turkeython

On November 23 we celebrated our traditional Turkeython race

The Ă ngel Ramos Foundation Science and Visitors Center celebrated its Observation Night on December 10, 2016.

The event consisted of several activities, among them nocturnal observations, educational games stations and talks by scientists from the Arecibo Observatory and the Caribbean Astronomy Society.

The Arecibo Observatory mascot participated in the St, Jorge Children’s Hospital Christmas parade

November 7, 2016

Arecibo Observatory Celebrates SRI International 70th Anniversary

On December 9 we celebrated our traditional crazy rally

On December 16, 2016 the AO Staff celebrated the end of year event in a local restaurant

National Astronomy and Ionosphere Center

The Arecibo Observatory Director’s message Welcome to Arecibo Observatory’s Vol.3 Newsletter. It’s been a fantastic time so far, full of challenges and discoveries for our team. I want to take the time to thank our users for their support throughout the years. Thanks to you, the Arecibo site has been, and will continue to be, a unique place for scientific innovation and collaboration. I also want to thank the fantastic Staff at AO. During my first months on site I have been impressed by your work ethic, technical knowledge and commitment to the Arecibo site. In my years in the aerospace sector I have never met a more dedicated team and I am proud to be a member of this organization. Thanks for all you do, and keep up the great work.

Francisco Córdova, MSCE, PE

We hope you’ve enjoyed this

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The AO Newsletter is published by The Arecibo Observatory.

Joan Schmelz (jschmelz@usra.edu) Editor

Director – Arecibo Observatory

The Arecibo Observatory is operated by SRI International, USRA and UMET under a cooperative agreement with the National Science Foundation.

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