Radio study of a WLQ SDSSJ1539+3954 showing extreme X-ray variability

SDSSJ1539+3954(z∼1.935), identified as a radio-quiet weak line quasar(WLQ) and a previously X-ray weak source, exhibited an exceptional X-ray variability phenomenon in 2019 and 2020 in a study conducted by Ni et.al(2020). Specifically, its X-ray flux increased more than 20 times from 2013 to 2019, followed by a nine-fold drop in 2020 within a period of ≤8 months.Several studies have revealed empirical correlations observed between X-ray and radio emission from the core of AGNs. To obtain insights into the radio properties of the SDSSJ1539+3954 and the possible connection between its X-ray and radio emission, we conducted a radio study in the frequency range 0.3-10 GHz using GMRT (in 2020, 2022 and 2024) and VLA (in 2022) following the X-ray brightening and dimming of the source. The source was not detected in the VLA-FIRST survey at 1.4 GHz. Our observations reveal detection of the source with the spectral index of ≈-0.6 in the frequency range 0.3-1.4 GHz and ≈-1.1 in 3-10 GHz. No significant variability is observed in the radio emission between the two GMRT observation epochs. The presence of a geometrically changing thick inner accretion disk can explain the X-ray variability in the WLQ. However, the steepening of the spectral index in the GHz frequency range raises questions about the nature of radio emission in the WLQ accreting at high-Eddington rates. We discuss various mechanisms driving the radio emission in this radio-quiet quasar with a possibility of predominant radio emission from a young radio source.