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arXiv · 2410.23778

Minute time scale variability in $γ$-ray flare of BL Lacertae

Joysankar Majumdar·Sakshi Maurya·Raj Prince
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Abstract

In October 2024, The object BL Lac experienced a brightest flaring event in gamma-ray ($>$100 MeV) with a historical $γ$-ray flux of $\sim$10$^{-5}$ erg cm$^{-2}$ s$^{-1}$. Soon after the event was followed across the waveband and in X-ray (0.3-10 keV) it was also found to be flaring with the maximum flux achieved during this event as 8.30$\times$10$^{-11}$ erg cm$^{-2}$ s$^{-1}$. The high gamma-ray significance enables us to probe the shortest time scale variability possible and for that, we produced the orbital binned light curve, 5 minutes binned light curve, and the 2 minutes binned light curve. A clear variation is seen in the 5-minute light curve and is fitted with the sum of exponentials to derive the rise and decay time scale which ranges between 3 to 12 minutes. The fastest variability time is also estimated to be an order of 1 minute from 2 minute. The estimated size of the emission region is very small (10$^{13}$ cm) compared to the size of the black hole event horizon. The location of the emission region is estimated to be very close to the supermassive black hole (10$^{14}$ cm) and much inside the BLR (0.1 pc). We discussed the possible way to explain this fast-flux variability in BL Lac.

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Joysankar Majumdar, Sakshi Maurya, Raj Prince. 2025-04-28. Minute time scale variability in $γ$-ray flare of BL Lacertae. https://arxiv.org/abs/2410.23778

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