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3,884 results on '"Ratheesh, A."'

151. Exploring the accretion-ejection geometry of GRS 1915+105 in the obscured state with future X-ray spectro-polarimetry

Author

Ratheesh, Ajay, Matt, Giorgio, Tombesi, Francesco, Soffitta, Paolo, Pesce-Rollins, Melissa, and Di Marco, Alessandro

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

GRS 1915+105 has been in a bright flux state for more than 2 decades, but in 2018 a significant drop in flux was observed, partly due to changes in the central engine along with increased X-ray absorption. The aim of this work is to explore how X-ray spectro-polarimetry can be used to derive the basic geometrical properties of the absorbing and reflecting matter. In particular, the expected polarisation of the radiation reflected off the disc and the putative outflow is calculated. We use \textit{NuSTAR} data collected after the flux drop to derive the parameters of the system from hard X-ray spectroscopy. The spectroscopic parameters are then used to derive the expected polarimetric signal, using results from a MonteCarlo radiative transfer code both in the case of neutral and fully ionised matter. From the spectral analysis, we find that the continuum emission becomes softer with increasing flux, and that in all flux levels the obscuring matter is highly ionised. This analysis, on the other hand, confirms that spectroscopy alone is unable to put constraints on the geometry of the reflectors. Simulations show that X-ray polarimetric observations, like those that will be provided soon by the Imaging X-ray Polarimetry Explorer (IXPE), will help to determine the geometrical parameters which are left unconstrained by the spectroscopic analysis., Comment: 14 pages, 13 figures, Accepted for publication in Astronomy & Astrophysics

Published
2021
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152. The Instrument of the Imaging X-ray Polarimetry Explorer

Author

Soffitta, Paolo, Baldini, Luca, Bellazzini, Ronaldo, Costa, Enrico, Latronico, Luca, Muleri, Fabio, Del Monte, Ettore, Fabiani, Sergio, Minuti, Massimo, Pinchera, Michele, Sgrò, Carmelo, Spandre, Gloria, Trois, Alessio, Amici, Fabrizio, Andersson, Hans, Attinà, Primo, Bachetti, Matteo, Barbanera, Mattia, Borotto, Fabio, Brez, Alessandro, Brienza, Daniele, Caporale, Ciro, Cardelli, Claudia, Carpentiero, Rita, Castellano, Simone, Castronuovo, Marco, Cavalli, Luca, Cavazzuti, Elisabetta, Ceccanti, Marco, Centrone, Mauro, Ciprini, Stefano, Citraro, Saverio, Amico, Fabio D', Alba, Elisa D', Di Cosimo, Sergio, Di Lalla, Niccolò, Di Marco, Alessandro, Di Persio, Giuseppe, Donnarumma, Immacolata, Evangelista, Yuri, Ferrazzoli, Riccardo, Hayato, Asami, Kitaguchi, Takao, La Monaca, Fabio, Lefevre, Carlo, Loffredo, Pasqualino, Lorenzi, Paolo, Lucchesi, Leonardo, Magazzu, Carlo, Maldera, Simone, Manfreda, Alberto, Mangraviti, Elio, Marengo, Marco, Matt, Giorgio, Mereu, Paolo, Morbidini, Alfredo, Mosti, Federico, Nakano, Toshio, Nasimi, Hikmat, Negri, Barbara, Nenonen, Seppo, Nuti, Alessio, Orsini, Leonardo, Perri, Matteo, Rollins, Melissa Pesce, Piazzolla, Raffaele, Pilia, Maura, Profeti, Alessandro, Puccetti, Simonetta, Rankin, John, Ratheesh, Ajay, Rubini, Alda, Santoli, Francesco, Sarra, Paolo, Scalise, Emanuele, Sciortino, Andrea, Tamagawa, Toru, Tardiola, Marcello, Tobia, Antonino, Vimercati, Marco, and Xie, Fei

