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New Activity of Repeating FRB 121102

Andrew Siemion, who heads up the Breakthrough Listen initiative and is director of the Berkeley SETI Research Center, sent out a message to astronomers on August 29 noting recent activity from the radio source FRB 121102. The heightened activity had been noted by Breakthrough Listen postdoctoral researcher Vishal Gajjar. You’ll recall that Fast Radio Bursts (FRBs) are powerful but extremely short-duration radio pulses whose sources generally remain unknown.

What tags FRB 121102 as especially interesting is that it is the only FRB known to repeat. In fact, more than 150 bursts have been observed coming from the dwarf galaxy 3 billion light years from Earth that is thought to be its place of origin. And now we have heightened activity in the form of 15 new bursts, as the Astronomer’s Telegram notes:

These are the highest frequency and widest bandwidth detections of bursts from FRB 121102 obtained to-date. Additional fully calibrated full-Stokes analysis employing coherent dedispersion on raw voltage data is ongoing. These observations may indicate FRB 121102 is currently in a heightened activity state [Law et al. arXiv:1705.07553], and follow-on observations are encouraged, particularly at higher radio frequencies.

Image: A sequence of 14 of the 15 detected bursts illustrate their dispersed spectrum and extreme variability. The streaks across the colored energy plot are the bursts appearing at different times and different energies because of dispersion caused by 3 billion years of travel through intergalactic space. In the top frequency spectrum, the dispersion has been removed to show the 300 microsecond pulse spike. Capturing this diverse set of bursts was made possible by the broad bandwidth that can be processed by the Breakthrough Listen backend at the Green Bank Telescope. Credit: Breakthrough Listen.

Do FRBs mark the catastrophic end of some kind of astronomical object? If so, the fact that FRB 121102 repeats sets it apart from the rest. A rotating neutron star with an extremely strong magnetic field is also a possibility. There is also a SETI possibility: High-energy laser bursts from a distant civilization could be observable by us. Harvard’s Avi Loeb, working with Manasvi Lingam, discussed the prospects in a recent paper, working out their parameters in terms of engineering requirements if FRBs were indeed produced by an extraterrestrial civilization (see Fast Radio Bursts: Signature of Distant Technology?)

Vishal Gajjar used the Breakthrough Listen backend instrument at the Green Bank Telescope in West Virginia to observe the recent activity of FRB 121102. Says Gajjar:

“The extraordinary capabilities of the backend receiver, which is able to record several gigahertz of bandwidth at a time, split into billions of individual channels, enable a new view of the frequency spectrum of FRBs, and should shed additional light on the processes giving rise to FRB emission.”

Indeed. According to this UC Berkeley news release, the backend instrument accumulated 400 terabytes of data in a five hour period on Saturday, August 26, with observations extending across the 4 to 8 GHz frequency band. What the team was looking for were the signatures of short pulses with a dispersion — a delay as a function of the frequency — that is caused by gas between the source and the Earth. Remember that these beams have been traveling for a long time. As Berkeley astronomer Steve Croft notes, they left their host galaxy when life on our planet consisted of nothing more than single-celled organisms.

The current active state of FRB 121102 could prove quite useful, allowing us to measure this source of FRBs at the highest precision yet. The 15 new pulses Gajjar observed show emissions at higher frequencies than have previously been seen. The brightest FRB 121102 emission occurred around 7 GHz. We’re a long way from being able to figure out what causes FRBs, but the Breakthrough Listen instrumentation is giving us the best look at the frequency spectrum of this powerful source yet.

The results of this work will be presented in an upcoming paper. The paper exploring artificial origins for FRBs is Loeb and Lingam, “Fast Radio Bursts from Extragalactic Light Sails,” Astrophysical Journal Letters Volume 837, Number 2 (8 March 2017). Preprint) available.


{ 37 comments… add one }
  • Tom Mazanec August 31, 2017, 11:35

    The new Analog Magazine has an Alternate View article by Dr. Cramer on FRBs as beams for solar sail starships.

    • Paul Gilster August 31, 2017, 13:58

      Had not seen that. Thanks!

