The Sub-TeV transient Gamma-Ray sky: challenges and opportunities (original) (raw)
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A brief history of gravitational wave research
For the benefit of the readers of this journal, the editors requested that we prepare a brief review of the history of the development of the theory, the experimental attempts to detect them, and the recent direct observations of gravitational waves (GWs). The theoretical ideas and disputes beginning with Einstein in 1916 regarding the existence and nature of gravitational waves and the extent to which one can rely on the electromagnetic analogy, especially the controversies regarding the quadrupole formula and whether gravitational waves carry energy, are discussed. The theoretical conclusions eventually received strong observational support from the binary pulsar. This provided compelling, although indirect, evidence for gravitational waves carrying away energy—as predicted by the quadrupole formula. On the direct detection experimental side, Joseph Weber started more than fifty years ago. In 1966, his bar for GW detection reached a strain sensitivity of a few times 10 −16. His announcement of coincident signals (now considered spurious), stimulated many experimental efforts from room temperature resonant masses to cryogenic detectors and laser-interferometers. Now there are km-sized interferometric detectors (LIGO Hanford, LIGO Livingston, Virgo and KAGRA). Advanced LIGO first reached a strain sensitivity of the order of 10 −22. During their first 130 days of observation (O1 run), with the aid of templates generated by numerical relativity, they did make the first detections: two 5-σ GW events and one likely event. Besides earth-based GW detectors, the drag-free sensitivity of the LISA Pathfinder has already reached to the LISA goal level, paving the road for space GW detectors. Over the whole GW spectrum (from aHz to THz) there are efforts for detection, notably the very-low-frequency band (pulsar timing array [PTA], 300 pHz – 100 nHz) and the extremely-low (Hubble)-frequency (cosmic microwave background [CMB] experiment, 1 aHz – 10 fHz).
Nuclear Physics B - Proceedings Supplements, 2005
One of the major goals of interferometric gravity wave detectors is to develop and exploit gravitational wave detection in conjunction with other observations, which are capable to observe the same process via a different channel. Among the promising candidates for close collaboration are the GRB and X-ray observatories, the large neutrino telescopes and the optical searches for supernovae and comparably energetic processes. Future coincident observation of astronomical events shall revolutionize the way we understand energetic processes and will provide new windows on compact and difficult to study astronomical objects such as stellar cores. I will discuss the status and the benefits of collaboration among gravitational wave detectors and astronomical/GRB/neutrino networks, with special emphasis on the practical experience with the LIGO detectors.
Annual Review of Nuclear and Particle Science, 2004
▪ The existence of gravitational radiation is a direct prediction of Einstein's theory of general relativity, published in 1916. The observation of gravitational radiation will open a new astronomical window on the universe, allowing the study of dynamic strong-field gravity, as well as many other astrophysical objects and processes impossible to observe with electromagnetic radiation. The relative weakness of the gravitational force makes detection extremely challenging; nevertheless, sustained advances in detection technology have made the observation of gravitational radiation probable in the near future. In this article, we review the theoretical and experimental status of this emerging field.
Gamma-ray bursts (GRBs) are the most brilliant events in the universe. The intrinsic luminosities of the bursts span more than five decades. At first glance, therefore, these events would hardly seem to be promising standard candles for cosmology. However, very recently, relations between the peak energy E peak of the burst spectrum in νF ν , the isotropic-equivalent energy E iso of the burst, and the radiated energy E γ of the burst -all in the rest frame of the burst sourcehave been found. In a way that is exactly analogous to the way in which the relation between the peak luminosity and the rate of decline of the light curve of Type Ia supernovae can be used to make Type Ia supernovae excellent standard candles for cosmology, so too, the relations between E peak , E iso , and E γ point toward a methodology for using GRBs as excellent standard candles for cosmology. In addition, GRBs occur over the broad redshift range from z = 0.1 to at least z = 4.5, and both they and their afterglows are easily detectable out to z > 8. Thus GRBs show great promise as cosmological "yardsticks" to measure the rate of expansion of the universe over time, and therefore the properties of dark energy (i.e., Ω M , Ω DE , w 0 , and w a ).
Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021), 2021
The detection of electromagnetic (EM) emission following the gravitational wave (GW) event GW170817 opened the era of multi-messenger astronomy with GWs and provided the first direct evidence that at least a fraction of binary neutron star (BNS) mergers are progenitors of short Gamma-Ray Bursts (GRBs). GRBs are also expected to emit very-high energy (VHE, > 100 GeV) photons, as proven by the recent MAGIC and H.E.S.S. observations. One of the challenges for future multi-messenger observations will be the detection of such VHE emission from GRBs in association with GWs. In the next years, the Cherenkov Telescope Array (CTA) will be a key instrument for the EM follow-up of GW events in the VHE range, owing to its unprecedented sensitivity, rapid response, and capability to monitor a large sky area via scan-mode operation. We present the CTA GW follow-up program, with a focus on the searches for short GRBs possibly associated with BNS mergers. We investigate the possible observational strategies and we outline the prospects for the detection of VHE EM counterparts to transient GW events.
Different approaches to the study of the gravitational radiation emitted by astrophysical sources
Annalen der Physik, 2000
Stars and black holes are sources of gravitational radiation in many phases of their life, and the signals they emit exhibit features that are characteristic of the generating process. Emitted since the beginning of star formation, these signals also contribute to create a stochastic background of gravitational waves. We shall show how the spectral properties of this background can be estimated in terms of the energy spectrum of each single event and of the star formation rate history, which is now deducible from astronomical observations. We shall further discuss the process of scattering of masses by stars and black holes, showing that, unlike black holes, stars emit signals that carry a clear signature of the nature of the source.
Chasing Gravitational Waves with the Cherenkov Telescope Array
arXiv (Cornell University), 2023
The detection of gravitational waves (GWs) from a binary neutron star (BNS) merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this GW event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a GW signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. Achieving such a feat will require a comprehensive real-time strategy capable of coordinating searches over potentially very large regions of the sky. This work will evaluate and provide estimations on the number of GW-CTA events determined from simulated BNS systems and short GRBs, considering both onand off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA.