Search for High-redshift Blazars with Fermi/LAT

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https://iopscience.iop.org/article/10.3847/1538-4357/abb8da

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https://doi.org/10.3847/1538-4357/abb8da
 http://hdl.handle.net/11603/21658

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
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UMBC Physics Department

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2020-11-10

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journal articles preprints
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Kreter, M.; Gokus, A.; Krauss, F.; Kadler, M.; Ojha, R.; Buson, S.; Wilms, J.; Böttcher, M.; Search for High-redshift Blazars with Fermi/LAT; The Astrophysical Journal, Volume 903, Number 2 (2020); https://iopscience.iop.org/article/10.3847/1538-4357/abb8da

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Abstract

High-z blazars (z ≥2.5) are the most powerful class of persistent γ-ray sources in the Universe. These objects possess the highest jet powers and luminosities and have black hole masses often in excess of 10⁹ solar masses. In addition, high-z blazars are important cosmological probes and serve as test objects for blazar evolution models. Due to their large distance, their high-energy emission typically peaks below the GeV range, which makes them difficult to study with Fermi/LAT. Therefore, only the very brightest objects are detectable and, to date, only a small number of high-z blazars have been detected with Fermi/LAT. In this work, we studied the monthly binned long-term γ-ray emission of a sample of 176 radio and optically detected blazars that have not been reported as known γ-ray sources in the 3FGL catalog. In order to account for false-positive detections, we calculated monthly Fermi/LAT light curves for a large sample of blank sky positions and derived the number of random fluctuations that we expect at various test statistic (TS) levels. For a given blazar, a detection of TS > 9 in at least one month is expected ∼15% of the time. Although this rate is too high to secure detection of an individual source, half of our sample shows such single-month γ-ray activity, indicating a population of high-energy blazars at distances of up to z=5.2. Multiple TS > 9 monthly detections are unlikely to happen by chance, and we have detected several individual new sources in this way, including the most distant γ-ray blazar, BZQ J1430+4204 (z = 4.72). Finally, two new γ-ray blazars at redshifts of z = 3.63 and z = 3.11 are unambiguously detected via very significant (TS > 25) flares in individual monthly time bins.