Swift Follow-up of Fermi-LAT detection of gamma-ray activity in BL Lac 4C +56.27
ATel #16929; Rukaiya Khatoon (North-West University), Markus Boettcher (North-West University)
on 2 Dec 2024; 13:37 UT
Credential Certification: Rukaiya Khatoon (rukaiyakhatoon12@gmail.com )
Subjects: X-ray, AGN, Blazar
On November 16, 2024, the BL Lac object 4C +56.27 (R.A = 276.02945 deg, Dec. = +56.85041 deg, (J2000), Le Bail et al. 2016, AJ, 151, 79), located at z=0.664 (Lawrence et al. 1986, AJ 91, 494), exhibited its highest recorded gamma-ray daily flux of (0.54+/-0.12) x 10^-6 photons cm^-2 s^-1 in Fermi-LAT data (ATEL#16913). This flux represents a 14-fold increase over the average flux in the 4FGL catalog. To investigate this activity, we conducted Swift follow-up observations from November 21-30, 2024, with ~2 ksec exposures per epoch.
Preliminary analysis of Swift-XRT data in the 0.3-10 keV band shows the spectrum is well-fitted by an absorbed power-law model (Galactic absorption fixed at N_H=4.84 x 10^20 cm^-2). Unabsorbed flux and photon indices are as follows:
November 21: ~3.60 (+1.70, -1.17) x 10^-12 erg cm^-2 s^-1, photon index =1.44+/-0.30
November 24: ~3.37 (+0.93, -0.67) x 10^-12 erg cm^-2 s^-1, photon index =1.97+/-0.24
November 27: ~3.23 (+0.83, -0.72) x 10^-12 erg cm^-2 s^-1, photon index =1.95+/-0.24
November 30: ~3.64 (+0.63, -0.62) x 10^-12 erg cm^-2 s^-1, photon index =2.15+/-0.19
All X-ray flux values are consistent within 1-sigma, indicating no significant variability. Additionally, ATEL#16926 reported another gamma-ray flare on November 28, 2024, with a daily-averaged flux (E > 100 MeV) of (0.8+/-0.1) x 10^-6 photons cm^-2 s^-1, exceeding the flux from November 16.
We encourage further multi-wavelength observations of 4C +56.27 to study its activity. We thank the Swift team for their prompt and efficient scheduling of these ToO observations.
