arXiv subjects

Adam T. Deller

Publications and source records attributed to Adam T. Deller.

At least 55 records · Page 3Linked to original sources

arXiv2021

Dissecting the Local Environment of FRB 190608 in the Spiral Arm of its Host Galaxy

We present a high-resolution analysis of the host galaxy of fast radio burst (FRB)~190608, an SB(r)c galaxy at $z=0.11778$ (hereafter HG 190608), to dissect its local environment and its contributions to the FRB properties. Our Hubble Space Telescope Wide Field Camera 3 ultraviolet and visible light image reveals that the subarcsecond localization of FRB~190608 is coincident with a knot of star-formation ($Σ_{\rm SFR} = 1.5 \times 10^{-2}~ M_{\odot} \, \rm \, yr^{-1} \, kpc^{-2}$) in the northwest spiral arm of HG~190608. Using H$β$ emission present in our Keck Cosmic Web Imager integral field spectrum of the galaxy with a surface brightness of $μ_{\rm Hβ}= \mathrm{(3.36\pm0.21)\times10^{-17}\;erg\;s^{-1}\;cm^{-2}\;arcsec^{-2}}$, we infer an extinction-corrected H$α$ surface brightness and compute a dispersion measure (DM) from the interstellar medium of HG 190608 of $\rm DM_{\rm Host,ISM} = 94 \pm 38~ \;pc\;cm^{-3}$. The galaxy rotates with a circular velocity $v_{\rm circ} = \rm 141 \pm 8~ km\;s^{-1}$ at an inclination $i_{\mathrm{gas}} = 37 \pm 3^\circ$, giving a dynamical mass $M_{\rm halo}^{\rm dyn} \approx 10^{11.96 \pm 0.08}~M_{\odot}$. This implies a halo contribution to the DM of $\rm DM_{\rm Host,Halo}= \rm 55\pm25 \;pc\;cm^{-3}$ subject to assumptions on the density profile and fraction of baryons retained. From the galaxy rotation curve, we infer a bar-induced pattern speed of $Ω_p=34\pm 6\;\mathrm{km\;s^{-1}\;kpc^{-1}}$ using linear resonance theory. We then calculate the maximum time since star-formation for a progenitor using the furthest distance to the arm's leading edge within the localization, and find $t_{\mathrm{enc}} = 21_{-6}^{+25}$ Myr. Unlike previous high-resolution studies of FRB environments, we find no evidence of disturbed morphology, emission, or kinematics for FRB 190608.

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arXiv2021

Characterizing the FRB host galaxy population and its connection to transients in the local and extragalactic Universe

We present the localization and host galaxies of one repeating and two apparently non-repeating Fast Radio Bursts. FRB20180301A was detected and localized with the Karl G. Jansky Very Large Array to a star-forming galaxy at $z=0.3304$. FRB20191228A, and FRB20200906A were detected and localized by the Australian Square Kilometre Array Pathfinder to host galaxies at $z=0.2430$ and $z=0.3688$, respectively. We combine these with 13 other well-localized FRBs in the literature, and analyze the host galaxy properties. We find no significant differences in the host properties of repeating and apparently non-repeating FRBs. FRB hosts are moderately star-forming, with masses slightly offset from the star-forming main-sequence. Star formation and low-ionization nuclear emission-line region (LINER) emission are major sources of ionization in FRB host galaxies, with the former dominant in repeating FRB hosts. FRB hosts do not track stellar mass and star formation as seen in field galaxies (more than 95% confidence). FRBs are rare in massive red galaxies, suggesting that progenitor formation channels are not solely dominated by delayed channels which lag star formation by Gigayears. The global properties of FRB hosts are indistinguishable from core-collapse supernovae (CCSNe) and short gamma-ray bursts (SGRBs) hosts, and the spatial offset (from galaxy centers) of FRBs is mostly inconsistent with that of the Galactic neutron star population (95% confidence). The spatial offsets of FRBs (normalized to the galaxy effective radius) also differ from those of globular clusters (GCs) in late- and early-type galaxies with 95% confidence.

