skip to main content


Title: Selection Effects in Periodic X-Ray Data from Maximizing Detection Statistics
Abstract

The Neutron Star Interior Composition Explorer (NICER) records exceptional data on pulsars’ energy-dependent X-ray pulse profiles. However, in searching for evidence of pulsations, Guillot et al. (2019) introduce a procedure to select an ordered subset of data that maximizes a detection statistic (the H-test). I show that this can degrade subsequent analyses using an idealized model with stationary expected count rates from both noise and signal. Specifically, the data-selection procedure biases the inferred mean count rate to be too low and the inferred pulsation amplitude to be too high, and the size of these biases scales strongly with the amount of data that is rejected and the true signal amplitude. The procedure also alters the H-test’s null distribution, rendering nominal significance estimates overly optimistic. While the idealized model does not capture all the complexities of real NICER data, it suggests that these biases could be important for NICER’s observations of J0740+6620 and other faint pulsars (observations of J0030+0451 are likely less affected). I estimate that these effects may introduce a bias of(10%)on average in the inferred modulation depth of lightcurves like J0740+6620's, and may be as large as(50%)for fainter pulsars. However, the change for a single data set like J0740+6620 is expected to be a shift between −5% and +20%. This could imply that the lower limit on J0740+6620's radius is slightly larger than it should be, although preliminary investigations suggest the radius constraints shift to larger radii by(1%)with the same overall statistical precision using real J0740+6620 data.

 
more » « less
NSF-PAR ID:
10363929
Author(s) / Creator(s):
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
927
Issue:
2
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 195
Size(s):
["Article No. 195"]
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We use ALMA observations of CO(2–1) in 13 massive (M*≳ 1011M) poststarburst galaxies atz∼ 0.6 to constrain the molecular gas content in galaxies shortly after they quench their major star-forming episode. The poststarburst galaxies in this study are selected from the Sloan Digital Sky Survey spectroscopic samples (Data Release 14) based on their spectral shapes, as part of the Studying QUenching at Intermediate-z Galaxies: Gas, anguLarmomentum, and Evolution (SQuIGGLE) program. Early results showed that two poststarburst galaxies host large H2reservoirs despite their low inferred star formation rates (SFRs). Here we expand this analysis to a larger statistical sample of 13 galaxies. Six of the primary targets (45%) are detected, withMH2109M. Given their high stellar masses, this mass limit corresponds to an average gas fraction offH2MH2/M*7%or ∼14% using lower stellar masses estimates derived from analytic, exponentially declining star formation histories. The gas fraction correlates with theDn4000 spectral index, suggesting that the cold gas reservoirs decrease with time since burst, as found in local K+A galaxies. Star formation histories derived from flexible stellar population synthesis modeling support this empirical finding: galaxies that quenched ≲150 Myr prior to observation host detectable CO(2–1) emission, while older poststarburst galaxies are undetected. The large H2reservoirs and low SFRs in the sample imply that the quenching of star formation precedes the disappearance of the cold gas reservoirs. However, within the following 100–200 Myr, theSQuIGGLEgalaxies require the additional and efficient heating or removal of cold gas to bring their low SFRs in line with standard H2scaling relations.

     
    more » « less
  2. Abstract

    We present a multiwavelength analysis of the galaxy cluster SPT-CL J0607-4448 (SPT0607), which is one of the most distant clusters discovered by the South Pole Telescope atz= 1.4010 ± 0.0028. The high-redshift cluster shows clear signs of being relaxed with well-regulated feedback from the active galactic nucleus (AGN) in the brightest cluster galaxy (BCG). Using Chandra X-ray data, we construct thermodynamic profiles and determine the properties of the intracluster medium. The cool-core nature of the cluster is supported by a centrally peaked density profile and low central entropy (K0=189+11keV cm2), which we estimate assuming an isothermal temperature profile due to the limited spectral information given the distance to the cluster. Using the density profile and gas cooling time inferred from the X-ray data, we find a mass-cooling rateṀcool=10060+90Myr−1. From optical spectroscopy and photometry around the [Oii] emission line, we estimate that the BCG star formation rate isSFR[OII]=1.70.6+1.0Myr−1, roughly two orders of magnitude lower than the predicted mass-cooling rate. In addition, using ATCA radio data at 2.1 GHz, we measure a radio jet powerPcav=3.21.3+2.1×1044erg s−1, which is consistent with the X-ray cooling luminosity (Lcool=1.90.5+0.2×1044erg s−1withinrcool= 43 kpc). These findings suggest that SPT0607 is a relaxed, cool-core cluster with AGN-regulated cooling at an epoch shortly after cluster formation, implying that the balance between cooling and feedback can be reached quickly. We discuss the implications for these findings on the evolution of AGN feedback in galaxy clusters.

