Localizing merging black holes with sub-arcsecond precision using gravitational-wave lensing

The current gravitational-wave localization methods rely mainly on sources with electromagnetic counterparts. Unfortunately, a binary black hole does not emit light. Due to this, it is generally not possible to localize these objects precisely. However, strongly lensed gravitational waves, which are forecasted in this decade, could allow us to localize the binary by locating its lensed host galaxy. Identifying the correct host galaxy is challenging because there are hundreds to thousands of other lensed galaxies within the sky area spanned by the gravitational-wave observation. However, we can constrain the lensing galaxy's physical properties through both gravitational-wave and electromagnetic observations. We show that these simultaneous constraints allow one to localize quadruply lensed waves to one or at most a few galaxies with the LIGO/Virgo/Kagra network in typical scenarios. Once we identify the host, we can localize the binary to two sub-arcsec regions within the host galaxy. Moreover, we demonstrate how to use the system to measure the Hubble constant as a proof-of-principle application.Comment: 5 pages (main text) + 5 pages (methods+references), 5 figures. Accepted to MNRA

Reconstructing patchy helium reionization using the cosmic microwave background and large-scale structure

The intergalactic helium became fully ionized by the end of cosmic noon ($z\sim2$). Similarly to the reionization of hydrogen, helium reionization is expected to be patchy, driven by luminous quasars that ionize the intergalactic gas in their surrounding environment. Probing the morphology of ionized electrons during this epoch can provide crucial information about early structure formation, including the clustering and luminosities of quasars, the accretion rates, variability, and lifetimes of active galactic nuclei, as well as the growth and evolution of supermassive black holes. In this study, we present how measurements of the cosmic microwave background (CMB) can be used to reconstruct the optical-depth fluctuations resulting from patchy helium reionization. As helium reionization occurred at lower redshifts, upcoming probes of large-scale structure surveys will present a significant opportunity to enhance the prospects of probing this epoch by their combined analysis with the CMB. Using a joint information-matrix analysis of hydrogen and helium reionization, we show that near-future galaxy and CMB surveys will have enough statistical power to detect optical-depth fluctuations due to doubly-ionized helium, providing a way of measuring the redshift and duration of helium reionization to high significance. We also show that modeling uncertainties in helium reionization can impact the measurement precision of parameters characterizing hydrogen reionization.Comment: 34 pages, 20 figures, and 3 tables. All comments are welcom

Dissecting the Stochastic Gravitational Wave Background with Astrometry

Astrometry, the precise measurement of star motions, offers an alternative avenue to investigate low-frequency gravitational waves through the spatial deflection of photons, complementing pulsar timing arrays reliant on timing residuals. Upcoming data from Gaia and Roman can not only cross-check pulsar timing array findings but also explore the uncharted frequency range bridging pulsar timing arrays and LISA. We present an analytical framework to evaluate the feasibility of detecting a gravitational wave background, considering measurement noise and the intrinsic variability of the stochastic background. Furthermore, we highlight astrometry's crucial role in uncovering key properties of the gravitational wave background, such as spectral index and chirality, employing information-matrix analysis. Finally, we simulate the emergence of quadrupolar correlations, commonly referred to as the generalized Hellings-Downs curves.Comment: 34 pages, 8 figures. Published version in JCAP. v2: minor correction

Subtracting Compact Binary Foregrounds to Search for Subdominant Gravitational-Wave Backgrounds in Next-Generation Ground-Based Observatories

Stochastic gravitational-wave backgrounds (SGWBs) derive from the superposition of numerous individually unresolved gravitational-wave (GW) signals. Detecting SGWBs provides us with invaluable information about astrophysics, cosmology, and fundamental physics. In this paper, we study SGWBs from binary black-hole (BBH) and binary neutron-star (BNS) coalescences in a network of next-generation ground-based GW observatories (Cosmic Explorer and Einstein Telescope) and determine how well they can be measured; this then limits how well we can observe other subdominant astrophysical and cosmological SGWBs. We simulate all-Universe populations of BBHs and BNSs and calculate the corresponding SGWBs, which consist of a superposition of (i) undetected signals, and (ii) the residual background from imperfect removal of resolved sources. The sum of the two components sets the sensitivity for observing other SGWBs. Our results show that, even with next-generation observatories, the residual background is large and limits the sensitivity to other SGWBs. The main contributions to the residual background arise from uncertainties in inferring the coalescence phase and luminosity distance of the detected signals. Alternative approaches to signal subtraction would need to be explored to minimize the BBH and BNS foreground in order to observe SGWBs from other subdominant astrophysical and cosmological sources.Comment: 19 pages, 10 figures, matches the published versio

