Blazars are very compact quasars associated with supermassive black holes (SMBHs) at the centers of active giant elliptical galaxies.

Using NASA’s Neil Gherels Swift Observatory, Indian astronomers have observed a blazar known as OJ 287. The results of the observing campaign, published May 25 on the arXiv preprint server, shed more light on the spectral changes of OJ 287, improving our knowledge about the behavior of this source.

Blazars are very compact quasars associated with supermassive black holes (SMBHs) at the centers of active giant elliptical galaxies. They belong to a larger group of active galaxies that host active galactic nuclei (AGNs) and are the most numerous extragalactic gamma-ray sources. Its characteristic features are relativistic jets pointing almost exactly toward Earth. Based on their optical emission properties, astronomers divide blazars into two classes: Flat Spectrum Radio Quasars (FSRQs), which have prominent and broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not. . OJ 287 is an optically bright BL Lac located about 3.5 billion light-years from Earth. Its supermassive black hole is estimated to be 100 million times more massive than the sun. The blazar exhibits a periodic variation from 11 to 12 years with a narrow double peak at maximum brightness, suggesting that it harbors a binary SMBH.

OJ 287 is one of the best-monitored blazars by the Swift spacecraft. Swift’s previous observations of OJ 287 have found that it displays peculiar spectral phases and that its spectra are representative of the entire blazar class. Recently, a team of astronomers led by Pankaj Kushwaha of the Mohali Indian Institute of Science Education and Research in India, decided to investigate this issue further, conducting another Swift survey of OJ 287.

In the current work, we focus on a detailed spectral investigation of the simultaneous X-ray optical spectrum of the lowest observed measured X-ray flux state of OJ 287 by the Swift observatory,” the researchers wrote. The new observations found that OJ 287 has an extended optical-ultraviolet synchrotron spectrum, with a power-law photon spectral index of 2.71, which continues at X-ray energies during the lowest (and intermediate) X-ray flux state. ). Taking this into account in the spectral fit, the astronomers inferred a hard intrinsic X-ray spectrum with a power-law photon spectral index at the 1.22 level, thus harder than the hardest spectrum reported for this blazar considering only the X-ray data. According to the study, the extended optical-ultraviolet spectrum of OJ 287 indicates a much more extensive spectrum of high-energy particles. Furthermore, the reported hard X-ray spectrum naturally reproduces most of the observed flat X-ray spectra of the source when combined with the corresponding optical ultraviolet spectrum.

source: https://arxiv.org/abs/2305.16144