2,233 research outputs found
A new redback pulsar candidate 4FGL J2054.2+6904
The Fermi catalogue contains about 2000 unassociated -ray sources.
Some of them were recently identified as pulsars, including so called redbacks
and black widows, which are millisecond pulsars in tight binary systems with
non- and partially-degenerate low-mass stellar companions irradiated by the
pulsar wind. We study a likely optical and X-ray counterpart of the Fermi
source 4FGL J2054.2+6904 proposed earlier as a pulsar candidate. We use
archival optical data as well as Swift/XRT and SRG/eROSITA X-ray data to
clarify its nature. Using Zwicky Transient Facility data in and bands
spanning over 4.7 years, we find a period of 7.5 h. The folded light
curve has a smooth sinusoidal shape with the peak-to-peak amplitude of
0.4 mag. The spectral fit to the optical spectral energy distribution
of the counterpart candidate gives the star radius of 0.50.1 and
temperature of 5500300 K implying a G2--G9-type star. Its X-ray spectrum
is well fitted by an absorbed power law with the photon index of 1.00.3
and unabsorbed flux of erg s cm. All
the properties of 4FGL J2054.26904 and its presumed counterpart suggest that
it is a member of the redback family.Comment: Accepted for publication in MNRAS, 6 pages, 6 figure
Optical spectral observations of three binary millisecond pulsars
We present the results of optical spectroscopy of stellar companions to three
binary millisecond pulsars, PSRs J06212514, J23171439 and J23024442,
obtained with the Gran Telescopio Canarias. The spectrum of the J06212514
companion shows a blue continuum and prominent Balmer absorption lines. The
latter are also resolved in the spectrum of the J23171439 companion, showing
that both are DA-type white dwarfs. No spectral features are detected for the
J23024442 companion, however, its broadband magnitudes and the spectral
shape of the continuum emission imply that this is also a DA-type white dwarf.
Based on the spectral analyses, we conclude that the companions of J06212514
and J23171439 are relatively hot, with effective temperatures 8600200 and 96002000~K, respectively, while the J23024442
companion is significantly cooler, 6000~K. We also estimated
the distance to J06212514 of 1.10.3 kpc and argue that its companion
and the companion of J23171439 are He-core white dwarfs providing
constraints on their cooling ages of 2 Gyr.Comment: 9 pages, 8 figures. Paper accepted to MNRA
- …