[en] Here, we consider the question of which of the 20-100 keV INTEGRAL sources may be detected by GLAST. There are clearly some source types that the two satellites will have in common, such as Active Galactic Nuclei, rotation-powered pulsars, and supernova remnants, but we have performed a detailed cross-correlation between the positions of the 499 INTEGRAL sources and the 271 EGRET sources that were detected at >100 MeV. We find that 31 of the EGRET sources have at least one INTEGRAL source in their error circle. Although source confusion is a problem in the Galactic Center region, we find 4 possible associations between EGRET sources and High-Mass X-ray Binaries in the Galactic disk. This could indicate that some fraction of HMXBs will be seen by GLAST

[en] The scientific goals and concept design of the Hard X-ray Imager (HXI) for MIRAX are presented to set the context for a discussion of the status of the HXI development. Emphasis is placed upon the RENA ASIC performance, the detector module upgrades, and a planned high altitude balloon flight to validate the HXI design and performance in a near-space environment

[en] We present a 50 ks Chandra/ACIS-I X-ray observation of the Bower et al. Very Large Array archival field. The observations reach a limiting sensitivity of ∼10^-4 counts s^-1, corresponding to a flux of a few times 10^-15 erg s^-1 cm^-2 for the models we explore. The Chandra observations were undertaken to search for X-ray counterparts to the eight transient sources without optical counterparts, and the two transient sources with optical counterparts seen by Bower et al. Neither of the sources with optical counterparts was detected in X-rays. One of the eight optical non-detections is associated with a marginal (2.4σ) X-ray detection in our Chandra image. A second optically undetected Bower et al. transient may be associated with a z = 1.29 X-ray-detected quasar or its host galaxy, or alternatively is undetected in X-rays and is a chance association with the nearby X-ray source. The X-ray flux upper limits, and the one marginal detection, are consistent with the interpretation of Ofek et al. that the optically undetected radio transients are flares from isolated old Galactic neutron stars. The marginal X-ray detection has a hardness ratio that implies a temperature too high for a simple one-temperature neutron star model, but plausible multi-component fits are not excluded, and in any case the marginal X-ray detection may be due to cosmic rays or particle background. The X-ray flux upper limits are also consistent with flare star progenitors at ∼> 1 kpc (which would require the radio luminosity of the transient to be unusually high for such an object) or less extreme flares from brown dwarfs at distances of around 100 pc.

[en] Determining the type of matter that is inside a neutron star (NS) has been a long-standing goal of astrophysics. Despite this, most of the NS equations of state (EOS) that predict maximum masses in the range 1.4-2.8 M_sun are still viable. Most of the precise NS mass measurements that have been made to date show values close to 1.4 M_sun, but a reliable measurement of an overmassive NS would constrain the EOS possibilities. Here, we investigate how optical astrometry at the microarcsecond level can be used to map out the orbits of High-mass X-ray Binaries (HMXBs), leading to tight constraints on NS masses. While previous studies by Unwin and coworkers and Tomsick and coworkers discuss the fact that the future Space Interferometry Mission should be capable of making such measurements, the current work describes detailed simulations for six HMXB systems, including predicted constraints on all orbital parameters. We find that the direct NS masses can be measured to an accuracy of ∼2.5% (1σ) in the best case (X Per), to ∼6.5% for Vela X-1, and to ∼10% for two other HMXBs.

[en] We use a 43 ks XMM-Newton observation to investigate the nature of sources first distinguished by a follow-up Chandra observation of the field surrounding INTEGRAL source IGR J17448-3232, which includes extended emission and a bright point source previously classified as a blazar. We establish that the extended emission is a heretofore unknown massive galaxy cluster hidden behind the Galactic bulge. The emission-weighted temperature of the cluster within the field of view is 8.8 keV, with parts of the cluster reaching temperatures of up to 12 keV; no cool core is evident. At a redshift of 0.055, the cluster is somewhat under-luminous relative to the X-ray luminosity-temperature relation, which may be attributable to its dynamical state. We present a preliminary analysis of its properties in this paper. We also confirm that the bright point source is a blazar, and we propose that it is either a flat spectrum radio quasar or a low-frequency peaked BL Lac object. We find four other fainter sources in the field, which we study and tentatively identify. Only one, which we propose is a foreground Galactic X-ray binary, is hard enough to contribute to IGR J17448-3232, but it is too faint to be significant. We thus determine that IGR J17448-3232 is in fact the galaxy cluster up to ≈45 keV and the blazar beyond

