arXiv subjects

M. Szanecki

Publications and source records attributed to M. Szanecki.

4 recordsLinked to original sources

arXiv2026

X-ray polarization in the soft state of Cyg X-1

We aim to identify the physical mechanism responsible for the observed X-ray emission and polarization of Cyg X-1 in the soft state. We performed a detailed spectral analysis of X-ray data obtained with NICER, NuSTAR, and INTEGRAL during observations simultaneous with IXPE on 2023 June 20, supplemented at higher energies with archival CGRO data. We developed a new model, retBB, which describes thermal disk emission and its returning reflection, and applied it together with accurate models of Comptonization and relativistically broadened reflection. Using the resulting spectral solution, we computed the expected polarization signal and compared it with the IXPE measurements. Our spectropolarimetric modeling shows that the observed polarization is in agreement with being produced by Comptonization in a corona undergoing a semi-relativistic outflow at a velocity of ~0.3c. Our spectral solutions admit either low or high black-hole spin values, depending on the adopted model setup. However, the observed polarization strongly favors a low spin. At high spin, the polarization angle would inevitably rotate significantly across the energy band, which is inconsistent with the observations. Apart from this rotation of the polarization angle, general relativistic effects do not play a significant role in producing the observed polarization. In particular, we find that, at most, returning disk radiation contributes only a minor amount.

astro-ph.HE↗

arXiv2015

Monte Carlo simulations of alternative sky observation modes with the Cherenkov Telescope Array

We investigate possible sky survey modes with the Middle Sized Telescopes (MST, aimed at covering the energy range from $\sim$100 GeV to 10 TeV) subsystem of the Cherenkov Telescope Array (CTA). We use the standard CTA tools, CORSIKA and sim_telarray, to simulate the development of gamma-ray showers, proton background and the telescope response. We perform simulations for the H.E.S.S.-site in Namibia, which is one of the candidate sites for the CTA experiment. We study two previously considered modes, parallel and divergent, and we propose a new, convergent mode with telescopes tilted toward the array center. For each mode we provide performance parameters crucial for choosing the most efficient survey strategy. For the non-parallel modes we study the dependence on the telescope offset angle. We show that use of both the divergent and convergent modes results in potential advantages in comparison with use of the parallel mode. The fastest source detection can be achieved in the divergent mode with larger offset angles ($\sim 6^{\circ}$ from the Field of View centre for the outermost telescopes), for which the time needed to perform a scan at a given sensitivity level is shorter by a factor of $\sim$2.3 than for the parallel mode. We note, however, the direction and energy reconstruction accuracy for the divergent mode is even by a factor of $\sim 2$ worse than for other modes. Furthermore, we find that at high energies and for observation directions close to the center of the array field of view, the best performance parameters are achieved with the convergent mode, which favors this mode for deep observations of sources with hard energy spectra.

astro-ph.IM↗

arXiv2015

Geomagnetic field and altitude effects on the performance of future IACT arrays

The performance of IACT's arrays is sensitive to the altitude and geomagnetic field (GF) of the observatory site. Both effects play important role in the region of the sub-TeV gamma-ray measurements. We investigate the influence of GF on detection rates and the energy thresholds for five possible locations of the future CTA observatory using the Monte Carlo simulations. We conclude that the detection rates of gamma rays and the energy thresholds of the arrays can be fitted with linear functions of the altitude and the component of the GF perpendicular to the shower axis core. These results can be directly extrapolated for any possible localization of the CTA. In this paper we also show the influence of both geophysical effects on the images of shower and gamma/hadron separation.

astro-ph.IM↗

arXiv2015

Influence of the Geomagnetic Field on the IACT detection technique for possible sites of CTA observatories

We investigate the influence of the geomagnetic field (GF) on the Imaging Air Cherenkov Telescope technique for two northern (Tenerife and San Pedro Martir) and three southern (Salta, Leoncito and Namibia (the H.E.S.S.-site)) site candidates for Cherenkov Telescope Array (CTA) observatories. We use the CORSIKA and sim_telarray programs for Monte Carlo simulations of gamma ray showers, hadronic background and the telescope response. We focus here on gamma ray measurements in the low energy, sub-100 GeV, range. Therefore, we only consider the performance of arrays of several large telescopes. Neglecting the GF effect, we find (in agreement with previous studies) that such arrays have lower energy thresholds, and larger collection areas below 30 GeV, when located at higher altitudes. We point out, however, that in the considered ranges of altitudes and magnetic field intensities, 1800-3600 m a.s.l. and 0-40 uT, respectively, the GF effect has a similar magnitude to this altitude effect. We provide the trigger-level performance parameters of the observatory affected by the GF effect, in particular the collection areas, detection rates and the energy thresholds for all five locations, which information may be useful in the selection of sites for CTA. We also find simple scaling of these parameters with the magnetic field strength, which can be used to assess the magnitude of the GF effect for other sites; in this work we use them to estimate the performance parameters for five sites: South Africa-Beaufort West, USA-Yavapai Ranch, Namibia-Lalapanzi, Chile-La Silla and India-Hanle. We roughly investigate the impact of the geophysical conditions on gamma/hadron separation procedures involving image shape and direction cuts.

astro-ph.IM↗