A puzzling paucity of double peaked X-ray pulsars
Accretion powered pulsars exhibit a variety of lightcurves. In this paper we propose to classify the observed lightcurves as single or double pulsed. We analyze the lightcurves of 89 accretion powered pulsars and assign them to these classes. We present three datasets: first in which the classification can be easily done, second for which the classification is more difficult and not certain, and third for which we were unable to classify the pulsar because of a lack of published data. We analyze a simple model in which the angles between the magnetic and rotation axis β , and between the rotation axis and the line of sight θ are random, and show that it is inconsistent with the data. We also present a model in which the angle between the magnetic axis and the rotation axis is restricted and compare it with the data. This leads to an upper limit on the angle $\beta < 50^\circ$. We conclude that there must be a mechanism that leads to alignment of the magnetic and spin axis in X-ray pulsars.

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: 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: 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: Observation of Z decays to four leptons with the CMS detector at the LHC
abstract: A bstractThe first observation of the Z boson decaying to four leptons in proton-proton collisions is presented. The analyzed data set corresponds to an integrated luminosity of 5.02 fb−1 at $ \sqrt{s}=7 $ TeV collected by the CMS detector at the Large Hadron Collider. A pronounced resonance peak, with a statistical significance of 9.7 σ, is observed in the distribution of the invariant mass of four leptons (electrons and/or muons) with mass and width consistent with expectations for Z boson decays. The branching fraction and cross section reported here are defined by phase space restrictions on the leptons, namely, 80 < m4ℓ < 100 GeV, where m4ℓ is the invariant mass of the four leptons, and mℓℓ > 4 GeV for all pairs of leptons, where mℓℓ is the two-lepton invariant mass. The measured branching fraction is $ \mathcal{B}\left( {Z\to 4\ell } \right)=\left( {4.2_{-0.8}^{+0.9}\left( {\mathrm{stat}.} \right)\pm 0.2\left( {\mathrm{syst}.} \right)} \right)\times {10^{-6 }} $ and agrees with the standard model prediction of 4.45 × 10−6. The measured cross section times branching fraction is $ \sigma \left( {\mathrm{pp}\to \mathrm{Z}} \right)\mathcal{B}\left( {\mathrm{Z}\to 4\ell } \right)=112_{-20}^{+23}\left( {\mathrm{stat}.} \right)_{-5}^{+7}\left( {\mathrm{syst}.} \right)_{-2}^{+3}\left( {\mathrm{lumi}.} \right) $ fb, also consistent with the standard model prediction of 120 fb. The four-lepton mass peak arising from Z → 4ℓ decays provides a calibration channel for the Higgs boson search in the H → ZZ → 4ℓ decay mode.

title: Search for narrow resonances and quantum black holes in inclusive and b-tagged dijet mass spectra from pp collisions at $ \sqrt{s}=7 $ TeV
abstract: A bstractA search for narrow resonances and quantum black holes is performed in inclusive and b-tagged dijet mass spectra measured with the CMS detector at the LHC. The data set corresponds to 5 fb−1 of integrated luminosity collected in pp collisions at $ \sqrt{s}=7 $ TeV. No narrow resonances or quantum black holes are observed. Model-independent upper limits at the 95% confidence level are obtained on the product of the cross section, branching fraction into dijets, and acceptance for three scenarios: decay into quark-quark, quark-gluon, and gluon-gluon pairs. Specific lower limits are set on the mass of string resonances (4.31 TeV), excited quarks (3.32 TeV), axigluons and colorons (3.36 TeV), scalar color-octet resonances (2.07 TeV), E6 diquarks (3.75 TeV), and on the masses of W′ (1.92 TeV) and Z′ (1.47 TeV) bosons. The limits on the minimum mass of quantum black holes range from 4 to 5.3 TeV. In addition, b-quark tagging is applied to the two leading jets and upper limits are set on the production of narrow dijet resonances in a model-independent fashion as a function of the branching fraction to b-jet pairs.

title: Search for a $W^\prime$ or Techni-$\rho$ Decaying into $WZ$ in $pp$ Collisions at $\sqrt{s}=7$ TeV
abstract: A search is performed in pp collisions at √s=7  TeV for exotic particles decaying via WZ to final states with electrons and muons. The data sample corresponds to an integrated luminosity of approximately 5  fb^(-1). No significant excess is observed in the data above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of the W′ boson described by the sequential standard model and on the W′ WZ coupling. W′ bosons with masses below 1143 GeV are excluded. Limits are also set in the context of low-scale technicolor models, under a range of assumptions concerning the model parameters.

title: Search for new physics with jets and missing transverse momentum in pp collisions at $ \sqrt {s} = 7 $ TeV
abstract: A search for new physics is presented based on an event signature of at least three jets accompanied by large missing transverse momentum, using a data sample corresponding to an integrated luminosity of 36 pb−1 collected in proton-proton collisions at $ \sqrt {s} = 7 $ TeV with the CMS detector at the LHC. No excess of events is observed above the expected standard model backgrounds, which are all estimated from the data. Exclusion limits are presented for the constrained minimal supersymmetric extension of the standard model. Cross section limits are also presented using simplified models with new particles decaying to an undetected particle and one or two jets.

title: Study of the mass and spin-parity of the Higgs boson candidate via its decays to Z boson pairs.
abstract: A study is presented of the mass and spin-parity of the new boson recently observed at the LHC at a mass near 125 GeV. An integrated luminosity of 17.3 fb(-1), collected by the CMS experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, is used. The measured mass in the ZZ channel, where both Z bosons decay to e or μ pairs, is 126.2 ± 0.6(stat) ± 0.2(syst) GeV. The angular distributions of the lepton pairs in this channel are sensitive to the spin-parity of the boson. Under the assumption of spin 0, the present data are consistent with the pure scalar hypothesis, while disfavoring the pure pseudoscalar hypothesis.