Kavli Affiliate: Robert Simcoe
| First 5 Authors: Kishalay De, Ilya Mereminskiy, Roberto Soria, Charlie Conroy, Erin Kara
| Summary:
We present the discovery and multi-wavelength 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
($1502 pm 24$ days) and luminous ($M_Kapprox -9.9 pm 0.2$) O-rich Mira donor
star located at a distance of $approx 14.6^{+2.9}_{-2.3}$ kpc. Combining
multi-color photometric data over the last $approx 25$ years, we show that the
IR counterpart underwent a recent (starting $approx 800$ days before the X-ray
flare) enhanced mass loss (reaching $approx 2.1 times 10^{-5}$ M$_odot$
yr$^{-1}$) episode resulting in an expanding dust shell obscuring the
underlying star. Multi-epoch follow-up from Swift, NICER and NuSTAR reveal a
$approx 200$ day long X-ray outburst reaching a peak luminosity of $L_X
approx 2.5 times 10^{36}$ erg s$^{-1}$, characterized by a heavily absorbed
($N_{rm H} approx 6times 10^{22}$ 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 active lifetimes of
the symbiotic X-ray binaries.
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