Arecibo L-band Feed Array Research Articles

Eight Millisecond Pulsars Discovered in the Arecibo PALFA Survey

Abstract We report on eight millisecond pulsars (MSPs) in binary systems discovered with the Arecibo L-Band Feed Array (PALFA) pulsar survey. Phase-coherent timing solutions derived from 2.5–5 yr of observations carried out at the Arecibo and Jodrell Bank observatories are provided. PSR J1921+1929 is a 2.65 ms pulsar in a 39.6 day orbit for which we detect γ-ray pulsations in archival Fermi data. PSR J1928+1245 is a very low-mass-function system with an orbital period of 3.3 hr that belongs to the non-eclipsing black widow population. We also present PSR J1932+1756, the longest-orbital-period (41.5 days) intermediate-mass binary pulsar known to date. In light of the numerous discoveries of binary MSPs over the past years, we characterize the Galactic distribution of known MSP binaries in terms of binary class. Our results support and strengthen previous claims that the scatter in the Galactic scale height distribution correlates inversely with the binary mass function. We provide evidence of observational biases against detecting the most recycled pulsars near the Galactic plane, which overestimates the scale height of lighter systems. A possible bimodality in the mass function of MSPs with massive white dwarfs is also reported.

The Arecibo L-band Feed Array Zone of Avoidance (ALFAZOA) Shallow Survey

Abstract The Arecibo L-band Feed Array Zone of Avoidance (ALFAZOA) Shallow Survey is a blind H i survey of the extragalactic sky behind the northern Milky Way conducted with the ALFA receiver on the 305 m Arecibo Radio Telescope. ALFAZOA Shallow covered 900 square degrees at full sensitivity from 30° ≤ l ≤ 75° and and an additional 460 square degrees at limited sensitivity at latitudes up to 20°. It has an rms sensitivity of 5–7 mJy and a velocity resolution of 9–20.6 km s−1, and detected 403 galaxies out to a recessional velocity of 12,000 km s−1, with an angular resolution of 3.′4 and a positional accuracy between 0.′2 and 1.′7. The survey is complete above an integrated line flux of F H i = 2.0 Jy km s−1 for half the survey, and above F H i = 2.8 Jy km s−1 for the other half. Of the ALFAZOA H i detections, 43% have at least one possible optical/near-infrared counterpart in the literature, and an additional 16% have counterparts that only included previous H i measurements. There are fewer counterparts in regions of high extinction and for galaxies with lower H i mass. Comparing the results of the survey to the predictions of Erdoǧdu et al., and using their nomenclature, ALFAZOA confirms the position and extent in the ZOA of the C7, Cζ, Pegasus, Corona Borealis, and Delphinus structures, but not of the Cygnus void. Two new structures are identified, both connected to the C7 overdensity; one extends to 35°, and the other crosses the ZOA.

H i-MaNGA: H i follow-up for the MaNGA survey

Abstract We present the H i-MaNGA programme of H i follow-up for the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. MaNGA, which is part of the Fourth phase of the Sloan Digital Sky Surveys, is in the process of obtaining integral field unit spectroscopy for a sample of ∼10 000 nearby galaxies. We give an overview of the H i 21cm radio follow-up observing plans and progress and present data for the first 331 galaxies observed in the 2016 observing season at the Robert C. Bryd Green Bank Telescope. We also provide a cross-match of the current MaNGA (DR15) sample with publicly available H i data from the Arecibo Legacy Fast Arecibo L-band Feed Array survey. The addition of H i data to the MaNGA data set will strengthen the survey’s ability to address several of its key science goals that relate to the gas content of galaxies, while also increasing the legacy of this survey for all extragalactic science.

