arXiv subjects

Samaresh Mondal

Publications and source records attributed to Samaresh Mondal.

21 records · Page 2Linked to original sources

arXiv2020

An extreme Ultraluminous X-ray source X-1 in NGC 5055

Aims. We analyzed multi-epoch X-ray data of the Ultraluminous X-ray source (ULX) NGC 5055 X-1, with luminosity up to $2.32\times10^{40}\ \rm erg\ s^{-1}$, in order to constrain the physical parameters of the source. Methods. We performed timing and spectral analysis of Chandra and XMM-Newton observations. We used spectral models which assume the emission is from an accreting black hole system. We fit the data with a multicolor disk (MCD) combined with a powerlaw (PL) or a thermal Comptonization (NTHCOMP) component, and compared those fits with a slim disk model. Results. The lightcurves of the source do not show significant variability. From the hardness ratios (3-10 keV/0.3-3 keV flux) we infer that the source is not spectrally variable. We found that the photon index is tightly, positively correlated with the unabsorbed 0.3-10 keV flux and the hydrogen column density. Furthermore, the temperature emissivity profile indicates a deviation from the standard sub-Eddington thin disk model. The source shows an inverse correlation between luminosity and inner disk temperature in all fitted models. Conclusions. Our analysis favors the source to be in an ultraluminous soft state. The positive correlations between the photon index and the flux, and between the photon index and the hydrogen column density may suggest the source is accreting at high Eddington ratios and might indicate the presence of a wind. The inverse luminosity relation with the inner disk temperature for all spectral models may indicate that the emission is geometrically beamed by an optically thick outflow.

astro-ph.HE↗

arXiv2019

The connection between merging double compact objects and the Ultraluminous X-ray Sources

We explore the different formation channels of merging double compact objects (DCOs: BH-BH/BH-NS/NS-NS) that went through a ultraluminous X-ray phase (ULX: X-ray sources with apparent luminosity exceeding $10^{39}$ erg s$^{-1}$). There are many evolutionary scenarios which can naturally explain the formation of merging DCO systems: isolated binary evolution, dynamical evolution inside dense clusters and chemically homogeneous evolution of field binaries. It is not clear which scenario is responsible for the majority of LIGO/Virgo sources. Finding connections between ULXs and DCOs can potentially point to the origin of merging DCOs as more and more ULXs are discovered. We use the StarTrack population synthesis code to show how many ULXs will form merging DCOs in the framework of isolated binary evolution. Our merger rate calculation shows that in the local Universe typically 50% of merging BH-BH progenitor binaries have evolved through a ULX phase. This indicates that ULXs can be used to study the origin of LIGO/Virgo sources. We have also estimated that the fraction of observed ULXs that will form merging DCOs in future varies between 5% to 40% depending on common envelope model and metallicity.

astro-ph.HE↗

arXiv2018

A Two Population Electron Synchrotron Model For Knots of Extended Jets

Radio observations by ALMA and upper limits on gamma ray flux by Fermi LAT have ruled out inverse Compton scattering of Cosmic Microwave Background radiation by relativistic electrons (IC/CMB) as the origin of X-ray emission from extended jets of six quasars 3C 273, PKS 0637-752, PKS 1136-135, PKS 1229-021, PKS 1354+195, and PKS 2209+080. Here we consider two populations of accelerated electrons in each knot of the extended jets to explain the radio to optical and the X-ray emission by synchrotron cooling of relativistic electrons. In all cases the jet power required is lower than the Eddington's luminosity and the observed knot emissions are well explained in this scenario.

astro-ph.HE↗