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Register a new userReconciling the 16.35-day period of FRB 20180916B with jet precession
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A repeating fast radio burst (FRB), FRB 20180916B (hereafter FRB 180916), was reported to have a 16.35-day period. This period might be related to a precession period. In this paper, we investigate two precession models to explain the periodic activity of FRB 180916. In both models, the radio emission of FRB 180916 is produced by a precessing jet. For the first disk-driven jet precession model, an extremely low viscous parameter (i.e., the dimensionless viscosity parameter $alpha lesssim 10^{-8}$) is required to explain the precession of FRB 180916, which implies its implausibility. For the second tidal force-driven jet precession model, we consider a compact binary consists of a neutron star/black hole and a white dwarf; the white dwarf fills its Roche lobe and mass transfer occurs. Due to the misalignment between the disk and orbital plane, the tidal force of the white dwarf can drive jet precession. We show that the relevant precession periods are several days to hundreds of days, depending on the specific accretion rates and component masses. The duration of FRB 180916 generation in the binary with extremely high accretion rate will be several thousand years.
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Fast Radio Burst FRB 20180916B in its host galaxy SDSS J015800.28+654253.0 at 149 Mpc is by far the closest-known FRB with a robust host galaxy association. The source also exhibits a 16.35-day period in its bursting. Here we present optical and infrared imaging as well as integral field spectroscopy observations of FRB 20180916B with the WFC3 camera on the Hubble Space Telescope and the MEGARA spectrograph on the 10.4-m Gran Telescopio Canarias. The 60-90 milliarcsecond (mas) resolution of the Hubble imaging, along with the previous 2.3-mas localization of FRB 20180916B, allow us to probe its environment with a 30-60 pc resolution. We constrain any point-like star-formation or HII region at the location of FRB 20180916B to have an H$alpha$ luminosity $L_mathrm{Halpha} lesssim 10^{37},mathrm{erg,s^{-1}}$ and, correspondingly, constrain the local star-formation rate to be $lesssim10^{-4},mathrm{M_odot,yr^{-1}}$. The constraint on H$alpha$ suggests that possible stellar companions to FRB 20180916B should be of a cooler, less massive spectral type than O6V. FRB 20180916B is 250 pc away (in projected distance) from the brightest pixel of the nearest young stellar clump, which is $sim380$,pc in size (full-width at half maximum). With the typical projected velocities of pulsars, magnetars, or neutron stars in binaries (60-750 km s$^{-1}$), FRB 20180916B would need 800 kyr to 7 Myr to traverse the observed distance from its presumed birth site. This timescale is inconsistent with the active ages of magnetars ($lesssim10$ kyr). Rather, the inferred age and observed separation are compatible with the ages of high-mass X-ray binaries and gamma-ray binaries, and their separations from the nearest OB associations.
Fast radio bursts (FRBs) are bright, coherent, short-duration radio transients of as-yet unknown extragalactic origin. FRBs exhibit a wide variety of spectral, temporal and polarimetric properties, which can unveil clues into their emission physics and propagation effects in the local medium. Here we present the high-time-resolution (down to 1 $mu$s) polarimetric properties of four 1.7-GHz bursts from the repeating FRB 20180916B, which were detected in voltage data during observations with the European VLBI Network (EVN). We observe a range of emission timescales spanning three orders of magnitude, with the shortest component width reaching 3-4 $mu$s (below which we are limited by scattering). This is the shortest timescale measured in any FRB, to date. We demonstrate that all four bursts are highly linearly polarised ($gtrsim 80%$), show no evidence for significant circular polarisation ($lesssim 15%$), and exhibit a constant polarisation position angle (PPA) during and between bursts. On short timescales ($lesssim 100$ $mu$s), however, there appear to be subtle (few degree) PPA variations across the burst profiles. These observational results are most naturally explained in an FRB model where the emission is magnetospheric in origin, as opposed to models where the emission originates at larger distances in a relativistic shock.
