AO Newsletter: Volume3 - Summer 2017

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A r e c i b o

O b s e r v a t o r y

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2017

Summer edition

The Mystery of Part Time Pulsars

By Gerrit Verschuur and Joan Schmelz

Paper: Two long-term intermittent pulsars discovered in the PALFA Survey Authors: A. G. Lyne and 33 coauthors, including AO staff member A. Seymour.

Reference: 2017, Astrophysical Journal, 834, 72 ADS link: http://adsabs.harvard.edu/abs/2017ApJ...834...72L

A new discovery has upended the widely held view that all pulsars are orderly ticking clocks of the universe. A survey done at the Arecibo Observatory in Puerto Rico has fortuitously discovered two extremely strange pulsars that undergo a “cosmic vanishing act.” Sometimes they are there, and then for very long periods of time, they are not.

Recognizing the existence of this strange behavior was fortuitous in itself. It took great patience on the part of a team of radio astronomers at Jodrell Bank in the UK led by Professor Andrew Lyne of the University of Manchester to confirm the existence of these mostly invisible pulsars.

Pulsars are rapidly rotating, highly magnetized neutron stars. They are about 20 miles across with masses of about 500,000 Earths. The rotation sends charged particles streaming out from the magnetic poles, causing beams of radio waves to sweep around the sky - like the light beams from a lighthouse. This results in pulses, which can be received by terrestrial radio telescopes.

Intermittent pulsars are a rarely observed population of pulsars, which have two states - one when they pulse like normal pulsars (the ON state), and another when they mysteriously fail to work, producing no radio waves at all (the OFF state).

“They switch instantaneously between the states,” notes Lyne. “They’re ON and then they’re gone, disappearing without any apparent warning.”

A 34-member pulsar study team, including Dr. Andrew Seymour, a USRA postdoc at Arecibo, used the 7-beam receiver to conduct routine pulsar searches in what they call the PALFA (Pulsar Arecibo L-Band Feed Array) Survey. The two recently discovered intermittent pulsars spend

most of their time in the OFF state. Three other similar pulsars are also known, but they are mostly ON. In September 2012, one of these new objects was discovered to be emitting very bright pulses, and it was labeled PSR J1929+1357. Of 169 new pulsars, follow-up observations of half of those had been initiated at Jodrell Bank and this candidate was confirmed as a pulsar in February 2013 using the 250ft Lovell Telescope at the second attempt.

“During the next 9 months it was observed no fewer than 650 times - 100 hours,” said Professor Benjamin Stappers of the Jodrell Bank Center for Astrophysics and a co-author on the publication. “It was ON on only 5 occasions - just 0.8% of the time.”

The most important implication of this discovery is that there must exist an extremely large number of these vanishing-act pulsars. The PALFA survey, which is aimed at a section of the Milky Way visible to the Arecibo dish, only covers each position in the survey once. It probably passed over 130 similar pulsars, but this was the only one that was ON at the time of observation. Furthermore, if it were not for the early signals at Jodrell Bank, this pulsar could easily have been discarded as a false detection, likely arising from radio-frequency interference.

The PALFA team estimates that there are about 3000 such intermittent pulsars in the survey area, far greater than the population of normal pulsars.

“These disappearing pulsars may far outnumber normal pulsars,” said Dr. Victoria Kaspi of McGill University in Canada and the Principal Investigator on the PALFA project. “In fact, they may redefine what we think of as normal.”

Why this odd behavior? After all, since the original pulsar discovery in 1967, they have been referred to as marvelously accurate cosmic clocks that tick steadily for millions years with a cadence that surpasses the ticking of our best laboratory clocks.

But these long-term intermittent pulsars are mostly invisible, which is about as useful as having a clock Continue

on the wall that is hidden behind a curtain for most of the time.

“The explanation of the ON-OFF behavior remains a puzzle,” says Seymour. “It indicates that the pulsar environment is changing, but just what those changes entail is open to debate.”

