An official website of the United States government
Context.Fast radio bursts (FRBs) are very energetic pulses in the radio wavelengths that have an unknown physical origin. They can be used to study the intergalactic medium thanks to their dispersion measure (DM). The DM has several contributions that can be measured (or estimated), including the contribution from the host galaxy itself, DMhost. The DMhostis generally difficult to measure, thus limiting the use of FRBs as cosmological probes and our understanding of their physical origin(s). Aims.In this work we empirically estimated DMhostfor a sample of 12 galaxy hosts of well-localized FRBs at 0.11 < z < 0.53 using a direct method based solely on the properties of the host galaxies themselves, referred to as DMhostdirect. We also explored possible correlations between DMhostand some key global properties of galaxies. Methods.We used VLT/MUSE observations of the FRB hosts to estimate our empirical DMhostdirect. The method relies on estimating the DM contribution of both the FRB host galaxy’s interstellar medium (DMhostISM) and its halo (DMhosthalo) separately. For comparison purposes, we also provide an alternative indirect method for estimating DMhostbased on the Macquart relation (DMhostMacquart). Results.We find an average ⟨DMhost⟩ = 80 ± 11 pc cm−3with a standard deviation of 38 pc cm−3(in the rest frame) using our direct method, with a systematic uncertainty of ∼30%. This is larger than the typically used value of 50 pc cm−3but consistent within the uncertainties. We report positive correlations between DMhostand both the stellar masses and the star formation rates of their hosts galaxies. In contrast, we do not find any strong correlation between DMhostand the redshift nor the projected distances to the center of the FRB hosts. Finally, we do not find any strong correlation between DMhostdirectand DMhostMacquart, although the average values of the two are consistent within the uncertainties. Conclusions.Our reported correlations between DMhostdirectand stellar masses and/or the star formation rates of the galaxies could be used in future studies to improve the priors used in establishing DMhostfor individual FRBs. Similarly, such correlations and the lack of a strong redshift evolution can be used to constrain models for the progenitor of FRBs, for example by comparing them with theoretical models. However, the lack of correlation between DMhostdirectand DMhostdirectindicates that there may be contributions to the DM of FRBs not included in our DMhostdirectmodeling, for example large DMs from the immediate environment of the FRB progenitor and/or intervening large-scale structures not accounted for in DMhostMacquart.
more »
« less
Single Pulse Dispersion Measure of the Crab Pulsar
Abstract We investigate the use of bright single pulses from the Crab pulsar to determine separately the dispersion measure (DM) for the Main Pulse and Interpulse components. We develop two approaches using cross-correlation functions (CCFs). The first method computes the CCF of the total intensity of each of the 64 frequency channels with a reference channel and converts the time lag of maximum correlation into a DM. The second method separately computes the CCF between every pair of channels for each individual bright pulse and extracts an average DM from the distribution of all channel-pair DMs. Both methods allow the determination of the DM with a relative uncertainty of better than 10−5and provide robust estimates for the uncertainty of the best-fit value. We find differences in DM between the Main Pulse, the Low Frequency Interpulse, and the High Frequency Interpulse using both methods in a frequency range from 4 to 6 GHz. Earlier observations of the High Frequency Interpulse carried out by Hankins et al. (2016) resulted in DMHFIP–DMMPof 0.010 ± 0.016 pc cm−3. Our results indicate a DMHFIP–DMMPof 0.0127 ± 0.0011 pc cm−3(with DMcompbeing the DM value of the respective emission component), confirming earlier results with an independent method. During our studies we also find a relation between the brightness of single pulses in the High Frequency Interpulse and their DM. We also discuss the application of the developed methods on the identification of substructures in the case of Fast Radio Bursts.
