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تسجيل مستخدم جديدTesting the Young Neutron Star Scenario with Persistent Radio Emission Associated with FRB 121102
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Recently a repeating fast radio burst (FRB) 121102 has been confirmed to be an extragalactic event and a persistent radio counterpart has been identified. While other possibilities are not ruled out, the emission properties are broadly consistent with Murase et al. (2016) that theoretically proposed quasi-steady radio emission as a counterpart of both FRBs and pulsar-driven supernovae. Here we constrain the model parameters of such a young neutron star scenario for FRB 121102. If the associated supernova has a conventional ejecta mass of $M_{rm ej}gtrsim{rm a few} M_odot$, a neutron star with an age of $t_{rm age} sim 10-100 rm yrs$, an initial spin period of $P_{i} lesssim$ a few ms, and a dipole magnetic field of $B_{rm dip} lesssim {rm a few} times 10^{13} rm G$ can be compatible with the observations. However, in this case, the magnetically-powered scenario may be favored as an FRB energy source because of the efficiency problem in the rotation-powered scenario. On the other hand, if the associated supernova is an ultra-stripped one or the neutron star is born by the accretion-induced collapse with $M_{rm ej} sim 0.1 M_odot$, a younger neutron star with $t_{rm age} sim 1-10$ yrs can be the persistent radio source and might produce FRBs with the spin-down power. These possibilities can be distinguished by the decline rate of the quasi-steady radio counterpart.
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Fast radio bursts (FRBs) are millisecond-duration, extragalactic radio flashes of unknown physical origin. FRB 121102, the only known repeating FRB source, has been localized to a star-forming region in a dwarf galaxy at redshift z = 0.193, and is sp
atially coincident with a compact, persistent radio source. The origin of the bursts, the nature of the persistent source, and the properties of the local environment are still debated. Here we present bursts that show ~100% linearly polarized emission at a very high and variable Faraday rotation measure in the source frame: RM_src = +1.46 x 10^5 rad m^-2 and +1.33 x 10^5 rad m^-2 at epochs separated by 7 months, in addition to narrow (< 30 mus) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, while the short burst durations argue for a neutron star origin. Such large rotation measures have, until now, only been observed in the vicinities of massive black holes (M_BH > 10^4 MSun). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole. The bursts may thus come from a neutron star in such an environment. However, the observed properties may also be explainable in other models, such as a highly magnetized wind nebula or supernova remnant surrounding a young neutron star.
The localization of the repeating fast radio burst (FRB), FRB 121102, suggests that it is associated with a persistent radio-luminous compact source in the FRB host galaxy. Using the FIRST radio catalog, I present a search for luminous persistent sou
rces in nearby galaxies, with radio luminosities >10% of the FRB 121102 persistent source luminosity. The galaxy sample contains about 30% of the total galaxy g-band luminosity within <108 Mpc, in a footprint of 10,600 deg^2. After rejecting sources likely due to active galactic nuclei activity or background sources, I remain with 11 candidates that are presumably associated with galactic disks or star formation regions. At least some of these candidates are likely to be due to chance alignment. In addition, I find 85 sources within 1 of galactic nuclei. Assuming the radio persistent sources are not related to galactic nuclei and that they follow the galaxy g-band light, the 11 sources imply a 95% confidence upper limit on the space density of luminous persistent sources of <5x10^-5 Mpc^-3, and that at any given time only a small fraction of galaxies host a radio luminous persistent source (<10^-3 L_*^-1). Assuming persistent sources life time of 100 yr, this implies a birth rate of <5x10^-7 yr^-1 Mpc^-3. Given the FRB volumetric rate, and assuming that all FRBs repeat and are associated with persistent radio sources, this sets a lower limit on the rate of FRB events per persistent source of >0.8 yr^-1. I argue that these 11 candidates are good targets for FRB searches and I estimate the FRB event rate from these candidates.
