Fast radio bursts:
puzzles and
fundamental physics
SERGEI POPOV (ICTP, TRIESTE)
Radiotransients
1507.00729, 1411.1067
Many different types of transient sources
are already detected at radio wavelengths.
However, detection of very short
and non-repeating flares of unknown sources
without identification at other bands
is a very complicated task.
Rotating Radio Transients (RRATs) –
millisecond radio bursts from neutron stars, have
been identified in 2006.
In 2007 the first example of a new class
of millisecond radio transients
have been announced:
the first extragalactic millisecond radio burst.
Millisecond extragalactic radio burstsScience318,777(2007)
Discovered in 2007.
Origin - unknown.
One of the most interesting discoveries in the XXIc.
No coincident bursts in other wavelengths.
No source identification.
[About the difference between RRATs and FRB
see 1512.02513]
Large dispersion measure.
If dispersion is due to intergalactic medium
then radio luminosity is ~1043 erg/s.
The first event
Discovered at Parkes
by Duncan Lorimer et al.
~30-40 Jy, < 5 msec.
3 degrees from
Small Magellanic cloud
1511.02870
Science318,777(2007)
Millisecond radio bursts – definite at last
1307.1628
2007 The first burst.
2011 Perytons. Doubts
2012 The second event. Galactic plane. Unclear.
2013 – Four more!
Rate ~few thousand per sky per day confirmed
A new type of astronomical phenomena
with unknown origin is established.
In this paper the final notation –
Fast Radio Bursts – was proposed.
FRBs. Different hypotheses
Millisecond extragalactic radio bursts of that intensity without immediate identification with other bursts
have not been predicted by earlier studies.
Since 2007 many hypotheses have been proposed.
A real flow started in late summer of 2013 after the paper by Thornton et al.
• Magnetars
• Super radio pulsars
• Evaporating black holes
bestiary.ca/
• Coalescing NSs
• Coalescing WDs
• Coalescing NS+BH
• Supramassive NSs
• Deconfinement of a NS
• Axion clouds and NSs
• Cosmic strings
• Charged BHs
• NS collapse
Neutron stars and exotics
R
A neutron star has mass ~solar and
radius ~10 km.
This gives free fall velocity v=(2GM/R)1/2 ~0.5 c
Free fall time scale t=R/v< 0.1 msec
Thus, it is easy to get very short events.
The same is true for BHs.
Absence of counterparts and, in general,
shortage of data allows to propose
very exotics scenarios for explanation
of Fast Radio Bursts.
So, model of FRBs can divided into two parts:
neutron stars and exotics.
In addition, NSs have strong magnetic fields
and they are known sources of strong short radio bursts.
A review on FRB models: 1810.05836. The on-line catalogue of proposed theories: frbtheorycat.org
Cosmic strings
Superconducting strings
Vachaspati 0802.0711
Also, the model of cosmic strings in application to FRBs
Was discussed in several other papers: 1110.1631, 1409.5516, ….
Strings can behave in a peculiar way.
In particular, cusps – where strings are bended,
can be formed, and they can move with superluminal velocity.
Such points on strings might become strong
sources of electro-magnetic radiation.
This is the base of this model of FRBs.
Primordial black holes
Keane et al. 1206.4135
Cannot be extragalactic due to low luminosity.
Might be visible from <~200 pc.
Predicted years ago (Rees 1977).
Evaporation in models with extra-dimensions
can provide larger energy release,
but still distance are not more than ~300 pc.
Can be accompanied by a burst of hard radiation
(if the source is near-by).
Supernova and pulsar
Shock wave after a SN in a close HMXB
can interact with the NS magnetosphere
forming a magnetotail.
Reconnection in the magnetotail
may result in a short radio flare
(Egorov, Postnov arXiv: 0810.2219).
So, radio bursts might be always accompanied by a supernova.
Coalescence of neutron stars
Might be accompanied by a GW burst.