A Correlated Search for Local Dwarf Galaxies in GALFA-H i and Pan-STARRS

Abstract In recent years, ultrafaint dwarf (UFD) galaxies have been found through systematic searches of large optical surveys. However, the existence of Leo T, a nearby gas-rich dwarf, suggests that there could be other nearby UFDs that are optically obscured but have gas detectable at nonoptical wavelengths. With this in mind, we perform a search of the full Galactic Arecibo L-band Feed Array H i (GALFA-H i) survey, a radio survey that covers one-third of the sky at velocities −650 < V LSR < +650 km s−1, for neutral hydrogen sources. We are able to probe regions of the sky at lower Galactic latitudes and smaller compared to previous explorations. We use the Source Finding Application on GALFA-H i and select all sources with similar properties to Leo T and other local dwarf galaxies. We find 690 dwarf galaxy candidates, one of which is particularly promising and likely a new galaxy near the Galactic plane (b = −8°) that is comparable in velocity width and H i-flux to other recently discovered local volume galaxies. We find we are sensitive to Leo T-like objects out to 1 Mpc at velocities clear from background H I emission. We check each candidate’s corresponding optical fields from Pan-STARRS and fit stars drawn from isochrones, but find no evidence of stellar populations. We thus find no other Leo T-like dwarfs within 500 kpc of the Milky Way in the one-third of the sky covered by the GALFA-H i footprint, and discuss our nondetection in a cosmological context.

Arecibo ALFA Array Observations in Search of Lunar Meteoroid-Strike EMPs

We present the preliminary results of a search for transient Electromagnetic Pulses (EMP) associated with the impact of meteoroids on the lunar surface as observed with the Arecibo Observatory ALFA (Arecibo L-band Feed Array) system. The ALFA system is a cluster of seven, dual-linear polarization feeds/beams arranged in a hexagonal manner and operated in the protected L-band region centered at 1.41 GHz. We analyzed 8 TB of data totaling nearly 5.5 h of on- and off-moon observations made in February 2016. We demonstrate the observing strategy and time–frequency methods for the detection and removal of the local-radar transient interference signals while identifying potential EMPs. Local out of band radar interference signals are observed as intermodulation artifacts in the protected L-band. Seven transient wideband EMP events with time scales of less than 10 μs have been detected following the extensive vetting process we describe. Assuming that these EMP-like events originate from gram-sized meteoroid strikes and using very approximate hypervelocity impact, plasma production theory, and EMP generation theory, we estimate the progenitor impact meteoroid kinetic energy to be approximately 1.8 × 107 J. Assuming that the observed EMPs are the result of 10 g meteoroid impacts, the resultant meteoroid flux is 3 × 10−7 km−2 h−1 based solely on lunar surface area observed and net observing period. Implications of the observed transient EMP events, measured lunar noise temperature and the comparison with energy estimates derived from the existing lunar impact optical observations are also discussed.

An Hα Imaging Survey of the Low Surface Brightness Galaxies Selected from the Spring Sky Region of the 40% ALFALFA H i Survey

Abstract We present a narrow Hα-band imaging survey of 357 low surface brightness galaxies (LSBGs) that are selected from the spring sky region of the 40% Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) H i Survey. All the Hα images are obtained from the 2.16 m telescope, operated by the Xinglong Observatory of the National Astronomical Observatories, Chinese Academy of Sciences. We provide the Hα fluxes and derive the global star formation rates (SFRs) of LSBGs after the Galactic extinction, internal extinction, and [N ii] contamination correction. Compared to normal star-forming galaxies, LSBGs have a similar distribution in the H i surface density (ΣH i ), but their SFRs and star formation surface density (ΣSFR) are much lower. Our results show that the gas-rich LSBGs selected from the ALFALFA survey obviously deviate from the Kennicutt–Schmidt law, in the relation between the star formation surface density (ΣSFR) and the gas surface density (Σgas). However, they follow the extended Schmidt law well when taking the stellar mass of the galaxy into consideration.

Total ALFALFA Neutral Hydrogen Fluxes for Extended Sources

Abstract A procedure is presented to improve on measurement of total H i fluxes for extended sources in the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey of neutral hydrogen sources in the nearby universe. A number of tests of the procedure are detailed, and we verify that we recover all of the flux measured with much larger telescope beams. Total fluxes are reported for all sources (1) exceeding 10 Jy km s−1 in the α.100 catalog, or (2) with Uppsala General Catalog diameters 3.0 arcmin or more, or (3) ALFALFA pipeline isophotal ellipse area more than 3.0 times the Arecibo beam. Total fluxes are also provided for a number of confused pairs and small groups including one or more of those high-flux sources. These data should be of use in baryonic Tully–Fisher studies and other applications where the measurement of the total reservoir of neutral atomic gas is important.

