arXiv subjects

Fernando Camilo

Publications and source records attributed to Fernando Camilo.

At least 37 records · Page 2Linked to original sources

arXiv2024

MeerKAT Pulsar Timing Array parallaxes and proper motions

We have determined positions, proper motions, and parallaxes of $77$ millisecond pulsars (MSPs) from $\sim3$ years of MeerKAT radio telescope observations. Our timing and noise analyses enable us to measure $35$ significant parallaxes ($12$ of them for the first time) and $69$ significant proper motions. Eight pulsars near the ecliptic have an accurate proper motion in ecliptic longitude only. PSR~J0955$-$6150 has a good upper limit on its very small proper motion ($<$0.4 mas yr$^{-1}$). We used pulsars with accurate parallaxes to study the MSP velocities. This yields $39$ MSP transverse velocities, and combined with MSPs in the literature (excluding those in Globular Clusters) we analyse $66$ MSPs in total. We find that MSPs have, on average, much lower velocities than normal pulsars, with a mean transverse velocity of only $78(8)$ km s$^{-1}$ (MSPs) compared with $246(21)$ km s$^{-1}$ (normal pulsars). We found no statistical differences between the velocity distributions of isolated and binary millisecond pulsars. From Galactocentric cylindrical velocities of the MSPs, we derive 3-D velocity dispersions of $σ_ρ$, $σ_ϕ$, $σ_{z}$ = $63(11)$, $48(8)$, $19(3)$ km s$^{-1}$. We measure a mean asymmetric drift with amplitude $38(11)$ km s$^{-1}$, consistent with expectation for MSPs, given their velocity dispersions and ages. The MSP velocity distribution is consistent with binary evolution models that predict very few MSPs with velocities $>300$ km s$^{-1}$ and a mild anticorrelation of transverse velocity with orbital period.

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arXiv2023

HI Galaxy Signatures in the SARAO MeerKAT Galactic Plane Survey -- II. The Local Void and its substructure

The Local Void is one of the nearest large voids, located at a distance of 23 Mpc. It lies largely behind the Galactic Bulge and is therefore extremely difficult to observe. We use HI 21 cm emission observations from the SARAO MeerKAT Galactic Plane Survey (SMGPS) to study the Local Void and its surroundings over the Galactic longitude range 329$^{\circ}< \ell <$ 55$^{\circ}$, Galactic latitude $|b| <$ 1.5$^{\circ}$, and redshift $cz <$ 7500 km/s. We have detected 291 galaxies to median rms sensitivity of 0.44 mJy per beam per 44 km/s channel. We find 17 galaxies deep inside the Void, 96 at the border of the Void, while the remaining 178 galaxies are in average density environments. The extent of the Void is ~ 58 Mpc. It is severely under-dense for the longitude range 350$^{\circ}< \ell <$ 35$^{\circ}$ up to redshift $z <$ 4500 km/s. The galaxies in the Void tend to have \HI masses that are lower (by approximately 0.25 dex) than their average density counterparts. We find several potential candidates for small groups of galaxies, of which two groups (with 3 members and 5 members) in the Void show signs of filamentary substructure within the Void.

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arXiv2023

HI Galaxy Signatures in the SARAO MeerKAT Galactic Plane Survey $-$ I. Probing the richness of the Great Attractor Wall across the inner Zone of Avoidance

This paper presents the first HI results extracted from the SARAO MeerKAT Galactic Plane Survey (SMGPS) $-$ a narrow strip ($b \sim 3^\circ$) along the southern Milky Way. The primary goal consisted in tracing the Great Attractor (GA) Wall across the innermost Zone of Avoidance. We reduced a segment spanning the longitude range $302^\circ \leq \ell \leq 332^\circ$ for the redshift range $z \leq 0.08$. The superb SMGPS sensitivity (rms = 0.3-0.5 mJy beam$^{-1}$ per 44 kms$^{-1}$ channel) and angular resolution ($\sim$ 31" $\times$ 26") lead to a detection limit of log$(M_{\rm HI}/$M$_\odot) \geq$ 8.5 at the GA distance ($V_{\rm hel} \sim 3500 - 6500$ kms$^{-1}$). A total of 477 galaxy candidates were identified over the full redshift range. A comparison of the few HI detections with counterparts in the literature (mostly HIZOA) found the HI fluxes and other HI parameters to be highly consistent. The continuation of the GA Wall is confirmed through a prominent overdensity of $N = 214$ detections in the GA distance range. At higher latitudes, the wall moves to higher redshifts, supportive of a possible link with the Ophiuchus cluster located behind the Galactic Bulge. This deep interferometric HI survey demonstrates the power of the SMGPS in improving our insight of large-scale structures at these extremely low latitudes, despite the high obscuration and continuum background.