     
    more » « less
  3. Abstract

    Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronicX˜2Σ+(010)state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding theX˜2Σ+(010)state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of174YbOH using high-resolution optical spectroscopy on the nominally forbiddenX˜2Σ+(010)A˜2Π1/2(000)transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of theX˜2Σ+(010)state, and accurately model the state’s structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on theX˜2Σ+(010)state and fit the molecule-frame dipole moment toDmol=2.16(1)Dand the effective electrong-factor togS=2.07(2). Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin–orbit and vibronic perturbations in the excitedA˜2Π1/2(000)state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.

     
    more » « less
  4. Abstract

    We present13CO(J= 1 → 0) observations for the EDGE-CALIFA survey, which is a mapping survey of 126 nearby galaxies at a typical spatial resolution of 1.5 kpc. Using detected12CO emission as a prior, we detect13CO in 41 galaxies via integrated line flux over the entire galaxy and in 30 galaxies via integrated line intensity in resolved synthesized beams. Incorporating our CO observations and optical IFU spectroscopy, we perform a systematic comparison between the line ratio12/13I[12CO(J=10)]/I[13CO(J=10)]and the properties of the stars and ionized gas. Higher12/13values are found in interacting galaxies compared to those in noninteracting galaxies. The global12/13slightly increases with infrared colorF60/F100but appears insensitive to other host-galaxy properties such as morphology, stellar mass, or galaxy size. We also present azimuthally averaged12/13profiles for our sample up to a galactocentric radius of 0.4r25(∼6 kpc), taking into account the13CO nondetections by spectral stacking. The radial profiles of12/13are quite flat across our sample. Within galactocentric distances of 0.2r25, the azimuthally averaged12/13increases with the star formation rate. However, Spearman rank correlation tests show the azimuthally averaged12/13does not strongly correlate with any other gas or stellar properties in general, especially beyond 0.2r25from the galaxy centers. Our findings suggest that in the complex environments in galaxy disks,12/13is not a sensitive tracer for ISM properties. Dynamical disturbances, like galaxy interactions or the presence of a bar, also have an overall impact on12/13, which further complicates the interpretations of12/13variations.

     
    more » « less
  5. Abstract

    One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, for example, thez-axis) with frequencyω0due to absorption of low-power microwaves of frequencyω0under the resonance conditions and in the absence of any applied bias voltage. The two-decades-old ‘standard model’ of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that componentISzof spin current vector(ISx(t),ISy(t),ISz)ω0is time-independent whileISx(t)andISy(t)oscillate harmonically in time with a single frequencyω0whereas pumped charge current is zeroI0in the same adiabaticω0limit. Here we employ more general approaches than the ‘standard model’, namely the time-dependent nonequilibrium Green’s function (NEGF) and the Floquet NEGF, to predict unforeseen features of spin pumping: namely precessing localized magnetic moments within a ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose conduction electrons are exposed to spin–orbit coupling (SOC) of either intrinsic or proximity origin, will pump both spinISα(t)and chargeI(t) currents. All four of these functions harmonically oscillate in time at both even and odd integer multiplesNω0of the driving frequencyω0. The cutoff order of such high harmonics increases with SOC strength, reachingNmax11in the one-dimensional FM or AFM models chosen for demonstration. A higher cutoffNmax25can be achieved in realistic two-dimensional (2D) FM models defined on a honeycomb lattice, and we provide a prescription of how to realize them using 2D magnets and their heterostructures.

     
    more » « less