arXiv subjects

M. A. Papa

Publications and source records attributed to M. A. Papa.

At least 19 recordsLinked to original sources

arXiv2026

Wide parameter-space O3 search for continuous gravitational waves from unknown neutron stars in binary systems

Continuous gravitational waves, i.e., persistent and nearly-monochromatic signals emitted by asymmetric spinning neutron stars, remain elusive. Searches for these signals from unknown binary systems are the most computationally challenging, but they are essential, given that binary accretion provides a natural mechanism for creating the required asymmetry, and around half of the known pulsars rotating above 25 Hz are part of a binary system. Here we report on a search of a large uncharted parameter-space region: for the first time we cover gravitational-wave frequencies above 520 Hz (from 50 to 1000 Hz), and, for the first time with advanced detectors, orbital periods lower than 3 days are explored. No signal is detected, and we set the most stringent constraints to date on the amplitude of signals of this kind. Our results exclude with $95\%$ confidence neutron stars within 100 pc and rotating faster than $\sim$ 495 Hz from having ellipticities above $5.2 \times 10^{-8}$. Within the same distance our results also exclude r-mode amplitudes above $1.5 \times 10^{-6}$ for stars rotating faster than $\sim$ 740 Hz.

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arXiv2025

Einstein@Home Searches for Gamma-ray Pulsars in the Inner Galaxy

The Fermi Large Area Telescope (LAT) has revealed a mysterious extended excess of GeV gamma-ray emission around the Galactic Center, which can potentially be explained by unresolved emission from a population of pulsars, particularly millisecond pulsars (MSPs), in the Galactic bulge. We used the distributed volunteer computing system Einstein@Home to search the Fermi-LAT data for gamma-ray pulsations from sources in the inner Galaxy, to try to identify the brightest members of this putative population. We discovered four new pulsars, including one new MSP and one young pulsar whose angular separation to the Galactic Center of 0.93° is the smallest of any known gamma-ray pulsar. We demonstrate a phase-resolved difference imaging technique that allows the flux from this pulsar to be disentangled from the diffuse Galactic Center emission. No radio pulsations were detected from the four new pulsars in archival radio observations or during the MPIfR-MeerKAT Galactic Plane Survey. While the distances to these pulsars remain uncertain, we find that it is more likely that they are all foreground sources from the Galactic disk, rather than pulsars originating from the predicted bulge population. Nevertheless, our results are not incompatible with an MSP explanation for the GC excess, as only one or two members of this population would have been detectable in our searches.

astro-ph.HE↗

arXiv2025

Search for continuous gravitational waves from unknown neutron stars in binary systems with long orbital periods in O3 data

Gravitational waves emitted by asymmetric rotating neutron stars are the primary targets of continuous gravitational-wave searches. Neutron stars in binary systems are particularly interesting due to the potential for non-axisymmetric deformations induced by a companion star. However, all-sky searches for unknown neutron stars in binary systems are very computationally expensive and this limits their sensitivity and/or breadth. In this paper we present results of a search for signals with gravitational-wave frequencies between $50$ and $150$~Hz, from systems with orbital periods between $100$ and $1\,000$ days and projected semi-major axes between $40$ and $200$~light-seconds. This parameter-space region has never been directly searched before. We do not detect any signal, and our results exclude gravitational-wave amplitudes above $1.25 \times 10^{-25}$ at $144.32$~Hz with $95\%$ confidence. Our improved search pipeline is more sensitive than any previous all-sky binary search by about $75\%$.

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arXiv2024

Bayesian $\mathcal{F}$-statistic-based parameter estimation of continuous gravitational waves from known pulsars

We present a new method and implementation to obtain Bayesian posteriors on the amplitude parameters $\{h_0, \cos ι, ψ, ϕ_0\}$ of continuous-gravitational waves emitted by known pulsars. This approach leverages the well-established $\mathcal{F}$-statistic framework and software. We further explore the benefits of employing a likelihood function that is analytically marginalized over $ϕ_0$, which avoids signal degeneracy problems in the $ψ$-$ϕ_0$ subspace. The method is tested on simulated signals, hardware injections in Advanced-LIGO detector data, and by performing percentile-percentile (PP) self-consistency tests of the posteriors via Monte-Carlo simulations. We apply our methodology to PSR J1526-2744, a recently discovered millisecond pulsar. We find no evidence for a signal and obtain a Bayesian upper limit $h_0^{95\%}$ on the gravitational-wave amplitude of approximately $7 \times 10^{-27}$, comparable with a previous frequentist upper limit.

