Explanipedia

Surface visualisation of bacterial biofilms using neutral atom microscopy Open

Nick A. von Jeinsen, David J. Ward, Matthew Bergin, Sam Lambrick, David M. Williamson , et al. · 2025

The scanning helium microscope (SHeM) is a new technology that uses a beam of neutral helium atoms to image surfaces non‐destructively and with extreme surface sensitivity. Here, we present the application of the SHeM to image bacterial bi…

A Study of Spectral Variability Between Flaring and Nonflaring State in M74 X-1 Open

A. K. Upadhyay, Tanuman Ghosh, Vikram Rana · 2025

We conducted an extensive long-term spectral and timing study of the ultraluminous X-ray (ULX) source M74 X-1, using data taken between 2001 and 2021 by Chandra and XMM-Newton X-ray observatories. Our analysis shows that flares are present…

Intriguing Nature of AM Her–type Candidate CXOU J204734.8+300105 Open

Rahul Sharma, Chetana Jain, Biswajit Paul, Anjan Dutta, Vikram Rana · 2025

The detection and characterization of periodic X-ray signals are crucial for identifying new compact objects and studying the mechanisms powering their emission. We report on the timing and spectral variability of CXOU J204734.8+300105, a …

Spectral analysis of ultraluminous X-ray pulsars with models of X-ray pulsars Open

Manish Kumar, Rahul Sharma, Biswajit Paul, Vikram Rana · 2024

A fraction of the ultraluminous X-ray (ULX) sources are known to be accreting neutron stars as they show coherent X-ray pulsations with pulse periods ranging from ${\sim} 1{\!-\!}30$ s. While initially thought to host intermediate-mass bla…

Energy dependence of quasi-periodic oscillations in accreting X-ray pulsars Open

Hemanth Manikantan, Biswajit Paul, Rahul Sharma, Pragati Pradhan, Vikram Rana · 2024

We present the results from an investigation of the energy dependence of quasi-periodic oscillations (QPOs) exhibited by accreting X-ray pulsars using data from archival XMM-Newton, NuSTAR, RXTE, and NICER observations. In a search for the…

Energy dependence of Quasi-periodic oscillations in accreting X-ray pulsars Open

Hemanth Manikantan, Biswajit Paul, Rahul Sharma, Pragati Pradhan, Vikram Rana · 2024

We present the results from an investigation of the energy dependence of Quasi-Periodic Oscillations (QPOs) exhibited by accreting X-ray pulsars using data from archival \textit{XMM-Newton}, \textit{NuSTAR}, \textit{RXTE}, and \textit{NICE…

A Broadband X-Ray Study of the Dwarf Nova SS Cyg during Quiescence and Outburst Open

Anirban Dutta, Vikram Rana, K. Mukai, R. Lopes de Oliveira · 2023

We present a broadband X-ray study (∼0.3–50 keV) of the dwarf nova SS Cyg highlighting the changes in the accretion during two phases, the quiescence and the outburst states. The investigation was based on simultaneous observations carried…

Investigating the orbital evolution of the eccentric HMXB GX 301–2 using long-term X-ray light curves Open

Hemanth Manikantan, Manish Kumar, Biswajit Paul, Vikram Rana · 2023

We report the orbital decay rate of the high-mass X-ray binary GX 301–2 from an analysis of its long-term X-ray light curves and pulsed flux histories from CGRO/BATSE, RXTE/ASM, Swift/BAT, Fermi/GBM, and MAXI by timing the pre-periastron f…

Investigating the orbital evolution of the eccentric HMXB GX 301$-$2 using long-term X-ray lightcurves Open

Hemanth Manikantan, Manish Kumar, Biswajit Paul, Vikram Rana · 2023

We report the orbital decay rate of the high mass X-ray binary GX 301$-$2 from an analysis of its long-term X-ray light curves and pulsed flux histories from CGRO/BATSE, RXTE/ASM, Swift/BAT, Fermi/GBM and MAXI by timing the pre-periastron …

An investigation of the "10 keV feature" in the spectra of Accretion Powered X-ray Pulsars with NuSTAR Open