more »
« less
- Award ID(s):
- 2020265
- PAR ID:
- 10369820
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 935
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 84
- Size(s):
- Article No. 84
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract I conducted a new search for dispersed radio pulses from the X-ray pulsar PSR J0537−6910 in the Large Magellanic Cloud (LMC) in a long (11.6 hr) archival 1.4 GHz Parkes search observation. I searched dispersion measures (DMs) between 0 and 10,000 pc cm−3and detected 49 pulses with a signal-to-noise ratio (S/N) greater than 7 at a wide range of DMs using the HEIMDALL and FETCH pulse detection and classification packages. All of the pulses were weak, with none having an S/N above 8.5. There was a significant excess of pulses observed in the DM range of the known pulsar population in the LMC, suggesting that these pulses may originate from LMC pulsars. Three repeat pulses, each having widths ≲1 ms, were detected in a single DM trial of 103.412 pc cm−3, which is in the LMC DM range. This is unlikely to occur by chance in a single DM trial in this search at the (marginally significant) 4.3σlevel. It remains unclear whether any of the detected pulses in the sample are from PSR J0537−6910 itself.more » « less
-
ABSTRACT We present four new fast radio bursts discovered in a search of the Parkes 70-cm pulsar survey data archive for dispersed single pulses and bursts. We searched dispersion measures (DMs) ranging between 0 and 5000 pc cm−3 with the HEIMDALL and FETCH detection and classification algorithms. All four of the fast radio bursts (FRBs) discovered have significantly larger widths (>50 ms) than almost all of the FRBs detected and catalogued to date. The large pulse widths are not dominated by interstellar scattering or dispersive smearing within channels. One of the FRBs has a DM of 3338 pc cm3, the largest measured for any FRB to date. These are also the first FRBs detected by any radio telescope so far, predating the Lorimer Burst by almost a decade. Our results suggest that pulsar survey archives remain important sources of previously undetected FRBs and that searches for FRBs on time-scales extending beyond ∼100 ms may reveal the presence of a larger population of wide-pulse FRBs.more » « less
-
Abstract The repeating fast radio burst FRB 20190520B is localized to a galaxy atz= 0.241, much closer than expected given its dispersion measure DM = 1205 ± 4 pc cm−3. Here we assess implications of the large DM and scattering observed from FRB 20190520B for the host galaxy’s plasma properties. A sample of 75 bursts detected with the Five-hundred-meter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delayτ(1.41 GHz) = 10.9 ± 1.5 ms, which is attributed to the host galaxy, and a mean scintillation bandwidth Δνd(1.41 GHz) = 0.21 ± 0.01 MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an Hαemission measure (galaxy frame) EMs= 620 pc cm−6× (T/104K)0.9, implying DMHαof order the value inferred from the FRB DM budget, pc cm−3for plasma temperatures greater than the typical value 104K. Combiningτand DMhyields a nominal constraint on the scattering amplification from the host galaxy , where describes turbulent density fluctuations andGrepresents the geometric leverage to scattering that depends on the location of the scattering material. For a two-screen scattering geometry whereτarises from the host galaxy and Δνdfrom the Milky Way, the implied distance between the FRB source and dominant scattering material is ≲100 pc. The host galaxy scattering and DM contributions support a novel technique for estimating FRB redshifts using theτ–DM relation, and are consistent with previous findings that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way.more » « less
-
Abstract Context.By providing information about the location of scattering material along the line of sight (LoS) to pulsars, scintillation arcs are a powerful tool for exploring the distribution of ionized material in the interstellar medium (ISM). Here, we present observations that probe the ionized ISM on scales of ∼0.001–30 au.Aims.We have surveyed pulsars for scintillation arcs in a relatively unbiased sample with DM < 100 pc cm−3. We present multifrequency observations of 22 low to moderate DM pulsars. Many of the 54 observations were also observed at another frequency within a few days.Methods.For all observations, we present dynamic spectra, autocorrelation functions, and secondary spectra. We analyze these data products to obtain scintillation bandwidths, pulse broadening times, and arc curvatures.Results.We detect definite or probable scintillation arcs in 19 of the 22 pulsars and 34 of the 54 observations, showing that scintillation arcs are a prevalent phenomenon. The arcs are better defined in low DM pulsars. We show that well-defined arcs do not directly imply anisotropy of scattering. Only the presence of reverse arclets and a deep valley along the delay axis, which occurs in about 20% of the pulsars in the sample, indicates substantial anisotropy of scattering.Conclusions.The survey demonstrates substantial patchiness of the ionized ISM on both astronomical-unit-size scales transverse to the LoS and on ∼100 pc scales along it. We see little evidence for distributed scattering along most lines of sight in the survey.more » « less
