65 research outputs found
A transient ultraviolet outflow in the short-period X-ray binary UW CrB
This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5–26555. These observations are associated with program(s) 12039.Accreting low mass X-ray binaries (LMXBs) are capable of launching powerful outflows such as accretion disc winds. In disc winds, vast amounts of material can be carried away, potentially greatly impacting the binary and its environment. Previous studies have uncovered signatures of disc winds in the X-ray, optical, near-infrared, and recently even the UV band, predominantly in LMXBs with large discs (Porb ≥ 20 hrs). Here, we present the discovery of transient UV outflow features in UW CrB, a high-inclination (i ≥ 77○) neutron star LMXB with an orbital period of only Porb ≈ 111 min. We present P-Cygni profiles identified for Si iv 1400Å and tentatively for N v 1240Å in one 15 min exposure, which is the only exposure covering orbital phase φ ≈ 0.7 − 0.8, with a velocity of ≈1500 km s−1. We show that due to the presence of black body emission from the neutron star surface and/or boundary layer, a thermal disc wind can be driven despite the short Porb, but explore alternative scenarios as well. The discovery that thermal disc winds may occur in NS-LMXBs with Porb as small as ≈111 min, and can potentially be transient on time scales as short as ≈15 min, warrants further observational and theoretical work.PostprintPeer reviewe
Search and identification of transient and variable radio sources using MeerKAT observations:a case study on the MAXI J1820+070 field
A new method for short duration transient detection in radio images: Searching for transient sources in MeerKAT data of NGC 5068
Transient surveys are a vital tool in exploring the dynamic universe, with
radio transients acting as beacons for explosive and highly energetic
astrophysical phenomena. However, performing commensal transient surveys using
radio imaging can require a significant amount of computing power, data storage
and time. With the instrumentation available to us, and with new and exciting
radio interferometers in development, it is essential that we develop efficient
methods to probe the radio transient sky. In this paper, we present results
from an commensal short duration transient survey, on time scales of 8 seconds,
128 seconds and 1 hour, using data from the MeerKAT radio telescope. The
dataset used was obtained as part of a galaxy observing campaign, and we focus
on the field of NGC 5068. We present a quick, wide field imaging strategy to
enable fast imaging of large datasets, and develop methods to efficiently
filter detected transient candidates. No transient candidates were identified
on the time scales of 8 seconds, 128 seconds and 1 hour, leading to competitive
limits on the transient surface densities of deg,
deg, and deg at
sensitivities of 56.4 mJy, 19.2 mJy, and 3.9 mJy for the respective time
scales. We find one possible candidate that could be associated with a stellar
flare, that was rejected due to strict image quality control. Further short
time-scale radio observations of this candidate could give definite results to
its origin.Comment: 11 pages (9 main, 2 appendix), 8 figures, 2 tables. Submitted to
MNRA
Search and identification of transient and variable radio sources using MeerKAT observations: a case study on the MAXI J1820+070 field
Many transient and variable sources detected at multiple wavelengths are also
observed to vary at radio frequencies. However, these samples are typically
biased towards sources that are initially detected in wide-field optical, X-ray
or gamma-ray surveys. Many sources that are insufficiently bright at higher
frequencies are therefore missed, leading to potential gaps in our knowledge of
these sources and missing populations that are not detectable in optical,
X-rays or gamma-rays. Taking advantage of new state-of-the-art radio facilities
that provide high quality wide-field images with fast survey speeds, we can now
conduct unbiased surveys for transient and variable sources at radio
frequencies. In this paper, we present an unbiased survey using observations
obtained by MeerKAT, a mid-frequency (1.4 GHz) radio array in South
Africa's Karoo Desert. The observations used were obtained as part of a weekly
monitoring campaign for X-ray binaries (XRBs) and we focus on the field of MAXI
J1820+070. We develop methods to optimally filter transient and variable
candidates that can be directly applied to other datasets. In addition to MAXI
J1820+070, we identify four likely active galactic nuclei, one source that
could be a Galactic source (pulsar or quiescent X-ray binary) or an AGN, and
one variable pulsar. No transient sources, defined as being undetected in deep
images, were identified leading to a transient surface density of
deg at a sensitivity of 1 mJy on timescales of one
week at 1.4 GHz.Comment: Submitted to MNRAS, 17 pages, 13 figure
Archeologisch onderzoek Zuster A Kortplantsoen te Wanneperveen : inventariserend veldonderzoek
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Archeologisch onderzoek Wierde Wierum : inventariserend veldonderzoek d.m.v. proefsleuven
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