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arXiv2023

The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems co-located with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to $\leq 11$ known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with 6 undetected in radio. Overall, >235 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot E$ decreases to its observed minimum near $10^{33}$ erg s$^{-1}$, approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties and fit results to guide and be compared with modeling results.

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arXiv2023

The 2022 high-energy outburst and radio disappearing act of the magnetar 1E 1547.0-5408

We report the radio and high-energy properties of a new outburst from the radio-loud magnetar 1E 1547.0$-$5408. Following the detection of a short burst from the source with Swift-BAT on 2022 April 7, observations by NICER detected an increased flux peaking at $(6.0 \pm 0.4) \times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ in the soft X-ray band, falling to the baseline level of $1.7\times10^{-11}$ erg s$^{-1}$ cm$^{-2}$ over a 17-day period. Joint spectroscopic measurements by NICER and NuSTAR indicated no change in the hard non-thermal tail despite the prominent increase in soft X-rays. Observations at radio wavelengths with Murriyang, the 64-m Parkes radio telescope, revealed that the persistent radio emission from the magnetar disappeared at least 22 days prior to the initial Swift-BAT detection and was re-detected two weeks later. Such behavior is unprecedented in a radio-loud magnetar, and may point to an unnoticed slow rise in the high-energy activity prior to the detected short-bursts. Finally, our combined radio and X-ray timing revealed the outburst coincided with a spin-up glitch, where the spin-frequency and spin-down rate increased by $0.2 \pm 0.1$ $μ$Hz and $(-2.4 \pm 0.1) \times 10^{-12}$ s$^{-2}$ respectively. A linear increase in spin-down rate of $(-2.0 \pm 0.1) \times 10^{-19}$ s$^{-3}$ was also observed over 147 d of post-outburst timing. Our results suggest that the outburst may have been associated with a reconfiguration of the quasi-polar field lines, likely signalling a changing twist, accompanied by spatially broader heating of the surface and a brief quenching of the radio signal, yet without any measurable impact on the hard X-ray properties.

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arXiv2022

The MeerKAT Pulsar Timing Array: First Data Release

We present the first 2.5 years of data from the MeerKAT Pulsar Timing Array (MPTA), part of MeerTime, a MeerKAT Large Survey Project. The MPTA aims to precisely measure pulse arrival times from an ensemble of 88 pulsars visible from the Southern Hemisphere, with the goal of contributing to the search, detection and study of nanohertz-frequency gravitational waves as part of the International Pulsar Timing Array. This project makes use of the MeerKAT telescope, and operates with a typical observing cadence of two weeks using the L-band receiver that records data from 856-1712 MHz. We provide a comprehensive description of the observing system, software, and pipelines used and developed for the MeerTime project. The data products made available as part of this data release are from the 78 pulsars that had at least $30$ observations between the start of the MeerTime programme in February 2019 and October 2021. These include both sub-banded and band-averaged arrival times, as well as the initial timing ephemerides, noise models, and the frequency-dependent standard templates (portraits) used to derive pulse arrival times. After accounting for detected noise processes in the data, the frequency-averaged residuals of $67$ of the pulsars achieved a root-mean-square residual precision of $< 1 μ\rm{s}$. We also present a novel recovery of the clock correction waveform solely from pulsar timing residuals, and an exploration into preliminary findings of interest to the international pulsar timing community. The arrival times, standards and full Stokes parameter calibrated pulsar timing archives are publicly available.

