Future Astrophysical Targets for Intensity Interferometry
Norman Murray Canadian Institute for Theoretical Astrophysics (CITA)
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The Multi Aperture Spectroscopic Telescope: Status and potential as an intensity interferometry facility
Sagi Ben Ami Weizmann Institute of Science
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Progress Toward Multi-Channel Intensity Interferometry with the Southern Connecticut Stellar Interferometer
Elliott Horch Southern Connecticut State University
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Intensity Interferometry with the H.E.S.S. telescopes
Naomi Vogel ECAP, FAU Erlangen-Nürnberg
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Intensity correlations: imaging and quantum optics in astrophysics
Robin Kaiser The French National Centre for Scientific Research
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Cosmology from the DESI Data Release 1
Otavio Alves University of Michigan–Ann Arbor
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What is S_8(z_low) actually?
Noah Sailer University of California, Berkeley
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Where are the supermassive black holes measured by PTAs?
Gabriela Sato-Polito Institute for Advanced Study (IAS) - School of Natural Sciences (SNS)
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Future Astrophysical Targets for Intensity Interferometry
Norman Murray Canadian Institute for Theoretical Astrophysics (CITA)
Interferometry is the use of wave interference to measure the properties of a source observed by two or more detectors. For example, the Event Horizon Telescope measures the phase and amplitude of 1.3 mm wavelength radiation at telescopes up to ten thousand kilometers apart to reveal event horizon scale images of supermassive black holes. Measuring wave phases in the optical has been demonstrated for baselines no longer than hundreds of meters. Intensity interferometry dispenses with the need to measure phases, allowing much larger baselines, and hence much higher spatial resolution. The technique has been in use for seven decades, but recent advances in detector technology have reinvigorated interest in the method. I will discuss the basics of intensity interferometry, the characteristics of the new detectors, and possible applications of broad astrophysical and cosmological interest. The latter include estimates of the Hubble constant from observations of the disks of active galactic nuclei (AGN), with possible impact on the Hubble tension. The same observations will provide detailed information on the AGN disk and line emission regions; the latter may be crucial for estimating the mass loss rates in AGN winds, which are believed to impact their host galaxies. Other possible applications include spatially resolved measurements of stellar oscillations, which, by analogy with helioseismology, would provide constraints on the run of temperature in stellar interiors, as well as the interior differential rotation. -
Intensity Interferometer Results on Sirius with 0.25 m Telescopes
We present the design and initial results of a stellar intensity interferometer using small 0.25 m Newtonian-style telescopes in an urban backyard setting. The primary purpose of the interferometer is to measure the angular diameters of stars. Recent advances in low jitter time-tagging equipment and Single Photon Avalanche Detectors have made the detection of second-order correlation signals, necessary for Intensity Interferometry as demonstrated by Hanbury Brown and Twiss in 1956, feasible with small telescopes. Using Sirius as a target star, we observe a strong second-order correlation spike with an integrated signal to noise ratio (SNR) ∼7 after 13.55 h of integration over a three-night period using a 3.3 m baseline. The measured signal agrees with the theoretical estimates of both coherence time, 𝜏coh = 0.74 ± 0.26 ps and SNR. We discuss the future expansion of this technique with multiple wavelengths simultaneously via a prism grating and multiple detectors. -
The Multi Aperture Spectroscopic Telescope: Status and potential as an intensity interferometry facility
Sagi Ben Ami Weizmann Institute of Science
The Multi-Aperture Spectroscopic Telescope is an array of 20x60cm prime-focus telescopes with single F/3 parabolic mirrors. The telescope array is being commissioned in the Negev Desert, with 10 telescopes expected to see first light by the end of the year. In the following talk, I will present the array, its various properties, including unique fiber coupling and imaging units, and its potential as an intensity interferometry facility. -
The VERITAS SII Observatory
Dave Kieda University of Utah
The VERITAS Imaging Atmospheric Cherenkov Telescope array was augmented in 2019 with high-speed focal plane electronics to allow VERITAS for Stellar Intensity Interferometry (VSII) observations. Since December 2019, VSII has been used to measure angular diameters of bright (OBA) stars at an effective wavelength of 416 nm. VSII observations have also served as a testbed to explore hardware and analysis improvements to advance the instrument's sensitivity. VSII has performed more than 730 hours of moonlit observations on 56 bright stars and binary systems ($ -1.46 < m_V < 4.22$). This talk will describe the VSII observatory, highlight selected observations made by the VSII observatory, and describe ongoing improvements in detector instrumentation and analysis. -
Progress Toward Multi-Channel Intensity Interferometry with the Southern Connecticut Stellar Interferometer
Elliott Horch Southern Connecticut State University
The renaissance in stellar intensity interferometry has resulted in two main types of telescope arrays: those using large "light bucket" telescopes and photomultiplier tubes, such as CTA, VERITAS, MAGIC, and others, and those that instead use smaller, more traditional astronomical telescopes with high-grade optics, such as the systems at the Cote d'Azur and Asiago Observatories. To detect and timestamp photons, these latter systems have used single-photon avalanche diode (SPAD) detectors. This talk will focus on the latter type of instrument, which is also being pursued at Southern Connecticut State University. The current status of our instrument, the Southern Connecticut Stellar Interferometer (SCSI), will be reviewed, and prospects for improved sensitivity will be discussed. Principal among these is the use of SPAD arrays, which are increasingly available, to record different wavelengths simultaneously. If a sufficient number of channels can be employed, this type of intensity interferometer can reach much fainter magnitudes than currently possible. The talk will also briefly discuss work toward wireless intensity interferometry with SCSI, which will make larger baselines easier to set up and use, and ideas for quantum-assisted intensity interferometry that might be employed with SCSI in the future. -
