Category Archives: Uncategorised

Real-time detections of 5 Fast Radio Bursts

 

08/05/19 — Five new Fast Radio Bursts have been published today by the UTMOST project.

Fast Radio Bursts are mysterious sources of energetic emission at radio frequencies, thought to lie billions of light years from the Earth. They last for only a few milliseconds and represent one of astronomy’s biggest puzzles.

The study, led by Swinburne PhD student Wael Farah, uses the real-time FRB detection system he created for the project, to catch FRBs within seconds of their arrival at the telescope, so that  data can be captured at the highest time and frequency resolution.

 

Screenshot_2019-05-07_10-08-10

One of the FRBs has remarkable time and frequency structure — as seen below:

Screenshot_2019-05-07_10-03-59

The FRB shows three peaks separated by approximately two milliseconds, with very similar frequency structure from peak to peak — seen as horizontal striations in the plot. These structures are probably due to the effects of ionised gas in the Milky Way galaxy as the radio burst travels to the Earth.

The 5 new FRBs were collected over 344 days of observing at the Molonglo telescope in a dedicated campaign, searching for the real-time detection system. Over 130 known pulsars were also seen giving off a total of 250,000 pulses during the campaign.

The study allows the FRB rate — the number of FRBs that occur across the whole sky each day — to be compared with experiments finding FRBs at other radio wavelengths, at the Parkes Radio Telescope and ASKAP (The Australian Square Kilometer Array Pathfinder) telescopes.

UTMOST operates in the frequency range 820 to 850 MHz, whereas Parkes and ASKAP operate at 1400 MHz.

The study finds fewer FRBs at this frequency than simple scaling of the rate at 1400 MHz suggests. It may be that FRBs are intrinsically less energetic at these wavelengths, and is a new clue to the nature of FRB progenitors.

The FRBs each present a different story. One of them, FRB181016, is one of the most energetic FRBs ever detected, probing into the high luminosities these events can attain. FRB170922 has the longest scattering tail published to date at around 30 milliseconds, while FRB181017 has  the shortest known at approximately 200 microseconds.

“UTMOST’s real-time detection system allows us to fully exploit its high time and frequency resolution and probe FRB properties previously unobtainable”, says ARC Laureate Fellow and project leader Prof. Matthew Bailes.

“Wael has used machine-learning on our high -performance computing cluster to detect and save FRBs from amongst millions of other radio events, such as mobile phones, lightning storms, and signals from the Sun and from pulsars”,   says project scientist Dr. Chris Flynn.

The UTMOST project is currently being augmented with a complete renovation of the North-South arm of the Molonglo Radio Telescope, allowing the source of FRBs on the sky to be pinpointed to the source galaxy they come from, and help solve the puzzle of the origin of FRBs.

The study has been submitted to the journal Monthly Notices of the Astronomical Society, and is available on arxiv as a preprint.

 

SMIRF — the “Survey for Magnetars, Intermittent pulsars, RRATs and FRBs” at UTMOST

 

SMIRF is the “Survey for Magnetars, Intermittent pulsars, RRATs and FRBs” running at the Molonglo Radio Telescope.

Led by Swinburne PhD student (now a postdoctoral fellow at the MPIfR in Bonn), Vivek Venkatraman Krishnan, the survey has set new records in real-time searches for transient phenomena in the radio region of spectrum.

Screenshot_2019-05-07_11-29-10The regions of the southern sky surveyed by SMIRF, showing pulsar timing, search regions for new pulsars and intermittant pulsars, for new Fast Radio Bursts (FRBs) — and following up known FRBs.

SMIRF makes use of the huge field of view of the Molonglo telescope to search large swathes of sky, while also using the high spatial resolution of the 1.6 km long telescope array to detect transient sources within the surveyed regions. Seaches for transient phenomena at radio wavelengths have rarely used arrayed telescopes in this manner before, but rather made use of very sensitive single dish telescopes with relatively tiny fields-of-view.

SMIRF has the capacity to survey the entire Southern arc of the Milky Way for variable and transient radio sources every 10 days. Typically, surveys making such a large area sweep across the sky are only undertaken once in a decade. SMIRF has the capacity to undertake such surveys many times per year. As part of his PhD thesis, Vivek also implemented into SMIRF fully autonomous operation of the telescope, so that it decides which regions of sky to survey under robotic control.

Regularly and frequently surveying the sky is the key to discovering and understanding intermittancy in pulsars. Over the 5 decades since the discovery of pulsars, several thousand have been isolated and characterised in search programs at radio telescopes around the world. In the last decade or so, about 50 of these have been identified as highly variable — disappearing for months at a time and only occasionally being “on” — or giving off occasional and quite sporadic single pulses of radio energy as they only indicator of their presence.