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arXiv2021

Quasi-Simultaneous Radio/X-ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125 During its Low-Luminosity Accretion-Disc State

3FGL J1544.6-1125 is a candidate transitional millisecond pulsar (tMSP). Similar to the well-established tMSPs - PSR J1023+0038, IGR J18245-2452, and XSS J12270-4859 -- 3FGL J1544.6-1125 shows $γ$-ray emission and discrete X-ray "low" and "high" modes during its low-luminosity accretion-disk state. Coordinated radio/X-ray observations of PSR J1023+0038 in its current low-luminosity accretion-disk state showed rapidly variable radio continuum emission-possibly originating from a compact, self-absorbed jet, the "propellering" of accretion material, and/or pulsar moding. 3FGL J1544.6-1125 is currently the only other (candidate) tMSP system in this state, and can be studied to see whether tMSPs are typically radio-loud compared to other neutron star binaries. In this work, we present a quasi-simultaneous Very Large Array and Swift radio/X-ray campaign on 3FGL J1544.6-1125. We detect 10 GHz radio emission varying in flux density from $47.7 \pm 6.0$ $μ$Jy down to $\sim$15 $μ$Jy (3$σ$ upper limit) at four epochs spanning three weeks. At the brightest epoch, the radio luminosity is $L_{5 GHz}$ $= (2.17 \pm 0.17) \times 10^{27}$ erg s$^{-1}$ for a quasi-simultaneous X-ray luminosity $L_{2-10 keV}$ $= (4.32 \pm 0.23) \times 10^{33}$ erg s$^{-1}$ (for an assumed distance of 3.8 kpc). These luminosities are close to those of PSR J1023+0038, and the results strengthen the case that 3FGL J1544.6-1125 is a tMSP showing similar phenomenology to PSR J1023+0038.

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arXiv2021

The Panchromatic Afterglow of GW170817: The full uniform dataset, modeling, comparison with previous results and implications

We present the full panchromatic afterglow light curve data of GW170817, including new radio data as well as archival optical and X-ray data, between 0.5 and 940 days post-merger. By compiling all archival data, and reprocessing a subset of it, we have evaluated the impact of differences in data processing or flux determination methods used by different groups, and attempted to mitigate these differences to provide a more uniform dataset. Simple power-law fits to the uniform afterglow light curve indicate a $t^{0.86\pm0.04}$ rise, a $t^{-1.92\pm0.12}$ decline, and a peak occurring at $155\pm4$ days. The afterglow is optically thin throughout its evolution, consistent with a single spectral index ($-0.584\pm0.002$) across all epochs. This gives a precise and updated estimate of the electron power-law index, $p=2.168\pm0.004$. By studying the diffuse X-ray emission from the host galaxy, we place a conservative upper limit on the hot ionized ISM density, $<$0.01 cm$^{-3}$, consistent with previous afterglow studies. Using the late-time afterglow data we rule out any long-lived neutron star remnant having magnetic field strength between 10$^{10.4}$ G and 10$^{16}$ G. Our fits to the afterglow data using an analytical model that includes VLBI proper motion from Mooley et al. (2018), and a structured jet model that ignores the proper motion, indicates that the proper motion measurement needs to be considered while seeking an accurate estimate of the viewing angle.

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arXiv2021

Chronicling the Host Galaxy Properties of the Remarkable Repeating FRB 20201124A

We present the Australian Square Kilometre Array Pathfinder (ASKAP) localization and follow-up observations of the host galaxy of the repeating fast radio burst (FRB) source, FRB20201124A, the fifth such extragalactic repeating FRB with an identified host. From spectroscopic observations using the 6.5-m MMT Observatory, we derive a redshift of $z=0.0979 \pm 0.0001$, a star formation rate inferred from H$α$ emission of SFR(H$α$) $\approx 2.1 M_{\odot}$ yr$^{-1}$, and a gas-phase metallicity of 12+log(O/H)$\approx 9.0$. By jointly modeling the 12-filter optical-mid-infrared (MIR) photometry and spectroscopy of the host, we infer a median stellar mass of $\approx 2 \times 10^{10} M_{\odot}$, internal dust extinction of $A_V\approx 1-1.5$ mag, and a mass-weighted stellar population age of $\approx 5-6$ Gyr. Connecting these data to the radio and X-ray observations, we cannot reconcile the broad-band behavior with strong AGN activity and instead attribute the dominant source of persistent radio emission to star formation, likely originating from the circumnuclear region of the host. The modeling also indicates a hot dust component contributing to the MIR luminosity at a level of $\approx 10-30\%$. We model the host galaxy's star formation and mass assembly histories, finding that the host assembled $>90\%$ of its mass by 1 Gyr ago and exhibited a fairly constant SFR for most of its existence, with no clear evidence of past star-burst activity.