The Arecibo Pisces–Perseus Supercluster Survey. I. Harvesting ALFALFA

Abstract We report a multi-objective campaign of targeted 21 cm H i line observations of sources selected from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey and galaxies identified by their morphological and photometric properties in the Sloan Digital Sky Survey. The aims of this program have been (1) to confirm the reality of some ALFALFA sources whose enigmatic nature suggest additional multiwavelength observations; (2) to probe the low signal-to-noise ratio (S/N) regime, below the ALFALFA reliability limit; and (3) to explore the feasibility of using optical morphology, color, and surface brightness to identify gas-rich objects in the region of the Pisces–Perseus Supercluster (PPS) whose H i fluxes are below the ALFALFA sensitivity limit at that distance. As expected, the reliability of ALFALFA detections depends strongly on the S/N of the H i line signal and its coincidence with a probable stellar counterpart identified by its optical properties, suggestive of ongoing star formation. The identification of low-mass, star-forming populations enables targeted H i line observations to detect galaxies with H i line fluxes below the ALFALFA sensitivity limits in fixed local volumes (D < 100 Mpc). The method explored here serves as the basis for extending the sample of gas-bearing objects as part of the ongoing Arecibo Pisces–Perseus Supercluster Survey (APPSS).

Survey of Ionized Gas of the Galaxy, Made with the Arecibo Telescope (SIGGMA): Inner Galaxy Data Release

Abstract The Survey of Ionized Gas of the Galaxy, Made with the Arecibo telescope (SIGGMA) provides a fully sampled view of the radio recombination line (RRL) emission from the portion of the Galactic plane visible with Arecibo. Observations use the Arecibo L-band Feed Array, which has a FWHM beam size of 3.′4. Twelve hydrogen RRLs from H163α to H174α are located within the instantaneous bandpass from 1225 MHz to 1525 MHz. We provide here cubes of average (“stacked”) RRL emission for the inner Galaxy region 32° ≤ ℓ ≤ 70°, , with an angular resolution of 6′. The stacked RRL rms at 5.1 km s−1 velocity resolution is ∼0.65 mJy beam−1, making this the most sensitive large-scale fully sampled RRL survey extant. We use SIGGMA data to catalog 319 RRL detections in the direction of 244 known H ii regions, and 108 new detections in the direction of 79 H ii region candidates. We identify 11 carbon RRL emission regions, all of which are spatially coincident with known H ii regions. We detect RRL emission in the direction of 14 of the 32 supernova remnants (SNRs) found in the survey area. This RRL emission frequently has the same morphology as the SNRs. The RRL velocities give kinematic distances in agreement with those found in the literature, indicating that RRLs may provide an additional tool to constrain distances to SNRs. Finally, we analyze the two bright star-forming complexes: W49 and W51. We discuss the possible origins of the RRL emission in directions of SNRs W49B and W51C.

A novel single-pulse search approach to detection of dispersed radio pulses using clustering and supervised machine learning

We present a novel two-stage approach which combines unsupervised and supervised machine learning to automatically identify and classify single pulses in radio pulsar search data. In the first stage, we identify astrophysical pulse candidates in the data, which were derived from the Pulsar Arecibo L-Band Feed Array (PALFA) survey and contain 47,042 independent beams, as trial single-pulse event groups (SPEGs) by clustering single-pulse events and merging clusters that fall within the expected DM and time span of astrophysical pulses. We also present a new peak scoring algorithm, to identify astrophysical peaks in S/N versus DM curves. Furthermore, we group SPEGs detected at a consistent DM for they were likely emitted by the same source. In the second stage, we create a fully labelled benchmark data set by selecting a subset of data with SPEGs identified (using stage 1 procedures), their features extracted and individual SPEGs manually labelled, and then train classifiers using supervised machine learning. Next, using the best trained classifier, we automatically classify unlabelled SPEGs identified in the full data set. To aid the examination of dim SPEGs, we develop an algorithm that searches for an underlying periodicity among grouped SPEGs. The results showed that RandomForest with SMOTE treatment was the best learner, with a recall of 95.6% and a false positive rate of 2.0%. In total, besides all 60 known pulsars from the benchmark data set, the model found 32 additional (i.e., not included in the benchmark data set) known pulsars, and several potential discoveries.