The small numbers of such pulsar related sources is most likely a consequence of the difficulty in finding them, rather than small numbers per se. Regular and frequent scanning of the Milky Way galaxy is the key to finding many more of them, characterising their properties, and working out their relationship to the much better studied pulsars.

This is where the SMIRF program excels. PhD student Vivek Venkatraman Krishnan implemented the processing engine that runs on the telescope’s high-performance computing cluster on 56 Graphics Processing Units (GPUs). Processing 22 gigabytes of data per second, it can use the stream of digitized radio data to make timing measurements of the known pulsars in the field of view, search for new puslars using Fast Fourier Transform techniques, while also operating commensally with the faccility’s Fast Radio Burst discovery program. It represents the state-of-the-art in such techniques, and presages the capacity required to make such searches with coming large scale facilities such as the SKA (Aquare Kilometer Array), which will use similar techniques.

The survey has found a new intermittant pulsar, seen in the plots below (showing the phase of the pulsar versus time, and the phase versus frequency):

Screenshot_2019-05-08_20-00-52

Two examples of single pulses produced by the newly found intermittant pulsar found are shown below:

Screenshot_2019-05-07_11-45-58

Around a dozen pulses from the new source were detected over the  course of 20 minutes, leading to good characterization of the source properties as an intermittant pulsar.

The first SMIRF paper, which gives a full system description overview and initial results, has been submitted to the Monthly Notices of the Royal Astronomical Society, and is available as a preprint.

 

FRB190322 found at UTMOST

At UTC 2019-03-22-07:00:12.3 (2019-03-22.29180903), we found a fast radio burst as part of the ongoing search program (UTMOST), at the Molonglo telescope.

FRB20190322_BEAM_245_193259

Molonglo is a 1.6 km long East-West array (Bailes et al 2017, PASA, 34, 45) and was operating in drift-scan mode with pointing centred on the meridian at the time of detection. Source localisation is excellent in Right Ascension (5 arcsec at 1-sigma) but poor in Declination (~1.2 deg at 1-sigma) (see Caleb et al 2017 MNRAS 468, 3746).

FRB190322 was found during a blind FRB search programme in real-time using an automated GPU-accelerated/machine learning based pipeline and the raw voltages were recorded for offline processing.

The optimal dispersion measure (DM) that maximizes the signal-to-noise ratio is: 724.2 pc cm^-3. The DM estimate of NE2001 model is ~47.1 pc cm^-3, and YMW16 model is ~46.78 pc cm^-3 at this position, resulting in an intergalactic excess of ~677 pc cm^-3. The upper limit on the DM-inferred redshift is thus z ~ 0.6.

An early estimate (lower limit) of the event’s apparent fluence is ~16 Jy ms (corrected for attenuation of the primary beam in the RA direction, but not in the Dec direction), width ~ 1.35 ms, with a detection signal-to-noise ratio = 12.

The most likely position is RA = 04:46:14.45, DEC = -66:55:27.8, J2000, Galactic: Gl = 278.166 deg, Gb = -36.921 deg. The 95% confidence localisation arc is as follows: (RA, DEC) in (hours, deg)

4.745128 -70.779222
4.749025 -70.278667
4.752725 -69.778056
4.756242 -69.277444
4.759589 -68.776806
4.762778 -68.276167
4.765822 -67.775500
4.768725 -67.274806
4.771503 -66.774111
4.774158 -66.273417
4.776700 -65.772694
4.779136 -65.271972
4.781472 -64.771222
4.783714 -64.270500
4.785867 -63.769722
4.787936 -63.268972
4.789925 -62.768194

A formula describing the localisation arc is:

RA = 4.7701477 + 5.677894e-3*(DEC + 67.024292) – 2.568521e-4*(DEC + 67.024292)**2

where RA is in hours, Dec is in deg, and is valid in the Dec [-71.3,-62.8]

For the dynamic spectra, and the localisation plots, follow this link.

Follow-up observations of the FRB are encouraged.

FRB181228 found at UTMOST

 

At UTC 2018-12-28-13:48:50.1 (2018-12-28.5755799), we found a bright fast radio burst as part of the ongoing search program (UTMOST), at the Molonglo telescope.

Screenshot_2019-01-07_13-29-11

Molonglo is a 1.6 km long East-West array (Bailes et al 2017, PASA, 34, 45) and was operating in drift-scan mode with pointing centred on the meridian at the time of detection. Source localisation is excellent in Right Ascension (5 arcsec at 1-sigma) but poor in Declination (~1.2 deg at 1-sigma) (see Caleb et al 2017 MNRAS 468, 3746).