      • Harry R Ray September 5, 2017, 9:43

        Paul Gilster: A picture is worth a thousand words! I have searched the internet over and over and I have NEVER come across an ACTUAL IMAGE of the “host” dwarf galaxy. Is there one? If so, I would appreciate it if you would post a website where it can be accessed on this blog in the comments section. Does it even have an NGS id number? I am specifically looking for a wide field image that has many other objects in it. The reason for this, is that SEVERAL studies have come to the colclusion that the REAL CAUSE of FRB’s is VARIABLE STARS IN OUR OWN GALAXY! All of these studies have rather CONTRIVED explanations for the FRBS dispersion measures, but a few have been peer reviewed and published, so some people in the astronomical community feel that these explanations STILL PASS MUSTER despite the contrivity.

    • Giulio Prisco September 1, 2017, 0:37

      Thanks, a very good overview by the indispensable Cramer!

      I archived Cramer’s text here to have a permanent url:

  • Steve August 31, 2017, 23:33

    I’m curious why none of the news articles are pointing out the fact that if the FRB’s came from a star, there would be x-rays accompanying the bursts, but no x-rays were detected in these bursts. I think that’s a pretty significant detail that’s being left out.


    • andy September 2, 2017, 7:38

      So, a scaled-up version of the Crab Nebula is ruled out but the Crab is not a precise analogue to the type of system being proposed. Judging by section 4.4 of that paper, a neutron star origin remains plausible given that the X-rays may be absorbed by supernova ejecta. Or it could be a massive black hole, a scaled-down version of a radio-loud low-luminosity active galactic nucleus.

  • Hary R Ray September 1, 2017, 9:35

    OK. We now have a bandwidth spectrum ranging from 783 MHz(UTMOST) to 7GHz for these FRB’s. Someone should start checking out FRB 121102 at wavelengths GREATER than 10 GHz PRONTO! NOW: PURE SPECULATION. The paper regarding the Green Bank observations of Boyajian’s Star has yet to come out. A PRELIMINARY report(most likely based on REALTIME data reduction)indicated NEGATIVE results for microwave emission SPIKES in the frequency range most likely used to power lightsails. However FRB’s are NOT observable in realtime doe to their ULTRASHORT durations. Should any show up after the data have been FULLY ANALYSED, think of the headlines THAT would generate!

    • Harry R Ray September 7, 2017, 9:48

      ANOTHER FRB from FRB 121102 detected on August 31 by ARTSApertif Radio Transient System somewhere BETWEEN 1250 and 1550 MHz.

  • Spaceman September 1, 2017, 12:21

    Hi Paul,

    Thank you for posting this interesting information on FRBs. Have FRBs been observed coming from all parts of the celestial sphere?

    • Paul Gilster September 1, 2017, 12:34

      I don’t think we’ve had enough of them to talk about their distribution across the celestial sphere. But now that we’re on the lookout for them, we should get a much better assessment.

      • DJ Kaplan September 1, 2017, 16:19

        I have yet to read about them coming from our galaxy yet.

  • Robin Datta September 1, 2017, 22:06

    If they were from an intelligent source, then that intelligence had the technology 3 billion(!) years ago. Lord knows what might have happened to them in the interim.

    • Vince September 2, 2017, 11:32

      Excellent point! One wonders if they would have survived the subsequent 3 billion years, or where/how far they might have traveled since then. Any civilization capable of surviving such huge geologic/stellar time scales would probably have transcended physical being into some kind of computer/conscious state of being.

      • ljk September 6, 2017, 9:29

        If they have survived they would be like gods to us.

  • Vince September 2, 2017, 0:42

    Very intriguing. The repeating is interesting. Hopefully it will enable us to pinpoint the source. I do find it odd that news reports all seem to dismiss a potential alien origin. At this point nothing can be ruled out, and a phenomenon 3 billion light years away certainly deserves kinda of speculation. What if it is some type of higky advanced civilization, but they are so far apart from us in space and time that we simply have yet to recognize the signs of artificial intelligence? Anyway, it may very well be a natural source such as magnetars, but I’m not prepared to rule anything out until we get much more conclusive evidence about the source of the repeated FRB’s. Great article, as always, btw.

