As telescopes and radio astronomy instrumentation get better and more sensitive, our ability to probe time-sensitive phenomena in our universe increases greatly. I use that sensitivity to learn more about short timescale events in the radio sky. Specifically working with radio surveys like the High Time Resolution Universe (HTRU) survey and the SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB), I look for sources like pulsars, rotating radio transients (RRATs), and fast radio bursts - single transient events. Understanding the nature of these different sources gives a better picture of the makeup of our galaxy and allows us to probe deeper and further in ways that have not previously been possible such as looking in greater detail at features and changes in the interstellar medium (ISM) between stars in the Milky Way. I am working with Willem van Straten and Matthew Bailes in conjunction with Simon Johnston at CSIRO to study pulsars, transient phenomena, and their relationship with the interstellar medium during my PhD at Swinburne.
Fast Radio Bursts (FRBs)
In recent radio surveys at Parkes astronomers looking for new pulsars also found a new type of pulsed object since called Fast Radio Bursts (FRBs). Fast radio bursts appear as single, bright, very short radio pulses that have never been seen to repeat. The pulses only last for a few milliseconds, similar to the duration of a pulsar pulse, but have properties that lead us to believe that they originate far outside the Milky Way, where normal pulsars cannot be detected.
So what could be the source of FRBs? Many different theories exist as to what causes FRB pulses but none has yet been confirmed. Some believe they are explosions in distant galaxies, or flares caused by distant magnetars, highly magnetic pulsars that emit bursts of powerful radiation. Others believe they originate in our own Galaxy, but from bursty flare stars. I work on several observing campaigns currently trying to answer these questions!
Based on the number of FRBs that have been found in radio surveys so far, we believe that up to 10,000 FRB bursts happen every day! Meaning that if our eyes could see at radio wavelengths, we could look up into the sky and see an FRB twinkle every 10 seconds!
FRBs are a new and exciting mystery object that I work to understand. Collecting data and testing theories is the best way to understand their origins and some of my most recent work focuses on these incredible new sources.
Pulsars and Radio Transients
Pulsars are a subclass of neutron stars. Neutron stars are what's left over after a large star goes supernova. The remaining core is extremely dense and spins very quickly. Neutron stars have two large radio jets that come out of each of the star's magnetic poles. As these beams sweep across the sky they act like a lighthouse in space, and if these beams cross our line of sight at Earth, we can observe this with a radio telescope, and we see a 'blip' every time the star rotates. In this case we call the star a pulsar. Pulsars have been observed to rotate anywhere between about 1 and 1000 times a second. That means a star a few kilometers wide spinning as fast as a kitchen blender!!
The pulses from pulsars are very regular, much like a clock, and interesting experiments can be done to monitor their pulses over time. Pulsar pulses can also be used to probe the interstellar medium (ISM) as things like density of charged electrons and turbulence of the medium can be determined from the interstellar medium's effect on pulsar pulses. For all the pulsars in our Galaxy (more than 2500 to date) we can measure the effects on their pulses from the ISM and build a map of the diffuse material between the stars. I use pulsars to study this medium and apply this work to making our measurements of pulsar pulses more precise.
A sub-class of pulsars called rotating radio transients (RRATs) only behave like pulsars a fraction of the time. We observe pulsed radio emission, like pulsars, but not for every rotation of the star. For a normal pulsar that rotates once per second, we would see 60 pulses in one minute. For an RRAT with the same period, we might expect anywhere between 0 and 59 pulses. Based on the number of RRATs we have seen so far and the amount of "on" time they spend on average, the total number of RRATs is likely much larger than the total number of 'normal' pulsars! The best way to find the RRATs is through high time resolution radio surveys. I work on these surveys to find new RRATs, and try to understand what makes them 'tick' so differently from normal pulsars.
Fun fact: The Crab pulsar (above image from NASA) is one of the youngest pulsars known and lives in the very distinctive Crab Nebula. The supernova explosion that produced the Crab pulsar occurred in the year 1054 and was documented by Chinese astronomers.
Observing Projects and Proposals
I am involved with a number of ongoing research proposals at the CSIRO Parkes Radio Telescope in Australia. The Parkes telescope continues to operate at the forefront of pulsar astronomy and many of the most groundbreaking pulsar discoveries have happened at Parkes. Below are listed a few of the projects in which I am currently active.
SUPERB - the SUrvey for Pulsars and Extragalactic Radio Bursts
More information about SUPERB can be found on our public webpage. SUPERB began in April 2014 and will be the most sensitive and most ambitious radio survey ever conducted at Parkes. The project will collect terabytes of data and search for isolated pulsars, pulsar binaries, and fast radio bursts, all in real time - something never before attempted. I am very excited about the results coming out of this survey in the next few years.
Transient Radio Neutron Stars
This project has been active at the Parkes telescope for more than three years and has been responsible for the majority of the known RRATs in the Galaxy. I currently lead this project where we focus on re-observing RRATs discovered during the High Time Resolution Universe survey (HTRU). An initial RRAT detection may be nothing more than a single radio pulse. Further observations are required to confirm the candidate and start understanding its underlying behavior. This project is slated to continue through 2014 with the goal of confirming some 50 new RRATs from the HTRU survey.
A Follow-up Campaign for Fast Radio Bursts
I began this observing project in April 2014 with the goal of understanding FRB emission. Currently, some theories about FRB origins propose that they are not from cataclysmic events, but rather regular, flare-type bursts that would be expected to repeat on some timescale. In this project we re-observe the positions of known FRBs in an attempt to detect repeated emission or set limits on possible repeating timescales. Based on the time on sky allocated to this project (80 hours this semester) we might even expect a new FRB to occur during our observations!
PULSE@Parkes PULar Student Exploration online at Parkes
PULSE@Parkes is a fantastic outreach program conducted by the astronomers at CSIRO Astronomy and Space Science center to give high school students around the world a taste of what it is like to be a pulsar astronomer. The team involved with this project brings students into the Parkes observing facilities in Sydney, or brings a remote set-up to the classroom and gives students the ability to control the operation of the Parkes Telescope and collect their own pulsar data. The sessions are conducted by pulsar astronomers who teach the students about pulsars and answer questions related to careers in science.
I only participate in this project when I travel to Sydney or when the team comes to Melbourne, but the program is incredibly rewarding for the students, teachers, and astronomers who participate. More information can be found on the PULSE@Parkes webpage.
Deeper, Wider, Faster: Optical counterparts to the fastest bursts in the sky
Although not an optical astronomer, I have recently joined a team currently looking for optical counterparts to fast radio bursts. As the progenitors of the bursts are still unknown, all efforts to search for similar types of bursts, in radio or other wavelengths, has been an area of increasing interest. This observing project uses the 4m optical telescope on Cerro Tololo in La Serena, Chile. We search optical fields with very deep imaging to detect any possible sources that might be affiliated with FRBs. The data taken during these observations will probe an entirely new regime of fast, dim optical transients.