A5087280078- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- SAS software applications and methods
- High-pressure geophysics and materials
- Astronomical Observations and Instrumentation
- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astro and Planetary Science
- Astrophysics and Cosmic Phenomena
- Astrophysics and Star Formation Studies
- Mechanics and Biomechanics Studies
- Geophysics and Gravity Measurements
- Particle Accelerators and Free-Electron Lasers
- Adaptive optics and wavefront sensing
- Galaxies: Formation, Evolution, Phenomena
- Atomic and Subatomic Physics Research
- Superconducting Materials and Applications
- Dark Matter and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Particle Detector Development and Performance
- Geophysics and Sensor Technology
- Solar and Space Plasma Dynamics
- Earthquake Detection and Analysis
- Statistical and numerical algorithms
Istanbul University
2016-2025
Astronomy and Space
2007-2025
Netherlands Institute for Radio Astronomy
2022
National Institute for Astrophysics
2016
Centrum Badań Kosmicznych
2016
Sabancı Üniversitesi
2006-2013
University of Arizona
2008-2012
University of California, Santa Barbara
2009
We present the first astrophysical measurement of pressure cold matter above nuclear saturation density, based on recently determined masses and radii three neutron stars. The at higher densities is below predictions equations state that account only for nucleonic degrees freedom, thus a challenge to microscopic theory star matter.
ABSTRACT We present a comprehensive study of spectroscopic radius measurements twelve neutron stars obtained during thermonuclear bursts or in quiescence. incorporate, for the first time, large number systematic uncertainties measurement apparent angular sizes, Eddington fluxes, and distances, composition interstellar medium, flux calibration X-ray detectors. also take into account results recent theoretical calculations rotational effects on star radii, atmospheric surface spectra,...
We present multiwavelength observations of the afterglow GRB 130427A, brightest (in total fluence) gamma-ray burst (GRB) past 29 yr. Optical spectroscopy from Gemini-North reveals redshift to be z = 0.340, indicating that its unprecedented brightness is primarily result relatively close proximity Earth; intrinsic luminosities both and are not extreme in comparison other bright GRBs. a large suite spanning 300 s 130 days after demonstrate shows simple, smooth evolution at all frequencies,...
Low mass X-ray binaries that show thermonuclear bursts are ideal sources for constraining the equation of state neutron star matter. The lack independent distance measurements most these sources, however, prevents a systematic exploration masses and radii stars, hence limiting studies. We present here measurement to low binary 4U 1608-52 is based on study interstellar extinction towards source. first model individual absorption edges elements Ne Mg in high resolution spectrum obtained with...
Bursting X-ray binaries in globular clusters are ideal sources for measuring neutron star masses and radii, hence, determining the equation of state cold, ultradense matter. We use time-resolved spectroscopic data from EXO 1745−248 during thermonuclear bursts that show strong evidence photospheric radius expansion to measure Eddington flux apparent surface area star. combine this with recent measurement distance cluster Terzan 5, where source resides, mass radius. find tightly constrained...
We report on the measurement of mass and radius neutron star in low-mass X-ray binary 4U 1820−30. The analysis spectroscopic data multiple thermonuclear bursts yields well-constrained values for apparent emitting area Eddington flux, both which depend a distinct way star. distance to source is that globular cluster NGC 6624, where resides. Combining these measurements, we uniquely determine probability density over stellar radius. find be M = 1.58 ± 0.06 M☉ R 9.1 0.4 km.
We calculate the number of dark matter particles that a neutron star accumulates over its lifetime as it rotates around center galaxy, when particle is self-interacting boson but does not self-annihilate. take into account interactions with baryonic and time evolution sphere collapses within star. show self-interactions play an important role in rapid accumulation core consider possibility determining exclusion region parameter space for mass interaction cross sections based on observation...
ABSTRACT We present a comprehensive study of interstellar X-ray extinction using the extensive Chandra supernova remnant (SNR) archive and use our results to refine empirical relation between hydrogen column density optical extinction. In analysis, we make large, uniform data sample assess various systematic uncertainties in measurement absorption. Specifically, address that originate from (i) emission models used fit SNR spectra; (ii) spatial variations within individual remnants; (iii)...
We report on NICER observations of the Magnetar SGR~1935+2154, covering its 2020 burst storm and long-term persistent emission evolution up to $\sim90$ days post outburst. During first 1120~seconds taken April 28 00:40:58 UTC we detect over 217 bursts, corresponding a rate $>0.2$ bursts s$^{-1}$. Three hours later is at 0.008 s$^{-1}$, remaining comparatively low level thereafter. The $T_{90}$ duration distribution peaks 840~ms; waiting times next fit with log-normal an average 2.1 s. 1-10...
