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
Soria, Roberto; Boyer, Martha L.; Conroy, Charlie; Chakrabarty, Deepto; De, Kishalay; Kasliwal, Mansi M.; Hillenbrand, Lynne A.; Kara, Erin; Yao, Yuhan; Jencson, Jacob E.; Lau, Ryan M.; Pasham, Dheeraj R.; Anand, Shreya; Karambelkar, Viraj; Ng, Mason; Moore, Anna M.; Hankins, Matthew J.; Lutovinov, Alexander; Ashley, Michael C. B.; Soon, Jamie; Travouillon, Tony; Panagiotou, Christos; Mereminskiy, Ilya; Grefenstette, Brian; Semena, Andrey; Simcoe, Robert; Srinivasaragavan, Gokul P.
United States, Russia, China, Australia, Japan
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 × 1036 erg s-1, characterized by a heavily absorbed (N H ≈ 6 × 1022 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.