Observations of GRB 100724B with the Fermi Gamma-Ray Burst Monitor find that the spectrum is dominated by the typical Band functional form, which is usually taken to represent a non-thermal emission component, but also includes a statistically highly significant thermal spectral contribution. The simultaneous observation of the thermal and non-thermal components allows us to confidently identify the two emission components. The fact that these seem to vary independently favors the idea that the thermal component is of photospheric origin while the dominant non-thermal emission occurs at larger radii. Our results imply either a very high efficiency for the non-thermal process or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux.

We report on the long-term X-ray monitoring with Swift, RXTE, Suzaku, Chandra, and

The center of our Galaxy hosts a supermassive black hole, Sagittarius (Sgr) A *. Young, massive stars within 0.5 pc of Sgr A * are evidence of an episode of intense star formation near the black hole a few million years ago, which might have left behind a young neutron star traveling deep into Sgr A * 's gravitational potential. On 2013 April 25, a short X-ray burst was observed from the direction of the Galactic center. With a series of observations with the Chandra and the Swift satellites, we pinpoint the associated magnetar at an angular distance of 2.4 ± 0.3 arcsec from Sgr A * , and refine the source spin period and its derivative (P = 3.7635537(2) s andṖ = 6.61(4) × 10 −12 s s −1), confirmed by quasi simultaneous radio observations performed with the Green Bank Telescope and Parkes Radio Telescope, which also constrain a dispersion measure of DM = 1750 ± 50 pc cm −3 , the highest ever observed for a radio pulsar. We have found that this X-ray source is a young magnetar at ≈0.07-2 pc from Sgr A *. Simulations of its possible motion around Sgr A * show that it is likely (∼90% probability) in a bound orbit around the black hole. The radiation front produced by the past activity from the magnetar passing through the molecular clouds surrounding the Galactic center region might be responsible for a large fraction of the light echoes observed in the Fe fluorescence features.

The Crab Nebula is the only hard X-ray source in the sky that is both bright enough and steady enough to be easily used as a standard candle. As a result, it has been used as a normalization standard by most X-ray/gamma-ray telescopes. Although small-scale variations in the nebula are well known, since the start of science operations of

During the summer of 2006, the accreting X-ray pulsar EXO 2030+375 underwent its first giant outburst since its discovery in 1985. Our observations include the first ever of the rise of a giant outburst of EXO 2030+375. EXO 2030+375 was monitored daily with the Rossi X-Ray Timing Explorer (RXTE ) from 2006 June to 2007 May. During the giant outburst we discovered evidence for a cyclotron feature at $11 keV. This feature was confidently detected for about 90 days, during the brighter portion of the outburst. Daily observations of the next five EXO 2030+375 orbits detected pulsations at all orbital phases and normal outbursts shifted to a later orbital phase than before the giant outburst. An accretion disk appears to be present in both the normal and giant outbursts, suggesting that the long-term behavior is a product of the state of the Be star disk and the accretion disk. Here we will present flux and frequency histories from our detailed RXTE observations of the giant outburst and the normal outbursts that surrounded it. A new orbital analysis is presented that includes observations from

After about 18 years of steadily spinning down, the accretion-powered pulsar 4U 1626-67, experienced a new torque reversal at the beginning of 2008. For the present study we have used all available Fermi/GBM data since its launch in 2008 June 11 and over 5 yr of hard X-ray Swift/BAT observations (starting from 2004 October up to the present time). From 2004 up to the end of 2007 the spin-down rate averaged at a mean rate of ∼ν = −4.8 × 10 −13 Hz s −1 until the torque reversal reported here. This second detected torque reversal was centered near MJD 54500 (2008 Feb 4) and it lasted approximately 150 days.During the reversal the source also underwent an increase in flux by a fraction of ∼2.5. Since then it has been following a steady spin-up at a mean rate of ∼ν = 4 × 10 −13 Hz s −1 . We present a detailed long-term timing analysis of this source and a long term spectral hardness ratio study in order to see whether there are spectral changes around this new observed torque reversal.

We present recent contemporaneous X-ray and optical observations of the Be/X-ray binary system A 0535+26 with the Fermi/Gamma-ray Burst Monitor (GBM) and several ground-based observatories. These new observations are put into the context of the rich historical data (since ∼1978) and discussed in terms of the neutron-star-Be-disk interaction. The Be circumstellar disk was exceptionally large just before the 2009 December giant outburst, which may explain the origin of the unusual recent X-ray activity of this source. We found a peculiar evolution of the pulse profile during this giant outburst, with the two main components evolving in opposite ways with energy. A hard 30-70 mHz X-ray quasi-periodic oscillation was detected with GBM during this 2009 December giant outburst. It becomes stronger with increasing energy and disappears at energies below 25 keV. In the long term a strong optical/X-ray correlation was found for this system, however in the medium term the Hα equivalent width and the V-band brightness showed an anti-correlation after ∼2002 August. Each giant X-ray outburst occurred during a decline phase of the optical brightness, while the Hα showed a strong emission. In late 2010 and before the 2011 February outburst, rapid V /R variations are observed in the strength of the two peaks of the Hα line. These had a period of ∼25 days and we suggest the presence of a global one-armed oscillation to explain this scenario. A general pattern might be inferred, where the disk becomes weaker and shows V /R variability beginning ∼6 months following a giant outburst.

OAO 1657-415 is an eclipsing X-ray binary wind-fed pulsar that has exhibited smooth spinup/spin-down episodes and has undergone several torque reversals throughout its long history of observation. We present a frequency history spanning nearly 19 years of observations from the Burst and Transient Source Experiment (CGRO/BATSE) and from the Gamma-Ray Burst Monitor (Fermi/GBM). Our analysis suggests two modes of accretion: one resulting in steady spin-up correlated with flux during which we believe a stable accretion disk is present and one in which the neutron star is spinning down at a lesser rate which is uncorrelated with flux. Orbital elements of the pulsar system are determined at several intervals throughout this history. With these ephemerides, statistically significant orbital decay with aṖ orb = (−9.74 ± 0.78) × 10 −8 is established.