Panoramic SETI Program Update and High-Energy Astrophysics Applications J er ome Mairea Shelley A. Wrightab Jamie Holderc David Andersond Wystan Benbowe

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Panoramic SETI: Program Update and High-Energy

Astrophysics Applications

J´erˆome Mairea, Shelley A. Wrighta,b, Jamie Holderc, David Andersond, Wystan Benbowe,

Aaron Browna, Maren Cosensa,b, Gregory Footec, William F. Hanlone, Olivier Hervetf, Paul

Horowitzg, Andrew W. Howardh, Ryan Leed, Wei Liud,i, Rick Raﬀantij, Nicolas Rault-Wangd,i,

Remington P. S. Stonek, Dan Werthimerd,i, James Wileya,b, and David A. Williamsf

aCenter for Astrophysics & Space Sciences, University of California San Diego, CA, USA

bDepartment of Physics, University of California San Diego, CA, USA

cDepartment of Physics and Astronomy, University of Delaware, DE, USA.

dSpace Sciences Laboratory, University of California Berkeley, CA, USA

eCenter for Astrophysics |Harvard & Smithsonian, Cambridge, MA, USA

fSanta Cruz Institute for Particle Physics and Department of Physics, University of California,

Santa Cruz, CA, USA

gDepartment of Physics, Harvard University, Cambridge, MA, USA

hAstronomy Department, California Institute of Technology, Pasadena, CA, USA

iDepartment of Astronomy, University of California Berkeley, CA, USA

jTechne Instruments, Oakland, CA, USA

kUniversity of California Observatories, Lick Observatory, CA, USA

ABSTRACT

Optical SETI (Search for Extraterrestrial Intelligence) instruments that can explore the very fast time domain,

especially with large sky coverage, oﬀer an opportunity for new discoveries that can complement multimessenger

and time domain astrophysics. The Panoramic SETI experiment (PANOSETI) aims to observe optical transients

with nanosecond to second duration over a wide ﬁeld-of-view (∼2,500 sq.deg.) by using two assemblies of tens

of telescopes to reject spurious signals by coincidence detection. Three PANOSETI telescopes, connected to a

White Rabbit timing network used to synchronize clocks at the nanosecond level, have been deployed at Lick

Observatory on two sites separated by a distance of 677 meters to distinguish nearby light sources (such as

Cherenkov light from particle showers in the Earth’s atmosphere) from astrophysical sources at large distances.

In parallel to this deployment, we present results obtained during four nights of simultaneous observations with

the four 12-meter VERITAS gamma-ray telescopes and two PANOSETI telescopes at the Fred Lawrence Whipple

Observatory. We report PANOSETI’s ﬁrst detection of astrophysical gamma rays, comprising three events with

energies in the range between ∼15 TeV and ∼50 TeV. These were emitted by the Crab Nebula, and identiﬁed

as gamma rays using joint VERITAS observations.

Keywords: Nanosecond timing, transients, Cherenkov shower, Cosmic Rays, Gamma Rays, SETI

1. INTRODUCTION

Astronomical instruments with precision time resolution can be employed to search for technosignatures by means

of detecting nano- to milli-second light pulses that could be emitted, for instance, for the purpose of interstellar

communications or energy transfer. Numerous programs have been conducted to search for technosignatures

using optical wavelengths1–7including near-infrared.8With 0.32 sq.deg. of instantaneous ﬁeld-of-view, the ﬁrst

optical SETI all-sky surveys9,10 used a transit observing approach to cover the sky in 150 clear nights. To

Further author information: (Send correspondence to J.M.)

J.M.: E-mail: jmaire@ucsd.edu

arXiv:2210.01356v1 [astro-ph.IM] 4 Oct 2022

eﬃciently and constantly survey the entire sky, however, groups of single-aperture telescopes capable of collecting

light instantaneously from diﬀerent parts of the sky are still required.