The Implementation of a Fast-folding Pipeline for Long-period Pulsar Searching in the PALFA Survey

Abstract The Pulsar Arecibo L-Band Feed Array (PALFA) survey, the most sensitive blind search for radio pulsars yet conducted, is ongoing at the Arecibo Observatory in Puerto Rico. The vast majority of the 180 pulsars discovered by PALFA have spin periods shorter than 2 s. Pulsar surveys may miss long-period radio pulsars owing to the summing of a finite number of harmonic components in conventional Fourier analyses (typically ∼16), or as a result of the strong effect of red noise at low modulation frequencies. We address this reduction in sensitivity by using a time-domain search technique: the fast-folding algorithm (FFA). We designed a program that implements an FFA-based search in the PALFA processing pipeline and tested the efficiency of the algorithm by performing tests under both ideal, white-noise conditions, as well as with real PALFA observational data. In the two scenarios, we show that the time-domain algorithm has the ability to outperform the FFT-based periodicity search implemented in the survey. We perform simulations to compare the previously reported PALFA sensitivity with that obtained using our new FFA implementation. These simulations show that for a pulsar having a pulse duty cycle of roughly 3%, the performance of our FFA pipeline exceeds that of our FFT pipeline for pulses with dispersion measure ≲ 40 pc cm−3 and for periods as short as ∼500 ms, and that the survey sensitivity is improved by at least a factor of two for periods ≳ 6 s. Early results from the implementation of the algorithm in PALFA, including discoveries, are also presented in this paper.

Where Are All of the Gas-bearing Local Dwarf Galaxies? Quantifying Possible Impacts of Reionization

Abstract We present an approach for comparing the detections and non-detections of Local Group (LG) dwarf galaxies in large H i surveys to the predictions of a suite of n-body simulations of the LG. This approach depends primarily on a set of empirical scaling relations to connect the simulations to the observations, rather than making strong theoretical assumptions. We then apply this methodology to the Galactic Arecibo L-band Feed Array Hi (GALFA-HI) Compact Cloud Catalog (CCC), and compare it to the suite Exploring the Local Volume In Simulations (ELVIS) of simulations. This approach reveals a strong tension between the naïve results of the model and the observations: while there are no LG dwarfs in the GALFA-HI CCC, the simulations predict ∼10. Applying a simple model of reionization can resolve this tension by preventing low-mass halos from forming gas. However, and if this effect operates as expected, the observations provide a constraint on the mass scale of the dwarf galaxy that reionization impacts. Combined with the observed properties of Leo T, the halo virial mass scale at which reionization impacts dwarf galaxy gas content is constrained to be , independent of any assumptions about star formation.

PALFA Discovery of a Highly Relativistic Double Neutron Star Binary

Abstract We report the discovery and initial follow-up of a double neutron star (DNS) system, PSR J1946+2052, with the Arecibo L-Band Feed Array pulsar (PALFA) survey. PSR J1946+2052 is a 17 ms pulsar in a 1.88 hr, eccentric (e = 0.06) orbit with a ≳1.2 M ⊙ companion. We have used the Jansky Very Large Array to localize PSR J1946+2052 to a precision of 0.″09 using a new phase binning mode. We have searched multiwavelength catalogs for coincident sources but did not find any counterparts. The improved position enabled a measurement of the spin period derivative of the pulsar ( P ˙ = 9 ± 2 × 10 − 19 ); the small inferred magnetic field strength at the surface (B S = 4 × 109 G) indicates that this pulsar has been recycled. This and the orbital eccentricity lead to the conclusion that PSR J1946+2052 is in a DNS system. Among all known radio pulsars in DNS systems, PSR J1946+2052 has the shortest orbital period and the shortest estimated merger timescale, 46 Myr; at that time it will display the largest spin effects on gravitational-wave waveforms of any such system discovered to date. We have measured the advance of periastron passage for this system, ω ˙ = 25.6 ± 0.3 deg yr − 1 , implying a total system mass of only 2.50 ± 0.04 M ⊙, so it is among the lowest-mass DNS systems. This total mass measurement combined with the minimum companion mass constrains the pulsar mass to ≲1.3 M ⊙.