FRB 20180916B is a well-studied repeating fast radio burst source. Its proximity (~150 Mpc), along with detailed studies of the bursts, have revealed many clues about its nature -- including a 16.3-day periodicity in its activity. Here we report on the detection of 18 bursts using LOFAR at 110-188 MHz, by far the lowest-frequency detections of any FRB to date. Some bursts are seen down to the lowest-observed frequency of 110 MHz, suggesting that their spectra extend even lower. These observations provide an order-of-magnitude stronger constraint on the optical depth due to free-free absorption in the sources local environment. The absence of circular polarization and nearly flat polarization angle curves are consistent with burst properties seen at 300-1700 MHz. Compared with higher frequencies, the larger burst widths (~40-160 ms at 150 MHz) and lower linear polarization fractions are likely due to scattering. We find ~2-3 rad/m^2 variations in the Faraday rotation measure that may be correlated with the activity cycle of the source. We compare the LOFAR burst arrival times to those of 38 previously published and 22 newly detected bursts from the uGMRT (200-450 MHz) and CHIME/FRB (400-800 MHz). Simultaneous observations show 5 CHIME/FRB bursts when no emission is detected by LOFAR. We find that the burst activity is systematically delayed towards lower frequencies by ~3 days from 600 MHz to 150 MHz. We discuss these results in the context of a model in which FRB 20180916B is an interacting binary system featuring a neutron star and high-mass stellar companion.
We present a reanalysis of GW151226, the second binary black hole merger discovered by the LIGO-Virgo Collaboration. Previous analysis showed that the best-fit waveform for this event corresponded to the merger of a $sim 14 , M_odot$ black hole with a $sim 7.5 , M_odot$ companion. In this work, we perform parameter estimation using a waveform model that includes the effects of orbital precession and higher-order radiative multipoles, and find that the mass and spin parameters of GW151226 have bimodal posterior distributions. The two modes are separated in mass ratio, $q$: the high-$q$ mode ($0.4 lesssim q < 1$) is consistent with the results reported in the literature. On the other hand, the low-$q$ mode ($q lesssim 0.4$), which describes a binary with component masses of $sim 29 , M_odot$ and $sim , 4.3 M_odot$, is new. The low-$q$ mode has several interesting properties: (a) the secondary black hole mass may fall in the lower mass gap of astrophysical black hole population; and (b) orbital precession is driven by the primary black hole spin, which has a dimensionless magnitude as large as $sim 0.88$ and is tilted away from the orbital angular momentum at an angle of $sim 47^circ$. The new low-$q$ mode has a log likelihood that is about six points higher than that of the high-$q$ mode, and can therefore affect the astrophysical interpretation of GW151226. Crucially, we show that the low-$q$ mode disappears if we neglect either higher multipoles or orbital precession in the parameter estimation. More generally, this work highlights how incorporating additional physical effects into waveform models used in parameter estimations can alter the interpretation of gravitational-wave sources.
The quasar B0605-085 (OH 010) shows a hint for probable periodical variability in the radio total flux-density light curves. We study the possible periodicity of B0605-085 in the total flux-density, spectra and opacity changes in order to compare it with jet kinematics on parsec scales. We have analyzed archival total flux-density variability at ten frequencies (408 MHz, 4.8 GHz, 6.7 GHz, 8 GHz, 10.7 GHz, 14.5 GHz, 22 GHz, 37 GHz, 90 GHz, and 230 GHz) together with the archival high-resolution very long baseline interferometry data at 15 GHz from the MOJAVE monitoring campaign. Using the Fourier transform and discrete autocorrelation methods we have searched for periods in the total flux-density light curves. In addition, spectral evolution and changes of the opacity have been analyzed. We found a period in multi-frequency total flux-density light curves of 7.9+-0.5 yrs. Moreover, a quasi-stationary jet component C1 follows a prominent helical path on a similar time scale of 8 years. We have also found that the average instantaneous speeds of the jet components show a clear helical pattern along the jet with a characteristic scale of 3 mas. Taking into account average speeds of jet components, this scale corresponds to a time scale of about 7.7 years. Jet precession can explain the helical path of the quasi-stationary jet component C1 and the periodical modulation of the total flux-density light curves. We have fitted a precession model to the trajectory of the jet component C1, with a viewing angle phi=2.6+-2.2 degrees, aperture angle of the precession cone Omega=23.9+-1.9 degrees and fixed precession period (in the observers frame) P = 7.9 yrs.
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