5,276 research outputs found
AX J0049.4-7323 - a close look at a neutron star interacting with a circumstellar disk
Detailed evidence on the system AX J0049.4-7323 is presented here to show how
the passage of the neutron star in the binary system disrupts the circumstellar
disk of the mass donor Be star. A similar effect is noted in three other
Be/X-ray binary systems. Together the observational data should provide
valuable tools for modelling these complex interactions.Comment: 4 pages, accepted for publication in MNRA
The X-ray Transient XTE J2012+381
We present optical and infrared observations of the soft X-ray transient
(SXT) XTE J2012+381 and identify the optical counterpart with a faint red star
heavily blended with a brighter foreground star. The fainter star is coincident
with the radio counterpart and appears to show weak H alpha emission and to
have faded between observations. The RXTE/ASM lightcurve of XTE J2012+381 is
unusual for an SXT in that after an extended linear decay, it settled into a
plateau state for about 40 days before undergoing a weak mini-outburst. We
discuss the nature of the object and suggest similarities to long orbital
period SXTs.Comment: 5 pages, 7 postscript figures included, uses mn.sty. Accepted for
publication in MNRA
A major outburst from the X-ray binary RX J0520.5-6932
We report on the analysis of 8 years of MAssive Compact Halo Objects (MACHO)
data for the source RX J0520.5-6932. A regular period of 24.4 days has been
confirmed, however this is manifest almost entirely in the red part of the
spectrum. A major outburst, lasting approximately 200 days, was observed which
increased the apparent brightness of the object by approximately 0.15
magnitudes without significantly altering its V-R colour index. This outburst
was also seen in X-ray data. The evidence from this analysis points to the
identification of this object as a Be/X-ray binary with a periodically variable
circumstellar disk and a very early optical counterpart.Comment: Paper has been accepted by MNRA
Influences on the fraction of hydrophobic and hydrophilic black carbon in the atmosphere
Black carbon (BC) is a short term climate forcer that directly warms the atmosphere, slows convection, and hinders quantification of the effect of greenhouse gases on climate change. The atmospheric lifetime of BC particles with respect to nucleation scavenging in clouds is controlled by their ability to serve as cloud condensation nuclei (CCN). To serve as CCN under typical conditions, hydrophobic BC particles must acquire hygroscopic coatings. However, the quantitative relationship between coatings and hygroscopic properties for ambient BC particles is not known nor is the time scale for hydrophobic-to-hydrophilic conversion. Here we introduce a method for measuring the hygroscopicity of externally and internally mixed BC particles by coupling a single particle soot photometer with a humidified tandem differential mobility analyzer. We test this technique using uncoated and coated laboratory generated model BC compounds and apply it to characterize the hygroscopicity distribution of ambient BC particles. From these data we derive that the observed number fraction of BC that is CCN active at 0.2% supersaturation is generally low in an urban area near sources and that it varies with the trajectory of the airmass. We anticipate that our method can be combined with measures of air parcel physical and photochemical age to provide the first quantitative estimates for characterizing hydrophobic-to-hydrophilic conversion rates in the atmosphere.Peer reviewe
Discovery of Radio Emission from Transient Anomalous X-ray Pulsar XTE J1810-197
We report the first detection of radio emission from any anomalous X-ray
pulsar (AXP). Data from the Very Large Array (VLA) MAGPIS survey with angular
resolution 6" reveals a point-source of flux density 4.5 +/- 0.5 mJy at 1.4 GHz
at the precise location of the 5.54 s pulsar XTE J1810-197. This is greater
than upper limits from all other AXPs and from quiescent states of soft
gamma-ray repeaters (SGRs). The detection was made in 2004 January, 1 year
after the discovery of XTE J1810-197 during its only known outburst. Additional
VLA observations both before and after the outburst yield only upper limits
that are comparable to or larger than the single detection, neither supporting
nor ruling out a decaying radio afterglow related to the X-ray turn-on. Another
hypothesis is that, unlike the other AXPs and SGRs, XTE J1810-197 may power a
radio synchrotron nebula by the interaction of its particle wind with a
moderately dense environment that was not evacuated by previous activity from
this least luminous, in X-rays, of the known magnetars.Comment: 13 pages, 1 figure, to appear in ApJ Letter
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