Multi-band observations of Swift J0840.7-3516: a new transient ultra-compact X-ray binary candidate
arXiv:2102.07947 · doi:10.1051/0004-6361/202140573
Abstract
We report on multi-band observations of the transient source Swift J0840.7-3516, which was detected in outburst in 2020 February by the Neil Gehrels Swift Observatory. The outburst episode lasted just ~5 days, during which the X-ray luminosity quickly decreased from ~3E37 erg/s at peak down to ~5E33 erg/s in quiescence (0.3-10 keV; at 10 kpc). Such a marked and rapid decrease in the flux was also registered at UV and optical wavelengths. In outburst, the source showed considerable aperiodic variability in the X-rays on timescales as short as a few seconds. The spectrum of the source in the energy range 0.3-20 keV was well described by a thermal, blackbody-like, component plus a non-thermal, power law-like, component and it softened considerably as the source returned to quiescence. The spectrum of the optical counterpart in quiescence showed broad emission features associated mainly with ionised carbon and oxygen, superposed on a blue continuum. No evidence for bright continuum radio emission was found in quiescence. We discuss possible scenarios for the nature of this source, and show that the observed phenomenology points to a transient ultra-compact X-ray binary system.
13 pages, 7 figures, accepted for publication on A&A
References in corpus (23)
- Modelling the behaviour of accretion flows in X-ray binaries
- An Analysis of the Shapes of Interstellar Extinction Curves. VII. Milky Way Spectrophotometric Optical-through-Ultraviolet Extinction and Its R-Dependence
- The observed spiral structure of the Milky Way
- The corona contracts in a black-hole transient
- Six new candidate ultracompact X-ray binaries
- Discovery of coherent millisecond X-ray pulsations in Aql X-1
- Optical spectroscopy of (candidate) ultra-compact X-ray binaries: constraints on the composition of the donor stars
- The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9
- IGR J16194-2810: a new symbiotic X-ray binary
- Accretion disks and coronae in the X-ray flashlight
- M-type giants as optical counterparts of X-ray sources 4U 1700+24 and 4U 1954+319
- Disk-jet coupling in low-luminosity accreting neutron stars
- NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371
- The return to quiescence of Aql X-1 following the 2010 outburst
- VLT spectroscopy and non-LTE modeling of the C/O-dominated accretion disks in two ultracompact X-ray binaries
- Swift J1357.2-0933: the faintest black hole?
- The peculiar Galactic center neutron star X-ray binary XMM J174457-2850.3
- NICER Discovery of Millisecond X-ray Pulsations and an Ultracompact Orbit in IGR J17494-3030
- The Galactic LMXB Population and the Galactic Centre Region
- The variable radio counterpart of Swift J1858.6-0814
- Simultaneous NICER and NuSTAR Observations of the Ultra-compact X-ray Binary 4U 1543-624
- Outbursts in ultracompact X-ray binaries
- A strongly changing accretion morphology during the outburst decay of the neutron star X-ray binary 4U 1608-52