The Optical Variability of SDSS Quasars from Multi-epoch Spectroscopy. III. A Sudden UV Cutoff in Quasar SDSS J2317+0005

TL;DR

This study investigates a sudden UV cutoff in a quasar, suggesting it may be caused by a dusty cloud eclipse or rapid outflow, with multi-epoch data revealing rapid continuum recovery.

Contribution

It presents the first detailed analysis of a sudden UV cutoff in a quasar, proposing a new eclipse or outflow mechanism based on multi-epoch spectroscopy and X-ray data.

Findings

The UV continuum dropped by a factor of 3.5 at 3000 Å during 23 days.

Broad emission line fluxes remained unchanged despite the continuum drop.

The continuum recovered within 42 days, indicating a transient obscuration or outflow.

Abstract

We have collected near-infrared to X-ray data of 20 multi-epoch heavily reddened SDSS quasars to investigate the physical mechanism of reddening. Of these, J2317+0005 is found to be a UV cutoff quasar. Its continuum, which usually appears normal, decreases by a factor 3.5 at 3000{\AA}, compared to its more typical bright state during an interval of 23 days. During this sudden continuum cut-off, the broad emission line fluxes do not change, perhaps due to the large size of the Broad Line Region (BLR), r > 23 / (1+z) days. The UV continuum may have suffered a dramatic drop out. However, there are some difficulties with this explanation. Another possibility is that the intrinsic continuum did not change, but was temporarily blocked out, at least towards our line of sight. As indicated by X-ray observations, the continuum rapidly recovers after 42 days. A comparison of the bright state and dim states would imply an eclipse by a dusty cloud with a reddening curve having a remarkably sharp rise shortward of 3500{\AA}. Under the assumption of being eclipsed by a Keplerian dusty cloud, we characterized the cloud size with our observations, however, which is a little smaller than the 3000\AA\ continuum-emitting size inferred from accretion disk models. Therefore, we speculate this is due to a rapid outflow or inflow with a dusty cloud passing through our line-of-sight to the center.