Intensity Interferometry with the H.E.S.S. telescopes
Naomi Vogel ECAP, FAU Erlangen-Nürnberg
Intensity Interferometry (II) is a method that can achieve high angular resolution and was first employed in the 1960s by Robert Brown and Richard Q. Twiss (HBT). Since then, significant advancements have been made, particularly in the construction of telescopes with large light collection areas, such as Imaging Atmospheric Cherenkov Telescopes (IACTs), exemplified by instruments like H.E.S.S. , MAGIC and VERITAS. Our II setup was designed to be mounted on the lid of the Phase I H.E.S.S. telescopes in Namibia. In April 2022, our first observation campaign was conducted, during which two telescopes operated in a single wavelength band. In April-May 2023, a third telescope was added, and observations were performed in two colors simultaneously for the first time in II. In this contribution I will introduce our setup and compare the different configurations, as well as present the latest results of four southern hemisphere stars. -
Intensity correlations: imaging and quantum optics in astrophysics
Robin Kaiser The French National Centre for Scientific Research
In this talk, I will give an introduction to intensity correlations for astrophysical imaging, as pioneered by Hanbury Brown and Twiss. This triggered a wider effort for the field of quantum optics, which I will put into a larger context beyond astrophysical imaging. I will also give an overview of the past results on intensity correlations for astrophysical imaging by our group in Nice and present the ongoing effort towards resolving a white dwarf and to search for signatures of random lasing in space. -
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Large Scale White Noise and Cosmology
Albert StebbinsThe generation of large scales white noise is a generic property of the dynamics of physical systems described by local non-linear partial differential equations. Non-linearities prevent the small scale dynamics to be erased by smoothing. Unresolved small scale dynamics act as an uncorrelated (white or Poissonian) noise (seemingly stochastic but actually deterministic) contribution to large scale dynamics. Such is the case for cosmic inhomogeneities. In the standard model of cosmology the primordial density power spectrum is taken to be sub-Poissonian and subsequent non-linear evolutions will inevitably produce white noise which will dominate on the largest scales. Non-observation of white noise on the Hubble scale precludes a power law extrapolation of the power spectrum below one comoving parsec and places severe constraints on a wide variety of phenomena in the early universe, including phase transitions, vorticity and gravitational radiation.
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Cosmology from the DESI Data Release 1
Otavio Alves University of Michigan–Ann Arbor
On April 4th, 2024, the Dark Energy Spectroscopic Instrument (DESI) released its first set of cosmological results based on measurements of the baryon acoustic oscillations (BAO) scale in the spatial distribution of galaxies and quasars, and in the Lyman-alpha forest. Those measurements constrain the expansion history of the Universe in the redshift range 0.1 < z < 4.16, with implications for studies of dark energy, neutrino cosmology and the Hubble constant. To make the most of the cosmological information content of the galaxy & quasar distributions, we now analyze the full shape of their power spectra, constraining the evolution of the large scale structure of the Universe over the range 0.1 < z < 2.1. In this talk, following a brief overview of the DESI instrument and observations, we will present the latest public results, discuss some of their main cosmological implications, highlight efforts towards the full shape results and expectations for the next data release.
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What is S_8(z_low) actually?
Noah Sailer University of California, Berkeley
Claims of a low clustering amplitude (S_8) at low redshifts from weak galaxy lensing measurements trace back nearly a decade, however, recent work suggests these results may be driven by large baryonic feedback or mischaracterization of linear alignments. I will present a complimentary approach to measure the evolution of S_8(z) using spectroscopically calibrated DESI galaxies and the latest CMB lensing measurements from Planck and ACT. These data are insensitive to many of the systematic complications present in galaxy lensing measurements, while our fiducial Hybrid Effective Field Theory model robustly regulates the information obtainable from smaller scales, such that our cosmological constraints are reliably derived from the (predominantly) linear regime. Our tomographic analysis of DESI Luminous Red Galaxies (LRG) prefers a slightly lower (5 − 7%) value of S_8 than primary CMB measurements with a statistical significance ranging from 1.8 − 2.3σ. Intriguingly, our lowest redshift LRG bin is most discrepant with a Planck cosmology, leaving open the possibility that structure growth is slowing down for redshifts z < 0.5. To address this possibility, I will conclude my talk with preliminary results from the DESI Bright Galaxy Survey, which enable tomographic S_8(z) measurements over the redshift range 0.1 \lesssim z \lesssim 0.4.
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Where are the supermassive black holes measured by PTAs?
Gabriela Sato-Polito Institute for Advanced Study (IAS) - School of Natural Sciences (SNS)
Pulsar timing arrays (PTAs) consist of a set of regularly monitored millisecond pulsars with extremely stable rotational periods. The arrival time of pulses can be altered by the passage of gravitational waves (GWs) between them and the Earth, thus serving as a galaxy-wide GW detector. Evidence for the first detection of low-frequency (~nHz) gravitational waves has recently been reported across multiple PTA collaborations, opening a new observational window into the Universe. Although the origin of the GW signal is yet to be determined, the dominant sources are expected to be inpiralling supermassive black holes (SMBHs). I will discuss a recent work in which we compare the GW detections by PTAs with the expected signal implied by existing electromagnetic observations in a simple but robust manner. This study suggests that the currently measured GW amplitude is larger than expected by a significant amount. I will then show that additional information regarding the typical number of sources contributing to the background can already be inferred from current PTA data.