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Detection of minute-timescale γ-ray variability in BL Lacertae by Fermi-LAT

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dc.contributor.author Pandey, Ashwani
dc.contributor.author Stalin, C. S
dc.date.accessioned 2023-01-18T06:14:45Z
dc.date.available 2023-01-18T06:14:45Z
dc.date.issued 2022-12
dc.identifier.citation Astronomy and Astrophysics, Vol. 668, A152 en_US
dc.identifier.issn 1432-0746
dc.identifier.uri http://hdl.handle.net/2248/8120
dc.description Open Access en_US
dc.description Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article is published in open access under the Subscribe-to-Open model. Subscribe to A&A to support open access publication.
dc.description.abstract BL Lacertae, the prototype of the BL Lacertae (BL Lac) category of blazars, underwent a giant γ-ray flare in April 2021. The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (hereafter Fermi-LAT) observed a peak γ-ray (0.1−500 GeV) flux of ∼2 × 10−5 ph cm−2 s −1 within a single orbit on 2021 April 27, which is historically the brightest γ-ray flux ever detected from the source. Here, we report, for the first time, the detection of significant minute-timescale GeV γ-ray flux variability in the BL Lac subclass of blazars by the Fermi-LAT. We resolved the source variability down to two-minute binned timescales with a flux halving time of ∼1 min, which is the shortest GeV variability timescale ever observed from blazars. The detected variability timescale is much shorter than the light-crossing time (∼14 min) across the central black hole of BL Lac, indicating a very compact γ-ray emission site within the outflowing jet. Such a compact emitting region requires the bulk Lorentz factor of the jet to be larger than 16 so that the jet power is not super Eddington. We found a minimum Doppler factor δmin of 15 using the δ function approximation for the γγ opacity constraint. For a conical jet geometry, considering Γ = δmin, the observed short variability timescale for BL Lac suggests that the very compact emission region lies at a distance of about 8.62 × 1014 cm from its central engine. en_US
dc.language.iso en en_US
dc.publisher EDP Sciences en_US
dc.relation.uri https://doi.org/10.1051/0004-6361/202244648
dc.rights © A. Pandey and C. S. Stalin 2022
dc.subject Galaxies: active en_US
dc.subject BL Lacertae objects: individual: BL Lacertae en_US
dc.subject BL Lacertae objects: general en_US
dc.title Detection of minute-timescale γ-ray variability in BL Lacertae by Fermi-LAT en_US
dc.type Article en_US

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