The prelude to and aftermath of the giant flare of 2004 December 27 : Persistent and pulsed X-ray properties of SGR 1806-20 from 1993 to 2005
We report on the evolution of key spectral and temporal parameters of SGR 1806-20 prior to and following the highly energetic giant flare of 2004 December 27. Using RXTE, we track the pulse frequency of the SGR and find that the spin-down rate varied erratically in the months before and after the flare. Contrary to the giant flare in SGR 1900+14, we find no evidence for a discrete jump in spin frequency at the time of the December 27th flare (|Δν/ν| < 5 × 10-6). In the months surrounding the flare, we find a strong correlation between pulsed flux and torque consistent with the model for magnetar magnetosphere electrodynamics proposed by Thompson et al. As with the flare in SGR 1900+14, the pulse morphology of SGR 1806-20 changes drastically following the flare. Using Chandra and other publicly available imaging X-ray detector observations, we construct a spectral history of SGR 1806-20 from 1993 to 2005. The usual magnetar persistent emission spectral model of a power law plus a blackbody provides an excellent fit to the data. We confirm the earlier finding by Mereghetti et al. of increasing spectral hardness of SGR 1806-20 between 1993 and 2004. However, our results indicate significant differences in the temporal evolution of the spectral hardening. Rather than a direct correlation between torque and spectral hardness, we find evidence for a sudden torque change that preceded a gradual hardening of the energy spectrum on a timescale of years. Interestingly, the spectral hardness, spin-down rate, phase-averaged flux, and pulsed flux of SGR 1806-20 all peak months before the flare epoch.

title: Large Torque Variations in Two Soft Gamma Repeaters
abstract: We have monitored the pulse frequencies of the two soft gamma repeaters SGR 1806-20 and SGR 1900+14 through the beginning of year 2001 using primarily Rossi X-Ray Timing Explorer Proportional Counter Array observations. In both sources, we observe large changes in the spin-down torque up to a factor of ~4, which persist for several months. Using long-baseline phase-connected timing solutions as well as the overall frequency histories, we construct torque noise power spectra for each SGR. The power spectrum of each source is very red (power-law slope ~-3.5). The torque noise power levels are consistent with some accreting systems on timescales of ~1 yr, yet the full power spectrum is much steeper in frequency than any known accreting source. To the best of our knowledge, torque noise power spectra with a comparably steep frequency dependence have been seen only in young, glitching radio pulsars (e.g., Vela). The observed changes in spin-down rate do not correlate with burst activity; therefore, the physical mechanisms behind each phenomenon are also likely unrelated. Within the context of the magnetar model, seismic activity cannot account for both the bursts and the long-term torque changes unless the seismically active regions are decoupled from one another.

title: Long-Term Spectral and Timing Behavior of the Black Hole Candidate XTE J1908+094
abstract: We present the long-term X-ray light curves and detailed spectral and timing analyses of XTE J1908+094 using the Rossi X-Ray Timing Explorer Proportional Counter Array observations covering two outbursts in 2002 and early 2003. At the onset of the first outburst, the source was found in a spectrally low/hard state lasting for ~40 days, followed by a 3 day long transition to the high/soft state. The source flux (in 2-10 keV) reached ~100 mcrab on 2002 April 6, then decayed rapidly. In power spectra, we detect strong band-limited noise and varying low-frequency quasi-periodic oscillations that evolved from ~0.5 to ~5 Hz during the initial low/hard state of the source. We find that the second outburst closely resembled the spectral evolution of the first. The X-ray transient's overall outburst characteristics led us to classify XTE J1908+094 as a black hole candidate. Here we also derive precise X-ray position of the source using Chandra observations that were performed during the decay phase of the first outburst and following the second outburst.