Recent observations of these odd pulsars is that their rotation rate slows down to 80% of the ON rate than when OFF. A property of “normal” pulsars is their pulse rate slows very gradually over time. The PALFA team suspects that the stream of charged particles, which drive the radio beams emanating from the pulsar, also causes the pulsar to spin down more rapidly. When OFF, this particle stream fails for some reason and the spin down rate is reduced. But as Seymour notes, there is as yet no agreement in the pulsar community as to

the ON-OFF mechanism.

The changing spin rate is inferred by calculating how many beats were missed during the pulsar’s invisible phases.

PALFA surveys are on-going, and no one can predict if and when more examples of this fascinating new phenomenon will be found.

Catching another intermittent pulsar in its ON mode is up to chance. Is there another candidate out there ready to reveal its secrets, or will it forever lurk hidden in the dark unknowns of space?

Lyne hopes that follow-up measurements of PSR J1929+1357 will provide a rare insight into the physics of the pulsar emission mechanism and the changing spin down phenomenon.

STORIES As part of the Arecibo Observatory Space Academy (AOSA), a pre-college program for high school students in Puerto Rico, Jose D. Maldonado and Wilbert A. Ruperto got the opportunity to conduct research at the Observatory and also to present this work at the 30th Annual Math Fair of the Department of Education of Puerto Rico. Here, each student details their personal story in this next addition of AOSA stories!

Wilbert A. Ruperto My research consisted of observing and determining the physical, orbital and chemical characteristics of two Potentially Hazardous Asteroids (PHAs) through the use of the world’s most sensitive planetary radar system at the Arecibo Observatory. These asteroids are considered potential dangers due to their relative close Earth encounters and their size. My work was mentored by Dr. Edgard Rivera-Valentin, Staff Planetary Scientist and Project Manager for AOSA, and by Ph.D. student and Academic Coordinator of AOSA, Luisa F. Zambrano-Marín.

My passion for studying asteroids began in my second semester at AOSA and grew as time progressed. I can recall the first time I stepped inside the control room of the observatory.

As I walked through the door, I encountered a set of amplifiers, computers, and cabling, all part of a complex system that permits the scientists to design and control the experiments. Danny, one of the radar operators, gave me a tour around the control room and explained to me the functionalities of the instruments.Then I found myself standing in front of the control room’s observation deck. It took just a few moments for me to get inspired by the magnitude of the facility and by all that I had learned that day.

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I remember I said to myself that someday, if I put enough work and effort, I was going to be there observing asteroids. From that point on, that became a dream and one of my goals in the academy. In the following months, I taught myself the necessary concepts and got familiarized with the existing scientific literature. After some time, I finally got the chance to attend my first observation run in November 2016 and then my second in January 2017. Later in January, I decided to join the Science Research course at my specialized high school, CROEM (Residential Center of Educative Opportunities of Mayagüez). This would grant me the opportunity to participate in the upcoming Math Fair. After weeks of extensive and intense work under the mentorship of the folks at Arecibo and my physics teacher at CROEM, Dr. Elba M. Sepúlveda, I completed what once was just a dream of mine.

As for the competition itself, I was thrilled and ready to present and share my findings to the judges and my peers. I decided to highlight the importance of this field of study and how mathematical concepts like equations and graphs are used to understand the nature of the asteroids and at the same time develop better planetary defense strategies. This captivated the attention of some attendees with whom I had the pleasure to talk and exchange ideas.

Jose D. Maldonado My project focused on the analysis of anomalous behavior in network flows with the purpose of effectively predicting a network’s future behavior. This project consisted of monitoring a controlled network for two weeks to make predictions of its behavior. Through this research, I was able to learn about my main fields of interest, Computer Science and Statistics, through the application of concepts from these fields to my work. It allowed me to take the theory I had studied independently and apply it towards the development of a solution to a real world problem in my field of interest, motivating me to keep learning about the topic at hand and investigating it.