[en] We present the optical/infrared (O/IR) light curve of the black hole X-ray binary GX 339-4 collected at the SMARTS 1.3 m telescope from 2002 to 2010. During this time the source has undergone numerous state transitions including hard-to-soft state transitions when we see large changes in the near-IR flux accompanied by modest changes in optical flux, and three rebrightening events in 2003, 2005, and 2007 after GX 339-4 transitioned from the soft state to the hard. All but one outburst show similar behavior in the X-ray hardness-intensity diagram. We show that the O/IR colors follow two distinct tracks that reflect either the hard or soft X-ray state of the source. Thus, either of these two X-ray states can be inferred from O/IR observations alone. From these correlations we have constructed spectral energy distributions of the soft and hard states. During the hard state, the near-IR data have the same spectral slope as simultaneous radio data when GX 339-4 was in a bright optical state, implying that the near-IR is dominated by a non-thermal source, most likely originating from jets. Non-thermal emission dominates the near-IR bands during the hard state at all but the faintest optical states, and the fraction of non-thermal emission increases with increasing optical brightness. The spectral slope of the optical bands indicate that a heated thermal source is present during both the soft and hard X-ray states, even when GX 339-4 is at its faintest optical state. We have conducted a timing analysis of the light curve for the hard and soft states and find no evidence of a characteristic timescale within the range of 4-230 days.

[en] We report multiwavelength observations of the black hole transient GX 339-4 during its outburst decay in 2011 using the data from RXTE, Swift, and SMARTS. Based on the X-ray spectral, temporal, and optical and infrared (OIR) properties, the source evolved from the soft intermediate to the hard state. Twelve days after the start of the transition toward the hard state, a rebrightening was observed simultaneously in the optical and the infrared bands. Spectral energy distributions (SEDs) were created from observations at the start, and close to the peak of the rebrightening. The excess OIR emission above the smooth exponential decay yields flat spectral slopes for these SEDs. Assuming that the excess is from a compact jet, we discuss the possible locations of the spectral break that mark the transition from optically thick to optically thin synchrotron components. Only during the rising part of the rebrightening, we detected fluctuations with the binary period of the system. We discuss a scenario that includes irradiation of the disk in the intermediate state, irradiation of the secondary star during OIR rise, and jet emission dominating during the peak to explain the entire evolution of the OIR light curve.

[en] We present the first analysis of the extended source CXOU J163802.6–471358, which was discovered serendipitously during the Chandra X-ray survey of the Norma region of the Galactic spiral arms. The X-ray source exhibits a cometary appearance with a point source and an extended tail region. The complete source spectrum is fitted well with an absorbed power law model and jointly fitting the Chandra spectrum of the full source with one obtained from an archived XMM-Newton observation results in best fit parameters N _H =1.5_−0.5^+0.7×10²³ cm⁻² and Γ=1.1_−0.6^+0.7 (90% confidence uncertainties). The unabsorbed luminosity of the full source is then L_X∼4.8×10³³d₁₀² erg s^–1 with d ₁₀ = d/10 kpc, where a distance of 10 kpc is a lower bound inferred from the large column density. The radio counterpart found for the source using data from the Molonglo Galactic Plane Survey epoch-2 shows an elongated tail offset from the X-ray emission. No infrared counterpart was found. The results are consistent with the source being a previously unknown pulsar driving a bow shock through the ambient medium.

[en] We use simultaneous Swift and RXTE observations of the black hole binary GX 339-4 to measure the inner radius of its accretion disk in the hard state down to 0.4% L_Edd via modeling of the thermal disk emission and the relativistically broadened iron line. For the luminosity range covered in this work, our results rule out a significantly truncated disk at 100-1000 R_g as predicted by the advection-dominated accretion flow paradigm. The measurements depend strongly on the assumed emission geometry, with most results providing no clear picture of radius evolution. If the inclination is constrained to roughly 20°, however, the measurements based on the thermal disk emission suggest a mildly receding disk at a luminosity of 0.4% L_Edd. The iron abundance varies between ∼1 and 2 solar abundances, with the i = 20° results indicating a negative correlation with luminosity, though this is likely due to a change in disk illumination geometry

[en] We report on an observation of SGR 1627–41 made with the Chandra X-Ray Observatory on 2011 June 16. Approximately three years after its outburst activity in 2008, the source's flux has been declining, as it approaches its quiescent state. For an assumed power-law spectrum, we find that the absorbed 2-10 keV flux for the source is 1.0^+0.3_–0.2 × 10^–13 erg cm^–2 s^–1 with a photon index of 2.9 ± 0.8 (N_H = 1.0 × 10²³ cm^–2). This flux is approximately consistent with that measured at the same time after the source's outburst in 1998. With measurements spanning three years after the 2008 outburst, we analyze the long-term flux and spectral evolution of the source. The flux evolution is well described by a double exponential with decay times of 0.5 ± 0.1 and 59 ± 6 days, and a thermal cooling model fit suggests that SGR 1627–41 may have a hot core (T_c ∼ 2 × 10⁸ K). We find no clear correlation between flux and spectral hardness as found in other magnetars. We consider the quiescent X-ray luminosities of magnetars and the subset of rotation-powered pulsars with high magnetic fields (B ∼> 10¹³ G) in relation to their spin-inferred surface magnetic field strength and find a possible trend between the two quantities.