The GALFA-H i Survey Data Release 2

Abstract We present the Galactic Arecibo L-Band Feed Array H i (GALFA-H i) survey data release 2 (DR2). The survey covers the 21 cm hyperfine transition of Galactic H i from −650 to 650 , with 0.184 channel spacing, 4′ angular resolution, and 150 mK rms noise per 1 velocity channel. DR2 covers the entirety of the sky available from the William E. Gordon 305 m antenna at Arecibo, from decl. −1°17′ to decl. + 37°57′ across all R.A.: 4 steradians or 32% of the sky. DR2 differs in a number of ways from data release 1, which was released in 2011. DR2 is built from a largely separate set of observations from DR1, which were taken in a much more consistent mode. This consistency, coupled with more careful attention to systematics and more advanced data reduction algorithms, leads to a much higher-quality DR2 data product. We present three data sets for public use: H i data cubes, far-sidelobe stray-radiation-corrected column density maps, and results of the Rolling Hough Transform linear feature detection algorithm.

ALFABURST: a commensal search for fast radio bursts with Arecibo

ALFABURST has been searching for Fast Radio Bursts (FRBs) commensally with other projects using the Arecibo L-band Feed Array (ALFA) receiver at the Arecibo Observatory since July 2015. We describe the observing system and report on the non-detection of any FRBs from that time until August 2017 for a total observing time of 518 hours. With current FRB rate models, along with measurements of telescope sensitivity and beam size, we estimate that this survey probed redshifts out to about 3.4 with an effective survey volume of around 600,000 Mpc$^3$. Based on this, we would expect, at the 99% confidence level, to see at most two FRBs. We discuss the implications of this non-detection in the context of results from other telescopes and the limitation of our search pipeline. During the survey, single pulses from 17 known pulsars were detected. We also report the discovery of a Galactic radio transient with a pulse width of 3 ms and dispersion measure of 281 pc cm$^{-3}$, which was detected while the telescope was slewing between fields.

Can the Discrepancy between Locally and Globally Derived Neutral Hydrogen Mass Functions be Explained by a Varying Value of M ⋆?

Abstract I investigate whether it is possible to reconcile the recent Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) observation that the neutral hydrogen mass function (HIMF) across different galactic densities has the same, non-flat, faint-end slope, with observations of isolated galaxies and many galaxy groups that show their HIMFs to have flat faint-end slopes. I find that a fairly simple model in which the position of the knee in the mass function of each individual group is allowed to vary is able to account for both of these observations. If this model reflects reality, the ALFALFA results point to an interesting “conspiracy” whereby the differing group HIMFs always sum up to form global HIMFs with the same faint-end slope in different environments. More generally, this result implies that global environmental HIMFs do not necessarily reflect the HIMFs in individual groups belonging to that environment and cannot be used to directly measure variations in group-specific HIMFs with environment.

PSR J1913+1102: a pulsar in a highly asymmetric and relativistic double neutron star system

AbstractPSR J1913+1102 is a double neutron star system (DNS) discovered in the Pulsar Arecibo L-band Feed Array survey. We have now very precisely measured the rate of advance of periastron for the system and the Einstein delay. From general relativity, this results in precise mass measurements: 1.65 ± 0.05 and 1.24 ± 0.05 M⊙ for the pulsar and neutron-star companion, respectively. This makes PSR J1913+1102 both the most massive double neutron star system known, and the most asymmetric in mass among compact DNS binaries. This asymmetry will allow for stringent limits on the effects of dipolar gravitational-wave radiation, predicted by alternative theories of gravity, as well as insight into heavy-element production from the eventual merger of this system and others like it. Further observations will also tighten constraints on formation and evolution models; this is crucial for understanding the DNS population, for which there are relatively few mass measurements.