Probing wave-optics effects and dark-matter subhalos with lensing of gravitational waves from massive black holes

The Laser Interferometer Space Antenna (LISA) will detect gravitational waves (GWs) emitted by massive black hole binaries (MBHBs) in the low-frequency ($\sim$mHz) band. Low-mass lenses, such as dark-matter (DM) subhalos, have sizes comparable to the wavelength of these GWs. Encounters with these lenses produce wave-optics (WO) effects that alter waveform phase and amplitude. Thus, a single event with observable WO effects can be used to probe the lens properties. In this paper, we first compute the probability of observing WO effects in a model-agnostic way. We perform parameter estimation over approximately 1000 MBHBs with total mass, mass ratio, and redshift spanning the ranges relevant to LISA. We then calculate lensing rates using three semi-analytical models of MBHB populations. In both cases, we use a waveform model that includes merger, ringdown, and higher-order modes. We use two lens population models: the theory-based Press-Schechter halo mass function and an observation-based model derived from Sloan Digital Sky Survey, called the measured velocity function. We find that the probability of detecting WO effects can be as large as $\sim 3\%$, $\sim1.5\%$, and $\sim 1 \%$ at $1\sigma$, $3\sigma$, and $5\sigma$ confidence levels, respectively. The most optimistic MBHB population model yields $\sim 8$, $\sim 4$, and $\sim 3$ events at the same confidence levels, while the rates drop to $\sim 0.01$ in the more pessimistic scenarios. The most likely lens masses probed by LISA are in the range $(10^3, 10^8)\, M_{\odot}$, and the most probable redshifts are in the range $(0.3, 1.7)$. Therefore, LISA observations of WO effects can probe DM subhalos, complementing strong lensing and other observations.Comment: 24 pages, 15 figures. Comments are welcom

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TÜBİTAK SOBAG15.10.200

Rotavirus Frequency in Children With Acute Gastroenteritis Who Were Hospitalized in Keçiören Education and Research Hospital Pediatric Clinic

Bu çalışmada hastanemizin pediatri servisinde akut gastroenterit tanısı alan hastalarda rotavirus sıklığının yaşa, cin- siyete, mevsimsel özelliklere göre dağılımının belirlenmesi, hastalığın seyrinin araştırılması ve nozokomiyal inf eksiyon sıklı- ğının saptanması amaçlanmıştır. Hastanemizin pediatri servisinde Ocak 2010-Aralık 2013 tarihleri arasında akut gastroen- terit tanısıyla izlenen 0-4 yaş arası 772 hastanın dışkı örneklerine ait kayıtlar retrospektif olarak incelenmiştir. Taze dışkı örneklerinde rotavirus antijenlerinin varlığı immünokromatograf ik test ile araştırılmıştır. Çalışmaya alınan 772 hastanın 174ünde (% 22.5) rotavirus antijeni pozitif olarak saptanmıştır. Pozitif lik saptanan hastaların yaş ortalaması 138 ay olup rotavirus antijen pozitif liği % 66.2 oranla en sık 2 yaş altında saptanmıştır. Hastaların 88inin (% 51) erkek, 86sının (% 49) kız olduğu gözlenmiştir. Kırk yedi hastada (% 27) yatıştan üç gün sonra rotavirus antijen pozitif liği bulunmuş ve nozokomiyal inf eksiyon olarak değerlendirilmiştir. Rotavirus antijeni pozitif olgu sayısında sonbahar ve kış mevsimlerinde artış izlenmiştir. Rotavirus inf eksiyonlarının özellikle çocukluk çağı akut gastroenteritleri arasında önemli bir sıklığa sahip olduğu bilinmektedir. Akut gastroenteritli hastalarda viral etkenlerin saptanması hem erken tanı ve semptomatik tedavi olanağı sağlayacak hem de ampirik antibiyotik kullanılmasını önleyecektir. Ülkemizde rotavirus sıklığının yüksek olması nedeniyle çocuklara rotavirus aşısının uygulanmasının bu inf eksiyondan korunmada yararlı olabile- ceği düşünülmüştür.This study aimed to determine the f requency of rotavirus acute gastroenteritis in pediatric patients who were hospitalized in our Pediatric Department, to evaluate distributions according to age, gender and seasonal f eatures, course of the disease and the incidence of nosocomial inf ections. The records of 772 patients between the ages of 0-4 years who were hospitalized in our Pediatric Department between January 2010 and December 2013 due to acute gastroenteritis were investigated retrospectively. Rotavirus antigens were detected in the f resh stool specimens by immunochromatographic test. Of 772 pediatric patients, 174 (22.5 %) were identif ed as positive f or rotavirus antigen, most f requently in 0-2 age group with a rate of 66.2 %. Of the 174 rotavirus antigen positive patients in this study, 96 (49 %) were f emale, 144 (51 %) were male and mean age was 13±8 months 47 of the patients (27 %) were positive f or rotavirus as nosocomial inf ections af ter three days on admis- sion. An increase in the number of cases with rotavirus antigen positivity was detected during autumn and winter. The results of this study indicated that rotavirus was a f requent cause of acute gastroenteritis in children. Detection of viral agents in patients with acute gastroenteritis will allow early diagnosis and symptomatic treatment as well as preventing inapproppria- te antibiotic use. Because of the high f requency of rotavirus in our country, rotavirus vaccination might be usef ul f or children in prevention of this inf ection

