Radio and X-ray monitoring of the accreting millisecond X-ray pulsar IGR J17591-2342 in outburst
Abstract
IGR J17591-2342 is a new accreting millisecond X-ray pulsar 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 ≳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 (LR ∝ LXβ). However, our monitoring revealed a large scatter in IGR J17591-2342's radio luminosity (at a similar X-ray luminosity, LX ~1036 erg s-1, and spectral state), with LR ~ 4 × 1029 erg s-1 during the first three reported observations, and up to a factor of 4 lower LR during later radio observations. None the less, 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. None the less, we cannot rule out that IGR J17591-2342 becomes a radio millisecond pulsar during quiescence.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2020
- DOI:
- 10.1093/mnras/stz3460
- arXiv:
- arXiv:1909.02323
- Bibcode:
- 2020MNRAS.492.1091G
- Keywords:
-
- stars: neutron;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 12 pages, 3 figures, 2 tables, accepted for publication in MNRAS