Arecibo Observatory Research Articles

Polarimetric Decomposition of Near-Earth Asteroids Using Arecibo Radar Observations

Abstract The polarization state of radar echoes from planetary bodies contains information about the scattering mechanisms present on the surface and thus the near-surface physical properties. Polarimetric radar scatter from complex surfaces, such as those observed for spacecraft-visited near-Earth asteroids (NEAs), is not well understood in terms of relating observed polarimetry to surface properties. Here we present an improved methodology for polarimetric analyses of ground-based radar observations of NEAs, extending techniques derived for larger bodies. We calculate the Stokes vector for delay-Doppler images of NEAs and use this to perform the m-chi decomposition and derive polarimetric products such as the degree of polarization, circular polarization ratio, and degree of linear polarization. We apply this methodology to radar observations of NEAs (53319) 1999 JM8, (101955) Bennu, and (33342) 1998 WT24 obtained by the Arecibo Observatory. We also perform numerical simulations of the m-chi decomposition for irregular boulders to augment the interpretation of the results for NEAs. Our analyses show that significant components of radar echoes are depolarized (random polarization) and linearly polarized. The numerical simulations confirm that depolarization is increased by single scattering from nonspherical wavelength-scale particles. Our analysis suggests that 1999 JM8 is possibly covered in regolith and that surface scatterers dominate the scattering properties of Bennu. The NEA 1998 WT24 displays diverse polarimetric properties, which we reconcile with optical and thermal observations by assuming a fine-grained regolith mantling a rugged, dense interior. In this work, we demonstrate the usefulness of radar polarimetry in characterizing the physical properties of planetary surfaces.

End of an era

Abstract Alastair Gunn looks back at the scientific and cultural legacy of an iconic instrument: the 305m Arecibo radio telescope

Fallen giant.

Engineering failures and a harsh climate conspired in the sudden collapse of the Arecibo telescope. Now, researchers are planning a rebirth.

A Data-Taking System for Planetary Radar Applications

Most planetary radar applications require recording of complex voltages at sampling rates of up to 20[Formula: see text]MHz. I describe the design and implementation of a sampling system that has been installed at the Arecibo Observatory, Goldstone Solar System Radar, and Green Bank Telescope. After many years of operation, these data-taking systems have enabled the acquisition of hundreds of datasets, many of which still await publication.

The NANOGrav 12.5 yr Data Set: Observations and Narrowband Timing of 47 Millisecond Pulsars

Abstract We present time-of-arrival (TOA) measurements and timing models of 47 millisecond pulsars observed from 2004 to 2017 at the Arecibo Observatory and the Green Bank Telescope by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). The observing cadence was three to four weeks for most pulsars over most of this time span, with weekly observations of six sources. These data were collected for use in low-frequency gravitational wave searches and for other astrophysical purposes. We detail our observational methods and present a set of TOA measurements, based on “narrowband” analysis, in which many TOAs are calculated within narrow radio-frequency bands for data collected simultaneously across a wide bandwidth. A separate set of “wideband” TOAs will be presented in a companion paper. We detail a number of methodological changes, compared to our previous work, which yield a cleaner and more uniformly processed data set. Our timing models include several new astrometric and binary pulsar measurements, including previously unpublished values for the parallaxes of PSRs J1832−0836 and J2322+2057, the secular derivatives of the projected semimajor orbital axes of PSRs J0613−0200 and J2229+2643, and the first detection of the Shapiro delay in PSR J2145−0750. We report detectable levels of red noise in the time series for 14 pulsars. As a check on timing model reliability, we investigate the stability of astrometric parameters across data sets of different lengths. We also report flux density measurements for all pulsars observed. Searches for stochastic and continuous gravitational waves using these data will be subjects of forthcoming publications.

