Using NASA’s Swift and Fermi space telescopes, Indian astronomers conducted a long-term multi-wavelength study of a nearby blazar called TXS 0518+211.
Blazars are also quasars
Blazars are very compact quasi-stellar objects (quasars) associated with supermassive black holes at the centers of active giant elliptical galaxies. They are the brightest and most extreme subclass of active galactic nuclei (AGN). A characteristic feature of blazars is highly collimated relativistic jets directed almost exactly toward Earth.
Astronomers usually divide blazars into two classes based on their optical emission properties: flat-spectrum radio quasars (FSRQs), which have prominent and broad optical emission lines, and BBL Lacertae (BL Lacs) objects, which do not.
Gamma-ray emitting blazar
TXS 0518+211 is a BL Lacertae-type object that was initially identified as a very high energy (VHE) gamma-ray emitter in 2009. The redshift of this blazar is still uncertain, with some studies indicating 0.18 and others indicating an upper limit of 0.34.
Previous observations of TXS 0518+211 have shown that it exhibits simultaneous bursts in the VHE and X-ray ranges. A team of astronomers led by Avik Kumar Das decided to study these bursts and the behavior of TXS 0518+211 in more detail.
“We present a long-term broad-band temporal and spectral study of a TeV BL Lac source TXS 0518+211 by analyzing nearly 16 years (MJD 54682—60670) of simultaneous optical, UV and X-ray light curves from Swift-XRT/UVOT and gamma-ray light curves from Fermi-LAT,” the researchers wrote in the article.
Blazar variability
Analyzing the fractional variability of TXS 0518+211 across all observation epochs, astronomers found that the blazar exhibited higher variability in the X-ray band compared to the optical/ultraviolet and gamma-ray bands. The fractional variability in the X-ray range was measured at approximately 1.10, while in other ranges it ranges from 0.35 to 0.45.
As for variability on short timescales, it turned out that none of the differential light curves (DLCs) of TXS 0518+211 show any clear signs of variability. The intranight optical variability of this blazar is generally consistent with the variability observed in BL Lacs of type IBL and HBL.
During one observation period, TXS 0518+211 showed simultaneous changes in all three wavebands, while during another period, a significant increase in X-ray flux was recorded without a corresponding counterpart in the optical/ultraviolet bands. Moreover, a significant decrease in X-ray flux has been recorded recently, but the levels of optical/ultraviolet and gamma radiation have remained almost stable.
According to astronomers, this behavior of the light curve in several wavelength ranges indicates a complex structure of the radiation region in the TXS 0518+211 jet.
According to phys.org