title: On the Dramatic Spin-up/Spin-down Torque Reversals in Accreting Pulsars
abstract: Dramatic torque reversals between spin-up and spin-down have been observed in half of the persistent X-ray 
pulsars monitored by the BATSE all-sky monitor on the Compton Gamma Ray Observatory. Theoretical models 
developed to explain early pulsar timing data can explain spin-down torques via a disk-magnetosphere interaction 
if the star nearly corotates with the inner accretion disk. To produce the observed BATSE torque reversals, however, these equilibrium models require the disk to alternate between two mass accretion rates, with ˙M5 producing accretion torques of similar magnitude but always of opposite sign. Moreover, in at least one pulsar (GX 114) undergoing secular spin-down, the neutron star spins down faster during brief (~20 day) hard X-ray flares—this is opposite the correlation expected from standard theory, assuming that BATSE pulsed flux increases with mass accretion rate. The 10 day to 10 yr intervals between torque reversals in these systems are much longer than any characteristic magnetic or viscous timescale near the inner disk boundary and are more suggestive of a global disk phenomenon. 
 
We discuss possible explanations of the observed torque behavior. Despite the preferred sense of rotation defined by the binary orbit, the BATSE observations are urprisingly consistent with an earlier suggestion for GX 1+4: the disks in these systems somehow alternate between episodes of prograde and retrograde rotation. We are unaware of any mechanism that could produce a stable retrograde disk in a binary undergoing Roche lobe overflow, but such flip-flop behavior does occur in numerical simulations of wind-fed systems. One possibility is that the disks in some of these binaries are fed by an X-ray–excited wind.

title: Chandra Observations of the Anomalous X-ray Pulsar 4U 0142+61
abstract: We present X-ray imaging, timing, and phase-resolved spectroscopy of the anomalous X-ray pulsar 4U 0142+61 using the Chandra X-Ray Observatory. The spectrum is well described by a power-law plus blackbody model with Γ = 3.35(2), kTBB = 0.458(3) keV, and NH = 0.91(2) × 1022 cm-2; we find no significant evidence for spectral features (0.5-7.0 keV). Time-resolved X-ray spectroscopy shows evidence for evolution in phase in either Γ, kTBB, or some combination thereof as a function of pulse phase. We derive a precise X-ray position for the source and determine its spin period, P = 8.68866(30) s. We have detected emission beyond 4'' from the central source and extending beyond 100'', likely due to dust scattering in the interstellar medium.

title: Characterization of the Crab Pulsar's Timing Noise
abstract: We present a power spectral analysis of the Crab pulsar’s timing noise, mainly using radio measurements from Jodrell Bank taken over the period 1982-1989, an interval bounded by sparse data sampling and a large glitch. The power spectral analysis is complicated by nonuniform data sampling and the presence of a steep red power spectrum that can distort power spectra measurement by causing severe power “leakage”. We develop a simple windowing method for computing red noise power spectra of uniformly sampled data sets and test it on Monte Carlo generated sample realizations of red power-law noise. We generalize time-domain methods of generating power-law red noise with even integer spectral indices to the case of noninteger spectral indices. The Jodrell Bank pulse phase residuals are dense and smooth enough that an interpolation onto a uniform time series is possible. A windowed power spectrum is computed revealing a periodic or nearly periodic component with a period of 568± 10 days and a 1/f 3 power-law noise component in pulse phase with a noise strength Sφ = (1.24±0.067)×10−16 cycles/sec over the analysis frequency range f = 0.003 − 0.1 cycles/day. This result deviates from past analyses which characterized the pulse phase timing residuals as either 1/f 4 power-law noise or a quasiperiodic process. The analysis was checked using the Deeter polynomial method of power spectrum estimation that was developed for the case of nonuniform sampling, but has lower spectral resolution. The timing noise is consistent with a torque noise spectrum rising with analysis frequency as f implying blue torque noise, a result not predicted by current models of pulsar timing noise. If the periodic or nearly periodic component is due to a binary companion, we find a mass function f(M) = (6.8 ± 2.4) × 10−16 M⊙ and a companion mass, Mc ≥ 3.2M⊕ assuming a Crab pulsar mass of 1.4M⊙.