OH Evolution in Molecular Clouds

We have conducted a OH 18 cm survey toward 141 molecular clouds in various environments, including 33 optical dark clouds, 98 Planck Galactic cold clumps (PGCCs), and 10 Spitzer dark clouds with the Arecibo telescope. The deviations from local thermal equilibrium are common for intensity ratios of both OH main lines and satellite lines. Line intensity of OH 1667 MHz is found to correlate linearly with visual extinction when is less than 3 mag. It was converted into OH column density by adopting the excitation temperature derived from Monte Carlo simulations with 1σ uncertainty. The relationship between OH abundance X(OH) relative to H2 and is found to follow an empirical formula, Linear correlation is found between OH and 13CO intensity. Besides, nonthermal velocity dispersions of OH and 13CO are closely correlated. These results imply tight chemical evolution and spatial occupation between OH and 13CO. No obvious correlation is found between column density and nonthermal velocity dispersion of OH and H i narrow self-absorption (HINSA), indicating different chemical evolution and spatial volume occupation between OH and HINSA. Using the age information of HINSA analysis, OH abundance X(OH) is found to increase linearly with cloud age, which is consistent with previous simulations. Fourteen OH components without corresponding CO emission were detected, implying the effectiveness of OH in tracing the "CO-dark" molecular gas.

Daily briefing: Arecibo telescope has suffered a catastrophic collapse

Daily briefing: Arecibo telescope has suffered a catastrophic collapse

Arecibo telescope will be dismantled

The National Science Foundation announced Nov. 19 that it will dismantle the famed Arecibo radio telescope, after broken cables put the structure’s stability in doubt. While best known for planetar...

The end has come for the iconic Arecibo telescope

The end has come for the iconic Arecibo telescope

Famed Arecibo telescope, on the brink of collapse, will be dismantled

Famed Arecibo telescope, on the brink of collapse, will be dismantled

Precise mass measurements for the double neutron star system J1829+2456

ABSTRACT PSR J1829+2456 is a radio pulsar in a relativistic binary system with another neutron star. It has a rotational period of 41 ms and a mildly eccentric (e = 0.14) 28 h orbit. We have continued its observations with the Arecibo radio telescope and have now measured the individual neutron star masses of this system: The pulsar and companion masses are $1.306\, \pm \, 0.007\, \mathrm{M}_{\odot}$ and $1.299\, \pm \, 0.007\, \mathrm{M}_{\odot}$ ($2\sigma - 95{{\ \rm per\ cent}}$ confidence, unless stated otherwise), respectively. We have also measured the proper motion for this system and used it to estimate a space velocity of $49^{+77}_{-30}$$\, \mathrm{km}\, \mathrm{s}^{-1}$ with respect to the local standard of rest. The relatively low values for companion mass, space velocity, and orbital eccentricity in this system make it similar to other double neutron star systems in which the second-formed neutron star is thought to have formed in a low-kick, low mass-loss, symmetric supernova.

A targeted search for repeating fast radio bursts associated with gamma-ray bursts

ABSTRACT The origin of fast radio bursts (FRBs) still remains a mystery, even with the increased number of discoveries in the last 3 yr. Growing evidence suggests that some FRBs may originate from magnetars. Large, single-dish telescopes such as Arecibo Observatory (AO) and Green Bank Telescope (GBT) have the sensitivity to detect FRB 121102-like bursts at gigaparsec distances. Here, we present searches using AO and GBT that aimed to find potential radio bursts at 11 sites of past gamma-ray bursts that show evidence for the birth of a magnetar. We also performed a search towards GW170817, which has a merger remnant whose nature remains uncertain. We place $10\sigma$ fluence upper limits of ≈0.036 Jy ms at 1.4 GHz and ≈0.063 Jy ms at 4.5 GHz for the AO data and fluence upper limits of ≈0.085 Jy ms at 1.4 GHz and ≈0.098 Jy ms at 1.9 GHz for the GBT data, for a maximum pulse width of ≈42 ms. The AO observations had sufficient sensitivity to detect any FRB of similar luminosity to the one recently detected from the Galactic magnetar SGR 1935+2154. Assuming a Schechter function for the luminosity function of FRBs, we find that our non-detections favour a steep power-law index (α ≲ −1.1) and a large cut-off luminosity (L0 ≳ 1041 erg s−1).

