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2025ApJ...994..191A - Astrophys. J., 994, 191 (2025/December-1)

Longtime Monitoring of TeV Radio Galaxies with HAWC.

ALFARO R., ALVAREZ C., ANITA-RANGEL E., ARTEAGA-VELAZQUEZ J.C., AVILA ROJAS D., AYALA SOLARES H.A., BABU R., BANGALE P., BELMONT-MORENO E., BERNAL A., CABALLERO-MORA K.S., CAPISTRAN T., CARRAMINANA A., CARREON F., CASANOVA S., COTTI U., COTZOMI J., COUTINO DE LEON S., DE LA FUENTE E., DEPAOLI D., DESIATI P., DI LALLA N., DIAZ HERNANDEZ R., DUVERNOIS M.A., DIAZ-VELEZ J.C., ENGEL K., ERGIN T., ESPINOZA C., FRAIJA N., FRAIJA S., GARCIA-GONZALEZ J.A., GARFIAS F., GONZALEZ MUNOZ A., GONZALEZ M.M., GONZALEZ J.A., GOODMAN J.A., GROETSCH S., HARDING J.P., HERZOG I., HUANG D., HUEYOTL-ZAHUANTITLA F., IRIARTE A., KAUFMANN S., KIEDA D., LARA A., LEE J., LEON VARGAS H., LONGINOTTI A.L., LUIS-RAYA G., MALONE K., MARTINEZ O., MARTINEZ-CASTRO J., MATTHEWS J.A., MIRANDA-ROMAGNOLI P., MORALES-SOTO J.A., MORENO E., MOSTAFA M., NAJAFI M., NAYERHODA A., NELLEN L., OMODEI N., OSORIO-ARCHILA M., PONCE E., PEREZ ARAUJO Y., PEREZ-PEREZ E.G., RHO C.D., RODRIGUEZ PARRA A., ROSA-GONZALEZ D., ROTH M., SALAZAR H., SANDOVAL A., SCHNEIDER M., SERNA-FRANCO J., SON Y., SPRINGER R.W., TIBOLLA O., TOLLEFSON K., TORRES I., TORRES-ESCOBEDO R., VARELA E., VILLASENOR L., WANG X., WANG Z., WATSON I.J., WU H., YU S., ZHOU H. and DE LEON C.

Abstract (from CDS):

We present the monitoring of the TeV-emitting radio galaxies M87, NGC 1275, 3C 264, and IC 310 with the High-Altitude Water Cherenkov Observatory (HAWC) over a period of approximately 7.5 yr. The analysis includes light curves at daily, weekly, and monthly timescales for the four sources. We report the detection of gamma-ray emission from M87 with a significance exceeding 5σ, providing the integrated TeV spectrum from the longest temporal coverage to date. The source is well described as a point-like source modeled by a power-law spectrum with spectral index Γ = 2.53 ± 0.29 and a flux of (7.09 ± 1.24) × 10–13 cm–2 s–1 TeV–1 at 1 TeV. The maximum energy of the detected emission in M87, at 1σ confidence level, reaches 26.5 TeV. HAWC's observation of M87 reveals a low flux spectrum for the longest observation to date of this radio galaxy. 3C 264 is marginally detected with a significance slightly below 4σ, while NGC 1275 and IC 310 are not detected. The weekly light curves show an increased number of fluxes above 2σ for M87 starting in 2019 and for 3C 264 starting in 2018, which can be interpreted as the moments at which these sources start to exhibit an enhanced steady TeV emission. Cumulative significance analysis reveals quantitative evidence for long-term variability. M87 shows enhanced emission from 2019, while 3C 264 exhibits increased activity from 2018, resembling variable sources like Markarian 421 rather than steady sources like the Crab. This supports the importance of monitoring radio galaxies to identify periods of higher activity and flares, enabling further multimessenger studies.

Abstract Copyright: © 2025. The Author(s). Published by the American Astronomical Society.

Journal keyword(s): Active galactic nuclei - Radio galaxies - High energy astrophysics

Simbad objects: 12

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