We report the detection of a single burst from the first-discovered repeating Fast Radio Burst source, FRB 121102, with CHIME/FRB, which operates in the frequency band 400-800 MHz. The detected burst occurred on 2018 November 19 and its emission exte
nds down to at least 600 MHz, the lowest frequency detection of this source yet. The burst, detected with a significance of 23.7$sigma$, has fluence 12$pm$3 Jy ms and shows complex time and frequency morphology. The 34 ms width of the burst is the largest seen for this object at any frequency. We find evidence of sub-burst structure that drifts downward in frequency at a rate of -3.9$pm$0.2 MHz ms$^{-1}$. Our best fit tentatively suggests a dispersion measure of 563.6$pm$0.5 pc cm$^{-3}$, which is ${approx}$1% higher than previously measured values. We set an upper limit on the scattering time at 500 MHz of 9.6 ms, which is consistent with expectations from the extrapolation from higher frequency data. We have exposure to the position of FRB 121102 for a total of 11.3 hrs within the FWHM of the synthesized beams at 600 MHz from 2018 July 25 to 2019 February 25. We estimate on the basis of this single event an average burst rate for FRB 121102 of 0.1-10 per day in the 400-800 MHz band for a median fluence threshold of 7 Jy ms in the stated time interval.
Fast radio bursts (FRBs) are bright flashes observed typically at GHz frequencies with millisecond duration, whose origin is likely extragalactic. Their nature remains mysterious, motivating searches for counterparts at other wavelengths. FRB 121102
is so far the only source known to repeatedly emit FRBs and is associated with a host galaxy at redshift $z simeq 0.193$. We conducted simultaneous observations of FRB 121102 with the Arecibo and MAGIC telescopes during several epochs in 2016--2017. This allowed searches for millisecond-timescale burst emission in very-high-energy (VHE) gamma rays as well as the optical band. While a total of five FRBs were detected during these observations, no VHE emission was detected, neither of a persistent nature nor burst-like associated with the FRBs. The average integral flux upper limits above 100 GeV at 95% confidence level are $6.6 times 10^{-12}~mathrm{photons cm^{-2} s^{-1}}$ (corresponding to luminosity $L_{rm VHE} lesssim 10^{45}~mathrm{erg s^{-1}}$) over the entire observation period, and $1.2 times 10^{-7}~ mathrm{photons cm^{-2} s^{-1}}$ ($L_{rm VHE} lesssim 10^{49}~mathrm{erg s^{-1}}$) over the total duration of the five FRBs. We constrain the optical U-band flux to be below 8.6 mJy at 5-$sigma$ level for 1-ms intervals around the FRB arrival times. A bright burst with U-band flux $29~mathrm{mJy}$ and duration $sim 12$ ms was detected 4.3 s before the arrival of one FRB. However, the probability of spuriously detecting such a signal within the sampled time space is 1.5% (2.2 $sigma$, post-trial), i.e. consistent with the expected background. We discuss the implications of the obtained upper limits for constraining FRB models.
We present optical, near- and mid-infrared imaging of the host galaxy of FRB 121102 with the Gemini North telescope, the Hubble Space Telescope and the Spitzer Space Telescope. The FRB 121102 host galaxy is resolved, revealing a bright star forming r
egion located in the outskirts of the irregular, low-metallicity dwarf galaxy. The star forming region has a half-light radius of 0.68 kpc (0.20 arcsec), encompassing the projected location of the compact (<0.7 pc), persistent radio source that is associated with FRB 121102. The half-light diameter of the dwarf galaxy is 5 to 7 kpc, and broadband spectral energy distribution fitting indicates that it has a total stellar mass of M*~10^8 Msun. The metallicity of the host galaxy is low, 12+log10 ([O/H])=8.0+-0.1. The properties of the host galaxy of FRB 121102 are comparable to those of extreme emission line galaxies, also known to host hydrogen-poor superluminous supernovae and long-duration gamma-ray bursts. The projected location of FRB 121102 within the star forming region supports the proposed connection of FRBs with newly born neutron stars or magnetars.
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