38 research outputs found
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 ⊙. This fast and energetic ( Ė=3×1035 erg s-1) millisecond pulsar was first detected as a gamma-ray point source in Fermi Large Area Telescope (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 discovery and timing of radio and gamma-ray pulsations, 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. © 2022. The Author(s). Published by the American Astronomical Society
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
. This fast and energetic ( 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.Comment: 15 pages, 6 figures, accepted by Ap
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
The NANOGrav 12.5-Year Data Set: Dispersion Measure Mis-Estimation with Varying Bandwidths
Noise characterization for pulsar-timing applications accounts for
interstellar dispersion by assuming a known frequency-dependence of the delay
it introduces in the times of arrival (TOAs). However, calculations of this
delay suffer from mis-estimations due to other chromatic effects in the
observations. The precision in modeling dispersion is dependent on the observed
bandwidth. In this work, we calculate the offsets in infinite-frequency TOAs
due to mis-estimations in the modeling of dispersion when using varying
bandwidths at the Green Bank Telescope. We use a set of broadband observations
of PSR J1643-1224, a pulsar with an excess of chromatic noise in its timing
residuals. We artificially restricted these observations to a narrowband
frequency range, then used both data sets to calculate residuals with a timing
model that does not include short-scale dispersion variations. By fitting the
resulting residuals to a dispersion model, and comparing the ensuing fitted
parameters, we quantify the dispersion mis-estimations. Moreover, by
calculating the autocovariance function of the parameters we obtained a
characteristic timescale over which the dispersion mis-estimations are
correlated. For PSR J1643-1224, which has one of the highest dispersion
measures (DM) in the NANOGrav pulsar timing array, we find that the
infinite-frequency TOAs suffer from a systematic offset of ~22 microseconds due
to DM mis-estimations, with correlations over ~1 month. For lower-DM pulsars,
the offset is ~7 microseconds. This error quantification can be used to provide
more robust noise modeling in NANOGrav's data, thereby increasing sensitivity
and improving parameter estimation in gravitational wave searches.Comment: 15 pages, 7 figure
The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars
We present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, aimed at detecting and characterizing low-frequency gravitational waves. The pulsars were observed with the Arecibo Observatory and/or the Green Bank Telescope at frequencies ranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximately monthly cadence, and six high-timing-precision pulsars were observed weekly. All were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. We describe our methods for data processing, time-of-arrival (TOA) calculation, and the implementation of a new, automated method for removing outlier TOAs. We fit a timing model for each pulsar that includes spin, astrometric, and (for binary pulsars) orbital parameters; time-variable dispersion delays; and parameters that quantify pulse-profile evolution with frequency. The timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of significant orbital-period variations. We fit models that characterize sources of noise for each pulsar. We find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. A companion paper uses these data to constrain the strength of the gravitational-wave background
An unusual pulse shape change event in PSR J1713+0747 observed with the Green Bank Telescope and CHIME
The millisecond pulsar J1713+0747 underwent a sudden and significant pulse
shape change between April 16 and 17, 2021 (MJDs 59320 and 59321).
Subsequently, the pulse shape gradually recovered over the course of several
months. We report the results of continued multi-frequency radio observations
of the pulsar made using the Canadian Hydrogen Intensity Mapping Experiment
(CHIME) and the 100-meter Green Bank Telescope (GBT) in a three-year period
encompassing the shape change event, between February 2020 and February 2023.
As of February 2023, the pulse shape had returned to a state similar to that
seen before the event, but with measurable changes remaining. The amplitude of
the shape change and the accompanying TOA residuals display a strong
non-monotonic dependence on radio frequency, demonstrating that the event is
neither a glitch (the effects of which should be independent of radio
frequency, ) nor a change in dispersion measure (DM) alone (which would
produce a delay proportional to ). However, it does bear some
resemblance to the two previous "chromatic timing events" observed in
J1713+0747 (Demorest et al. 2013; Lam et al. 2016), as well as to a similar
event observed in PSR J1643-1224 in 2015 (Shannon et al. 2016).Comment: 19 pages, 8 figures. Submitted to ApJ. Data available at
https://doi.org/10.5281/zenodo.723645
The NANOGrav 11 Year Data Set: Pulsar-timing Constraints on the Stochastic Gravitational-wave Background
We search for an isotropic stochastic gravitational-wave background (GWB) in the newly released 11 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). While we find no evidence for a GWB, we place constraints on a population of inspiraling supermassive black hole (SMBH) binaries, a network of decaying cosmic strings, and a primordial GWB. For the first time, we find that the GWB constraints are sensitive to the solar system ephemeris (SSE) model used and that SSE errors can mimic a GWB signal. We developed an approach that bridges systematic SSE differences, producing the first pulsar-timing array (PTA) constraints that are robust against SSE errors. We thus place a 95% upper limit on the GW-strain amplitude of A GWB < 1.45 × 10−15 at a frequency of f = 1 yr−1 for a fiducial f −2/3 power-law spectrum and with interpulsar correlations modeled. This is a factor of ~2 improvement over the NANOGrav nine-year limit calculated using the same procedure. Previous PTA upper limits on the GWB (as well as their astrophysical and cosmological interpretations) will need revision in light of SSE systematic errors. We use our constraints to characterize the combined influence on the GWB of the stellar mass density in galactic cores, the eccentricity of SMBH binaries, and SMBH–galactic-bulge scaling relationships. We constrain the cosmic-string tension using recent simulations, yielding an SSE-marginalized 95% upper limit of Gμ < 5.3 × 10−11—a factor of ~2 better than the published NANOGrav nine-year constraints. Our SSE-marginalized 95% upper limit on the energy density of a primordial GWB (for a radiation-dominated post-inflation universe) is ΩGWB(f) h 2 < 3.4 × 10−10
Multimessenger Gravitational-wave Searches with Pulsar Timing Arrays:Application to 3C 66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65 ± 0.02) × 109 M o˙ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over "blind"pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences
The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars
We present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, aimed at detecting and characterizing low-frequency gravitational waves. The pulsars were observed with the Arecibo Observatory and/or the Green Bank Telescope at frequencies ranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximately monthly cadence, and six high-timing-precision pulsars were observed weekly. All were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. We describe our methods for data processing, time-of-arrival (TOA) calculation, and the implementation of a new, automated method for removing outlier TOAs. We fit a timing model for each pulsar that includes spin, astrometric, and (for binary pulsars) orbital parameters; time-variable dispersion delays; and parameters that quantify pulse-profile evolution with frequency. The timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of significant orbital-period variations. We fit models that characterize sources of noise for each pulsar. We find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. A companion paper uses these data to constrain the strength of the gravitational-wave background