SRG/eROSITA No. 5: Discovery of Quasiperiodic Eruptions Every ∼3.7 days from a Galaxy at <i>z</i> > 0.1
R. Arcodia, P. Baldini, A. Merloni, A. Rau, K. Nandra, Joheen Chakraborty, Andrew Goodwin, M. J. Page, Johannes Büchner, Megan Masterson, I. M. Monageng, Zaven Arzoumanian, David N. Buckley, Erin Kara, G. Ponti, M. E. Ramos-Ceja, M. Salvato, Keith C. Gendreau, I. Grotova, M. Krumpe
Abstract
Abstract Quasiperiodic eruptions (QPEs) are repeating soft-X-ray bursts from the nuclei of galaxies, tantalizingly proposed to be extreme-mass-ratio inspirals. Here, we report the discovery of a new galaxy showing X-ray QPEs, the fifth found through a dedicated blind search of the Spectrum–Roentgen–Gamma/eROSITA all-sky survey data, hereafter named eRO-QPE5. Its QPE duration ( t dur ∼ 0.6 days), recurrence time ( t recur ∼ 3.7 days), integrated energy per eruption (∼3.4 × 10 47 erg), and black hole mass ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">BH</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>5.4</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>7</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> ) sit at the high end of the known population. Like other eROSITA or X-ray-discovered QPEs, no previous or concurrent optical–IR transient is found in archival photometric data sets, and the optical spectrum looks almost featureless. With a spectroscopic redshift of 0.1155, eRO-QPE5 is the most distant QPE source discovered to date. Given the number of recent discoveries, we test for possible correlations and confirm a connection between t dur and t recur , while we do not find any significant correlation involving either M BH or the QPE temperature. The slope of the t dur – t recur relation (1.14 ± 0.16) is roughly consistent with predictions from star–disk collision models, with a preference for those suggesting that QPEs are powered by stellar debris streams around the orbiter. Considering this and previous discoveries, eROSITA has proved extremely successful in finding many QPE candidates, given its grasp—namely, its its sensitivity and large field of view—and scanning capabilities over the full sky. We advocate the need for sensitive wide-area- and time-domain-oriented surveys from future-generation soft-X-ray missions.