4U 0614+091 observed at low variability, soft state
ATel #4083; Thomas J. Maccarone (Southampton), Maithili Kalamkar (Amsterdam), Anthony Rushton (ESO/Onsala Space Observatory)
on 1 May 2012; 19:09 UT
Credential Certification: Tom Maccarone (tjm@phys.soton.ac.uk)
Subjects: Request for Observations, Neutron Star
We report the results of Swift power spectral observation of the
neutron star X-ray binary 4U 0614+091, taken on 2012-04-30 at 16:57:30. This system is normally found in a hard (i.e. island) state, but recent MAXI data (MAXI transient alert:
2012-04-26 07:18:44 UT) showed some evidence for softening and brightening. The source shows a
featureless power spectrum with 7.6+-2.4% fractional rms amplitude
in 0.04-10 Hz, and hardness ratios consistent with a Gamma=2.3 power law
spectrum. Neutron stars in low mass X-ray binaries generally show such
a power spectrum only when they have moved into soft (i.e. banana) states
(see e.g. van Straten et al., 2000, ApJ, 540, 1049 for a discussion specific to 4U
0614+091). The count rate of 76 counts/sec from 0.5-10 keV
corresponds to a luminosity of 4.7*10^36 ergs/sec assuming a distance
of 3 kpc and a 1 keV blackbody spectrum, indicating that the source
has also become unusually bright. Given that strong jet ejections are
often seen in black hole systems when they make transitions from hard
to soft states, eMERLIN observations are scheduled to take place soon
within the next 24-48 hours to see if this neutron star behaves in the
same way. Further observations at all wavelengths are encouraged.
