Two New Bursting Neutron Star Low-mass X-Ray Binaries: Swift J185003.2-005627 and Swift J1922.7-1716

We discuss the origin of two triggers of Swift 's Burst Alert Telescope (BAT) that occurred in 2011. The triggers were identified with Swift J185003.2-005627, a previously unknown X-ray source, and the known but unclassified X-ray transient Swift J1922.7-1716. We investigate the BAT data and follow-up observations obtained with Swift 's X-ray and ultraviolet/optical telescopes to demonstrate that both triggers are consistent with thermonuclear X-ray bursts. This implies that both sources are neutron star low-mass X-ray binaries. The total duration of ##IMG## [http://ej.iop.org/icons/Entities/sime.gif] {sime 7 minutes and estimated energy output of ##IMG## [http://ej.iop.org/icons/Entities/sime.gif] {sime (3-7) × 10 39 erg fall in between that of normal and intermediately long X-ray bursts. From the observed peaks of the X-ray bursts, we estimate a distance of ##IMG## [http://ej.iop.org/icons/Entities/lsim.gif] {lsim 3.7 kpc for Swift J185003.2-005627 and ##IMG## [http://ej.iop.org/icons/Entities/lsim.gif] {lsim 4.8 kpc for Swift J1922.7-1716. We characterize the outburst and quiescent X-ray properties of the two sources. They have comparable average outburst luminosities of ##IMG## [http://ej.iop.org/icons/Entities/sime.gif] {sime 10 35-36 erg s –1 , and a quiescent luminosity equal to or lower than ##IMG## [http://ej.iop.org/icons/Entities/sime.gif] {sime 2 × 10 32 erg s –1 (0.5-10 keV). Swift J185003.2-005627 returned to quiescence ##IMG## [http://ej.iop.org/icons/Entities/sime.gif] {sime 20 d after its BAT trigger, while Swift J1922.7-1716 appears to exhibit long accretion outbursts that last several months to years. We identify a unique counterpart for Swift J1922.7-1716 in the ultraviolet/optical data. Finally, we serendipitously detect a flare lasting ##IMG## [http://ej.iop.org/icons/Entities/sime.gif] {sime 500 s from an uncataloged X-ray/optical object that we tentatively classify as a flaring M-dwarf.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98579/1/0004-637X_759_1_8.pd