Unveiling the gravitational universe at μ-Hz frequencies

AbstractWe propose a space-based interferometer surveying the gravitational wave (GW) sky in the milli-Hz to μ-Hz frequency range. By the 2040s, the μ-Hz frequency band, bracketed in between the Laser Interferometer Space Antenna (LISA) and pulsar timing arrays, will constitute the largest gap in the coverage of the astrophysically relevant GW spectrum. Yet many outstanding questions related to astrophysics and cosmology are best answered by GW observations in this band. We show that a μ-Hz GW detector will be a truly overarching observatory for the scientific community at large, greatly extending the potential of LISA. Conceived to detect massive black hole binaries from their early inspiral with high signal-to-noise ratio, and low-frequency stellar binaries in the Galaxy, this instrument will be a cornerstone for multimessenger astronomy from the solar neighbourhood to the high-redshift Universe.

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Constraining the nanohertz gravitational wave background with the Parkes Pulsar Timing Array

Proceedings of the International Astronomical Union ◽

10.1017/s174392131202354x ◽

2012 ◽

Vol 8 (S291) ◽

pp. 177-177

Author(s):

Ryan Shannon

Keyword(s):

Gravitational Wave ◽

Gravitational Waves ◽

Direct Detection ◽

Massive Black Hole ◽

Black Hole Binaries ◽

Pulsar Timing ◽

The Galaxy ◽

Gravitational Wave Background ◽

Pulsar Timing Array ◽

The Universe

AbstractThe direct detection of gravitational waves will usher in a new era of astrophysics, enabling the study of regions of the universe opaque to electromagnetic radiation or electromagnetically quiet. An ensemble of pulsars (referred to as a pulsar timing array) provides a set of clocks distributed across the Galaxy sensitive to gravitational waves with periods on the order of five years (frequencies of many nanohertz). Plausible source of gravitational waves in this frequency band include massive black hole binaries in the throes of mergers and oscillating cosmic strings. The stochastic gravitational wave background, the sum of gravitational waves emitted throughout the universe, is the most likely signal to be detected by a pulsar timing array.While the detection of gravitational waves will be a milestone in pulsar astronomy, a constraining limit on the strength of the gravitational wave background can be used to constrain cosmological models and early Universe physics. Here we present a new algorithm that can be used to constrain the strength of the GWB with a pulsar timing array. We then apply this technique to Parkes Pulsar Timing Array observations and place a new limit on the strength of the GWB. We conclude by discussing the astrophysical implications of this limit and the prospects for detecting gravitational waves with pulsars.

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Applying clock comparison methods to pulsar timing observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab742 ◽

2021 ◽

Author(s):

Siyuan Chen ◽

François Vernotte ◽

Enrico Rubiola

Keyword(s):

Low Frequency ◽

Noise Signal ◽

Time Of Arrival ◽

Massive Black Hole ◽

Black Hole Binaries ◽

Pulsar Timing ◽

Celestial Bodies ◽

Clock Comparison ◽

Pulsar Timing Array ◽

Frequency Metrology

Abstract Frequency metrology outperforms any other branch of metrology in accuracy (parts in 10−16) and small fluctuations (<10−17). In turn, among celestial bodies, the rotation speed of millisecond pulsars (MSP) is by far the most stable (<10−18). Therefore, the precise measurement of the time of arrival (TOA) of pulsar signals is expected to disclose information about cosmological phenomena, and to enlarge our astrophysical knowledge. Related to this topic, Pulsar Timing Array (PTA) projects have been developed and operated for the last decades. The TOAs from a pulsar can be affected by local emission and environmental effects, in the direction of the propagation through the interstellar medium or universally by gravitational waves from super massive black hole binaries. These effects (signals) can manifest as a low-frequency fluctuation over time, phenomenologically similar to a red noise. While the remaining pulsar intrinsic and instrumental background (noise) are white. This article focuses on the frequency metrology of pulsars. From our standpoint, the pulsar is an accurate clock, to be measured simultaneously with several telescopes in order to reject the uncorrelated white noise. We apply the modern statistical methods of time-and-frequency metrology to simulated pulsar data, and we show the detection limit of the correlated red noise signal between telescopes.

