IGR J17591 - 2342 is a new accreting millisecond X-ray pulsar ( AMXP ) that was recently discovered in outburst in 2018 .
Early observations revealed that the source ’ s radio emission is brighter than that of any other known neutron star low-mass X-ray binary ( NS-LMXB ) at comparable X-ray luminosity , and assuming its likely \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ > $ } } } 6 kpc distance .
It is comparably radio bright to black hole LMXBs at similar X-ray luminosities .
In this work , we present the results of our extensive radio and X-ray monitoring campaign of the 2018 outburst of IGR J17591 - 2342 .
In total we collected 10 quasi-simultaneous radio ( VLA , ATCA ) and X-ray ( Swift -XRT ) observations , which make IGR J17591 - 2342 one of the best-sampled NS-LMXBs .
We use these to fit a power-law correlation index \beta = 0.37 ^ { +0.42 } _ { -0.40 } between observed radio and X-ray luminosities ( L _ { \mathrm { R } } \propto L _ { \mathrm { X } } ^ { \beta } ) .
However , our monitoring revealed a large scatter in IGR J17591 - 2342 ’ s radio luminosity ( at a similar X-ray luminosity , L _ { \mathrm { X } } \sim 10 ^ { 36 } erg s ^ { -1 } , and spectral state ) , with L _ { \mathrm { R } } \sim 4 \times 10 ^ { 29 } erg s ^ { -1 } during the first three reported observations , and up to a factor of 4 lower L _ { \mathrm { R } } during later radio observations .
Nonetheless , the average radio luminosity of IGR J17591 - 2342 is still one of the highest among NS-LMXBs , and we discuss possible reasons for the wide range of radio luminosities observed in such systems during outburst .
We found no evidence for radio pulsations from IGR J17591 - 2342 in our Green Bank Telescope observations performed shortly after the source returned to quiescence .
Nonetheless , we can not rule out that IGR J17591 - 2342 becomes a radio millisecond pulsar during quiescence .