English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present a detailed NIR/optical/UV study of the transient low mass X-raybinary 1RXS J180408.9-342058 performed during its 2015 outburst, aimed atdetermining the nature of its companion star. We obtained three optical spectraat the 2.1 m San Pedro Martir Observatory telescope (Mexico). We performedoptical and NIR photometric observations with both the REM telescope and theNew Technology Telescope (NTT) in La Silla. We obtained optical and UVobservations from the Swift archive. Finally, we performed optical polarimetryof the source by using the EFOSC2 instrument mounted on the NTT. The opticalspectrum of the source is almost featureless since the hydrogen and He Iemissions lines, typically observed in LMXBs, are not detected. Similarly,carbon and oxygen lines are neither observed. We marginally detect the He II4686 AA emission line, suggesting the presence of helium in the accretion disc.No significant optical polarisation level was observed. The lack of hydrogenand He I emission lines in the spectrum implies that the companion is likelynot a main sequence star. Driven by the tentative detection of the He II 4686AA emission line, we suggest that the system could harbour a helium whitedwarf. If this is the case, 1RXS J180408.9-342058 would be an ultra-compactX-ray binary. By combining an estimate of the mass accretion rate together withevolutionary tracks for a He white dwarf, we obtain a tentative orbital periodof ~ 40 min. On the other hand, we also built the NIR-optical-UV spectralenergy distribution (SED) of the source at two different epochs. One SED wasgathered when the source was in the soft X-ray state, and it is consistent withthe presence of a single thermal component. The second SED, obtained when thesource was in the hard X-ray state, shows a thermal component together with atail in the NIR, likely indicating the presence of a (transient) jet.

1RXS J180408.9-342058: an ultra compact X-ray binary candidate with a transient jet