SETIBURST: A Robotic, Commensal, Realtime Multi-science Backend for the Arecibo Telescope

Abstract Radio astronomy has traditionally depended on observatories allocating time to observers for exclusive use of their telescopes. The disadvantage of this scheme is that the data thus collected is rarely used for other astronomy applications, and in many cases, is unsuitable. For example, properly calibrated pulsar search data can, with some reduction, be used for spectral line surveys. A backend that supports plugging in multiple applications to a telescope to perform commensal data analysis will vastly increase the science throughput of the facility. In this paper, we present “SETIBURST,” a robotic, commensal, realtime multi-science backend for the 305 m Arecibo Telescope. The system uses the 1.4 GHz, seven-beam Arecibo L-band Feed Array (ALFA) receiver whenever it is operated. SETIBURST currently supports two applications: SERENDIP VI, a SETI spectrometer that is conducting a search for signs of technological life, and ALFABURST, a fast transient search system that is conducting a survey of fast radio bursts (FRBs). Based on the FRB event rate and the expected usage of ALFA, we expect 0–5 FRB detections over the coming year. SETIBURST also provides the option of plugging in more applications. We outline the motivation for our instrumentation scheme and the scientific motivation of the two surveys, along with their descriptions and related discussions.

TWO LONG-TERM INTERMITTENT PULSARS DISCOVERED IN THE PALFA SURVEY

ABSTRACT We report the discovery of two long-term intermittent radio pulsars in the ongoing Pulsar Arecibo L-Band Feed Array survey. Following discovery with the Arecibo Telescope, extended observations of these pulsars over several years at Jodrell Bank Observatory have revealed the details of their rotation and radiation properties. PSRs J1910+0517 and J1929+1357 show long-term extreme bimodal intermittency, switching between active (ON) and inactive (OFF) emission states and indicating the presence of a large, hitherto unrecognized underlying population of such objects. For PSR J1929+1357, the initial duty cycle was f ON = 0.008, but two years later, this changed quite abruptly to f ON = 0.16. This is the first time that a significant evolution in the activity of an intermittent pulsar has been seen, and we show that the spin-down rate of the pulsar is proportional to the activity. The spin-down rate of PSR J1929+1357 is increased by a factor of 1.8 when it is in active mode, similar to the increase seen in the other three known long-term intermittent pulsars. These discoveries increase the number of known pulsars displaying long-term intermittency to five. These five objects display a remarkably narrow range of spin-down power ( ) and accelerating potential above their polar caps. If confirmed by further discoveries, this trend might be important for understanding the physical mechanisms that cause intermittency.

Pattern recognition in the ALFALFA.70 and Sloan Digital Sky Surveys: a catalogue of ∼500 000 H i gas fraction estimates based on artificial neural networks

The application of artificial neural networks (ANNs) for the estimation of HI gas mass fraction (\fgas) is investigated, based on a sample of 13,674 galaxies in the Sloan Digital Sky Survey (SDSS) with HI detections or upper limits from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA). We show that, for an example set of fixed input parameters ($g-r$ colour and $i$-band surface brightness), a multidimensional quadratic model yields \fgas\ scaling relations with a smaller scatter (0.22 dex) than traditional linear fits (0.32 dex), demonstrating that non-linear methods can lead to an improved performance over traditional approaches. A more extensive ANN analysis is performed using 15 galaxy parameters that capture variation in stellar mass, internal structure, environment and star formation. Of the 15 parameters investigated, we find that $g-r$ colour, followed by stellar mass surface density, bulge fraction and specific star formation rate have the best connection with \fgas. By combining two control parameters, that indicate how well a given galaxy in SDSS is represented by the ALFALFA training set (\pr) and the scatter in the training procedure (\sigf), we develop a strategy for quantifying which SDSS galaxies our ANN can be adequately applied to, and the associated errors in the \fgas\ estimation. In contrast to previous works, our \fgas\ estimation has no systematic trend with galactic parameters such as M$_{\star}$, $g-r$ and SFR. We present a catalog of \fgas\ estimates for more than half a million galaxies in the SDSS, of which $\sim$ 150,000 galaxies have a secure selection parameter with average scatter in the \fgas\ estimation of 0.22 dex.