Study of the upper transition height using ISR observations and IRI predictions over Arecibo

The temporal and spatial variation of the upper transition height ( H T ) is studied using the measurements of the Incoherent Scatter Radar (ISR) at Arecibo Observatory ( 18.35 ° N , 66.75 ° W ) , Puerto Rico (magnetic latitude 30 ° N ). Observed ion compositions, electron densities, electron and ion temperatures are analysed to understand the diurnal and seasonal variations of H T at low and high solar activity covering solar cycles 23 and 24. The results show that during the low solar activity conditions, the mean H T is very low (around 750 km during the daytime and 500 km at night), while during high solar activity conditions, it reaches about 1600 km. Under very quiet geomagnetic conditions, the mean H T is about 700 km during day time and 500 km during night time. The obtained results are compared with the International Reference Ionosphere (IRI) model predictions using the TBT15 model ion composition option. During low and moderate solar activity conditions, the TBT15 model overestimates about 5–10% at night and 15–20% in the afternoon. Furthermore, from the current investigation using the IRI’s TBT15 and DY85 model ion composition options, it is found that the newer TBT15 model option is more appropriate to investigate H T variations as compared to the DY85 model option.

Repeating behaviour of FRB 121102: periodicity, waiting times, and energy distribution

ABSTRACT Detections from the repeating fast radio burst FRB 121102 are clustered in time, noticeable even in the earliest repeat bursts. Recently, it was argued that the source activity is periodic, suggesting that the clustering reflected a not-yet-identified periodicity. We performed an extensive multiwavelength campaign with the Effelsberg telescope, the Green Bank telescope, and the Arecibo Observatory to shadow the Gran Telescope Canaria (optical), NuSTAR (X-ray) and INTEGRAL (γ-ray). We detected 36 bursts with Effelsberg, one with a pulse width of 39 ms, the widest burst ever detected from FRB 121102. With one burst detected during simultaneous NuSTAR observations, we place a 5σ upper limit of 5 × 1047 erg on the 3–79 keV energy of an X-ray burst counterpart. We tested the periodicity hypothesis using 165 h of Effelsberg observations and find a periodicity of 161 ± 5 d. We predict the source to be active from 2020 July 9 to October 14 and subsequently from 2020 December 17 to 2021 March 24. We compare the wait times between consecutive bursts within a single observation to Weibull and Poisson distributions. We conclude that the strong clustering was indeed a consequence of a periodic activity and show that if the few events with millisecond separation are excluded, the arrival times are Poisson distributed. We model the bursts’ cumulative energy distribution with energies from ∼1038–1039 erg and find that it is well described by a power law with slope of γ = −1.1 ± 0.2. We propose that a single power law might be a poor descriptor of the data over many orders of magnitude.

A precise mass measurement of PSR J2045 + 3633

ABSTRACT We present the results of a timing analysis undertaken with the goal of obtaining an improved mass measurement of the recycled pulsar J2045 + 3633. Using regular high-cadence observations with the Effelsberg, Nançay, and Lovell radio telescopes, together with targeted campaigns with the Arecibo Telescope and Effelsberg, we have assembled a 6-yr timing data set for this pulsar. We measure highly significant values for the proper motion and the related rate of change of orbital semimajor axis ($\dot{x}$), and have obtained high-precision values of the rate of advance of periastron time ($\dot{\omega }$), and two of the Shapiro delay parameters (h3 and ς). This has allowed us to improve the measurements of the pulsar and companion masses by an order of magnitude, yielding (with 1σ uncertainties) $1.251^{+0.021}_{-0.021}\, \text{M}_{\odot }$ for PSR J2045 + 3633, and $0.873^{+0.016}_{-0.014}\, \text{M}_{\odot }$ for its white dwarf companion, and has allowed us to place improved constraints on the geometrical orientation of the binary system. Using our measurements of the binary component masses and the orbital size, we consider possible evolutionary scenarios for the system.