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Low‐Frequency Gravitational Waves from Massive Black Hole Binaries: Predictions forLISAand Pulsar Timing Arrays

The Astrophysical Journal ◽

10.1086/375187 ◽

2003 ◽

Vol 590 (2) ◽

pp. 691-706 ◽

Cited By ~ 205

Author(s):

J. Stuart B. Wyithe ◽

Abraham Loeb

Keyword(s):

Black Hole ◽

Gravitational Waves ◽

Low Frequency ◽

Massive Black Hole ◽

Black Hole Binaries ◽

Pulsar Timing

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Detection of Small Magnetic Fields Using Serial Magnetic Tunnel Junctions with Various Geometrical Characteristics

Sensors ◽

10.3390/s20195704 ◽

2020 ◽

Vol 20 (19) ◽

pp. 5704

Author(s):

Zhenhu Jin ◽

Yupeng Wang ◽

Kosuke Fujiwara ◽

Mikihiko Oogane ◽

Yasuo Ando

Keyword(s):

Magnetic Fields ◽

Signal To Noise Ratio ◽

Low Frequency ◽

High Signal ◽

Free Layer ◽

Signal To Noise ◽

Noise Spectral Density ◽

Junction Area ◽

Geometrical Characteristics ◽

Noise Ratio

Thanks to their high magnetoresistance and integration capability, magnetic tunnel junction-based magnetoresistive sensors are widely utilized to detect weak, low-frequency magnetic fields in a variety of applications. The low detectivity of MTJs is necessary to obtain a high signal-to-noise ratio when detecting small variations in magnetic fields. We fabricated serial MTJ-based sensors with various junction area and free-layer electrode aspect ratios. Our investigation showed that their sensitivity and noise power are affected by the MTJ geometry due to the variation in the magnetic shape anisotropy. Their MR curves demonstrated a decrease in sensitivity with an increase in the aspect ratio of the free-layer electrode, and their noise properties showed that MTJs with larger junction areas exhibit lower noise spectral density in the low-frequency region. All of the sensors were able detect a small AC magnetic field (Hrms = 0.3 Oe at 23 Hz). Among the MTJ sensors we examined, the sensor with a square-free layer and large junction area exhibited a high signal-to-noise ratio (4792 ± 646). These results suggest that MTJ geometrical characteristics play a critical role in enhancing the detectivity of MTJ-based sensors.

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Modelling a bright z = 6 galaxy at the faint end of the AGN luminosity function

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1012 ◽

2020 ◽

Vol 494 (3) ◽

pp. 3453-3463

Author(s):

Maxime Trebitsch ◽

Marta Volonteri ◽

Yohan Dubois

Keyword(s):

Black Hole ◽

High Redshift ◽

Galactic Nuclei ◽

Stellar Populations ◽

Star Forming ◽

Relative Contribution ◽

Lyman Break Galaxies ◽

The Galaxy ◽

Galaxy Population ◽

High Redshift Universe

ABSTRACT Recent deep surveys have unravelled a population of faint active galactic nuclei (AGNs) in the high-redshift Universe, leading to various discussions on their nature and their role during the Epoch of Reionization. We use cosmological radiation hydrodynamics simulations of a bright galaxy at z ∼ 6 (${M_\star } \gtrsim 10^{10}\, {\rm M}_{\odot }$) hosting an actively growing supermassive black hole to study the properties of these objects. In particular, we study how the black hole and the galaxy coevolve and what is the relative contribution of the AGNs and of the stellar populations to the luminosity budget of the system. We find that the feedback from the AGN has no strong effect on the properties of the galaxy, and does not increase the total ionizing luminosity of the host. The average escape fraction of our galaxy is around $f_{\rm esc} \sim 5{{\ \rm per\ cent}}$. While our galaxy would be selected as an AGN in deep X-ray surveys, most of the ultraviolet (UV) luminosity is originating from stellar populations. This confirms that there is a transition in the galaxy population from star-forming galaxies to quasar hosts, with bright Lyman-break galaxies with MUV around −22 falling in the overlap region. Our results also suggest that faint AGNs do not contribute significantly to reionizing the Universe.