My interest for this topic began at the ten-day long Academics and Training for the Advancement of Cybersecurity Knowledge in Puerto Rico (ATACK PR) Cybersecurity Camp at the University of Puerto Rico – Río Piedras Campus. There, while learning about the different techniques used in the field of Cybersecurity for detection and prevention of attacks, one of our professors mentioned that he was helping an undergraduate student with research on possible ways to detect anomalies in network flows. At the time, I had no knowledge of what network flows were and why the detection of their anomalies was important, but I had a strong desire to learn more about the topic. When the camp ended, I contacted the professor to discuss the possibility of me doing research on the topic, and what I needed to start detecting network flows and anomalies in them. He was thrilled with the initiative, and provided me with reading material on past research done on the topic and offering me all the help I needed. After reading the material, I contacted Arun Venkataraman, IT Manager at the Arecibo Observatory, for help with the process of data collection and analysis, and started investigating possible ways to find trends in network flow anomalies; with the idea that if they can be predicted, they can be avoided and the proper precautions can be taken to prevent them in the future. The professor was impressed with the idea, and suggested that I look into statistical methods used for predictions that could be applied for network flows. After doing some research, I discovered that, since network flows were essentially a time series of packets going through a network at a certain point, I could apply time-series analysis methods and make efficient predictions on the behavior of the series of network flows.

After various months of trial-and-error, and with the help of my project mentors Arun Venkataraman, Dr. Edgard G. Rivera Valentin, Edwin Benvenutti, Mathematics Teacher at CROEM, and Edgardo Lorenzo, Statistics Professor at the University of Puerto Rico – Mayagüez, I was able to efficiently make predictions on the behavior of network flows. The Arecibo Observatory Space Academy gave me the knowledge and tools necessary to make this research idea a reality, and pushed me towards expanding my knowledge to reach my goal. While the end result was successful, nothing truly compares to the feeling of discovery and the journey when working towards reaching your goal. I was constantly expanding my knowledge about the fields entailed in my research through independent study, with my mentors making suggestions and giving tips throughout the way. I was learning by doing, applying techniques that weren’t previously applied to my topic of interest. This is why I always recommend the Arecibo Observatory Space Academy to my peers: the program gives you the tools and suggestions needed for your research project, but it is you who decides how to use these tools and apply them to your own research. These experiences are the ones that motivate me to keep investigating, and confirm that one is never too young to investigate if they have the desire and drive to do whatever it takes to make it happen.

Why are Quasars so Bright?

By Gerrit Verschuur and Joan Schmelz Paper: RadioAstron Observations of the Quasar 3C273: A Challenge to the Brightness Temperature Limit Authors: Y.Y. Kovalev and 19 coauthors, including AO staff members T. Ghosh and C. J. Salter Reference: 2016, Astrophysical Journal Letters, 820, 19 ADS link: http://adsabs.harvard.edu/abs/2016ApJ...820L...9K

Remarkable new observations derived by linking Arecibo Observatory’s 305-meter dish with the Russian RadioAstron Space Radio Telescope have provided results that are causing much head scratching in radio astronomical circles. What used to be a well-understood explanation of the mechanism that generates intense radio signals from tiny and very distant quasar nuclei has now been tested in previously impossible ways.

The RadioAstron satellite (launched in 2011 by the Russian Federal Space Agency) carries a 10-m radio dish and is traveling around the earth in a highly elliptical orbit that takes it out to 350,000 km from Earth - almost the distance to the Moon. When the signals it receives from a distant quasar are combined with simultaneous data acquired by its earth-based partners at Arecibo in Puerto Rico, Green Bank in West Virginia, Socorro in New Mexico, and Bonn in Germany, the observations simulate a dish up to 350,000 km in diameter. This network of telescopes operates 330 MHz (92cm), 1.7 GHz (18cm), 4.7 GHz (6.2cm) and 22 GHz (1.3cm).

“Arecibo’s huge diameter helps compensate for the small size of the RadioAstron dish,” commented Dr. Chris Salter, a senior staff astronomer at Arecibo Observatory.

“Arecibo's participation is critical to the success of many RadioAstron experiments.”