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arXiv2022

Discovery, Timing, and Multiwavelength Observations of the Black Widow Millisecond Pulsar PSR J1555-2908

We report the discovery of PSR J1555-2908, a 1.79 ms radio and gamma-ray pulsar in a 5.6 hr binary system with a minimum companion mass of 0.052 $M_\odot$. This fast and energetic ($\dot E = 3 \times 10^{35}$ erg/s) millisecond pulsar was first detected as a gamma-ray point source in Fermi LAT sky survey observations. Guided by a steep spectrum radio point source in the Fermi error region, we performed a search at 820 MHz with the Green Bank Telescope that first discovered the pulsations. The initial radio pulse timing observations provided enough information to seed a search for gamma-ray pulsations in the LAT data, from which we derive a timing solution valid for the full Fermi mission. In addition to the radio and gamma-ray pulsation discovery and timing, we searched for X-ray pulsations using NICER but no significant pulsations were detected. We also obtained time-series r-band photometry that indicates strong heating of the companion star by the pulsar wind. Material blown off the heated companion eclipses the 820 MHz radio pulse during inferior conjunction of the companion for ~10% of the orbit, which is twice the angle subtended by its Roche lobe in an edge-on system.

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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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arXiv2020

The dynamic magnetosphere of Swift J1818.0$-$1607

Radio-loud magnetars display a wide variety of radio-pulse phenomenology seldom seen among the population of rotation-powered pulsars. Spectropolarimetry of the radio pulses from these objects has the potential to place constraints on their magnetic topology and unveil clues about the magnetar radio emission mechanism. Here we report on eight observations of the magnetar Swift J1818.0$-$1607 taken with the Parkes Ultra-Wideband Low receiver covering a wide frequency range from 0.7 to 4 GHz over a period of 5 months. The magnetar exhibits significant temporal profile evolution over this period, including the emergence of a new profile component with an inverted spectrum, two distinct types of radio emission mode switching, detected during two separate observations, and the appearance and disappearance of multiple polarization modes. These various phenomena are likely a result of ongoing reconfiguration of the plasma content and electric currents within the magnetosphere. Geometric fits to the linearly polarized position angle indicate we are viewing the magnetar at an angle of $\sim$99$^{\circ}$ from the spin axis, and its magnetic and rotation axes are misaligned by $\sim$112$^{\circ}$. While conducting these fits, we found the position angle swing had reversed direction on MJD 59062 compared to observations taken 15 days earlier and 12 days later. We speculate this phenomena may be evidence the radio emission from this magnetar originates from magnetic field lines associated with two co-located magnetic poles that are connected by a coronal loop.

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arXiv2020

The ELM Survey. VIII. 98 Double White Dwarf Binaries

We present the final sample of 98 detached double white dwarf (WD) binaries found in the Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting <0.3 Msun He-core WDs completed in the Sloan Digital Sky Survey footprint. Over the course of the survey we observed ancillary low mass WD candidates like GD278, which we show is a P=0.19 d double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too large to be WDs given their Gaia parallaxes. Here, we define a clean sample of ELM WDs that is complete within our target selection and magnitude range 15<g_0<20 mag. The measurements are consistent with 100% of ELM WDs being 0.0089 < P < 1.5 d double WD binaries, 35% of which belong to the Galactic halo. We infer these are mostly He+CO WD binaries given the measurement constraints. The merger rate of the observed He+CO WD binaries exceeds the formation rate of stable mass transfer AM CVn binaries by a factor of 25, and so the majority of He+CO WD binaries must experience unstable mass transfer and merge. The shortest-period systems like J0651+2844 are signature {\it LISA} verification binaries that can be studied with gravitational waves and light.

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arXiv2019

Discovery of Millisecond Pulsars in the Globular Cluster Omega Centauri

The globular cluster Omega Centauri is the most massive and luminous cluster in the Galaxy. The $γ$-ray source FL8Y J1326.7$-$4729 is coincident with the core of the cluster, leading to speculation that hitherto unknown radio pulsars or annihilating dark matter may be present in the cluster core. Here we report on the discovery of five millisecond pulsars in Omega Centauri following observations with the Parkes radio telescope. Four of these pulsars are isolated with spin periods of 4.1, 4.2, 4.6 and 6.8 ms. The fifth has a spin period of 4.8 ms and is in an eclipsing binary system with an orbital period of 2.1 hours. Deep radio continuum images of the cluster centre with the Australian Telescope Compact Array reveal a small population of compact radio sources making it likely that other pulsars await discovery. We consider it highly likely that the millisecond pulsars are the source of the $γ$-ray emission. The long-term timing of these pulsars opens up opportunities to explore the dynamics and interstellar medium of the cluster.