  • andy September 2, 2017, 8:54

    If the exoplanet community is having a debate on whether the use of the term “Earth-like” is misleading the public, perhaps the FRB community needs to have a similar debate about whether talking about aliens/SETI in every story about FRBs is also misleading. There’s definitely something interesting going on but from what I can see, invoking aliens as an explanation is wildly premature.

  • Vince September 2, 2017, 11:28

    Until there is hard evidence, no explanation, whether alien or other, cannot be ruled out. Of course people will speculate aliens, it’s our natural curiosity to do so. Hopefully with more repeating FRB’s from that source, we’ll get answers. At this stage I think it’s highly premature to give one theory more credence than any other. A 3 billion light years distant FRB repeator deserves careful thoughtful scrutiny. Also, any alien technology that ancient and far away might take some digging to interpret, particularly if it were highly advanced. It might be largely beyond our recognition if say, from a Type 3 civilization

    • Ron S. September 2, 2017, 16:38

      “it’s highly premature to give one theory more credence than any other”

      This is where you make a mistake. You are, in effect, arguing for the application of the principle of indifference to set the (Bayesian) prior probability. Except we have a preponderance of data that similar phenomena are indeed natural in origin, and we have zero evidence of ETI.

      The prior probability therefore strongly favors a natural origin. Not a certainty of course but a sensible opening position.

      • David September 2, 2017, 22:05

        According to Cramer these look more like an artificially produced wave than the natural ones. I am not a radio wave expert and would like to hear more about why he or others think that. Maybe Paul could explain it.

        • Paul Gilster September 3, 2017, 12:41

          Looking at the Cramer article, what I see is this:

          “There is no known physical phenomenon that can account for these bizarre characteristics. It is not physically plausible that such a vast release of energy in the radio domain would be “pure” and not accompanied by electromagnetic radiation in other forms. This raises an important question: If no natural phenomenon can make an FRB, what does that leave?”

          In other words, I think he’s simply saying that FRBs remain a mystery, and that one possibility is an artificial origin. He also points to the Loeb and Lingam paper, which said this:

          “…astrophysical explosions tend to be single bursts, while artificial beacons can repeat.”

          But I don’t see any other pointers toward artificiality. So we need to keep pulling in data to resolve the matter.

        • Ron S. September 3, 2017, 13:13

          Cramer’s construction (or interpretation) to see the phenomenon as alien is quite contrived in my view. That is, first assume it’s alien propulsion and then come up with a supposed technology that fits the available data. Of course it is similarly possible to construct a hypothesis that fits a novel natural cause. But he doesn’t attempt this, perhaps preferring to indulge himself.

          It is also interesting to note that if this is evidence of alien propulsion that multiple civilizations distributed across the universe ~3 Gyr ago came up with the very same propulsion technology, and subsequently stopped using it at around the same epoch. Otherwise the data would show evidence of more recent events. That inclines me to further speculate that the alien hypothesis is highly suspect.

          There are indeed natural phenomena with a broadband radio signature and little in the way of higher energy photons. All it takes is charges accelerated in a magnetic field (synchroton radiation), quite common in stellar atmospheres includes energetic high mass stars and accretion disks of denser objects. Not this particular signature, but I don’t see why not. Many phenomena with a distinct EM signature (e.g. GRB) are associated with a fairly well defined epoch in the universe’s early history.

          • Michael T September 4, 2017, 7:23

            Maybe there’s a partial explanation for the seeming 3 Gy clustering, even IF it’s the work of ETs.

            Cramer quotes work estimating a 700 year interval between sail beam observations from within our galaxy.

            If it’s that rare, then observations will tend to favour detections of distant, ancient signals because many more distant galaxies will be in the field of view (or conversely will be ‘lucky’ enough to include a beam pointed towards us).

            As these sources seem to be very powerful, this effect might he more noticeable than for intrinsically weaker sugnals, that would simply be undetectable at great distances.

