X-ray emission from an FU Orionis star in early outburst: HBC 722

¹ Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: armin.liebhart@univie.ac.at; manuel.guedel@univie.ac.at
² CASA, University of Colorado, Boulder, CO 80309-0389, USA
e-mail: stephen.skinner@colorado.edu
³ Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USA
e-mail: joel@astro.as.utexas.edu

Received: 21 August 2014
Accepted: 17 September 2014

Abstract

Aims. We conducted the first X-ray observations of the newly erupting FU Ori-type outburst in HBC 722 (V2493 Cyg) with the aim to characterize its X-ray behavior and near-stellar environment during early outburst.

Methods. We used data from the XMM-Newton and Chandra X-ray observatories to measure X-ray source temperatures and luminosities as well as the gas column densities along the line of sight toward the source.

Results. We report a Chandra X-ray detection of HBC 722 with an X-ray luminosity of L_X ≈ 4 × 10³⁰ ergs s^-1. The gas column density exceeds values expected from optical extinction and standard gas-to-dust ratios. We conclude that dust-free gas masses are present around the star, such as strong winds launched from the inner disk, or massive accretion columns. A tentative detection obtained by XMM-Newton two years earlier after an initial optical peak revealed a fainter X-ray source with only weak absorption.