There are several scenarios in which
strong radio transient appear as a result
of neutron star coalescence
(Lipunov, Panchenko; Hansen, Lyutikov;
Postnov, Pshirkov).
In application to FRBs the first paper is
Totani (1307.4985).
http://www.int.washington.edu/PROGRAMS/14-2a/
Easy to obtain rapid rotation and strong magnetic field.
But there are many uncertainties.
White dwarf coalescence
Is accompanied by a SN Ia and, probably, X-ray emission due to fall back.
Kashiyamaetal.1307.7708
http://cerncourier.com/cws/article/cern/31855
Energy release is due to magnetic field lines reconnection at the polar cap.
This also allows to obtain necessary duration of the burst.
Supramassive neutron stars
“blitzar”
http://www.astro.ru.nl/~falcke/PR/blitzar/
Falcke, Rezzola 1307.1409
Neutron star can be stable against
collapse due to rapid rotation.
Such situation can appear after
NS-NS coalescence, accretion, or
immediately after a NS birth.
Collapse can happen, as it was
suggested, thousand years after
the NS formation.
Collapse can be accompanied
by a SN-like event, short GRB and
a GW burst.
Double-peaked events can also
appear in this scenario.
White holes (from black)
1409.4031
We do not know exactly, how BHs evaporate.
In loop quantum gravity this can include a white hole
formation on late stages of the process.
BH evaporation was proposed as a possible
explanation for FRBs. In this case a shock wave
interacts with external magnetic field.
In the case of a WH formation emission is related
to quantum gravity effects.
http://www.nature.com/news/quantum-bounce-could-make-black-holes-explode-1.15573
Initial calculations have not predict radio emission.
But the authors of 1409.4031 suggest that
there are many uncertainties in the model,
and radio emission is also possible.
Wavelength corresponds to the size of the hole.
Axions
1411.3900, 1410.4323, 1512.06245, 1707.04827
Axions are dark matter particle candidates
For FRBs axions miniclusters are important.
They are formed in young universe.
Typical mass – similar to a large asteroid.
Typical size – solar radius.
A cluster can be more compact due to formation of Bose-Einstein condensate.
Then, the size can be ~few hundred km, this corresponds to expected size of
emitting region in FRB sources (duration multiplied by the velocity of light).
Mass of such compact cluster can be about the mass of the Earth!
When such cluster flies into a NS magnetosphere then due to the
Primakoff effect axions start to be converted into photons.
Thus, a flare of electromagnetic radiation is generated.
Deconfinement – formation of a quark star
http://astrobites.org
1506.08645
During its evolution the whole NS or its part
can experience deconfinement:
normal matter is converted into quarks.
This is accompanied by huge energy release.
Also there attempts to reproduce FRB in the model of so-called “quark nova” (1505.08147).
Falling asteroids
1502.05171,seealso1512.06519
For explanation of FRBs researchers actively used
mechanisms proposed previously (~30-40 years ago)
for cosmic GRBs. Here is one of them.
Free-fall time scale in the vicinity of a NS is ~ few msec.
Energy release can be explained by potential energy.
After a massive asteroid falls onto a NS
an outflowing envelope is formed.
This can result in a radio and X-ray flare.
On modification to explain repeating FRBs see 1603.08207.
On evaporation of asteroid by PSRs see 1605.05746.
Magnetar model
1401.6674
The first idea of possible connection between FRBs and magnetars
has been proposed already in 2007: arXiv 0710.2006.
This hypothesis has been based on rate and energetics considerations, mainly.
FRB bursts might be related to giant flares of magnetars
Later this approach was developed by Lyubarsky (2014).
In the model by Lyubarsky the radio burst happens
due to synchrotron maser emission
after interaction between a magnetic pulse after
a giant flare of a magnetar with surrounding nebula.
The first burst detected in real time
Absence of any transients
at other wavelengths
closed the models of a SN
and a GRB as a soiurce
of FRBs.
1412.0342
In may 2014 for the first time a burst was detected in real time.