Combining the signals produces what are called fringes, and it was recently reported that quasar 3C273 was detected at a baseline of 170,000 km (106,000 miles). This remarkable achievement showed that 3C273 has structure in its core at least as small as 26 microarcseconds across.

At the distance of 3C273, this corresponds to a physical diameter of 2.7 light months. The ability to see such detail is not matched by any other telescope in the world. Optical telescopes, even the Hubble Space Telescope, do not come anywhere near this ability to see detailed structure.

To relate this angular scale to human experience, it is as if you were able to see a coin of the size of US quarter (5 cm across) at the Moon. Or if a spy satellite were in geosynchronous orbit, it would be able to see details as small as a fingernail.

So far RadioAstron and its terrestrial partners have not detected details smaller than the 26 microarcseconds in 3C273’s core, but already the observations are pushing the

theory of radio source emission mechanisms beyond their limit.

Radio astronomers measure the apparent brightness of objects such as quasars in terms of the temperature a solid body subtending the same angular size would have to possess in order to shine with the same intensity. The smaller the angular diameter of the object producing the radio signals, the higher its source temperature must be to produce the observed signal.

The 3C273 data reveal that its brightness temperature must be about 4 × 1013 K, that is, a 4 followed by 13 zeroes, or 40 trillion degrees. The problem is that the maximum allowed by present theories for radio emission from a quasar is about 1012 K, which is to say around one trillion degrees centigrade.

“Temperatures this high test our understanding of the physics in the vicinity o f supermassive black hole at the heart of 3C273,” noted Dr. Tapasi Ghosh, the VLBI staff astronomer at Arecibo Observatory. “We hope that Arecibo–RadioAstron observations of other sources will help shed light on this mystery.”

“We conclude that it is difficult to interpret the data in terms of conventional incoherent synchrotron radiation,” noted Dr. Yuri Kovalev of the Lebedev Physical Institute in Moscow and the lead author on the paper. Yet the theory of quasar radio emission that has held sway for nearly 60 years is based on synchrotron radiation.

“Arecibo Observatory may have celebrated its 50th anniversary in 2013, but it continues to make vital observations that challenge our understanding,” said Dr. Joan Schmelz, Director of Universities Space Research Association (USRA) operations at Arecibo Observatory.

“These impressive contributions to the RadioAstron measurements are just one example.”

The RadioAstron project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Science and the Lavochkin Association of the Russian Space Agency. Scientists at partner institutions in Russia and elsewhere in the world, including Puerto Rico, West Virginia, Massachusetts, New Mexico, Virginia, Germany, the Netherlands and Australia, collaborate to make RadioAstron the international success that it has turned out to be. Crucial to that success has been the availability of the huge collecting area that is provided by the 305-m diameter dish at Arecibo, Puerto Rico, without which the effectiveness of the small RadioAstron antenna would be vastly reduced.

Radar Observations and Shape Model of Asteroid 16 Psyche Authors: Michael K. Shepard and 21 coauthors, including AO staff members Patrick A. Taylor and Linda A. Rodriguez-Ford.

Paper Reference: Icarus 281, p. 388-403. Published 2017.

ADS link: http://adsabs.harvard.edu/abs/2017Icar..281..388S

M-class asteroids are a relatively rare type of asteroid in the main asteroid belt, located between the orbits of Mars and Jupiter. For many years, planetary scientists have thought that they were the remnants of small protoplanets that were shattered in the violent early days of the solar system, leaving only an exposed metal core behind. Unfortunately, determining whether an asteroid is mostly metallic is very difficult with traditional optical telescopes. For the past decade, we have used the Arecibo Planetary Radar to probe these objects, for only a radar telescope can give an unambiguous indication of a metallic composition.

Asteroid 16 Psyche is the largest M-class asteroid in the main-belt and is of special interest because

it is the target of a newly selected NASA Discovery Mission, also called Psyche. Until our study, scientists had only the most rudimentary knowledge of Psyche’s size and shape – information critical for mission planning purposes.