FRB181228 was found during a blind FRB search programme in real-time using an automated GPU-accelerated/machine learning based pipeline and the raw voltages were recorded for offline processing.

The optimal dispersion measure (DM) that maximizes the signal-to-noise ratio is: 354 pc cm^-3. The DM estimate of NE2001 model is ~58 pc cm^-3, and YMW16 model is ~61 pc cm^-3 at this position, resulting in an intergalactic excess of ~290 pc cm^-3. The upper limit on the DM-inferred redshift is thus z ~ 0.26.

An early estimate (lower limit) of the apparent fluence of the event is ~ 18 Jy ms (corrected for attenuation of the primary beam in the RA direction, but not in the Dec direction), width ~ 2.19 ms, with a detection signal-to-noise ratio = 12.

The most likely position is RA = 06:09:23.7, DEC = -45:58:02, J2000, Galactic: Gl = 253.3915 deg, Gb = -26.0633 deg. The 95% confidence localisation arc is as follows: (RA, DEC) in (hours, deg)

6.152928 -48.822722
6.153536 -48.321778
6.154128 -47.820833
6.154706 -47.319889
6.155267 -46.818972
6.155814 -46.318028
6.156344 -45.817083
6.156864 -45.316139
6.157369 -44.815167
6.157861 -44.314222
6.158342 -43.813278
6.158808 -43.312333
6.159264 -42.811389

A formula describing the localisation arc is:
RA = 6.016988 – 4.092281e-3*(DEC – 45.967341) – 2.804353e-05*(DEC – 45.967341)**2
where RA is in hours, Dec is in deg, and is valid in the Dec range [-50.3,-41.6]

For the dispersion sweep, and the localisation plots, follow this link

Follow-up observations of the FRBs are encouraged.

UTMOST publishes timing results for over 200 pulsars

 

A major part of UTMOST’s time on sky is spent observing pulsars — the extremely dense remnants of supernova explosions. Discovered just over 50 years ago, pulsars allow us to make tests of fundamental physical theory (such as relativity), examine the properties of dense matter, and map the properties of the ionised gas in the Milky Way and other galaxies, just to name a few.

UTMOST has now published our first results for timing the pulses of over 200 pulsars in the Southern Sky. Led by PhD student Fabian Jankowski — who now has a postdoctoral position at Manchester University — the project timed over 400 pulsars. For 205 of these (8 of which are in binaries, and 4 of which are millisecond pulsars) we publish updated timing models, together with their flux densities, flux density variability, and pulse widths at 843 MHz, derived from observations spanning between 1.4 and 3 years.

Screenshot_2018-12-13_12-12-02
Over 200 individual pulses from the pulsar J0820-1350, seen in this stacked image, showing the special property of drifting “sub-pulses”. UTMOST is has detected single pulses from more than 100 different pulsars, although most do not show such exotic behaviour.

The paper, which has been accepted for publication in the Monthly Notices of the Royal Astronomical Society, is available on the astrophysics archive.

Magnetar XTE J1810-197 seen in radio outburst

A magnetar is a highly magnetic neutron star — formed when a star ends its life in a supernova explosion.  They are the most magnetic objects known in the Universe.

“XTE J1810-197” is one such magnetar – it was discovered in 2006 by an X-ray satellite, and was picked up at a wide range of radio wavelengths as well. It was the first magnetar found to also exhibited pulsar-like behaviour. Over the following year it faded gradually away and become more and more difficult to pick up.

On December 8th 2018, observers in the UK using the Lovell telescope picked it up strongly as part of regular monitoring looking for just such an event. The reported the sudden intense change in its radio emission as an Astronomer’s Telegram.

PhD student Marcus Lower used UTMOST to observe the magnetar on December 12th 2018, and picked it up very strongly — sufficiently so to see many individual pulses as the magnetar rotates every 5 or so seconds.

J1809-1943_121218

The pulse from the magnetar is seen clearly running vertically through the plot, which shows intriguing fine structure which is typical of magnetars.

An Astronomer’s Telegram reporting our detection of XTE J1810-197 at low radio frequencies can be found here.

 

 

 

 

Two new FRBs discovered by UTMOST

At UTC 2018-10-16-04:16:56.3, we found a bright fast radio burst (FRB181016) as part of the ongoing search program (UTMOST), at the Molonglo telescope.

A second, unrelated FRB (FRB181017) was found the following day at UTC 2018-10-17-10:24:37.4 (2018-10-17.4337662).