This allowed to trigger searches of an afterglow in other energy ranges.
Localization
Radius of uncertainty circle ~10 arcmin
Usually FRBs are seen just in one beam.
Repeating bursts
1603.00581
Repeating bursts are detected firstly from FRB 121102.
The source was found at Arecibo.
Initially 10 events reported.
Rate ~ 3/hour
Weak bursts (<0.02-0.3 Jy)
Variable spectral parameters.
Unclear if it is a unique source,
or it is a close relative of other FRBs.
VLA, Arecibo and all the rest
1705.07553
During periods of activity rate is few per hour.
Simultaneous detection with Arecibo, VLA
and other instruments.
The source is also detected at 4-8 GHz
and polarization is measured (1801.03965).
Host galaxy of the FRB
1701.01098, 1701.01099, 1701.01100
Thanks to precise localization of FRB 121102
it became possible to identify a host galaxy.
This a dwarf galaxy with high starformation rate
at z~0.2 (~1 Gpc).
H-alpha emission in the host galaxy
of FRB 121102
1705.04693
Coincidence of the FRB position
with a H-alpha region is an argument
in favour of models involving
young neutron stars.
H-alpha region can also contribute
to the observed dispersion measure.
Keck observations.
Rectangles show the areas observed at Subaru.
Early ideas
Exotics: strings, axions,
white holes, etc. Catastrophic events:
SN, GRBs, coalescence, …
Mainstream:
magnetars and pulsarsCompact objects + smth.:
asteroids on NSs, etc.
Magnetars or/and Pulsars
Giant flares:
Rate
Energetics
Time scale
Giant pulses:
Energetics
Time scale
Typical
distances
can be
~1 Gpc
Typical
distances
might be
~100 MpcCan belong
to young
population
(collapse) or
old population
(coalescence)
Might belong
to young
population
Problems with exact
emission mechanism
Can repeat.
No counterparts.
Problems with
efficiency
(too high, see
Lyutikov 2017)
Problems with
polarization, but see
Beloborodov 2019
SGR 1935+2154
Astronomers’ Telegram: 13681-13769
GCN: 27666-27669
Discovered in 2014 (see, Israel et al. 2016).
P=3.25 sec
Distance ~7-12 kpc (2005.03517)
Intermediate flare (Kozlova et l. 2016)
Activated in April 2020.
Finally, on April, 28 2020
A simultaneous burst
in radio and X/gamma
was detected.
CHIME data
2005.10324
STARE2 data
2005.10828
Konus-Wind data
2005.11178
AGILE data
Comparison of SGR 1935 detection with monitoring of the repeating source FRB 180916 (at 149 Mpc)
2005.12164
Insight-HXMT data and FAST
2005.11071, see results of a new data reduction in 2302.00176 2005.11479
FRB associated vs. others
2006.11358
CHIME
http://chime.phas.ubc.ca/
CHIME – burst per day!
1601.02444
CHIME catalogue
2106.04352
www.chime-frb.ca/catalog
Second large sample of CHIME repeaters
2301.08762
Database
https://www.herta-experiment.org/frbstats2208.03508
January 2023
Estimates of the rate
1611.00458
587 per day with flux above 1 Jy.
Black solid line –
new data.
Dotted lines –
95% uncertainty.
Grey line is plotted under assumption
that index is the Log N – Log S
distribution is equal to 3/2.
See also 1612.00896
Rate and luminosity function
2003.04848
Periodicity in FRB bursts
2001.10275
FRB 180916.J0158+65
CHIME (+Effelsberg)
The source is localized in a near-by massive spiral galaxy.
Period ~16.35 days
157 day periodicity of FRB 121102
2003.03596, see also 2008.03461
A binary system?
2002.01920
Precession?
2002.05752 2002.04595
Realistic values of oblateness
due to strong magnetic field
can explain the 16-day precission.
About triaxial precession see
2107.12874, 2107.12911.
