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Register a new userChandra follow-up of bursters with low persistent emission
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We report on Chandra ACIS-S observations of five type I X-ray bursters with low persistent emission: SAX J1324.5-6313, SAX J1752.3-3128, SAX J1753.5-2349, SAX J1806.5-2215 and SAX J1818.7+1424. We designate candidate persistent sources for four X-ray bursters. All candidates are detected at a persistent luminosity level of 10^(32-33) erg/s, comparable to soft X-ray transients in quiescence. From the number of bursters with low persistent emission detected so far with the Wide Field Cameras, we estimate a total of such sources in our Galaxy between 30 and 4000.
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We investigated the X-ray emission properties of the powerful radio galaxy 3C 459 revealed by a recent Chandra follow-up observation carried out in October 2014 with a 62 ks exposure. We performed an X-ray spectral analysis from a few selected regions on an image obtained from this observation and also compared the X-ray image with a 4.9 GHz VLA radio map available in the literature. The dominant contribution comes from the radio core but significant X-ray emission is detected at larger angular separations from it, surrounding both radio jets and lobes. According to a scenario in which the extended X-ray emission is due to a plasma collisionally heated by jet-driven shocks and not magnetically dominated, we estimated its temperature to be ~0.8 keV. This hot gas cocoon could be responsible for the radio depolarization observed in 3C 459, as recently proposed also for 3C 171 and 3C 305. On the other hand, our spectral analysis and the presence of an oxygen K edge, blueshifted at 1.23 keV, cannot exclude the possibility that the X-ray radiation originating from the inner regions of the radio galaxy could be intercepted by some outflow of absorbing material intervening along the line of sight, as already found in some BAL quasars.
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The IceCube DeepCore is a dense infill array of the IceCube Neutrino Observatory at the South Pole. While IceCube is best suited for detecting neutrinos with energies of several 100 GeV and above, DeepCore allows to probe neutrinos with lower energies. We focus on a sample of neutrinos with energies above approximately 10 GeV, which was originally optimised for oscillation experiments. Recently, it has been adapted to enable searches for transient sources of astrophysical neutrinos in the sky. In particular, this low-energy dataset can be used to conduct follow-up searches of gravitational wave transients detected by the LIGO-Virgo instruments. A study of this, which complements IceCubes follow-up of gravitational wave events using high-energy neutrino samples, will be discussed here.
We report on the results of optical follow-up observations of the counterpart of GRB 970508, starting 7 hours after the event. Multi-color U, B, V, R$_{c}$ and I$_{c}$ band observations were obtained during the first three consecutive nights. The counterpart was monitored regularly in R$_{c}$ until $sim$ 4 months after the burst. The light curve after the maximum follows a decline that can be fitted with a power law with exponent $alpha$ = --1.141 $pm$ 0.014. Deviations from a smooth power law decay are moderate (r.m.s. = 0.15 magnitude). We find no flattening of the light curve at late times. The optical afterglow fluence is a significant fraction, $sim$ 5%, of the GRB fluence. The optical energy distribution can be well represented by a power law, the slope of which changed at the time of the maximum (the spectrum became redder).
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