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arXiv2021

Gaia EDR3 parallaxes of type I X-ray bursters and their implications on the models of type I X-ray bursts: a generic approach to the Gaia parallax zero-point and its uncertainty

Light curves of photospheric radius expansion (PRE) bursts, a subset of type I X-ray bursts, have been used as standard candles to estimate the "nominal PRE distances" for 63% of PRE bursters (bursters), assuming PRE burst emission is spherically symmetric. Model-independent geometric parallaxes of bursters provide a valuable chance to test models of PRE bursts (PRE models), and can be provided in some cases by Gaia astrometry of the donor stars in bursters. We searched for counterparts to 115 known bursters in the Gaia Early Data Release 3, and confirmed 4 bursters with Gaia counterparts that have detected (>3sigma, prior to zero-point correction) parallaxes. We describe a generic approach to the Gaia parallax zero point as well as its uncertainty using an ensemble of Gaia quasars individually determined for each target. Assuming the spherically symmetric PRE model is correct, we refined the resultant nominal PRE distances of three bursters (i.e. Cen X-4, Cyg X-2 and 4U 0919-54), and put constraints on their compositions of the nuclear fuel powering the bursts. Finally, we describe a method for testing the correctness of the spherically symmetric PRE model using parallax measurements, and provide preliminary results.

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arXiv2021

Astrometric accuracy of snapshot Fast Radio Burst localisations with ASKAP

The recent increase in well-localised fast radio bursts (FRBs) has facilitated in-depth studies of global FRB host properties, the source circumburst medium, and the potential impacts of these environments on the burst properties. The Australian Square Kilometre Array Pathfinder (ASKAP) has localised 11 FRBs with sub-arcsecond to arcsecond precision, leading to sub-galaxy localisation regions in some cases and those covering much of the host galaxy in others. The method used to astrometrically register the FRB image frame for ASKAP, in order to align it with images taken at other wavelengths, is currently limited by the brightness of continuum sources detected in the short-duration ('snapshot') voltage data captured by the Commensal Real-Time ASKAP Fast Transients (CRAFT) software correlator, which are used to correct for any frame offsets due to imperfect calibration solutions and estimate the accuracy of any required correction. In this paper, we use dedicated observations of bright, compact radio sources in ASKAP's low- and mid-frequency bands to investigate the typical astrometric accuracy of the positions obtained using this so-called 'snapshot' technique. Having captured these data with both the CRAFT software and ASKAP hardware correlators, we also compare the offset distributions obtained from both data products to estimate a typical offset between the image frames resulting from the differing processing paths, laying the groundwork for future use of the longer-duration, higher signal-to-noise ratio data recorded by the hardware correlator. We find typical offsets between the two frames of $\sim 0.6$ and $\sim 0.3$ arcsec in the low- and mid-band data, respectively, for both RA and Dec. We also find reasonable agreement between our offset distributions and those of the published FRBs.