We report on a complete set of early optical afterglows gamma-ray bursts (GRBs) obtained with the Robotic Optical Transient Search Experiment (ROTSE-III) telescope network from 2005 March through 2007 June. This is comprised 12 and Swift/X-Ray Telescope observations, median ROTSE-III response time 45 s after start γ-ray emission (8 GCN notice time). These span 4 orders magnitude in luminosity, contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding flares,...
Aql X--1 is one of the most prolific low mass X-ray binary transients (LMXBTs) showing outbursts almost annually. We present results our spectral analyses RXTE/PCA observations 2000 and 2011 outbursts. investigate changes related to changing disk-magnetosphere interaction modes X--1. The light curves LMXBTs typically show phases fast rise exponential decay. decay phase shows a "knee" where flux goes from slow rapid stage. assume that corresponds weak propeller stage at which fraction...
We present optical and near-infrared (NIR) photometry for three gamma-ray burst supernovae (GRB-SNe): GRB 120729A, 130215A / SN 2013ez 130831A 2013fu. In the case of 2013ez, we also spectroscopy at t-t0=16.1 d, which covers rest-frame 3000-6250 Angstroms. Based on Fe II (5169) Si (II) (6355), our spectrum indicates an unusually low expansion velocity 4000-6350 km/s, lowest ever measured a GRB-SN. Additionally, determined brightness shape each accompanying relative to template supernova (SN...
We present Chandra ACIS-S sub-array observations of the quiescent neutron star low-mass X-ray binaries X7 and X5 in globular cluster 47 Tuc. The large reduction photon pile-up compared to previous deep exposures enables a substantial improvement spectroscopic determination radius mass these stars. Modeling thermal emission from surface with non-magnetized hydrogen atmosphere accounting for numerous sources uncertainties, we obtain $R=11.1^{+0.8}_{-0.7}$ km an assumed stellar $M=1.4$...
The masses and radii of low-magnetic field neutron stars can be measured by combining different observable quantities obtained from their X-ray spectra during thermonuclear bursts. One these is the apparent radius each star as inferred flux spectral temperature cooling tails bursts, when flash believed to have engulfed entire star. In this paper, we analyze 13,095 446 bursts observed 12 sources in order assess possible systematic effects measurements stars. We first show that vast majority...
We use time-resolved spectroscopy of thermonuclear X-ray bursts observed from SAX J1748.9−2021 to infer the mass and radius neutron star in binary. Four source with Rossi Timing Explorer enable us measure angular size Eddington limit on surface. Combined a distance measurement globular cluster NGC 6440, which resides, we obtain two solutions for mass, R = 8.18 ± 1.62 km M 1.78 0.3 M☉ or 10.93 2.09 1.33 0.33 M☉.
Measurements of neutron star masses and radii are instrumental for determining the equation state their interiors, understanding dividing line between stars black holes, obtaining accurate statistics source populations in Galaxy. We report here on measurement mass radius low-mass X-ray binary KS 1731-260. The analysis spectroscopic data multiple thermonuclear bursts yields well-constrained values apparent angular area Eddington flux source, both which depend a distinct way star. 1731-260 is...
Abstract We report on X-ray (NICER/NuSTAR/MAXI/Swift) and radio (MeerKAT) timing spectroscopic analysis from a 3 month monitoring campaign in 2022 of high-intensity outburst the dipping neutron star low-mass binary 1A 1744−361. The 0.5–6.8 keV NICER hardness–intensity color–color diagrams observations throughout suggest that 1744−361 spent most its an atoll-state, but we show source exhibited Z-state-like properties at peak outburst, similar to small sample other atoll-state sources. A with...
We present a detailed spectral study of an intermittent-AMXP Aql X-1 during the \textit{pulse-on} and \textit{pulse-off} stages by using archival RXTE data. first perform temporal analysis Z$_n^2$ technique in three different energy bands, 3.0 -- 13.0~keV, 13.0 23.0~keV 23.0 33.0~keV, for last 128~s time segment data including region. show that pulse is most significant softest band. We, then, spectrum represented best via combination absorbed blackbody, disk blackbody gaussian line. modeled...
Abstract We present a detailed spectral study of an intermittent-AMXP Aql X-1 during the pulse-on and pulse-off stages by using archival RXTE data. first perform temporal analysis Z$_n^2$ technique in three different energy bands, 3.0 – 13.0 keV, 23.0 keV 33.0 for last 128 s time segment data including region. show that pulse is most significant softest band. We, then, spectrum represented best via combination absorbed blackbody, disk blackbody gaussian line. modeled four segments...
We present the results of 45 transit observations obtained for transiting exoplanet HAT-P-32b. The transits have been observed using several telescopes mainly throughout YETI network. In 25 cases, complete light curves with a timing precision better than $1.4\:$min obtained. These used to refine system properties, namely inclination $i$, planet-to-star radius ratio $R_\textrm{p}/R_\textrm{s}$, and between semimajor axis stellar $a/R_\textrm{s}$. First analyses by Hartman et al. (2011)...