In 2005, we obtained data that confirmed Psyche was dominantly metallic. In late 2015, we were able to obtain 18 new delay-Doppler radar images of Psyche with the Arecibo Planetary Radar. When combined with our previous radar observations, new optical observations from two adaptive optics telescopes, optical light curves, and three stellar occultations, we were able to generate a 3D shape model of Psyche with a resolution of about 15 km.

Our model shows evidence for two crater-like depressions and suggests that there is significant variation in the metal content and color of the asteroid over the surface.

This work would have been impossible without the Arecibo facility. It contains the only radar telescope in the world capable of imaging main-belt asteroids.

The radar-derived shape model of asteroid 16 Psyche. It is roughly ellipsoidal with dimensions 279 x 232 x 189 km.

Colors represent the deviation in topography from the surface mean. All sides are shown. The numbers in the top left corner of each image are the longitude and latitude, respectively, of the image center.

Two crater-like depressions are evident in the southern hemisphere, shown in the lower right figure.

Mid-latitude Radio-Frequency Auroras

By Eliana Nossa, Shikha Raizada, and David Hysell

Paper Title: Dynamic instability in the lower thermosphere inferred from irregular sporadic E layers Paper Authors: D.L. Hysell, E. Nossa, M.F. Larsen, J. Munro, S. Smith, M.P. Sulzer, and S.A. González Paper Reference: J. Geophys. Res., (2012), 117, A08305, doi:10.1029/2012JA017910.

Radio-frequency (RF) auroras, like the beautiful example shown in Figure 1 , are often dancing across the night skies of Puerto Rico. Unlike their high-latitude cousins, however, these tropical phantasms do not generate optical emission and are not associated with solar activity. These are mid-latitude RF echoes observed with coherent radar and displaying radio signatures similar to those detected from the northern lights.

The Arecibo Observatory has been key to understanding the nature of these mid-latitude RF auroras.

This unique cluster of diverse and highly sensitive equipment includes both radar and optical instruments. The ionized particles are observed with Arecibo’s incoherent scatter radar (ISR) and show billowy behavior as well as unexplained changes in the density and temperature distributions. At the same time, the neutral particles are observed with Arecibo’s lidars, which also show the billowy behavior and temperature changes. An example of the neutral billows using the sodium resonance lidar is shown in Figure 2. The background ionospheric medium is observed simultaneously with Arecibo’s imagers and ionosondes.

RF auroras appear to result from the interaction between neutral particles in the thermosphere and charged particles in the ionosphere. Neutral winds produce a shear that generates Kelvin-Helmholtz rolls. Current work suggests that RF auroras are produced by neutral particles that drag ions and result in coherent echoes. This finding is motivating a new area of research that focuses on the study of ion behavior to infer neutral winds. Recent work reported convective instabilities and other neutral dynamics during the daytime, opening up new possibilities to expand our understanding of ion-neutral coupling in the lower ionosphere and adding to our understanding of RF auroras.

Figure 1. Mid-latitude RF auroras observed on the night of September 30, 2008, with a coherent scatter radar located on St. Croix and looking perpendicular to the earth's magnetic field line over the Arecibo Observatory at an altitude close to 105 km. The contour corresponds to the island of Puerto Rican and the “X” to the location of the Arecibo Observatory. The color scale indicates variations in Doppler, intensity, and spectral width.

Figure 2. Altitudinal and temporal distribution of Na atoms obtained using a resonance lidar over Arecibo. The main layer between 80-100 km has been saturated to reveal the structures between 101-110 km. Sarkhel et al. (2012) found atmospheric conditions to be dynamically unstable and conducive to a Kelvin-Helmholtz instability during this event.

2017 REU Summer Students

USRA New Hires

On April 1 we celebrated the 20th aniversary of the Angel Ramos Science & Visitors Center

As part of its 20th anniversary celebration, the Angel Ramos Foundation Science & Visitors Center (S&VC) of the Arecibo Observatory, announces its new affiliation with the Smithsonian Institution. The S&VC will become the third organization in Puerto Rico to join the Smithsonian Affiliate network.