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arXiv2021

A High-Resolution View of Fast Radio Burst Host Environments

We present Hubble Space Telescope (HST/WFC3) ultraviolet and infrared observations of eight fast radio burst (FRB) host galaxies with sub-arcsecond localizations, including the hosts of three known repeating FRBs. We quantify their spatial distributions and locations with respect to their host galaxy light distributions, finding that they occur at moderate host normalized-offsets of 1.4 $r_e$ ([0.6,2.1] $r_e$; 68% interval), occur on fainter regions of their hosts in terms of IR light, but overall trace the radial distribution of IR light in their galaxies. The FRBs in our tested distribution do not clearly trace the distributions of any other transient population with known progenitors, and are statistically distinct from the locations of LGRBs, H-poor SLSNe, SGRBs, and Ca-rich transients. We further find that most FRBs are not in regions of elevated local star formation rate and stellar mass surface densities in comparison to the mean global values of their hosts. We also place upper limits to the IR flux at the FRB positions of $m_{\rm IR}\gtrsim\!24.8-27.6$~AB~mag, constraining both satellite and background galaxies to luminosities well below the host luminosity of FRB121102. We find that 5/8 FRB hosts exhibit clear spiral arm features in IR light, and that the positions of all well-localized FRBs located in such hosts are consistent with their spiral arms, although not on their brightest regions. Our results do not strongly support the primary progenitor channel of FRBs being connected either with the most massive (stripped-envelope) stars, or with events which require kicks and long delay times (neutron star mergers).

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arXiv2021

Clumpy Star Formation and AGN Activity in Dwarf-Dwarf Galaxy Merger Mrk 709

Nearby, low-metallicity dwarf starburst galaxies hosting active galactic nuclei (AGNs) offer the best local analogs to study the early evolution of galaxies and their supermassive black holes (BHs). Here we present a detailed multi-wavelength investigation of star formation and BH activity in the low-metallicity dwarf-dwarf galaxy merger Mrk 709. Using Hubble Space Telescope H$α$ and continuum imaging combined with Keck spectroscopy, we determine that the two dwarf galaxies are likely in the early stages of a merger (i.e., their first pass) and discover a spectacular $\sim 10$ kpc-long string of young massive star clusters ($t \lesssim 10$ Myr; $M_\star \gtrsim 10^5~M_\odot$) between the galaxies triggered by the interaction. We find that the southern galaxy, Mrk 709 S, is undergoing a clumpy mode of star formation resembling that seen in high-redshift galaxies, with multiple young clusters/clumps having stellar masses between $10^7$ and $10^8~M_\odot$. Furthermore, we present additional evidence for a low-luminosity AGN in Mrk 709 S (first identified by Reines et al. 2014 (arXiv:1405.0278) using radio and X-ray observations), including the detection of the coronal [Fe X] optical emission line. The work presented here provides a unique glimpse into processes key to hierarchical galaxy formation and BH growth in the early Universe.

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arXiv2021

Discovery of UV millisecond pulsations and moding in the low mass X-ray binary state of transitional millisecond pulsar J1023+0038

PSR J1023+0038 is a rapidly-spinning neutron star with a low-mass-binary companion that switches between a radio pulsar and low-luminosity disk state. In 2013, it transitioned to its current disk state accompanied by brightening at all observed wavelengths. In this state, PSR J1023+0038 now shows optical and X-ray pulsations and abrupt X-ray luminosity switches between discrete 'low' and 'high' modes. Continuum radio emission, denoting an outflow, is also present and brightens during the X-ray low modes. Here, we present a simultaneous optical, ultraviolet (UV) and X-ray campaign comprising Kepler ($400-800$ nm), Hubble Space Telescope ($180-280$ nm), XMM-Newton ($0.3-10$ keV) and NuSTAR ($3 - 79$ keV). We demonstrate that low and high luminosity modes in the UV band are strictly simultaneous with the X-ray modes and change the UV brightness by a factor of $\sim25$\% on top of a much brighter persistent UV component. We find strong evidence for UV pulsations (pulse fraction of $0.82\pm0.19$\%) in the high-mode, with a similar waveform as the X-ray pulsations making it the first known UV millisecond pulsar. Lastly, we find that the optical mode changes occur synchronously with the UV/X-ray mode changes, but optical modes are inverted compared to the higher frequencies. There appear to be two broad-band emission components: one from radio to near-infrared/optical that is brighter when the second component from optical to hard X-rays is dimmer (and vice-versa). We suggest that these components trace switches between accretion into the neutron star magnetosphere (high-energy high-mode) versus ejection of material (low-energy high-mode). Lastly, we propose that optical/UV/X-ray pulsations can arise from a shocked accretion flow channeled by the neutron star's magnetic field.

