Abstract
We investigate the X-ray and UV emission from the contact binary star KIC 9832227, which was observed with XMM-Newton for one orbital cycle. The binary is detected with an average X-ray ...luminosity of 3.4 × 10
30
erg s
−1
. The X-ray emission is restricted to energies below 3 keV and originates from a multitemperature plasma with temperatures up to 1 keV. The X-ray spectrum has at least two distinct components, a cooler, mostly steady component, and a hotter component exhibiting significant variability. The variable X-ray emission appears to originate from a compact flare near the contact region between the two stars that is being eclipsed by the secondary. We analyze the eclipse profile to constrain the location, size, and density of the flaring region. The remaining X-ray emission is not eclipsed and could originate from the polar region on the primary star or an extended corona. The UV emission exhibits the same nearly sinusoidal modulation at half the orbital period that is observed at longer wavelengths. The primary and secondary eclipses have slightly different depths, which is generally attributed to starspot activity. Using simulations of the UV light curve with stellar atmosphere models, we deduce the presence of a starspot near the polar region of the primary, and we determine the time of primary eclipse.
We investigate the gamma-ray and X-ray emission from the transient gamma-ray source Fermi J0035+6131, which was discovered with the Fermi Large Area Telescope (LAT) near the Galactic plane at b = 1 ...3, and we discuss potential multi-wavelength counterparts of the gamma-ray source. Our analysis of over 9 years of Fermi LAT data revealed two flaring events lasting 10-30 hr during which the gamma-ray flux increased by a factor of >300 compared to the long-term average. We also analyzed X-ray data obtained with XMM-Newton and Swift and identified several sources with a hard X-ray spectrum inside the Fermi LAT confidence region. The two brightest X-ray sources have known counterparts at other wavelengths and are associated with the compact radio source VCS4 J0035+6130 and the B1 IV:nn star HD 3191, respectively. VCS4 J0035+6130, which is also detected in the near infrared, is likely an active galaxy serendipitously located behind the Galactic disk and is the most compelling candidate for the counterpart of the gamma-ray source. HD 3191 appears to be part of an X-ray binary with a compact companion and is unlikely to be associated with Fermi J0035+6131.
We present an analysis of XMM-Newton and RXTE data from three observations of the neutron star LMXB 4U 1636-536. The X-ray spectra show clear evidence of a broad, asymmetric iron emission line ...extending over the energy range 4-9 keV. The line profile is consistent with relativistically broadened Fe K alpha emission from the inner accretion disk. The Fe K alpha line in 4U 1636-536 is considerably broader than the asymmetric iron lines recently found in other neutron star LMXBs, which indicates a high disk inclination. We find evidence that the broad iron line feature is a combination of several K alpha lines from iron in different ionization states.
The Fermi LAT has detected numerous transient gamma-ray sources near the Galactic plane, several of which have been shown to be located within our Galaxy. We present an analysis of LAT Pass 8 data of ...seven previously reported, but still unidentified transient gamma-ray sources located within 10{\deg} of the Galactic plane. We detect significant gamma-ray emission lasting several days for three of these sources: Fermi J0035+6131, Fermi J0905-3527, and Fermi J0910-5041. However, we were not able to detect the increase in gamma-ray emission that has previously been reported in the other four cases. We also review available multiwavelength data for the transients and discuss potential counterparts.
MGRO J1908+06 is a bright, extended TeV gamma-ray source located near the Galactic plane. The TeV emission has previously been attributed to the pulsar wind nebula of the radio-faint gamma-ray pulsar ...PSR J1907+0602 discovered with Fermi. However, studies of the TeV morphology with VERITAS have shown that MGRO J1908+06 is somewhat larger than other pulsar wind nebulae of similar age and that the TeV spectrum does not soften with distance from the pulsar as is observed for other pulsar wind nebulae. Although MGRO J1908+06 is very bright in gamma rays with a flux corresponding to ~80% of the Crab Nebula flux at 20 TeV, no extended emission at other energies has so far been detected. We report on our analysis of X-ray data obtained with XMM-Newton of the region near MGRO J1908+06. We searched the data for point-like sources and detected several hard-spectrum X-ray sources that could be associated with the TeV emission, including the gamma-ray pulsar PSR J1907+0602. We also performed an extended source analysis to search for diffuse emission from MGRO J1908+06 but found no evidence of diffuse X-ray emission coincident with the TeV source. We place an upper limit of \(8.7\times10^{33}\rm~erg~s^{-1}\) on the X-ray luminosity of MGRO J1908+06 in the 1-10 keV energy range. The corresponding limit on the ratio of gamma-ray to X-ray luminosity is consistent with the ratios found for other pulsar wind nebulae of similar age.
ApJ 862:83 (6pp), 2018 We investigate the gamma-ray and X-ray emission from the transient gamma-ray
source Fermi J0035+6131, which was discovered with the Fermi Large Area
Telescope (LAT) near the ...Galactic plane at $b=1.3^\circ$, and we discuss
potential multi-wavelength counterparts of the gamma-ray source. Our analysis
of over 9 years of Fermi LAT data revealed two flaring events lasting 10-30 hr
during which the gamma-ray flux increased by a factor of >300 compared to the
long-term average. We also analyzed X-ray data obtained with XMM-Newton and
Swift and identified several sources with a hard X-ray spectrum inside the
Fermi LAT confidence region. The two brightest X-ray sources have known
counterparts at other wavelengths and are associated with the compact radio
source VCS4 J0035+6130 and the B1 IV:nn star HD 3191, respectively. VCS4
J0035+6130, which is also detected in the near infrared, is likely an active
galaxy serendipitously located behind the Galactic disk and is the most
compelling candidate for the counterpart of the gamma-ray source. HD 3191
appears to be part of an X-ray binary with a compact companion and is unlikely
to be associated with Fermi J0035+6131.
We present an analysis of X-ray and ultraviolet (UV) data of the dwarf nova VW Hyi that were obtained with XMM–Newton during the quiescent state. The X-ray spectrum indicates the presence of an ...optically thin plasma in the boundary layer that cools as it settles on to the white dwarf. The plasma has a continuous temperature distribution that is well described by a power law or a cooling flow model with a maximum temperature of 6–8 keV. We estimate from the X-ray spectrum a boundary layer luminosity of 8 × 1030 erg s−1, which is only 20 per cent of the disc luminosity. The rate of accretion on to the white dwarf is 5 × 10−12 M⊙ yr−1, about half of the rate in the disc. From the high-resolution X-ray spectra, we estimate that the X-ray emitting part of the boundary layer is rotating with a velocity of 540 km s−1, which is close to the rotation velocity of the white dwarf but is significantly smaller than the Keplerian velocity. We detect a 60-s quasi-periodic oscillation of the X-ray flux, which is likely to be due to the rotation of the boundary layer. The X-ray and the UV flux show strong variability on a time-scale of ∼1500 s. We find that the variability in the two bands is correlated and that the X-ray fluctuations are delayed by ∼100 s. The correlation indicates that the variable UV flux is emitted near the transition region between the disc and the boundary layer and that accretion rate fluctuations in this region are propagated to the X-ray emitting part of the boundary layer within ∼100 s. An orbital modulation of the X-ray flux suggests that the inner accretion disc is tilted with respect to the orbital plane. The elemental abundances in the boundary layer are close to their solar values.
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