Ultra-long spin periods?
2003.12509
E.g., fall-back can help to obtain long spin periods,
as in the case of the source in RCW 103 (6.7 hours).
Or, enhanced spin down due to winds can be at work.
Or, kick can help to spin-down the NS.
Second localization of a FRB
1906.11476
ASKAP
FRB 180924
non-repeating
16 Jy
DM~360
linear polarization
RM~14
Localization
~0.12 arcsec
z=0.32
Massive lenticular
or early-type
Third localization
1907.01542
DSA-10 antenna
1.4 GHz
FRB 190523
non-repeating
DM=760
Massive galaxy
z=0.66
SFR<~1/3 of Galactic
Fifth localization
2001.02222
FRB180916.J0158+65
Repeator
Near-by spiral galaxy
See data on the immediate (60 pc) vicinity of the source
in 2011.03257
FRB from M81?
2103.01295
CHIME
Low DM~83
Even a globular cluster in M81?
2105.11445
Analysis of 23 hosts
2302.05465
6 repeaters and 17 one-off
21 out of 23 are starforming
FRBs
Exotics, etc.:
strings, PBHs,
GRBs, SN, WDs,
white holes, …
Neutron stars
Exotics:
coalescence,
deconfinement,
supramassive NSs,
axion clouds,
falling asteroids …
Known types
of transients:
Erot vs. Emag
Magnetar flares: Emag
High-energy flare
Normal magnetars:
core collapse SN
“Exotic” magnetars:
coalescence, AIC, ….
rate,
no counterparts
repeaters
SGR 1935
host galaxies
Giant pulses: Erot
No counterparts
All proposed models are good,
but mostly not for FRBs.
Many types of transients predicted.
Promising for future.
Now we know who, we do not know how
Origin of magnetars
“Normal”:
single core-collapse
Coalescence
(NS+NS, NS+WD, WD+WD).
Muraseetal.2016
Magnetosphere or outer shocks?
Zhang 2020 (Nature)
Synchrotron maser
The first detailed magnetar model
with emission mechanism
was developed by Lyubarsky (2014).
Synchrotron maser emission
(Alsop & Arons 1988; Hoshino & Arons 1991).
To obtain high frequency it is necessary to
have a relativistic (magnetized) shock.
In FRB models emission is typically
generated due to interaction with
a nebula at ~1013-1016 cm from the NS.
See a review, e.g. in
Lyubarsky 2021
Numerous models with synchrotron masers
Beloborodov 2020
Anisotropic synchrotron maser emission at the
reverse shock in the flare’s weakly magnetized matter
Khangulyan et al. 2022
A burst produces a blast wave. A shock appears due to
interaction of the blast and the wind. At the shock the
maser mechanism is operating.
Magnetospheric processes
About early magnetospheric models see e.g. Katz (2014), Kumar et al. (2017).
Yangetal.2020
Electron-positron pairs bunches produce
coherent curvature radiation
Perturbations of a NS magnetic field (including reconnection)
might result in generation of waves, particle production and
acceleration.
At the end, this can produce a burst of radio emission.
Early models were based on analogy with radio pulsars,
i.e. rotational energy losses
(Pen & Connor 2015; Cordes & Wasserman 2016).
New models usually assume magnetic energy dissipation.
Magnetospheric models can face difficulties:
- total energy budget (e.g., size of bunches)
- propagation from the inner magnetosphere (external plasma)
- unobserved correlations, e.g. Luminosity-Frequency
- narrow spectra
Variety of models: some examples
Lyubarsky 2020Lu et al. 2020Lyutikov 2020, 2021
Alfven waves+
two-stream instability
Relativistic magnetic reconnection
in the outer magnetosphere of the magnetar
Free electron laser.