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arXiv2021

Probabilistic Association of Transients to their Hosts (PATH)

We introduce a new method to estimate the probability that an extragalactic transient source is associated with a candidate host galaxy. This approach relies solely on simple observables: sky coordinates and their uncertainties, galaxy fluxes and angular sizes. The formalism invokes Bayes' rule to calculate the posterior probability P(O_i|x) from the galaxy prior P(O), observables x, and an assumed model for the true distribution of transients in/around their host galaxies. Using simulated transients placed in the well-studied COSMOS field, we consider several agnostic and physically motivated priors and offset distributions to explore the method sensitivity. We then apply the methodology to the set of 13~fast radio bursts (FRBs) localized with an uncertainty of several arcseconds. Our methodology finds nine of these are securely associated to a single host galaxy, P(O_i|x)>0.95. We examine the observed and intrinsic properties of these secure FRB hosts, recovering similar distributions as previous works. Furthermore, we find a strong correlation between the apparent magnitude of the securely identified host galaxies and the estimated cosmic dispersion measures of the corresponding FRBs, which results from the Macquart relation. Future work with FRBs will leverage this relation and other measures from the secure hosts as priors for future associations. The methodology is generic to transient type, localization error, and image quality. We encourage its application to other transients where host galaxy associations are critical to the science, e.g. gravitational wave events, gamma-ray bursts, and supernovae. We have encoded the technique in Python on GitHub: https://github.com/FRBs/astropath.

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arXiv2020

Disentangling the Cosmic Web Towards FRB 190608

FRB 190608 was detected by ASKAP and localized to a spiral galaxy at $z_{host}=0.11778$ in the SDSS footprint. The burst has a large dispersion measure ($DM_{FRB}=339.8$ $pc/cm^3$) compared to the expected cosmic average at its redshift. It also has a large rotation measure ($RM_{FRB}=353$ $rad/m^2$) and scattering timescale ($τ=3.3$ $ms$ at $1.28$ $GHz$). Chittidi et al (2020) perform a detailed analysis of the ultraviolet and optical emission of the host galaxy and estimate the host DM contribution to be $110\pm 37$ $pc/cm^3$. This work complements theirs and reports the analysis of the optical data of galaxies in the foreground of FRB 190608 to explore their contributions to the FRB signal. Together, the two manuscripts delineate an observationally driven, end-to-end study of matter distribution along an FRB sightline; the first study of its kind. Combining KCWI observations and public SDSS data, we estimate the expected cosmic dispersion measure $DM_{cosmic}$ along the sightline to FRB 190608. We first estimate the contribution of hot, ionized gas in intervening virialized halos ($DM_{halos} \approx 7-28$ $pc/cm^3$). Then, using the Monte Carlo Physarum Machine (MCPM) methodology, we produce a 3D map of ionized gas in cosmic web filaments and compute the DM contribution from matter outside halos ($DM_{IGM} \approx 91-126$ $pc/cm^3$). This implies a greater fraction of ionized gas along this sightline is extant outside virialized halos. We also investigate whether the intervening halos can account for the large FRB rotation measure and pulse width and conclude that it is implausible. Both the pulse broadening and the large Faraday rotation likely arise from the progenitor environment or the host galaxy.

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arXiv2020

Extremely band-limited repetition from a fast radio burst source

The fast radio burst (FRB) population is observationally divided into sources that have been observed to repeat and those that have not. There is tentative evidence that the bursts from repeating sources have different properties than the non-repeating ones. In order to determine the occurrence rate of repeating sources and characterize the nature of repeat emission, we have been conducting sensitive searches for repetitions from bursts detected with the Australian Square Kilometre Array Pathfinder (ASKAP) with the 64-m Parkes radio telescope, using the recently commissioned Ultra-wideband Low (UWL) receiver system, over a band spanning 0.7$-$4.0 GHz. We report the detection of a repeat burst from the source of FRB 20190711A. The detected burst is 1 ms wide and has a bandwidth of just 65 MHz. We find no evidence of any emission in the remaining part of the 3.3 GHz UWL band. While the emission bandwidths of the ASKAP and UWL bursts show $ν^{-4}$ scaling consistent with a propagation effect, the spectral occupancy is inconsistent with diffractive scintillation. This detection rules out models predicting broad-band emission from the FRB 20190711A source and puts stringent constraints on the emission mechanism. The low spectral occupancy highlights the importance of sub-banded search methods in detecting FRBs.

