Astrophysical Phenomena and Observations

A linear relation between the hydrogen column density (NH) and optical extinction (AV) in the Galaxy has long been observed. A number of studies found differing results in the slope of this relation. Here, we utilize the data on 22 supernova remnants that have been observed with the latest generation X-ray observatori…

• TOLGA GÜVER

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• SERTAÇ SERKAN DOĞRU

We present the first astrophysical measurement of the pressure of cold matter above nuclear saturation density, based on recently determined masses and radii of three neutron stars. The pressure at higher densities is below the predictions of equations of state that account only for nucleonic degrees of freedom, and t…

• TOLGA GÜVER

We drop the complexification procedure from the Newman-Janis algorithm and introduce more physical arguments and symmetry properties, and we show how one can generate regular and singular rotating black hole and non-black-hole solutions in Boyer-Lindquist coordinates. We focus on generic rotating regular black holes a…

• MUSTAFA AZREG

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• YUKI KANEKO

We report on the measurement of the mass and radius of the neutron star in the low-mass X-ray binary 4U 1820−30. The analysis of the spectroscopic data on multiple thermonuclear bursts yields well-constrained values for the apparent emitting area and the Eddington flux, both of which depend in a distinct way on the ma…

• TOLGA GÜVER

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• CAN GÜNGÖR

Soft gamma repeaters (SGRs) and anomalous x-ray pulsars form a rapidly increasing group of x-ray sources exhibiting sporadic emission of short bursts. They are believed to be magnetars, that is, neutron stars powered by extreme magnetic fields, B ~ 10(14) to 10(15) gauss. We report on a soft gamma repeater with low ma…

• ERSİN GÖĞÜŞ

Low-mass X-ray binaries (LMXBs) that show thermonuclear bursts are ideal sources for constraining the equation of state of neutron star matter. The lack of independent distance measurements for most of these sources, however, prevent a systematic exploration of the masses and radii of the neutron stars, hence limiting…

• TOLGA GÜVER

Bursting X-ray binaries in globular clusters are ideal sources for measuring neutron star masses and radii, and hence, for determining the equation of state of cold, ultradense matter. We use time-resolved spectroscopic data from EXO 1745−248 during thermonuclear bursts that show strong evidence for photospheric radiu…

• TOLGA GÜVER

We present a new study of the collisional runaway scenario to form an intermediate-mass black hole (IMBH, MBH≳ 100 M⊙) at the centre of a young, compact stellar cluster. The first phase is the formation of a very dense central core of massive stars (M*≃ 30–120 M⊙) through mass segregation and gravothermal collapse. Pr…

• MEHMET ATAKAN GÜRKAN

The majority of short gamma-ray bursts (SGRBs) are thought to originate from the merger of compact binary systems collapsing directly to form a black hole. However, it has been proposed that both SGRBs and long gamma-ray bursts (LGRBs) may, on rare occasions, form an unstable millisecond pulsar (magnetar) prior to fin…

• ÖZGECAN ÖNAL TAŞ