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arXiv2023

Deep Einstein@Home all-sky search for continuous gravitational waves in LIGO O3 public data

We present the results of an all-sky search for continuous gravitational waves in the public LIGO O3 data. The search covers signal frequencies $20$ Hz $\leq f \leq 800$ Hz and a spin-down range down to $-2.6\times 10^{-9}$ Hz s$^{-1}$1, motivated by detectability studies on synthetic populations of Galactic neutron stars. This search is the most sensitive all-sky search to date in this frequency/spin-down region. The initial search was performed using the first half of the public LIGO O3 data (O3a), utilizing Graphical Processing Units provided in equal parts by the volunteers of the Einstein@Home computing project and by the ATLAS cluster. After a hierarchical follow-up in seven stages, 12 candidates remain. Six are discarded at the eighth stage, by using the remaining O3 LIGO data (O3b). The surviving six can be ascribed to continuous-wave fake signals present in the LIGO data for validation purposes. We recover these fake signals with very high accuracy with our last stage search, which coherently combines all O3 data. Based on our results, we set upper limits on the gravitational wave amplitude $h_0$, and translate these in upper limits on the neutron star ellipticity and on the $r$-mode amplitude. The most stringent upper limits are at $203$ Hz, with $h_0=8.1 \times 10^{-26}$ at the 90% confidence level. Our results exclude neutron stars rotating faster than $5$ ms with ellipticities greater than $5\times 10^{-8} \left[{d\over{100~\textrm{pc}}}\right]$ within a distance $d$ from Earth and $r$-mode amplitudes $α\geq 10^{-5} \left[{d\over{100~\textrm{pc}}}\right]$ for neutron stars spinning faster than $150$ Hz.

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arXiv2022

The TRAPUM L-band survey for pulsars in Fermi-LAT gamma-ray sources

More than 100 millisecond pulsars (MSPs) have been discovered in radio observations of gamma-ray sources detected by the Fermi Large Area Telescope (LAT), but hundreds of pulsar-like sources remain unidentified. Here we present the first results from the targeted survey of Fermi-LAT sources being performed by the Transients and Pulsars with MeerKAT (TRAPUM) Large Survey Project. We observed 79 sources identified as possible gamma-ray pulsar candidates by a Random Forest classification of unassociated sources from the 4FGL catalogue. Each source was observed for 10 minutes on two separate epochs using MeerKAT's L-band receiver (856-1712 MHz), with typical pulsed flux density sensitivities of $\sim$100$\,μ$Jy. Nine new MSPs were discovered, eight of which are in binary systems, including two eclipsing redbacks and one system, PSR J1526$-$2744, that appears to have a white dwarf companion in an unusually compact 5 hr orbit. We obtained phase-connected timing solutions for two of these MSPs, enabling the detection of gamma-ray pulsations in the Fermi-LAT data. A follow-up search for continuous gravitational waves from PSR J1526$-$2744 in Advanced LIGO data using the resulting Fermi-LAT timing ephemeris yielded no detection, but sets an upper limit on the neutron star ellipticity of $2.45\times10^{-8}$. We also detected X-ray emission from the redback PSR J1803$-$6707 in data from the first eROSITA all-sky survey, likely due to emission from an intra-binary shock.

astro-ph.HE↗

arXiv2022

Constraints on r-modes and mountains on millisecond neutron stars in binary systems

Continuous gravitational waves are nearly monochromatic signals emitted by asymmetries in rotating neutron stars. These signals have not yet been detected. Deep all-sky searches for continuous gravitational waves from isolated neutron stars require significant computational expense. Deep searches for neutron stars in binary systems are even more expensive, but potentially these targets are more promising emitters, especially in the hundreds-Hz region, where ground-based gravitational wave detectors are most sensitive. We present here an all-sky search for continuous signals with frequency between 300 and 500 Hz, from neutron stars in binary systems with orbital period between 15 and 60 days, and projected semi-major axis between 10 and 40 light-seconds. This is the only binary search on Advanced-LIGO data that probes this frequency range. Compared to previous results, our search is over an order of magnitude more sensitive. We do not detect any signals, but our results exclude plausible and unexplored neutron star configurations, for example, neutron stars with relative deformations greater than 3e-6 within 1 kpc from Earth and r-mode emission at the level of alpha ~ few 1e-4 within the same distance.

