2025ApJ...978...31A

Query : 2025ApJ...978...31A

2025ApJ...978...31A - Astrophys. J., 978, 31 (2025/January-1)

The NANOGrav 15 yr Data Set: Looking for Signs of Discreteness in the Gravitational-wave Background.

AGAZIE G., ANUMARLAPUDI A., ARCHIBALD A.M., ARZOUMANIAN Z., BAIER J.G., BAKER P.T., BECSY B., BLECHA L., BRAZIER A., BROOK P.R., BROWN L., BURKE-SPOLAOR S., CASEY-CLYDE J.A., CHARISI M., CHATTERJEE S., COHEN T., CORDES J.M., CORNISH N.J., CRAWFORD F., CROMARTIE H.T., CROWTER K., DECESAR M.E., DEMOREST P.B., DENG H., DOLCH T., FERRARA E.C., FIORE W., FONSECA E., FREEDMAN G.E., GARVER-DANIELS N., GENTILE P.A., GLASER J., GOOD D.C., GULTEKIN K., HAZBOUN J.S., JENNINGS R.J., JOHNSON A.D., JONES M.L., KAISER A.R., KAPLAN D.L., KELLEY L.Z., KERR M., KEY J.S., LAAL N., LAM M.T., LAMB W.G., LARSEN B., LAZIO T.J.W., LEWANDOWSKA N., LIU T., LORIMER D.R., LUO J., LYNCH R.S., MA C.-P., MADISON D.R., McEWEN A., McKEE J.W., McLAUGHLIN M.A., McMANN N., MEYERS B.W., MEYERS P.M., MINGARELLI C.M.F., MITRIDATE A., NATARAJAN P., NG C., NICE D.J., OCKER S.K., OLUM K.D., PENNUCCI T.T., PERERA B.B.P., POL N.S., RADOVAN H.A., RANSOM S.M., RAY P.S., ROMANO J.D., RUNNOE J.C., SARDESAI S.C., SCHMIEDEKAMP A., SCHMIEDEKAMP C., SCHMITZ K., SHAPIRO-ALBERT B.J., SIEMENS X., SIMON J., SIWEK M.S., SOSA FISCELLA S.V., STAIRS I.H., STINEBRING D.R., STOVALL K., SUSOBHANAN A., SWIGGUM J.K., TAYLOR S.R., TURNER J.E., UNAL C., VALLISNERI M., VIGELAND S.J., WAHL H.M., WILLSON L., WITT C.A., WRIGHT D. and YOUNG O.

Abstract (from CDS):

The cosmic merger history of supermassive black hole binaries (SMBHBs) is expected to produce a low-frequency gravitational wave background (GWB). Here we investigate how signs of the discrete nature of this GWB can manifest in pulsar timing arrays (PTAs) through excursions from, and breaks in, the expected ${f}_{\mathrm{GW}}^{-2/3}$ power law of the GWB strain spectrum. To do this, we create a semianalytic SMBHB population model, fit to North American Nanohertz Observatory for Gravitational Waves (NANOGrav's) 15 yr GWB amplitude, and with 1000 realizations, we study the populations' characteristic strain and residual spectra. Comparing our models to the NANOGrav 15 yr spectrum, we find two interesting excursions from the power law. The first, at 2 nHz, is below our GWB realizations with a p-value significance p = 0.05-0.06 (≈1.8σ-1.9σ). The second, at 16 nHz, is above our GWB realizations with p = 0.04-0.15 (≈1.4σ-2.1σ). We explore the properties of a loud SMBHB that could cause such an excursion. Our simulations also show that the expected number of SMBHBs decreases by 3 orders of magnitude, from ∼106 to ∼103, between 2 and 20 nHz. This causes a break in the strain spectrum as the stochasticity of the background breaks down at ${26}_{-19}^{+28}\,\mathrm{nHz}$, consistent with predictions pre-dating GWB measurements. The diminished GWB signal from SMBHBs at frequencies above the 26 nHz break opens a window for PTAs to detect continuous GWs from individual SMBHBs or GWs from the early Universe.

Abstract Copyright: © 2024. The Author(s). Published by the American Astronomical Society.

Journal keyword(s): Gravitational wave astronomy - Gravitational waves - Quasars - Supermassive black holes

Simbad objects: 3

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Number of rows : 3
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 [VV2000] J092952.2+355449 QSO 09 29 52.1764010208 +35 54 49.809696264   17.34 17.15     ~ 34 0
2 SDSS J114857.33+160023.1 QSO 11 48 57.3461957928 +16 00 23.086900872   18.80 18.49     ~ 21 0
3 [VV2000] J163302.7+234928 QSO 16 33 02.6637519552 +23 49 28.517168676   15.94 15.67     ~ 39 0

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