Molonglo is a 1.6 km long East-West array (Bailes et al 2017) and was operating in drift-scan mode with pointing centred on the meridian at the time of detection. Source localisation is excellent in Right Ascension (5 arcsec at 1-sigma) but poor in Declination (~1.2 deg at 1-sigma) (see Caleb et al 2017).

FRB181016 and FRB181017 were found during a blind FRB search programme in real-time using an automated GPU-accelerated/machine learning based pipeline and the raw voltages were recorded for offline processing. 

FRB180116 : The dispersion measure (DM) that maximizes the signal-to-noise ratio is: 1984 pc cm^-3. The DM estimate of NE2001 model is ~90 pc cm^-3, and YMW16 model is ~69 pc cm^-3 at the position of the FRB, resulting in an intergalactic excess of ~1900 pc cm^-3. The upper limit on the DM-inferred redshift is thus z ~ 1.8.

An early estimate (lower limit) of the event’s apparent fluence is ~ 70 Jy ms (corrected for attenuation of the primary beam in the RA direction, but not in the Dec direction), width ~ 6.88 ms, with a detected signal-to-noise ratio = 20.

The most likely position is RA = 15:46:20.5, DEC = -25:24:32, J2000, Galactic: Gl = 345.51 deg, Gb = 22.67 deg. The 95% confidence localisation arc is as follows: (RA, DEC) in (hours, deg)

15.769447 -28.263972
15.769986 -27.763111
15.770511 -27.262250
15.771028 -26.761389
15.771531 -26.260500
15.772025 -25.759639
15.772508 -25.258778
15.772983 -24.757917
15.773447 -24.257028
15.773900 -23.756167
15.774344 -23.255306
15.774781 -22.754417
15.775206 -22.253556

A formula describing the localisation arc is:

RA = 15.768768 – 1.106528e-3*(DEC – 25.409019) – 2.038129e-05*(DEC – 25.409019)**2

Where RA is in hours, Dec is in deg, and is valid in the Dec [-29.8,-21.1]

Screenshot_2018-10-17_15-44-23

Dedispersed dynamic spectrum of FRB181016. A small amount of residual RFI is seen in the left half of the plot at a frequency of ~840-842 MHz, and is not part of the FRB.

localisation

Localisation plot for FRB181016, with the center of the localisation arc marked by the green cross. The telescope boresight position is marked by the blue cross.

 

FRB180117 : The dispersion measure (DM) that maximizes the signal-to-noise ratio is: 240 pc cm^-3. The DM estimate of NE2001 model is ~38 pc cm^-3, and YMW16 model is ~27 pc cm^-3 at the position of the FRB, resulting in an intergalactic excess of ~205 pc cm^-3. The upper limit on the DM-inferred redshift is thus z ~ 0.2.

An early estimate (lower limit) of the event’s apparent fluence is ~ 95 Jy ms (corrected for attenuation of the primary beam in the RA direction, but not in the Dec direction), width ~ 2.6 ms, with a signal-to-noise ratio = 66.

The most likely position is RA =22:05:55 , DEC = -08:50:30, J2000, Galactic: Gl =  50.5 deg, Gb = -47.0 deg. The 95% confidence localisation arc is as follows: (RA, DEC) in (hours, deg)

22.098256 -11.698444
22.098303 -11.197472
22.098350 -10.696472
22.098403 -10.195500
22.098456 -9.694500
22.098511 -9.193528
22.098569 -8.692528
22.098631 -8.191556
22.098692 -7.690556
22.098756 -7.189583
22.098822 -6.688583
22.098892 -6.187611

A formula describing the localisation arc is:

RA = 22.101947 +2.654839e-4*(DEC -8.943028) + 4.195246e-06*(DEC -8.9430278)**2

Where RA is in hours, Dec is in deg, and is valid in the Dec [-13.20,-4.68]

frb181017

Dedispersed dynamic spectrum of FRB181017

FRB20181017_localisation_2610649 (1)

Localisation plot for FRB181017, with the center of the localisation arc marked by the green cross. The telescope boresight position is marked by the blue cross.

Follow-up observations of the FRBs are encouraged.

FRB180528 – UTMOST’s 6th FRB

 

On 2018-05-28-04:24:00.9 UTC (2018-05-28.18334375), UTMOST found a new FRB (FRB180528) as part of the ongoing search program at the Molonglo Radio Telescope (see Bailes et al. 2017, arxiv.org/abs/1708.09619). This is the sixth Molonglo FRB overall (See Atel #10867, ATel #10697 and Caleb et al. 2017, MNRAS, 468, 3746). The FRB was discovered in real time, and voltage capture was successfully triggered (see Farah et al 2018, https://arxiv.org/abs/1803.05697).

The dispersion measure (DM) of the FRB is: 899 pc cm^-3, which is substantially in excess of the Galactic DM as estimated by the NE2001 (www.nrl.navy.mil/rsd/RORF/ne2001/) model (~69 pc cm^-3). The upper limit on the DM-inferred redshift z is thus z~0.7. The S/N in the detection beam is 14, and a preliminary estimate of the event’s fluence is ~ 18 +/- 4 Jyms. This is a lower limit as the event’s position is poorly constrained in the North-South direction within the primary beam. The FRB’s estimated width (full width half power) is 1.3 ms.

Source localisation is excellent in the Right Ascension (~ 5 arcsec at 1-sigma) but poor in Declination (~1.2 deg at 1-sigma). The most likely position is RA = 06:38:48.7, DEC = -49:53:59, J2000, Galactic: Gl = 258.87 deg, Gb = -22.35 deg. The 95% confidence localisation arc is as follows: (RA, DEC) in (hours,deg)

6.642039 -53.065500
6.642700 -52.664778
6.643347 -52.264056
6.643978 -51.863306
6.644594 -51.462583
6.645197 -51.061833
6.645786 -50.661083
6.646361 -50.260361
6.646925 -49.859611
6.647475 -49.458861
6.648014 -49.058139
6.648542 -48.657389
6.649056 -48.256639
6.649561 -47.855889
6.650056 -47.455139
6.650539 -47.054389
6.651011 -46.653667

A formula describing the localisation arc is:

RA = 6.39652461344 – 0.00642068726059*(DEC – 49.8996671717) – 3.9200674396e-05*(DEC -49.8996671717)**2

Where RA is in hours, DEC is in deg, and is valid in the DEC range [-54,-46].

2018-05-30

Waterfall plot for FRB180528.

FRB20180528_localisation_860559

Localisation plot for FRB180528, with the center of the localisation arc marked by the green square. The telescope boresight position is marked by the blue square. The positions of 3 pulsars are also marked.

 

 

 

 

Remarkable time and frequency structure in FRB170827

UTMOST has made the first ever discovery of an FRB with an automated system, enabling remarkable time and frequency structures to be seen in the event.

Screenshot_2018-03-21_12-49-33

The FRB occurred on 27th Aug 2017. It was the first one discovered by Swinburne University of Technology PhD student Wael Farah — who had trained the computers on-site at Molonglo observatory to recognise FRB candidates from the many sources of interference radio telescopes see. His software works so quickly that he is able to save the full time and frequency resolution data on the event for later analysis. This feat has never been acheived before for an initial detection of an FRB.

The data reveal remarkable time and frequency structure in the FRB (as seen above). The event has a complex profile in time — with at least three peaks in the emission clearly visible. It also has striking striations and patchiness in the emission as a function of the observing frequency.

Where does this patchiness in the FRB’s spectrum arise? It can be partly explained by the effect the Milky Way gas has on a pulse coming from the distant universe — as we think is the case for FRBs. But this can’t be the whole story, as the striations in the spectrum are so narrow that something else must be affecting the pulse. One possibility is that the striations are intrinsic to the source itself and are telling us about the still unknown mechanism that makes FRBs. They might also arise in the Intergalactic Medium — the tenuous ionised gas that lies between galaxies — and telling us about the properties of this gas as the pulse traverses space over hundreds of millions of years before reaching Earth.

A paper describing this remarkable FRB has been submitted to Monthly Notices of the Royal Astronomical Society.

Congratulations to Wael Farah for this very fine achievement!

UTMOST welcomes Cherie Day and Vivek Gupta

UTMOST is delighted to welcome two new PhD students, Cherie Day  and Vivek Gupta.

Cherie Day joins us from the University of California Berkeley, where she did a B.A. in Astrophysics. She has been closely involved with testing the prototype HERA dish/feed combination and antenna design work for HYPERION, and worked on exoplanet transits with SOFIA .

Vivek has an M.Tech. degree in Engineering Physics from the Indian Institute of Technology (Banaras Hindu University) Varanasi, and has worked as an intern with Dr. Joseph Lazio at CalTech (June- August 2016), characterizing variations in the dispersion measures of several pulsars observed by NANOGrav in its 9 year data release.

Cherie and Vivek are both going to work on the UTMOST-2D project with Adam Deller, Chris Flynn and Matthew Bailes, to bring accurate localisation on the sky of Fast Radio Bursts to the UTMOST project.

A very warm welcome to both our new PhD students!