Hemanth Manikantan, Biswajit Paul, Vikram Rana · 2023

Some of the accreting X-ray pulsars are reported to exhibit a peculiar spectral feature at $\sim$10 keV, known as the "10 keV feature". The feature has been characterized as either an emission line or an absorption line, and its origin is …

Constraint on the Accretion of NGC 6946 X-1 Using Broadband X-Ray Data Open

Tanuman Ghosh, Vikram Rana · 2023

We analyze broadband X-ray data of NGC 6946 X-1 and probe plausible accretion scenarios in this ULX. NGC 6946 X-1 is a persistent soft source with broadband continuum spectra described by two thermal disk components. The cool accretion dis…

Synchrotron Cutoff in Ultraluminous X-Ray Sources Open

Tanuman Ghosh, Shiv K. Sethi, Vikram Rana · 2023

The origin of spectral curvature at energies E ≃ 10 keV in ultraluminous X-ray sources (ULXs) is not well understood. In this paper, we propose a novel mechanism based on synchrotron radiation to explain this cutoff. We show that relativis…

Correction to: Super-Eddington accretion on to a stellar mass ultraluminous X-ray source NGC 4190 ULX1 Open

Tanuman Ghosh, Vikram Rana · 2023

Constraint on the accretion of NGC 6946 X-1 using broadband X-ray data Open

Tanuman Ghosh, Vikram Rana · 2023

We analyze broadband X-ray data of NGC 6946 X-1 and probe plausible accretion scenarios in this ULX. NGC 6946 X-1 is a persistent soft source with broadband continuum spectra described by two thermal disk components. The cool accretion dis…

Changes in the distribution of circum-binary material around the HMXB GX 301-2 during a rapid spin-up episode of the neutron star Open

Hemanth Manikantan, Biswajit Paul, Kinjal Roy, Vikram Rana · 2023

Some accretion-powered X-ray pulsars with supergiant companion stars undergo occasional rapid spin-up episodes that last for weeks to a few months. We explore the changes in the accretion environment of the pulsar GX 301-2 during its lates…

A broadband X-ray study of the dwarf nova SS Cyg during quiescence and outburst Open

Anirban Dutta, Vikram Rana, K. Mukai, R. Lopes de Oliveira · 2023

We present a broadband X-ray study (∼\,0.3-50 keV) of the dwarf nova SS Cyg highlighting the changes in the accretion during two phases, the quiescence and the outburst states. The investigation was based on simultaneous observations carri…

Study of Complex Absorption and Reflection in a Unique Intermediate Polar Paloma Open

Anirban Dutta, Vikram Rana · 2022

We present the broadband (0.3–40.0 keV) X-ray analysis of a unique intermediate polar Paloma using simultaneous data from XMM-Newton and NuSTAR observatories. The X-ray power spectra show strong modulations over orbital period compared to …

Science with the Daksha High Energy Transients Mission Open

V. Bhalerao, D. Sawant, Archana Pai, Shriharsh P. Tendulkar, S. Vadawale , et al. · 2022

We present the science case for the proposed Daksha high energy transients mission. Daksha will comprise of two satellites covering the entire sky from 1~keV to $>1$~MeV. The primary objectives of the mission are to discover and characteri…

Daksha: On Alert for High Energy Transients Open

V. Bhalerao, S. Vadawale, Shriharsh P. Tendulkar, D. Bhattacharya, Vikram Rana , et al. · 2022

We present Daksha, a proposed high energy transients mission for the study of electromagnetic counterparts of gravitational wave sources, and gamma ray bursts. Daksha will comprise of two satellites in low earth equatorial orbits, on oppos…

Synchrotron cutoff in Ultraluminous X-ray sources Open

Tanuman Ghosh, Shiv K. Sethi, Vikram Rana · 2022

The origin of spectral curvature at energies $E\simeq 10$ keV in ultraluminous X-ray sources is not well understood. In this paper, we propose a novel mechanism based on synchrotron radiation to explain this cutoff. We show that relativist…