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GALEX absolute calibration and extinction coefficients based on white dwarfs

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2506 ◽

2019 ◽

Vol 489 (4) ◽

pp. 5046-5052 ◽

Cited By ~ 1

Author(s):

Renae E Wall ◽

Mukremin Kilic ◽

P Bergeron ◽

B Rolland ◽

C Genest-Beaulieu ◽

...

Keyword(s):

Galaxy Evolution ◽

White Dwarfs ◽

Signal To Noise Ratio ◽

Model Atmosphere ◽

Absolute Calibration ◽

High Signal ◽

Extinction Coefficients ◽

Near Ultraviolet ◽

The Galaxy ◽

Far Ultraviolet

ABSTRACT We use 1837 DA white dwarfs with high signal-to-noise ratio spectra and Gaia parallaxes to verify the absolute calibration and extinction coefficients for the Galaxy Evolution Explorer (GALEX). We use white dwarfs within 100 pc to verify the linearity correction to the GALEX data. We find that the linearity correction is valid for magnitudes brighter than 15.95 and 16.95 for the far-ultraviolet (FUV) and near-ultraviolet (NUV) bands, respectively. We also use DA white dwarfs beyond 250 pc to calculate extinction coefficients in the FUV and NUV bands: RFUV = 8.01 ± 0.07 and RNUV = 6.72 ± 0.04. These are consistent with the predicted extinction coefficients for Milky Way-type dust in the FUV, but smaller than predictions in the NUV. With well understood optical spectra and state-of-the-art model atmosphere analysis, these white dwarfs currently provide the best constraints on the extinction coefficients for the GALEX data.

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Principles of Gravitational-Wave Detection with Pulsar Timing Arrays

Symmetry ◽

10.3390/sym13122418 ◽

2021 ◽

Vol 13 (12) ◽

pp. 2418

Author(s):

Michele Maiorano ◽

Francesco De Paolis ◽

Achille A. Nucita

Keyword(s):

Gravitational Wave ◽

Gravitational Waves ◽

Low Frequency ◽

Black Hole Binaries ◽

Pulsar Timing ◽

Time Correlations ◽

Array Detection ◽

Square Kilometer Array ◽

Gravitational Wave Background ◽

Pulsar Timing Array

Pulsar timing uses the highly stable pulsar spin period to investigate many astrophysical topics. In particular, pulsar timing arrays make use of a set of extremely well-timed pulsars and their time correlations as a challenging detector of gravitational waves. It turns out that pulsar timing arrays are particularly sensitive to ultra-low-frequency gravitational waves, which makes them complementary to other gravitational-wave detectors. Here, we summarize the basics, focusing especially on supermassive black-hole binaries and cosmic strings, which have the potential to form a stochastic gravitational-wave background in the pulsar timing array detection band, and the scientific goals on this challenging topic. We also briefly outline the recent interesting results of the main pulsar timing array collaborations, which have found strong evidence of a common-spectrum process compatible with a stochastic gravitational-wave background and mention some new perspectives that are particularly interesting in view of the forthcoming radio observatories such as the Five hundred-meter Aperture Spherical Telescope, the MeerKAT telescope, and the Square Kilometer Array.

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Reaching thermal noise at ultra-low radio frequencies

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038663 ◽

2020 ◽

Vol 642 ◽

pp. A85 ◽

Cited By ~ 1

Author(s):

F. de Gasperin ◽

G. Brunetti ◽

M. Brüggen ◽

R. van Weeren ◽

W. L. Williams ◽

...