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arXiv2019

Multiband Optical Light Curves of Black-Widow Pulsars

We collect new and archival optical observations of nine "black-widow" millisecond pulsar binaries. New measurements include direct imaging with the Keck, Gemini-S, MDM, and LCO 2~m telescopes. This is supplemented by synthesized colors from Keck long-slit spectra. Four black-widow optical companions are presented here for the first time. Together these data provide multicolor photometry covering a large fraction of the orbital phase. We fit these light curves with a direct (photon) heating model using a version of the ICARUS light-curve modeling code. The fits provide distance and fill-factor estimates, inclinations, and heating powers. We compare the heating powers with the observed GeV luminosities, noting that the ratio is sensitive to pulsar distance and to the gamma-ray beaming. We make a specific correction for "outer-gap" model beams, but even then some sources are substantially discrepant, suggesting imperfect beaming corrections and/or errors in the fit distance. The fits prefer large metal abundance for half of the targets, a reasonable result for these wind-stripped secondaries. The companion radii indicate substantial Roche-lobe filling, $f_c \approx 0.7-1$ except for PSR J0952$-$0607, which with $f_c< 0.5$ has a companion density $ρ\approx 10\,{\rm g\,cm^{-3}}$, suggesting unusual evolution. We note that the direct-heating fits imply large heating powers and rather small inclinations, and we speculate that unmodeled effects can introduce such bias.

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arXiv2019

The First Pulsar Discovered by FAST

To assist with the commissioning (Jiang et al. 2019) of the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we performed a pulsar search, with the primary goal of developing and testing the pulsar data acquisition and processing pipelines. We tested and used three pipelines, two (P1 and P2 hereafter) searched for the periodic signature of pulsars whereas the other one was used to search for bright single pulses (P3 hereafter). A pulsar candidate was discovered in the observation on the 22nd August, 2017, and later confirmed by the Parkes radio telescope on the 10th September, 2017. This pulsar, named PSR J1900-0134, was the first pulsar discovered by FAST. The pulsar has a pulse period of 1.8 s and a dispersion measure (DM) of 188\,pc\,cm$^{-3}$.

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arXiv2019

Wideband polarized radio emission from the newly revived magnetar XTE J1810$-$197

The anomalous X-ray pulsar XTE J1810$-$197 was the first magnetar found to emit pulsed radio emission. After spending almost a decade in a quiescent, radio-silent state, the magnetar was reported to have undergone a radio outburst in December, 2018. We observed radio pulsations from XTE J1810$-$197 during this early phase of its radio revival using the Ultra-Wideband Low receiver system of the Parkes radio telescope, obtaining wideband (704 MHz to 4032 MHz) polarization pulse profiles, single pulses and flux density measurements. Dramatic changes in polarization and rapid variations of the position angle of linear polarization across the main pulse and in time have been observed. The pulse profile exhibits similar structures throughout our three observations (over a week time scale), displaying a small amount of profile evolution in terms of polarization and pulse width across the wideband. We measured a flat radio spectrum across the band with a positive spectral index, in addition to small levels of flux and spectral index variability across our observing span. The observed wideband polarization properties are significantly different compared to those taken after the 2003 outburst, and therefore provide new information about the origin of radio emission.