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arXiv2020

Estimating fast transient detection pipeline efficiencies at UTMOST via real-time injection of mock FRBs

Dedicated surveys using different detection pipelines are being carried out at multiple observatories to find more Fast Radio Bursts (FRBs). Understanding the efficiency of detection algorithms and the survey completeness function is important to enable unbiased estimation of the underlying FRB population properties. One method to achieve end-to-end testing of the system is by injecting mock FRBs in the live data-stream and searching for them blindly. Mock FRB injection is particularly effective for machine-learning-based classifiers, for which analytic characterisation is impractical. We describe a first-of-its-kind implementation of a real-time mock FRB injection system at the upgraded Molonglo Observatory Synthesis Telescope (UTMOST) and present our results for a set of 20,000 mock FRB injections. The injections have yielded clear insight into the detection efficiencies and have provided a survey completeness function for pulse width, fluence and DM. Mock FRBs are recovered with uniform efficiency over the full range of injected DMs, however the recovery fraction is found to be a strong function of the width and Signal-to-Noise (SNR). For low widths ($\lesssim 20$ ms) and high SNR ($\gtrsim$ 9) the recovery is highly effective with recovery fractions exceeding 90%. We find that the presence of radio frequency interference causes the recovered SNR values to be systematically lower by up to 20% compared to the injected values. We find that wider FRBs become increasingly hard to recover for the machine-learning-based classifier employed at UTMOST. We encourage other observatories to implement live injection set-ups for similar testing of their surveys.

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arXiv2020

Host Galaxy Properties and Offset Distributions of Fast Radio Bursts: Implications for their Progenitors

We present observations and detailed characterizations of five new host galaxies of fast radio bursts (FRBs) discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) and localized to $\lesssim 1''$. Combining these galaxies with FRB hosts from the literature, we introduce criteria based on the probability of chance coincidence to define a sub-sample of 10 highly-confident associations (at $z=0.03-0.52$), three of which correspond to known repeating FRBs. Overall, the FRB host galaxies exhibit a broad, continuous range of color ($M_u-M_r = 0.9 - 2.0$), stellar mass ($M_\star = 10^{8} - 6\times 10^{10}\,M_{\odot}$), and star-formation rate (${\rm SFR} = 0.05 - 10\,M_{\odot}\,{\rm yr}^{-1}$) spanning the full parameter space occupied by $z<0.5$ galaxies. However, they do not track the color-magnitude, SFR-$M_\star$, nor BPT diagrams of field galaxies surveyed at similar redshifts. There is an excess of "green valley" galaxies and an excess of emission-line ratios indicative of a harder radiation field than that generated by star-formation alone. From the observed stellar mass distribution, we rule out the hypothesis that FRBs strictly track stellar mass in galaxies ($>99\%$ c.l.). We measure a median offset of 3.3 kpc from the FRB to the estimated center of the host galaxies and compare the host-burst offset distribution and other properties with the distributions of long- and short-duration gamma-ray bursts (LGRBs and SGRBs), core-collapse supernovae (CC-SNe), and Type Ia SNe. This analysis rules out galaxies hosting LGRBs (faint, star-forming galaxies) as common hosts for FRBs ($>95\%$ c.l.). Other transient channels (SGRBs, CC- and Type Ia SNe) have host galaxy properties and offsets consistent with the FRB distributions. All of the data and derived quantities are made publicly available on a dedicated website and repository.

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arXiv2020

Limits on precursor and afterglow radio emission from a fast radio burst in a star-forming galaxy