title: Search for microscopic black holes in pp collisions at $ \sqrt{s}=8 $ TeV
abstract: A bstractA search for microscopic black holes and string balls is presented, based on a data sample of pp collisions at $ \sqrt{s}=8 $ TeV recorded by the CMS experiment at the Large Hadron Collider and corresponding to an integrated luminosity of 12 fb−1. No excess of events with energetic multiparticle final states, typical of black hole production or of similar new physics processes, is observed. Given the agreement of the observations with the expected standard model background, which is dominated by QCD multijet production, 95% confidence level limits are set on the production of semiclassical or quantum black holes, or of string balls, corresponding to the exclusions of masses below 4.3 to 6.2 TeV, depending on model assumptions. In addition, model-independent limits are set on new physics processes resulting in energetic multiparticle final states.

title: Search for supersymmetry in events with b-quark jets and missing transverse energy in pp collisions at 7 TeV
abstract: Results are presented from a search for physics beyond the standard model based on events with large missing transverse energy, at least three jets, and at least one, two, or three b-quark jets. The study is performed using a sample of proton-proton collision data collected at sqrt(s)=7 TeV with the CMS detector at the LHC in 2011, with the missing transverse energy distribution as the principal search variable. The integrated luminosity of the sample is 4.98 inverse femtobarns. The observed number of events is found to be consistent with the standard model expectation, which is evaluated using control samples in the data. The results are used to constrain cross sections for the production of supersymmetric particles decaying to b-quark-enriched final states in the context of simplified model spectra.

title: Search for $B^0_s \to \mu^+ \mu^-$ and $B^0 \to \mu^+ \mu^-$ decays
abstract: A search for the rare decays B_s to mu+ mu- and B^0 to mu^+ mu^- is performed in pp collisions at sqrt(s) = 7 TeV, with a data sample corresponding to an integrated luminosity of 5 inverse femtobarns collected by the CMS experiment at the LHC. In both decays, the number of events observed after all selection requirements is consistent with the expectation from background plus standard model signal predictions. The resulting upper limits on the branching fractions are Br(B_s to mu^+ mu^-) < 7.7E-9 and Br(B^0 to mu^+ mu^-) < 1.8E-9 at 95% confidence level.

title: Search for supersymmetry in pp collisions at $ \sqrt {s} = 7 $ TeV in events with a single lepton, jets, and missing transverse momentum
abstract: Results are reported from a search for physics beyond the standard model in proton-proton collisions at a center-of-mass energy of 7 TeV, focusing on the signature with a single, isolated, high-transverse-momentum lepton (electron or muon), energetic jets, and large missing transverse momentum. The data sample comprises an integrated luminosity of 36 pb−1, recorded by the CMS experiment at the LHC. The search is motivated by models of new physics, including supersymmetry. The observed event yields are consistent with standard model backgrounds predicted using control samples obtained from the data. The characteristics of the event sample are consistent with those expected for the production of $ {\text{t}\bar{\text{t}}} $ and W + jets events. The results are interpreted in terms of limits on the parameter space for the constrained minimal supersymmetric extension of the standard model.

title: Measurement of dijet angular distributions and search for quark compositeness in pp collisions at √s = 7 TeV.
abstract: Dijet angular distributions are measured over a wide range of dijet invariant masses in pp collisions at √s = 7 TeV, at the CERN LHC. The event sample, recorded with the CMS detector, corresponds to an integrated luminosity of 36 pb⁻¹. The data are found to be in good agreement with the predictions of perturbative QCD, and yield no evidence of quark compositeness. With a modified frequentist approach, a lower limit on the contact interaction scale for left-handed quarks of Λ⁺ = 5.6 TeV (Λ⁻ = 6.7 TeV) for destructive (constructive) interference is obtained at the 95% confidence level.