SRGA J181414.6-225604: A New Galactic Symbiotic X-Ray Binary Outburst Triggered by an Intense Mass-loss Episode of a Heavily Obscured Mira Variable
Kishalay De, I. A. Mereminskiy, Roberto Soria, Charlie Conroy, Erin Kara, Shreya Anand, M. C. B. Ashley, Martha L. Boyer, Deepto Chakrabarty, Brian W. Grefenstette, M. Hankins, Lynne A. Hillenbrand, J. Jencson, Viraj Karambelkar, M. M. Kasliwal, Ryan M. Lau, A. Lutovinov, Anna Moore, Mason Ng, Christos Panagiotou, Dheeraj R. Pasham, А. Н. Семена, Robert A. Simcoe, Jamie Soon, Gokul P. Srinivasaragavan, Tony Travouillon, Yuhan Yao
Abstract
Abstract We present the discovery and multiwavelength characterization of SRGA J181414.6-225604, a Galactic hard X-ray transient discovered during the ongoing SRG/ART-XC sky survey. Using data from the Palomar Gattini-IR survey, we identify a spatially and temporally coincident variable infrared (IR) source, IRAS 18111-2257, and classify it as a very-late-type (M7–M8), long-period (1502 ± 24 days), and luminous ( M K ≈ −9.9 ± 0.2) O-rich Mira donor star located at a distance of ≈14.6 +2.9 −2.3 kpc. Combining multicolor photometric data over the last ≈25 yr, we show that the IR counterpart underwent a recent (starting ≈800 days before the X-ray flare) enhanced mass-loss (reaching ≈2.1 × 10 −5 M ⊙ yr −1 ) episode, resulting in an expanding dust shell obscuring the underlying star. Multi-epoch follow-up observations from Swift, NICER, and NuSTAR reveal a ≈200 day long X-ray outburst reaching a peak luminosity of L X ≈ 2.5 × 10 36 erg s −1 , characterized by a heavily absorbed ( N H ≈ 6 × 10 22 cm −2 ) X-ray spectrum consistent with an optically thick Comptonized plasma. The X-ray spectral and timing behavior suggest the presence of clumpy wind accretion, together with a dense ionized nebula overabundant in silicate material surrounding the compact object. Together, we show that SRGA J181414.6-225604 is a new symbiotic X-ray binary in outburst, triggered by an intense dust-formation episode of a highly evolved donor. Our results offer the first direct confirmation for the speculated connection between enhanced late-stage donor mass loss and the active lifetimes of symbiotic X-ray binaries.