The deepest $Chandra$ view of RBS 797: evidence for two pairs of equidistant X-ray cavities

TL;DR

This study presents the discovery of four symmetric X-ray cavities in galaxy cluster RBS 797, indicating complex AGN activity with possible binary black holes or rapid jet reorientation.

Contribution

First deep Chandra observation revealing four equidistant, radio-filled cavities in RBS 797, suggesting dual outbursts or jet reorientation.

Findings

Detection of two additional N-S cavities at similar radii as E-W cavities.

Cavities are associated with radio emission at 1.4 and 4.8 GHz.

Estimated ages of cavities indicate nearly simultaneous outbursts.

Abstract

We present the first results of a deep $Chandra$ observation of the galaxy cluster RBS 797, whose previous X-ray studies revealed two pronounced X-ray cavities in the east-west (E-W) direction. Follow-up VLA radio observations of the central active galactic nucleus (AGN) uncovered different jet and lobe orientations, with radio lobes filling the E-W cavities and perpendicular jets showing emission in the north-south (N-S) direction over the same scale ($\approx$30 kpc). With the new $\sim$427 ks total exposure, we report the detection of two additional, symmetric X-ray cavities in the N-S direction at nearly the same radial distance as the E-W ones. The newly discovered N-S cavities are associated with the radio emission detected at 1.4 GHz and 4.8 GHz in archival VLA data, making RBS 797 the first galaxy cluster found to have four equidistant, centrally-symmetric, radio-filled cavities. We derive the dynamical and radiative ages of the four cavities from X-ray and radio data, respectively, finding that the two outbursts are approximately coeval, with an age difference of $\lessapprox$10 Myr between the E-W and N-S cavities. We discuss two scenarios for the origin of the two perpendicular, equidistant cavity systems: either the presence of a binary AGN which is excavating coeval pairs of cavities in perpendicular directions, or a fast ($<$10 Myr) jet reorientation event which produced subsequent, misaligned outbursts.