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arXiv2020

Einstein@Home all-sky search for continuous gravitational waves in LIGO O2 public data

We conduct an all-sky search for continuous gravitational waves in the LIGO O2 data from the Hanford and Livingston detectors. We search for nearly-monochromatic signals with frequency between 20.0 Hz and 585.15 Hz and spin-down between -2.6e-9 Hz/s and 2.6e-10 Hz/s. We deploy the search on the Einstein@Home volunteer-computing project and follow-up the waveforms associated with the most significant results with eight further search-stages, reaching the best sensitivity ever achieved by an all-sky survey up to 500 Hz. Six of the inspected waveforms pass all the stages but they are all associated with hardware-injections, which are fake signals simulated at the LIGO detector for validation purposes. We recover all these fake signals with consistent parameters. No other waveform survives, so we find no evidence of a continuous gravitational wave signal at the detectability level of our search. We constrain the h0 amplitude of continuous gravitational waves at the detector as a function of the signal frequency, in half-Hz bins. The most constraining upper limit at 163.0 Hz is h0 = 1.3e25, at the 90% confidence level. Our results exclude neutron stars rotating faster than 5 ms with equatorial ellipticities larger than 1e-7 closer than 100 pc. These are deformations that neutron star crusts could easily support, according to some models.

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arXiv2020

Discovery of a Gamma-ray Black Widow Pulsar by GPU-accelerated Einstein@Home

We report the discovery of 1.97 ms period gamma-ray pulsations from the 75 minute orbital-period binary pulsar now named PSR J1653-0158. The associated Fermi Large Area Telescope gamma-ray source 4FGL J1653.6-0158 has long been expected to harbor a binary millisecond pulsar. Despite the pulsar-like gamma-ray spectrum and candidate optical/X-ray associations -- whose periodic brightness modulations suggested an orbit -- no radio pulsations had been found in many searches. The pulsar was discovered by directly searching the gamma-ray data using the GPU-accelerated Einstein@Home distributed volunteer computing system. The multi-dimensional parameter space was bounded by positional and orbital constraints obtained from the optical counterpart. More sensitive analyses of archival and new radio data using knowledge of the pulsar timing solution yield very stringent upper limits on radio emission. Any radio emission is thus either exceptionally weak, or eclipsed for a large fraction of the time. The pulsar has one of the three lowest inferred surface magnetic-field strengths of any known pulsar with $B_{\rm surf} \approx 4 \times 10^{7}\,$G. The resulting mass function, combined with models of the companion star's optical light curve and spectra, suggests a pulsar mass $\gtrsim 2\,M_{\odot}$. The companion is light-weight with mass $\sim 0.01\,M_{\odot}$, and the orbital period is the shortest known for any rotation-powered binary pulsar. This discovery demonstrates the Fermi Large Area Telescope's potential to discover extreme pulsars that would otherwise remain undetected.

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arXiv2019

Gravitational waves from compact dark matter objects in the solar system

Dark matter could be composed of compact dark objects (CDOs). A close binary of CDOs orbiting in the interior of solar system bodies can be a loud source of gravitational waves (GWs) for the LIGO and VIRGO detectors. We perform the first search ever for this type of signal and rule out close binaries, with separations of order 300 m, orbiting near the center of the Sun with GW frequencies (twice the orbital frequency) between 50 and 550 Hz and CDO masses above $\approx 10^{-9} M_\odot$. This mass limit is eight orders of magnitude lower than the mass probed in a LIGO search at extra galactic distances.