The Panoramic SETI experiment (PANOSETI11–14) is an all-sky observatory project aiming to detect tran-

sients that will cover a wide range of timescales in a search for nanosecond to second pulsed light signals across all

optical wavelengths. Each part of the sky is observed simultaneously from two locations for direct detection and

conﬁrmation of transients. Based upon two assemblies of twenty-four 0.46-m Fresnel-lens telescopes equipped

with fast, low-noise silicon photo-multipliers operating in the 0.32–0.85 µm spectral range, the PANOSETI in-

strument can detect ﬂashes of light that could have been sent from kiloparsec distances and beamed toward our

direction. For instance, a pulse of light emitted by a laser delivering 20 ns shaped pulses of megajoule energies

and collimated with a 10-m telescope located at 1 kpc away from us would be orders of magnitude brighter than

the entire broadband visible stellar background from our perspective.4

The small aperture, wide ﬁeld-of-view, and low cost of the PANOSETI telescopes also make them potentially

well-suited for gamma-ray astronomy at the highest energies. When a high-energy gamma-ray photon or cosmic-

ray particle enters the Earth’s atmosphere, it initiates a particle cascade which can be detected via the pulse of

blue Cherenkov radiation it emits. Ground-based gamma-ray telescopes exploit this eﬀect, using large aperture

(>10 m) mirrors and fast photo-detector cameras to record Cherenkov images of the showers. Subsequent

analysis of these images allows determination of the nature of the primary (photon or particle), its arrival

direction and its energy. The energy range covered by this technique is typically from around 100 GeV to tens

of TeV, reaching 100 TeV only for the brightest sources. Hundreds of astrophysical gamma-ray sources, both

Galactic and extragalactic, have been identiﬁed using this technique∗. At higher energies, direct detection of the

shower particles is used; recent results from the LHAASO collaboration have revealed the existence of gamma-ray

emitters extending up to PeV energies.15 The main beneﬁt of this particle detection approach is that it provides

the large eﬀective area (>1 km2) which is required to measure the extremely low ﬂux of gamma rays at the

highest energy. Cherenkov telescopes can operate in the same energy range, but are typically non-imaging, to

reduce unit cost (e.g., TAIGA-HiScore16). The unit cost of PANOSETI telescopes is approximately two orders

of magnitude less than a large aperture imaging Cherenkov telescope, such as those that make up the VERITAS

array. A large array of low-cost PANOSETI telescopes, each equipped with a 1,000 pixel camera, would permit

applying the beneﬁts of the imaging technique (excellent angular resolution, energy resolution and background

discrimination) to the PeV regime.

We describe in Sect.2the recent deployment of a third PANOSETI telescope at Lick Observatory providing

a baseline separation of 677-m. We report in Sect.3results obtained from joint PANOSETI and VERITAS

observations at the Whipple Observatory in November 2021.

2. PANOSETI: PROGRAM UPDATE

The PANOSETI experiment aims to observe 2,350 square degrees instantaneously by making use of multiple

large ﬁeld-of-view telescopes. PANOSETI is currently in its ﬁnal design phase, and at ﬁnal production two

dedicated observatories will house 24 telescopes per site. Each part of the sky is observed simultaneously from

two locations for direct detection and conﬁrmation of optical transients.

Each telescope is equipped with a 0.46-m f/1.32 Fresnel-lens which focuses the light onto a 32x32-pixel photon-

counting detector subdivided into 16 adjacent 8x8-pixel Multi-Pixel Photon Counter (Hamamatsu S13361-

3050AE-08) detector arrays operating in the 0.32 - 0.85 µm spectral range. These silicon photomultipliers (SiPMs)

are comprised of Geiger-mode-operated avalanche photodiodes highly linear in pulse intensity, with a high in-

ternal gain to enable single-photon detection while featuring low dark count (<1 Mcps per SiPM), high photon

detection eﬃciency in the visible (45%), and nanosecond timing resolution. Each PANOSETI detector contains

four custom readout boards that make use of a 64-bit Application-Speciﬁc Integrated Circuit (ASIC) capable of

pulse shaping and trigger detection of individual pulses. Each detector board reads four 8x8 pixel SiPM arrays

that feed four ASICs, amplifying the signal and delivering a per-pixel trigger signal to a Field Programmable Gate

Array (FPGA). A 1 Gb per second ﬁber connection provides data communications to a central multi-telescope

10 Gb network switch connected to a central computer.

∗http://tevcat.uchicago.edu/

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PanoramicSETI:ProgramUpdateandHigh-EnergyAstrophysicsApplicationsJer^omeMairea,ShelleyA.Wrighta,b,JamieHolderc,DavidAndersond,WystanBenbowe,AaronBrowna,MarenCosensa,b,GregoryFootec,WilliamF.Hanlone,OlivierHervetf,PaulHorowitzg,AndrewW.Howardh,RyanLeed,WeiLiud,i,RickRaantij,NicolasRault-Wangd,i,Rem...

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Panoramic SETI Program Update and High-Energy Astrophysics Applications J er ome Mairea Shelley A. Wrightab Jamie Holderc David Andersond Wystan Benbowe

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