“The Arecibo Observatory and the Smithsonian share a common vision: to unlock the mysteries of the universe and share them with the world”, says Andrew Ortiz, director of the S&VC. “Through this alliance, we will be able to share the Smithsonian with our community and will be able to create lasting experiences that will broaden knowledge and perspectives on science, history, world cultures, and the arts. This collaboration will provide the basis for a world of possibilities and new experiences for our visitors.”

The newly refurbished and extended S&VC, modernized exhibition space, and state-of-the-art auditorium welcomes nearly 100,000 visitors a year and supports STEM Education at all levels throughout Puerto Rico and beyond. The new exhibits are focused on the work done at the Arecibo Observatory promoting the expansion of the visitor’s knowledge in the areas of radio astronomy, atmospheric science and planetary studies, in a fun way.

“The Smithsonian is very honored,” stated Harold A. Closter, director of Smithsonian Affiliations “to begin this new partnership with the Angel Ramos Foundation Science & Visitors Center (S&VC) of the Arecibo Observatory. This partnership builds on a long history of collaborative research between Arecibo and the Smithsonian Astrophysical Observatory, resulting in numerous and profound discoveries about the fundamental nature of our universe.

Working together we hope to share the excitement of these discoveries with audiences of all ages, and inspire future generations to aim for the stars.”

“It’s an honor for the Arecibo Observatory to partner with such a prestigious and historic institution as the Smithsonian. Together we will continue our quest to share knowledge and science within our local communities in Puerto Rico and with the millions of science enthusiasts around the World”, stated Eng. Francisco Córdova, Director of the Arecibo Observatory.

March 2017

Dr. Scott Bolton, PI of NASA's Juno mission, and his family joined us at AO to provide a Juno Mission Status update to the Arecibo Observatory Space Academy students and the public at the Angel Ramos Foundation Science and Visitor Center. Dr. Bolton interacted directly with AOSA students, answering their questions about how to become a NASA mission PI.

March 2017

Dr. Elianna Nossa gave a special talk to a group of girls from the Girls in Aviation program.

“We had a great time with this young girls who aspire to greater things in science.”

- Dr. Eliana Nossa

April 2017

Starfleet-PR, official chapter of Star Trek TM in Puerto Rico (recognized by the international organization Starfleet that has the endorsement of Paramount Pictures to celebrate events related to Star Trek) celebrated a Special Event at the Observatory of Arecibo Science & Vistors Center.

May 2017

The Arecibo Observatory won 4 prizes at the Relay for Life event in Arecibo. But our greatest achievement was to give hope to all the patients and survivors of the cancer disease

National Astronomy and Ionosphere Center

The Arecibo Observatory IT department message The Arecibo Observatory website, www.naic.edu, is currently being redesigned to better serve our visitors and staff. The initial phase saw development of a new website, outreach.naic.edu, which launched on May 4th, 2017. The site was built using the Drupal 7 Content Management System (CMS) and showcased the power of this approach, while maintaining a responsive layout.

The Staff & Scientist Portal is the next phase nearing completion (Q2). Most of the frequently-accessed content available under the old NAIC website was migrated to the new framework. Each of the three scientific disciplines pursued at the Observatory--Astronomy, Space & Atmospheric Sciences, Planetary Sciences--has a corresponding Content Editor (respectively Robert Minchin, Edvier Cabassa and Edgard Rivera) to ensure that the material is accurate, up-to-date and complete.

The Web Developer and Communications Officer are responsible for the functionality and aesthetic impact of the product. A workshop for new Content Editors is planned for the following quarter.

A new e-Commerce section is planned as an extension to the Galaxy Shop at the Angel Ramos Foundation Visitor Center. Web visitors may purchase (pre-pay) their entrance tickets and buy souvenirs online.

“This development process will continue to require a considerable amount of effort and time but I think in the long run, standardizing on a CMS will give all content editors a common platform that will allow for workflow improvements, and, ultimately, more effective services to the AO community."

– Jorge L. Herrera, Web Developer.

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