Stars

Repeating Fast Radio Burst (FRB)

Here's some of their characteristics :


• According to SETI, a criterion for ET signal is narrow band width of about 1 Hz because nature cannot produce such kind of EM waves (see "Search for ET"). The ET origin is ruled out, since the FRB band width is much wider.


• The measured radio frequency has a range from 1400 to 400 MHz. The component frequencies of each burst are delayed by different amounts of time due to dispersion. The amount is larger than expected for a source inside the Milky Way and consistent with propagation through an ionized plasma. The lower frequencies measured by CHIME may allow closer inspection of the source since frequencies in such range suffered less scattering by the inter-galactic medium.



	Dispersion of the radio signal is measured by : As shown by the "Table of Bursts", the observed DM of some 40 FRBs has a range of 375 - 1909 parsec/cm3. These data are compatible with a theoretical model of supernova remnant having a range of DM from 104 pc/cm3 to zero as the ember of the explosion fading away (Figure 08-26c). Simulations of the FRBs as young stars in the spiral arms showed that the signals would need to pass through more matter to scatter as they did. This suggests that they may be located in the dense environments such as inside a supernova remnant (SNR) like the Crab Nebula.
Figure 08-26c Dispersion Measure [view large image]	See "Radio Wave Bursts from Space Keep Hitting Earth and We Don’t Know Why".

• Distribution of the FRBs is isotropic consistent with extragalactic origin. In addition, the first repeating FRB 121102 has been pin-pointed to a galaxy (Figure 08-26e) and appears to be very polarized.


• Detection of repeating FRB eliminates models involving cataclysmic events for the source. The second repeating FRB 180814 has a red shift up to z = 0.1 at ~ 1.5 billion lyr away (corresponding to about 400 Mpc).


• FRB 180814 was found to be repeating five times within a period of 2 months.


• Since the pulse lasts for only few milliseconds, the size of the source should be < c x 10^-3 ~ 30 km. This is similar to the size of neutron stars.



		The energy delivered in a pulse of FRB can be estimated from a "Table of Bursts", which indicates the Peak Flux to be about 1 Jy = 10-23 ergs/sec-cm2-Hz. Taking the duration, frequency range and distance of FRB 180814, the energy packed in the pulse would be about 1032 ergs; while the most powerful magnetar
Figure 08-26d Radio Telescopes [view large image]	Figure 08-26e FRB 121102	SGR180620 releases 1047 ergs in the explosion. The energy released in supernova is even more in the range of 1051 ergs (Figure 08-26f).

		A search of astronomical objects reveals that the "magnetar" seems to fit the above description quite well. The match is based on the size, location, polarization, and amount of energy released. A magnetar is a type of neutron star with very strong magnetic field ~ 1015 Gauss. They can be produced in two different ways. One type appears to be a transient object in supernova explosion. It exists only several 100 seconds before collapsing into a black hole
Figure 08-26f Magnetar, Transient [view large image]	Figure 08-26g Magnetar [view large image]	(Figure 08-26f). Thus, it can never be a repeating FRB.

	The other kind is produced in a process similar to the production of pulsar (Figure 08-26g). The difference is its very fast spinning rate generating the very strong magnet field, which decays in about 10000 years. Extremely violent starquakes are believed to be induced when the intense magnetic fields fracture the crusts, Figure 08-27h depicts the sequence of events which could lead up to FRB instead of GRB in some cases. Similar to Earthquakes, Starquake can be repeating called aftershocks.
Figure 08-26h Starquake [view large image]	The Figure below shows the CHIME measurements of the repeating FRB 180814.

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