Bunches of particles oscillate and
emit coherently
Polarization variability from burst to burst
Luo et al. 2020
FRB 180301
On other hand,
in the case of
FRB 121102
the polarization
angle was stable
for many months
(Michilli et al. 2018)
Periodicity in the burst structure
Andersen et al. 2022
CHIME
FRB191221
single burst
217 msec
Might be a strong argument in favour of magnetospheric models, see 2211.07669
A microsecond periodicity?
2105.10987
FRB 20200120E. The one in a GC in M81
2-3 microsecond structure
Narrow radio spectra (of repeaters)
Pastor-Marazuela et al. 2020, see also Sand et al. 2022 Kumar et al. 2020
No coincident bursts at significantly different frequencies for FRB 20180916B
.
A very narrow spectra of FRB 20190711A
Frequency drift
Sand et al. 2020
Sad trombone ~5% of CHIME bursts demonstrate complex structure downward drifting (Pleunis et al. 2021)
Rapid variations
Nimmo et al. 2021
FRB 20180916B
Effelsberg telescope
1.7 GHz
Constant PA
in and between
the bursts
(with slight variations
at the shortest time scale
<100 microseconds).
Single components of bursts
down to 3-4 microseconds.
The Galactic magnetar burst was peculiar
Ridnaia et al. 2021
Correlation of
high-energy properties
of the burst with
radio can be
in favour of
magnetospheric models.
But Oct. 2022
bursts may be do not
support the uniqueness
of radio+gamma bursts.
Delay between radio and X/gamma-rays
In radio the pulses appear a little bit earlier
(Mereghetti et al. 2020; Li et al. 2021).
2302.00176
This peculiarity also can be
explained in both frameworks
(Lyutikov 2021; Yuan et al. 2020).
Tau_p1 – delay between
X-ray and FRB
for the first pulse
Tau_p2 – delay between
X-ray and FRB
for the secondpulse
Repeaters vs. (yet?)non-repeaters
r- spectral running
Pleunis et al. 2021
Search for lensing (and PBHs limit)
2204.06001, 2204.06014
Idea:
direct detection of a second image
of the same FRB in the time domain
CHIME observation
The expected lensing rate
as a function of the lens mass
for the sightline toward
FRB 20191219F.
Where do we stand?
FRBs are due to strongly magnetized NSs
Ridnaiaetal.2021
SGR 1935
Magnetic energy is released
A coherent emission
mechanism might operate
Still, it is not for sure that all FRBs are explained by a single model and that all exotics is ruled out. Review: 2212.03972
Conclusions and hopes
• Counterparts
• Spin periodicity
• More Galactic events
• Delay between hard and radio emission
• Clear differences between events
from sources of (presumably) different origin
• Magnetars are THE sources
(small contributions from other types
of sources are not excluded, yet)
• Two main frameworks are formulated
(relativistic shocks and magnetospheres)
• Both explain many observed features
• Both have some problems
• Both cannot be proved or falsified, right now
• Differences between repeaters
and non-repeaters
• Different hosts – different origin
See a set of reviews (Caleb, Keane; Lyubarsky; Nicastro et al.; Pilia) in a special issue on FRBs in Universe (2021).
arXiv: 2210.14268
Test of equivalence principle
1512.07670
See also 1509.00150, 1601.04558
Also FRBs can be used to test
Lorentz-invariance,
especially, if a FRB is
accompanied by a gamma-ray flare.
Improvements on the limit of parameter γ
1602.07643
Independent distance evaluation allows to use FRBs
to put constraints on the post-Newtonian parameter γ
(если эта идентификация верна) позволяют улучшить предел на параметр γ.
CHIME data and equivalence principle
2111.11451, see also 2111.11447
Limits on the photon mass
1602.07835
See also 1602.09135
Now this result is just of historic interest,
as it was shown that association of the source
with a proposed host galaxy is spurious.
New limits on photon mass
1701.03097
FRB121102
Total DM
Total-Galactic
Total-Galactic-IGM
More results and better limits
1907.00583
Limits with 9 localized bursts
2006.09680
Photon mass constraint from
17 well-localized FRBs
2301.12103