IDV Observations & Study of the Quasar 0917+624

TL;DR

This study presents long-term radio observations of quasar 0917+624, analyzing its intra-day variability patterns over several years and linking spectral index changes to variability phases.

Contribution

It provides the first extensive multi-year IDV monitoring of 0917+624, revealing the correlation between spectral index and IDV activity, and offers insights into the source's scintillation behavior.

Findings

IDV ceased in 2000 after being prominent in the 1980s-1990s

Spectral index is steeper during weak/non-IDV phases

Weak IDV activity detected in some observing sessions

Abstract

We carried out intra-day variability (IDV) observations from August 2005 to January 2010 with the Urumqi 25m radio telescope for a dozen IDV sources including the quasar 0917+624. This target exhibited pronounced centimeter-band, intra-day variability during the 1980s--1990s, but its strong IDV phase ceased in 2000. The source showed no IDV in the majority of the Urumqi observing sessions, although weak IDV activity was detected in some. Multifrequency UMRAO data for 0917+624 show that the spectral index is steeper during the weak and non-IDV phases than during the strong IDV phase, supporting the idea that the size of the scintillating component may be enlarged in the weak/non IDV phases.