            Mike T

          • andy September 4, 2017, 16:08

            I’m basically in agreement with Ron S here. A lot of the “aliens” hypotheses that get advanced don’t seem to go too much into the consequences of what’s being proposed. E.g. supposing this thing is beamed interstellar propulsion, then there are going to be a lot more events than the ones we see where the beam does not happen to be pointing at the Earth. How frequent does that make interstellar civilisations, and what is the likelihood that Earth remains unvisited for 4.5 billion years under such a scenario? Supposing we were to build our own interstellar craft powered by intergalactic beacon and travel to Alpha Centauri or some other local star system, what kind of effect does such a beam have at a range of a few parsecs? Etc. etc.

  • Vince September 2, 2017, 19:29

    I just favor keeping an open mind until we have definitive evidence, that’s all. It may very well be an exotic, heretofore unknown natural phenomena producing the repeating FRB, and that will be a very important scientific discovery. It’s worth pointing out too, that, regardless of whether this particular phenomena turns out to be ETI or not, a highly advanced, Type II or III civilization may be so beyond us in evolutionary/technology that their signals, in whatever form, could very well be essentially incomprehensible to us, at least initially. I’m just excited to find out what is causing the FRB’s, regardless of whether they are natural or artificial.

  • Digbijoy September 3, 2017, 1:48

    A latest report by experts from Arizona who analyzed Tabby’s star in UV and in mid IR, show that the dimming has been sharper in short blue wavelengths than in IR, indicating it is most likely fine dust rather than an alien megastructure


    • Harry R Ray September 11, 2017, 9:58

      IT’S OFFICIAL: The Alien Megastructure is dead!!! BUT: Long live the Alien Microstructure??? Swift and Spitzer data to be released in a paper by Meng et al CONFIRMS the RECENT data collected by Boyajian et al that EXTREMELY FINE MICROSCOPIC DUST(?) is the ONLY CAUSE of the flux differentials at Boyajian’s Star! This dust can ONLY be in the form of a VERY ASYMETRIC CIRCUMSTELLAR RING at a still yet to be determined distance from Boyajian’s Star(i.e., the interstellar medium theory is ALSO dead). VERY IMPORTANT: They have ABSOLUTELY NO IDEA WHAT CAUSED A RING(ACTUALLY: a TAURUS of some kind is actually a BETTER DESCRIPTION of this phenomenon)with such asymetric patterns and long-term fading! A whole lot more work is needed to resolve all of the remaining conundrums!

  • Jose Moutinho September 3, 2017, 13:18

    The radiotelescope of Molongo, Australia, has detected 4 FRBs from another source.See the UTMOST site.

  • DJ Kaplan September 5, 2017, 16:45

    Well, in terms of artificial sources, we will likely NEVER know the intent and actual origin of any ETI source of any signal, unless one of them happens to be encoded with a signal that we can understand.

    The only metric of whether a signal of this sort may be ETI sourced, is the degree to which our “natural” explanations become more and more absurd. If we are forced to turn the laws of nature inside-out and on its head in order to avoid an ETI explanation, then the ETI explanation begins to have a little more weight. We will still likely never understand its origin or purpose.

    • Ron S. September 5, 2017, 20:53

      “The only metric…”

      Not true. Unless a signal has been deliberately encoded to mimic noise or some commonplace background natural source there are numerous signal processing and statistical methods to determine that a signal is likely to be artificial rather than natural. Indeed they are used in terrestrial applications. Some you might be able to guess.

      I would also caution you against using a “god of the gaps” style of argument. Just because an astrophysical explanation remains elusive or is far fetched is a poor argument in favor of ETI.

      • DJ Kaplan September 6, 2017, 14:02

        Point taken.
        However, consider if, as, and when we make our first certain discovery of verifiable ET signal. Expect us to begin going back over all our data again, perhaps a little more willing to allow the ETI explanation to receive equal weight with other explanations.

  • ljk September 6, 2017, 9:33

    Time to read His Master’s Voice by Stanislaw Lem again…


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