Hard X-Ray Flares and Spectral Variability in NGC 4395 ULX1 Open

Tanuman Ghosh, Vikram Rana, Matteo Bachetti · 2022

We report the detection of flaring events in NGC 4395 ULX1, a nearby ultraluminous X-ray source (ULX), for the first time, using recent XMM-Newton observations. The flaring episodes are spectrally harder than the steady-emission intervals,…

Spectral variability in NGC 1042 ULX1 Open

Tanuman Ghosh, Vikram Rana · 2022

We report X-ray spectral variability in an ultraluminous X-ray source NGC 1042 ULX1, using archival XMM-Newton and recent NuSTAR observations. In long-term evolution, the source has shown a trend of variation in spectral hardness. The vari…

Study of Complex Absorption and Reflection in a Unique Intermediate Polar Paloma Open

Anirban Dutta, Vikram Rana · 2022

We present the broadband (0.3-40.0 keV) X-ray analysis of a unique intermediate polar Paloma using simultaneous data from XMM-Newton and NuSTAR observatories. The X-ray power spectra show strong modulations over orbital period compared to …

Hard X-ray flares and spectral variability in NGC 4395 ULX1 Open

Tanuman Ghosh, Vikram Rana, Matteo Bachetti · 2022

We report the detection of flaring events in NGC 4395 ULX1, a nearby ultraluminous X-ray source (ULX), for the first time, using recent XMM-NEWTON observations. The flaring episodes are spectrally harder than the steady emission intervals,…

A broad-band X-ray study of the asynchronous polar CD Ind Open

Anirban Dutta, Vikram Rana · 2022

We present a simultaneous broad-band analysis of X-ray data obtained with the XMM–Newton and the Nuclear Spectroscopic Telescope Array (NuSTAR) for the asynchronous polar source, CD Ind. The spin-folded light curve in the soft 0.3–3.0 keV …

Super-Eddington accretion on to a stellar mass ultraluminous X-ray source NGC 4190 ULX1 Open

Tanuman Ghosh, Vikram Rana · 2021

We present the results of high-quality XMM-NEWTON observations of a ultraluminous X-ray source (ULX) in the galaxy NGC 4190. The detection of spectral cutoff in NGC 4190 ULX1 spectra rules out the interpretation of the ULX to be in a stand…

A new transient ultraluminous X-ray source in NGC 7090 Open

D. J. Walton, Marianne Heida, Matteo Bachetti, Felix Fürst, Murray Brightman , et al. · 2020

We report on the discovery of a new, transient ultraluminous X-ray source (ULX) in the galaxy NGC 7090. This new ULX, which we refer to as NGC 7090 ULX3, was discovered via monitoring with Swift during 2019–2020, and to date has exhibited …

Measuring the masses of magnetic white dwarfs: a <i>NuSTAR</i> legacy survey Open

A. W. Shaw, C. O. Heinke, K. Mukai, John A. Tomsick, Victor Doroshenko , et al. · 2020

The hard X-ray spectrum of magnetic cataclysmic variables can be modelled to provide a measurement of white dwarf mass. This method is complementary to radial velocity measurements, which depend on the (typically rather uncertain) binary i…

Measuring the masses of magnetic white dwarfs: A NuSTAR Legacy Survey Open

A. W. Shaw, K. Mukai, C. O. Heinke, G. R. Sivakoff, J. A. Tomsick , et al. · 2020

The hard X-ray spectrum of magnetic cataclysmic variables can be modelled to provide a measurement of white dwarf mass. This method is complementary to radial velocity measurements, which depend on the (typically rather uncertain) binary i…

A tale of two periods: determination of the orbital ephemeris of the super-Eddington pulsar NGC 7793 P13 Open

Felix Fürst, D. J. Walton, Marianne Heida, Fiona A. Harrison, D. Barret , et al. · 2018

We present a timing analysis of multiple XMM-Newton and NuSTAR observations of the ultra-luminous pulsar NGC 7793 P13 spread over its 65 d variability period. We use the measured pulse periods to determine the orbital ephemeris, confirm a …

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