The Relationship Between Atherosclerotic Risk Factors and Coronary Artery Disease in Coronary Artery Ectasia

Aim: Coronary artery ectasia (CAE)is described as the dilatation of all or a portion of the coronary arteries by 1.5 times or more wider than the diameter of adjacent normal coronary artery segment. The incidence of CAE varies between 1.5 to 5%. Although the etiology of CAE has not been enlightened, it is generally considered to be a variant of coronary atherosclerosis. In our study, the association between atherosclerotic risk factors and coronary artery disease in patients with coronary artery ectasia was investigated. Methods: Between January 2008 - May 2012 , 5595 patients were screened retrospectively. Atherosclerotic risk factors were determined in all patients. Patients were grouped as the CAE with coronary artery disease (CAD) and the CAE who had no CAD. Results: CAE was diagnosed in 135 (2.4%) patients. The mean age was 62.2 years and 81.5% were male. 71.1% of the patients had CAD. In CAE patients with CAD, diabetes mellitus (DM) and hypertension (HT) was significantly higher in frequency than CAE patients without CAD. In logistic regression analysis, the presence of DM was increased the risk of CAD 2.59-fold, HT was increased the risk of CAD 3,39-fold. Between the two groups there was no significant difference for other atherosclerotic risk factors. Right coronary arteries were the most common vascular involvement (45.9%). Conclusion: In our study, the frequency of CAE was determined as 2.4%. DM and HT which are well-known risk factors for CAD, were seen more frequently in CAE patients with CAD

Lensing or luck? False alarm probabilities for gravitational lensing of gravitational waves

Strong gravitational lensing of gravitational waves (GWs) has been forecasted to become detectable in the upcoming observing runs. However, definitively distinguishing pairs of lensed sources from random associations is a challenging problem. We investigate the degree to which unlensed events mimic lensed ones because of the overlap of parameters due to a combination of random coincidence and errors in parameter estimation. We construct a mock catalog of lensed and unlensed events. We find that the false alarm probability (FAP) based on coincidental overlaps of the chirp mass, sky location, and coalescence phase are approximately $11\%$, $1\%$, and $10\%$ per pair, respectively. Combining all three, the overall FAP per pair is $\sim10^{-4}$. As the number of events, $N$, in the GW catalogs increases, the number of random pairs of events increases as $\sim N^2$. Meanwhile, the number of lensed events will increase linearly with $N$, implying that for sufficiently high $N$, the false alarms will always dominate over the true lensing events. This issue can be compensated for by placing higher thresholds on the lensing candidates (e.g., selecting a higher signal-to-noise ratio (SNR) threshold), which will lead to better parameter estimation and, thus, lower FAP per pair -- at the cost of dramatically decreasing the size of the lensing sample (by \sim 1/\mbox{SNR}^3). We show that with our simple overlap criteria for current detectors at design sensitivity, the false alarms will dominate for realistic lensing rates ($\lesssim10^{-3}$) even when selecting the highest SNR pairs. These results highlight the necessity to design alternative identification criteria beyond simple waveform and sky location overlap. Future GW detectors Cosmic Explorer and Einstein Telescope may provide sufficient improvement in parameter estimation, allowing for the conclusive detection of strong lensing of GWs.Comment: 17 pages, 14 figure