Keyword(s):

Thermal Noise ◽

Signal To Noise Ratio ◽

Low Frequency ◽

Galaxy Cluster ◽

Cosmic Ray ◽

Radio Halo ◽

Cosmic Ray Acceleration ◽

The Galaxy ◽

Background Turbulence ◽

Post Shock

Context. Ultra-low frequency observations (< 100 MHz) are particularly challenging because they are usually performed in a low signal-to-noise ratio regime due to the high sky temperature and because of ionospheric disturbances whose effects are inversely proportional to the observing frequency. Nonetheless, these observations are crucial for studying the emission from low-energy populations of cosmic rays. Aims. We aim to obtain the first thermal-noise limited (∼1.5 mJy beam−1) deep continuum radio map using the Low Frequency Array’s Low Band Antenna (LOFAR LBA) system. Our demonstration observation targeted the galaxy cluster RX J0603.3+4214 (known as the Toothbrush cluster). We used the resulting ultra-low frequency (39–78 MHz) image to study cosmic-ray acceleration and evolution in the post shock region considering the presence of a radio halo. Methods. We describe the data reduction we used to calibrate LOFAR LBA observations. The resulting image was combined with observations at higher frequencies (LOFAR 150 MHz and VLA 1500 MHz) to extract spectral information. Results. We obtained the first thermal-noise limited image from an observation carried out with the LOFAR LBA system using all Dutch stations at a central frequency of 58 MHz. With eight hours of data, we reached an rms noise of 1.3 mJy beam−1 at a resolution of 18″ × 11″. Conclusions. The procedure we developed is an important step towards routine high-fidelity imaging with the LOFAR LBA. The analysis of the radio spectra shows that the radio relic extends to distances of 800 kpc downstream from the shock front, larger than what is allowed by electron cooling time. Furthermore, the shock wave started accelerating electrons already at a projected distance of < 300 kpc from the crossing point of the two clusters. These results may be explained by electrons being re-accelerated downstream by background turbulence, possibly combined with projection effects with respect to the radio halo.

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The effect of differential accretion on the gravitational wave background and the present-day MBH binary population

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2361 ◽

2020 ◽

Vol 498 (1) ◽

pp. 537-547 ◽

Cited By ~ 2

Author(s):

Magdalena S Siwek ◽

Luke Zoltan Kelley ◽

Lars Hernquist

Keyword(s):

Gravitational Wave ◽

Analytical Models ◽

Galaxy Mergers ◽

Mass Ratio ◽

Massive Black Hole ◽

Black Hole Binaries ◽

Pulsar Timing ◽

Coalescence Rate ◽

Gravitational Wave Background ◽

First Time

ABSTRACT Massive black hole binaries (MBHBs) form as a consequence of galaxy mergers. However, it is still unclear whether they typically merge within a Hubble time, and how accretion may affect their evolution. These questions will be addressed by pulsar timing arrays (PTAs), which aim to detect the gravitational wave (GW) background (GWB) emitted by MBHBs during the last Myr of inspiral. Here, we investigate the influence of differential accretion on MBHB merger rates, chirp masses, and the resulting GWB spectrum. We evolve an MBHB sample from the Illustris hydrodynamic cosmological simulation using semi-analytical models and for the first time self-consistently evolve their masses with binary accretion models. In all models, MBHBs coalesce with median total masses up to 1.5 × 108 M⊙, up to 3−4 times larger than in models neglecting accretion. In our model with the largest plausible impact, the median mass ratio of coalescing MBHBs increases by a factor 3.6, the coalescence rate by $52.3{{\ \rm per\ cent}}$, and the GWB amplitude by a factor 4.0, yielding a dimensionless GWB strain $A_{yr^{-1}} = 1 \times 10^{-15}$. Our model that favours accretion on to the primary MBH reduces the median mass ratio of coalescing MBHBs by a factor of 2.9, and yields a GWB amplitude $A_{yr^{-1}} = 3.1 \times 10^{-16}$. This is nearly indistinguishable from our model neglecting accretion, despite higher MBHB masses at coalescence. We further predict binary separation and mass ratio distributions of stalled MBHBs in the low-redshift Universe, and find that these depend sensitively on binary accretion models. This presents the potential for combined electromagnetic and GW observational constraints on merger rates and accretion models of MBHB populations.

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