# X-ray observations of SU UMa throughout six outbursts

## TL;DR

This study presents RXTE X-ray observations of six outbursts of the dwarf nova SU UMa, revealing consistent X-ray behavior, delays between optical and X-ray changes, and spectral variations that challenge existing models.

## Contribution

It provides detailed X-ray monitoring of SU UMa's outbursts, highlighting discrepancies with current accretion disk instability models and boundary layer expectations.

## Key findings

- X-ray count rate drops by a factor of ten during outbursts
- Half-day delay between optical rise and X-ray suppression
- X-ray flux remains high during quiescence, contrary to models

## Abstract

We present RXTE observations covering six normal outbursts of the dwarf nova SU UMa, the prototype of its class. The outbursts showed consistent X-ray behaviour with the X-ray count rate dropping suddenly by a factor of our, and with evidence for a half day delay between the optical rise and the X-ray suppression. In contrast to SS Cyg, an X-ray flux increase at the beginning of outburst was not observed, although it is expected from boundary layer models. The X-ray flux was high and decreasing during quiescence, in conflict with the disc instability model. The X-ray spectrum of SU UMa was softer in outburst than during quiescence, and it was consistent with constant reflection.