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arXiv2018

Searching a Thousand Radio Pulsars for Gamma-ray Emission

Identifying as many gamma-ray pulsars as possible in the Fermi Large Area Telescope (LAT) data helps test pulsar emission models by comparing predicted and observed properties for a large, varied sample with as little selection bias as possible. It also improves extrapolations from the observed population to estimate the contribution of unresolved pulsars to the diffuse gamma-ray emission. We use a recently developed method to determine the probability that a given gamma-ray photon comes from a known position in the sky, convolving the photon's energy with the LAT's energy-dependent point-spread-function (PSF), without the need for an accurate spatial and spectral model of the gamma-ray sky around the pulsar. The method is simple and fast and, importantly, provides probabilities, or _weights_, for gamma rays from pulsars too faint for phase-integrated detection. We applied the method to over a thousand pulsars for which we obtained rotation ephemerides from radio observations, and discovered gamma-ray pulsations from 16 pulsars, 12 young and 4 recycled. PSR J2208+4056 has spindown power Edot = 8e32 erg/s, about three times lower than the previous observed gamma-ray emission "deathline". PSRs J2208+4056 and J1816-0755 have radio interpulses, constraining their geometry and perhaps enhancing their gamma-ray luminosity. We discuss whether the deathline is an artifact of selection bias due to the pulsar distance.

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arXiv2018

A Serendipitous Pulsar Discovery in a Search for a Companion to a Low-Mass White Dwarf

We report the discovery of a previously unidentified pulsar as part of a radio campaign to identify neutron star companions to low-mass white dwarfs (LMWDs) using the Robert C.\ Byrd Green Bank Telescope (GBT). PSR J0802-0955, which is coincident with the position of a WD with a mass of 0.2 solar masses, has a pulse period of 571 ms. Because of its relatively long pulse period, the lack of radial velocity (RV) variations in the radio data, and GBT's large beam size at the observing frequency of 340 MHz, we conclude that PSR J0802-0955 is unassociated with the LMWD at roughly the same position and distance.

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arXiv2015

Timing Gamma-ray Pulsars with the Fermi Large Area Telescope: Timing Noise and Astrometry

We have constructed timing solutions for 81 gamma-ray pulsars covering more than five years of Fermi data. The sample includes 37 radio-quiet or radio-faint pulsars which cannot be timed with other telescopes. These timing solutions and the corresponding pulse times of arrival are prerequisites for further study, e.g. phase-resolved spectroscopy or searches for mode switches. Many gamma-ray pulsars are strongly affected by timing noise, and we present a new method for characterizing the noise process and mitigating its effects on other facets of the timing model. We present an analysis of timing noise over the population using a new metric for characterizing its strength and spectral shape, namely its time-domain correlation. The dependence of the strength on spin frequency and spin-down rate is in good agreement with previous studies. We find that noise process power spectra $S(f)$ for unrecycled pulsars are steep, with strong correlations over our entire data set and spectral indices $S(f)\propto f^{-α}$ of 5 to 9. One possible explanation for these results is the occurrence of unmodelled, episodic 'microglitches'. Finally, we show that our treatment of timing noise results in robust parameter estimation, and in particular we measure a precise timing position for each pulsar. We extensively validate our results with multi-wavelength astrometry, and using our updated position, we firmly identify the X-ray counterpart of PSR J1418-6058.

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arXiv2015

Properties and Evolution of the Redback Millisecond Pulsar Binary PSR J2129-0429

PSR J2129-0429 is a "redback" eclipsing millisecond pulsar binary with an unusually long 15.2 hour orbit. It was discovered by the Green Bank Telescope in a targeted search of unidentified Fermi gamma-ray sources. The pulsar companion is optically bright (mean $m_R = 16.6$ mag), allowing us to construct the longest baseline photometric dataset available for such a system. We present ten years of archival and new photometry of the companion from LINEAR, CRTS, PTF, the Palomar 60-inch, and LCOGT. Radial velocity spectroscopy using the Double-Beam Spectrograph on the Palomar 200-inch indicates that the pulsar is massive: $1.74\pm0.18 M_\odot$. The G-type pulsar companion has mass $0.44\pm0.04 M_\odot$, one of the heaviest known redback companions. It is currently 95\% Roche-lobe filling and only mildly irradiated by the pulsar. We identify a clear 13.1 mmag yr$^{-1}$ secular decline in the mean magnitude of the companion as well as smaller-scale variations in the optical lightcurve shape. This behavior may indicate that the companion is cooling. Binary evolution calculations indicate that PSR J2129-0429 has an orbital period almost exactly at the bifurcation period between systems that converge into tighter orbits as black widows and redbacks and those that diverge into wider pulsar--white dwarf binaries. Its eventual fate may depend on whether it undergoes future episodes of mass transfer and increased irradiation.

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