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arXiv2019

Detection and timing of gamma-ray pulsations from the $707$ Hz pulsar J0952$-$0607

The Low-Frequency Array radio telescope discovered the $707$ Hz binary millisecond pulsar (MSP) J0952$-$0607 in a targeted radio pulsation search of an unidentified $\textit{Fermi}$ gamma-ray source. This source shows a weak energy flux of $F_γ= 2.6 \times 10^{-12}\,\text{erg}\,\text{cm}^{-2}\,\text{s}^{-1}$ in the energy range between $100\,\text{MeV}$ and $100\,\text{GeV}$. Here we report the detection of pulsed gamma-ray emission from PSR$\,$J0952$-$0607 in a very sensitive gamma-ray pulsation search. The pulsar's rotational, binary, and astrometric properties are measured over seven years of $\textit{Fermi}$-Large Area Telescope data. For this we take into account the uncertainty on the shape of the gamma-ray pulse profile. We present an updated radio-timing solution now spanning more than two years and show results from optical modeling of the black-widow-type companion based on new multi-band photometric data taken with HiPERCAM on the Gran Telescopio Canarias on La Palma and ULTRACAM on the New Technology Telescope at ESO La Silla. PSR$\,$J0952$-$0607 is now the fastest-spinning pulsar for which the intrinsic spin-down rate has been reliably constrained ($\dot{P}_\text{int} \lesssim 4.6 \times 10^{-21}\,\text{s}\,\text{s}^{-1}$). The inferred surface magnetic field strength of $B_\text{surf} \lesssim 8.2 \times 10^{7}\,\text{G}$ is among the ten lowest of all known pulsars. This discovery is another example of an extremely fast spinning black-widow pulsar hiding within an unidentified $\textit{Fermi} gamma-ray source. In the future such systems might help to pin down the maximum spin frequency and the minimum surface magnetic field strength of MSPs.

astro-ph.HE↗

arXiv2018

Implementing a semicoherent search for continuous gravitational waves using optimally-constructed template banks

All-sky surveys for isolated continuous gravitational waves present a significant data-analysis challenge. Semicoherent search methods are commonly used to efficiently perform the computationally-intensive task of searching for these weak signals in the noisy data of gravitational-wave detectors such as LIGO and Virgo. We present a new implementation of a semicoherent search method, Weave, that for the first time makes full use of a parameter-space metric to generate banks of search templates at the correct resolution, combined with optimal lattices to minimize the required number of templates and hence the computational cost of the search. We describe the implementation of Weave and associated design choices, and characterize its behavior using semi-analytic models.

astro-ph.IM↗

arXiv2013

Einstein@Home discovery of four young gamma-ray pulsars in Fermi LAT data

We report the discovery of four gamma-ray pulsars, detected in computing-intensive blind searches of data from the Fermi Large Area Telescope (LAT). The pulsars were found using a novel search approach, combining volunteer distributed computing via Einstein@Home and methods originally developed in gravitational-wave astronomy. The pulsars PSRs J0554+3107, J1422-6138, J1522-5735, and J1932+1916 are young and energetic, with characteristic ages between 35 and 56 kyr and spin-down powers in the range $6\times10^{34}$ - $10^{36}$ erg s$^{-1}$. They are located in the Galactic plane and have rotation rates of less than 10 Hz, among which the 2.1 Hz spin frequency of PSR J0554+3107 is the slowest of any known gamma-ray pulsar. For two of the new pulsars, we find supernova remnants coincident on the sky and discuss the plausibility of such associations. Deep radio follow-up observations found no pulsations, suggesting that all four pulsars are radio-quiet as viewed from Earth. These discoveries, the first gamma-ray pulsars found by volunteer computing, motivate continued blind pulsar searches of the many other unidentified LAT gamma-ray sources.

astro-ph.HE↗

arXiv2013

Einstein@Home Discovery of 24 Pulsars in the Parkes Multi-beam Pulsar Survey

We have conducted a new search for radio pulsars in compact binary systems in the Parkes multi-beam pulsar survey (PMPS) data, employing novel methods to remove the Doppler modulation from binary motion. This has yielded unparalleled sensitivity to pulsars in compact binaries. The required computation time of approximately 17000 CPU core years was provided by the distributed volunteer computing project Einstein@Home, which has a sustained computing power of about 1 PFlop/s. We discovered 24 new pulsars in our search, of which 18 were isolated pulsars, and six were members of binary systems. Despite the wide filterbank channels and relatively slow sampling time of the PMPS data, we found pulsars with very large ratios of dispersion measure (DM) to spin period. Among those is PSR J1748-3009, the millisecond pulsar with the highest known DM (approximately 420 pc/cc). We also discovered PSR J1840-0643, which is in a binary system with an orbital period of 937 days, the fourth largest known. The new pulsar J1750-2536 likely belongs to the rare class of intermediate-mass binary pulsars. Three of the isolated pulsars show long-term nulling or intermittency in their emission, further increasing this growing family. Our discoveries demonstrate the value of distributed volunteer computing for data-driven astronomy and the importance of applying new analysis methods to extensively searched data.

