Astronomers reveal eclipsing absorber in active galaxy NGC 6814

A analysis workforce led by Prof. Wang Junxian and Ph.D. college students Kang Jialai from College of Science and Know-how of China (USTC) of the Chinese language Academy of Science (CAS) has revealed a wonderful, composite eclipsing absorber (see the 3D animated diagram beneath) chargeable for a extremely distinct X-ray eclipse occasion in energetic galaxy NGC 6814. The paper, titled “What will be learnt from a extremely informative X-ray occultation occasion in NGC 6814? A fabulous absorber” was printed in Month-to-month Notices of the Royal Astronomical Society on August 23.

Within the nucleus of every massive galaxy is a supermassive black hole (SMBH). Some SMBHs are dramatically accreting surrounding supplies, emitting highly effective radiation throughout the whole electromagnetic band, often known as active galactic nuclei (AGN). AGN ubiquitously produce sturdy X-ray emissions, believed to originate in a compact area close to the central black hole, the so-called corona.

An X-ray eclipse occasion refers to a situation the place sure obscuring cloud strikes throughout our line of sight, (totally or partially) masking the corona, thus leaving distinctive options within the noticed mild curves and spectra. On account of their small dimension and much distance, neither the corona nor the encircling cloud could possibly be spatially resolved. Nevertheless, an X-ray eclipse occasion, with ample time-domain info, gives a novel alternative to depict the occasion.

Such eclipse occasions are uncommon and unpredictable, with lower than 5 full eclipse occasions with clear ingress/egress durations captured thus far. In the meantime, the interpretation of those occasions can also be difficult, as a result of AGN is intrinsically variable and one can hardly distinguish the intrinsic variation from the variation brought on by the eclipsing absorption.

To be able to tangle this complexity, the analysis workforce for the primary time includes the intrinsic “softer-when-brighter” conduct through the evaluation of the eclipse occasion, utilizing flux-color plot to supply further constraint to the spectral becoming. Making use of this system to the eclipse occasion in NGC 6814, captured by a high-quality statement of XMM-Newton telescope, the workforce revealed the existence of Compton-thick absorption, which is invisible within the spectra and thus unnoticed earlier than.

As well as, within the case of NGC 6814, the workforce discovered that, to concurrently clarify the noticed partial protection of the absorber, and the lengthy length of the eclipse however very brief ingress/egress, the eclipsing absorber shall be a lot bigger than that of the corona, and clumpy (composed of many small clouds, as a substitute of a single one). Furthermore, the workforce exhibits the 2 extra layers of absorber with fairly small column density detected within the high-resolution RGS spectra are seemingly the fragments ablated or tidal stretched/disrupted from the principle eclipsing absorber, analog to the “comet dust” round comets.

Taken collectively, the analysis workforce depicts the entire image: the eclipsing absorber is a clumpy, multi-phase cloud cluster (as illustrated by the 3D animated diagram), which is likely to be part of the disk “wind,” launched from the inside area (<1000 Rg, the place Rg is the gravitational radius of the central supermassive black hole) of the accretion disk, shifting with a line-of-sight velocity of ~10,000 km/s and an outflowing velocity of ~5,000 km/s. In the meantime, the corona is discovered to be very small, with a diameter lower than 10 Rg.

The work highlights how X-ray occultation occasions can promote our understanding of the fuel surrounding SMBHs and the distinctive usefulness of the flux-color plot whereas analyzing uncommon X-ray occultation occasions.