We present a new fast radio burst (FRB) at 920 MHz discovered during commensal observations conducted with the Australian Square Kilometre Array Pathfinder (ASKAP) as part of the Commensal Real-time ASKAP Fast Transients (CRAFT) survey. FRB 191001 was detected at a dispersion measure (DM) of 506.92(4) pc cm$^{-3}$ and its measured fluence of 143(15) Jy ms is the highest of the bursts localized to host galaxies by ASKAP to date. The subarcsecond localization of the FRB provided by ASKAP reveals that the burst originated in the outskirts of a highly star-forming spiral in a galaxy pair at redshift $z=0.2340(1)$. Radio observations show no evidence for a compact persistent radio source associated with the FRB 191001 above a flux density of $15 μ$Jy. However, we detect diffuse synchrotron radio emission from the disk of the host galaxy that we ascribe to ongoing star formation. FRB 191001 was also detected as an image-plane transient in a single 10 s snapshot with a flux density of 19.3 mJy in the low-time-resolution visibilities obtained simultaneously with CRAFT data. The commensal observation facilitated a search for repeating and slowly varying radio emissions 8 hr before and 1 hr after the burst. We found no variable radio emission on timescales ranging from 1 ms to 1.4 hr. We report our upper limits and briefly review FRB progenitor theories in the literature that predict radio afterglows. Our data are still only weakly constraining of any afterglows at the redshift of the FRB. Future commensal observations of more nearby and bright FRBs will potentially provide stronger constraints.

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arXiv2020

First Constraints on Compact Dark Matter from Fast Radio Burst Microstructure

Despite existing constraints, it remains possible that up to $35\%$ of all dark matter is comprised of compact objects, such as the black holes in the 10-100\,M$_\odot$ range whose existence has been confirmed by LIGO. The strong gravitational lensing of transients such as FRBs and GRBs has been suggested as a more sensitive probe for compact dark matter than intensity fluctuations observed in microlensing experiments. Recently ASKAP has reported burst substructure down to $15μ$s timescales in FRBs in the redshift range $0.3-0.5$. We investigate here the implications of this for the detectability of compact dark matter by FRBs. We find that a sample size of $\sim130$ FRBs would be required to constrain compact dark matter to less than the existing 35$\%$ limit with 95$\%$ confidence, if it were distributed along $\gtrsim 1\,$Gpc-long FRB sightlines through the cosmic web. Conversely, existing constraints on the fraction of compact dark matter permit as many as 1 in $\approx 40$ of all $z \lesssim 0.4$ FRBs to exhibit micro-lensed burst structure. Approximately $170$ FRBs intercepting halos within $\sim 50\,$kpc would be required to exclude the fraction of compact dark matter in each intercepted halo to a similar level. Furthermore, we consider the cumulative effects of lensing of the FRB signal by a macroscopic dark matter distribution. We conclude that lensing from a uniform distribution of compact objects is likely not observable, but suggest that FRBs may set meaningful limits on power-law distributions of dark matter.

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arXiv2020

Very long baseline astrometry of PSR J1012+5307 and its implications on alternative theories of gravity

PSR J1012+5307, a millisecond pulsar in orbit with a helium white dwarf (WD), has been timed with high precision for about 25 years. One of the main objectives of this long-term timing is to use the large asymmetry in gravitational binding energy between the neutron star and the WD to test gravitational theories. Such tests, however, will be eventually limited by the accuracy of the distance to the pulsar. Here, we present VLBI (very long baseline interferometry) astrometry results spanning approximately 2.5 years for PSR J1012+5307, obtained with the Very Long Baseline Array as part of the MSPSRPI project. These provide the first proper motion and absolute position for PSR J1012+5307 measured in a quasi-inertial reference frame. From the VLBI results, we measure a distance of $0.83^{+0.06}_{-0.02}$kpc (all the estimates presented in the abstract are at 68% confidence) for PSR J1012+5307, which is the most precise obtained to date. Using the new distance, we improve the uncertainty of measurements of the unmodeled contributions to orbital period decay, which, combined with three other pulsars, places new constraints on the coupling constant for dipole gravitational radiation $κ_D=(-1.7\pm1.7)\times 10^{-4}$ and the fractional time derivative of Newton's gravitational constant $\dot{G}/G = -1.8^{\,+5.6}_{\,-4.7}\times 10^{-13}\,{\rm yr^{-1}}$ in the local universe. As the uncertainties of the observed decays of orbital period for the four leading pulsar-WD systems become negligible in $\approx10$ years, the uncertainties for $\dot{G}/G$ and $κ_D$ will be improved to $\leq1.5\times10^{-13}\,{\rm yr^{-1}}$ and $\leq1.0\times10^{-4}$, respectively, predominantly limited by the distance uncertainties.

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