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arXiv2013

The Einstein@Home search for radio pulsars and PSR J2007+2722 discovery

Einstein@Home aggregates the computer power of hundreds of thousands of volunteers from 193 countries, to search for new neutron stars using data from electromagnetic and gravitational-wave detectors. This paper presents a detailed description of the search for new radio pulsars using Pulsar ALFA survey data from the Arecibo Observatory. The enormous computing power allows this search to cover a new region of parameter space; it can detect pulsars in binary systems with orbital periods as short as 11 minutes. We also describe the first Einstein@Home discovery, the 40.8 Hz isolated pulsar PSR J2007+2722, and provide a full timing model. PSR J2007+2722's pulse profile is remarkably wide with emission over almost the entire spin period. This neutron star is most likely a disrupted recycled pulsar, about as old as its characteristic spin-down age of 404 Myr. However there is a small chance that it was born recently, with a low magnetic field. If so, upper limits on the X-ray flux suggest but can not prove that PSR J2007+2722 is at least ~ 100 kyr old. In the future, we expect that the massive computing power provided by volunteers should enable many additional radio pulsar discoveries.

astro-ph.IM↗

arXiv2013

Multimessenger astronomy with gravitational waves and high-energy neutrinos

Many of the astrophysical sources and violent phenomena observed in our Universe are potential emitters of gravitational waves (GW) and high-energy neutrinos (HEN). Both GWs and HENs may escape very dense media and travel unaffected over cosmological distances, carrying information from the innermost regions of the astrophysical engines. Such messengers could also reveal new, hidden sources that have not been observed by conventional photon-based astronomy. Coincident observation of GWs and HENs may thus play a critical role in multimessenger astronomy. This is particularly true at the present time owing to the advent of a new generation of dedicated detectors: IceCube, ANTARES, VIRGO and LIGO. Given the complexity of the instruments, a successful joint analysis of this data set will be possible only if the expertise and knowledge of the data is shared between the two communities. This review aims at providing an overview of both theoretical and experimental state-of-the-art and perspectives for such a GW+HEN multimessenger astronomy.

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arXiv2011

Arecibo PALFA Survey and Einstein@Home: Binary Pulsar Discovery by Volunteer Computing

We report the discovery of the 20.7 ms binary pulsar J1952+2630, made using the distributed computing project Einstein@Home in Pulsar ALFA survey observations with the Arecibo telescope. Follow-up observations with the Arecibo telescope confirm the binary nature of the system. We obtain a circular orbital solution with an orbital period of 9.4 hr, a projected orbital radius of 2.8 lt-s, and a mass function of f = 0.15 solar masses by analysis of spin period measurements. No evidence of orbital eccentricity is apparent; we set a 2-sigma upper limit e < 1.7e-3. The orbital parameters suggest a massive white dwarf companion with a minimum mass of 0.95 solar masses, assuming a pulsar mass of 1.4 solar masses. Most likely, this pulsar belongs to the rare class of intermediate mass binary pulsars. Future timing observations will aim to determine the parameters of this system further, measure relativistic effects, and elucidate the nature of the companion star.

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arXiv2010

Pulsar Discovery by Global Volunteer Computing

Einstein@Home aggregates the computer power of hundreds of thousands of volunteers from 192 countries to "mine" large data sets. It has now found a 40.8 Hz isolated pulsar in radio survey data from the Arecibo Observatory taken in February 2007. Additional timing observations indicate that this pulsar is likely a disrupted recycled pulsar. PSR J2007+2722's pulse profile is remarkably wide with emission over almost the entire spin period; the pulsar likely has closely aligned magnetic and spin axes. The massive computing power provided by volunteers should enable many more such discoveries.

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