The NIBLES bivariate luminosity–H I mass distribution function revised using Arecibo follow-up observations

We present a modified optical luminosity–H I mass bivariate luminosity function based on H I line observations from the Nançay Interstellar Baryons Legacy Extragalactic Survey (NIBLES), including data from our new, four times more sensitive follow-up H I line observations obtained with the Arecibo radio telescope. The follow-up observations were designed to probe the underlying H I mass distribution of the NIBLES galaxies that were undetected or marginally detected in H I at the Nançay Radio Telescope. Our total follow-up sample consists of 234 galaxies, and it spans the entire luminosity and color range of the parent NIBLES sample of 2600 nearby (900 < cz < 12 000 km s−1) SDSS galaxies. We incorporated the follow-up data into the bivariate analysis by scaling the NIBLES undetected fraction by an Arecibo-only distribution. We find the resulting increase in low H I mass-to-light ratio densities to be about 10% for the bins −1.0 ≤ log(MHI/M⊙/Lr/L⊙) ≤ −0.5, which produces an increased H I mass function (HIMF) low mass slope of α = −1.14 ± 0.07, being slightly shallower than the values of −1.35 ± 0.05 obtained by recent blind H I surveys. Applying the same correction to the optically corrected bivariate luminosity function from our previous paper produces a larger density increase of about 0.5 to 1 dex in the lowest H I mass-to-light ratio bins for a given luminosity while having a minimal effect on the resulting HIMF low mass slope, which still agrees with blind survey HIMFs. This indicates that while low H I-mass-to-light ratio galaxies do not contribute much to the one-dimensional HIMF, their inclusion has a significant impact on the densities in the two-dimensional distribution.

Cosmicflows-4: The Catalog of ∼10,000 Tully–Fisher Distances

Abstract We present the distances of 9792 spiral galaxies lying within 15,000 km s−1 using the relation between luminosity and rotation rate of spiral galaxies. The sample is dominantly, but not exclusively, drawn from galaxies detected in the course of the ALFALFA H i survey with the Arecibo Telescope. Relations between H i line widths and luminosity are calibrated at SDSS u, g, r, i, z bands and WISE W1 and W2 bands. By exploiting secondary parameters, particularly color indices, we address discrepancies between measured distances at different wave bands with unprecedented detail. We provide a catalog that includes reduced kinematic, photometric, and inclination parameters. We also describe a machine-learning algorithm, based on the random forest technique, that predicts the dust attenuation in spirals lacking infrared photometry. We determine a Hubble Constant value of H 0 = 75.1 ± 0.2(stat.), with potential systematics up to ±3 km s−1 Mpc−1.

Arecibo radio telescope goes dark after snapped cable shreds dish

Arecibo radio telescope goes dark after snapped cable shreds dish

A dish disaster

The iconic Arecibo Observatory has taken a massive blow

Plasma Cavity Formation During Ionospheric Heating at Arecibo

AbstractThe formation of an anomalous, high‐altitude plasma cavity was observed during the 11–15 June 2019 ionospheric heating campaign at Arecibo Observatory. The cavity was induced by interactions of the transmitted 5.125‐MHz heater wave with the ionospheric plasma. Simultaneous ion line and plasma line measurements were taken by the Arecibo Incoherent Scatter Radar (ISR). We used a novel experimental technique, enabling rapid pulsing of the heater, to collect ISR spectral data of the heated ionosphere without high frequency (HF)‐induced enhanced ion line (HFIL), simplifying the analysis. ISR data were analyzed using Tikhonov regularization, revealing that the cavity was confined to a very narrow altitude range around 350 km and constituted a deep depletion of the electron density, along with strong electron temperature enhancement, and ion temperature enhancement. We report on the details of these observations, and the possibility for unique combinations of physical interactions to explain the underlying mechanisms.