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

While X-ray Spectroscopy, Timing and Imaging have improved verymuch since 1962, when the first astronomical non-solar source was discovered, especially with the launch of Newton/X-ray Multi-Mirror Mission, Rossi/X-ray Timing Explorer and Chandra/Advanced X-ray Astrophysics Facility, the progress of X-ray polarimetry has been meager. This is in part due to the lack of sensitive polarization detectors, in part due to the fate of approved missions and in part because the celestial X-ray sources appeared less polarized than expected. Only one positive measurement has been available until now. Indeed the eight Orbiting Solar Observatory measured the polarization of the Crab nebula in the 70s. The advent of techniques of microelectronics allowed for designing a detector based on the photoelectric effect in gas in an energy range where the optics are efficient in focusing X-rays. Herewe describe the Instrument, which is the major contribution of the Italian collaboration to the SmallExplorer mission called IXPE, the Imaging X-ray Polarimetry Explorer, which will be flown in late 2021. The instrument, is composed of three Detector Units, based on this technique, and a Detector Service Unit. Three Mirror Modules provided by Marshall Space Flight Center focus X-rays onto the detectors. In the following we will show the technological choices, their scientific motivation and the results from the calibration of the Instrument. IXPE will perform imaging, timing and energy resolved polarimetry in the 2-8 keV energy band opening this window of X-ray astronomy to tens of celestial sources of almost all classes., Comment: 25 pages, 12 figures, 5 tables (accepted for publication in Astronomical Journal)

Published
2021
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153. Design, Construction, and Test of the Gas Pixel Detectors for the IXPE Mission

Author

Baldini, L., Barbanera, M., Bellazzini, R., Bonino, R., Borotto, F., Brez, A., Caporale, C., Cardelli, C., Castellano, S., Ceccanti, M., Citraro, S., Di Lalla, N., Latronico, L., Lucchesi, L., Magazzù, C., Magazzù, G., Maldera, S., Manfreda, A., Marengo, M., Marrocchesi, A., Mereu, P., Minuti, M., Mosti, F., Nasimi, H., Nuti, A., Oppedisano, C., Orsini, L., Pesce-Rollins, M., Pinchera, M., Profeti, A., Sgrò, C., Spandre, G., Tardiola, M., Zanetti, D., Amici, F., Andersson, H., Attinà, P., Bachetti, M., Baumgartner, W., Brienza, D., Carpentiero, R., Castronuovo, M., Cavalli, L., Cavazzuti, E., Centrone, M., Costa, E., D'Alba, E., D'Amico, F., Del Monte, E., Di Cosimo, S., Di Marco, A., Di Persio, G., Donnarumma, I., Evangelista, Y., Fabiani, S., Ferrazzoli, R., Kitaguchi, T., La Monaca, F., Lefevre, C., Loffredo, P., Lorenzi, P., Mangraviti, E., Matt, G., Meilahti, T., Morbidini, A., Muleri, F., Nakano, T., Negri, B., Nenonen, S., O'Dell, S. L., Perri, M., Piazzolla, R., Pieraccini, S., Pilia, M., Puccetti, S., Ramsey, B. D., Rankin, J., Ratheesh, A., Rubini, A., Santoli, F., Sarra, P., Scalise, E., Sciortino, A., Soffitta, P., Tamagawa, T., Tennant, A. F., Tobia, A., Trois, A., Uchiyama, K., Vimercati, M., Weisskopf, M. C., Xie, F., Zanetti, F., and Zhou, Y.

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Physics - Instrumentation and Detectors
Abstract

Due to be launched in late 2021, the Imaging X-Ray Polarimetry Explorer (IXPE) is a NASA Small Explorer mission designed to perform polarization measurements in the 2-8 keV band, complemented with imaging, spectroscopy and timing capabilities. At the heart of the focal plane is a set of three polarization-sensitive Gas Pixel Detectors (GPD), each based on a custom ASIC acting as a charge-collecting anode. In this paper we shall review the design, manufacturing, and test of the IXPE focal-plane detectors, with particular emphasis on the connection between the science drivers, the performance metrics and the operational aspects. We shall present a thorough characterization of the GPDs in terms of effective noise, trigger efficiency, dead time, uniformity of response, and spectral and polarimetric performance. In addition, we shall discuss in detail a number of instrumental effects that are relevant for high-level science analysis -- particularly as far as the response to unpolarized radiation and the stability in time are concerned., Comment: To be published in Astroparticle Physics

Published
2021
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155. Staging 2.0: refining transdiagnostic clinical staging frameworks to enhance reliability and utility for youth mental health

Author

Scott, Jan, Iorfino, Frank, Capon, William, Crouse, Jacob, Nelson, Barnaby, Chanen, Andrew M, Dwyer, Dominic, Conus, Philippe, Bechdolf, Andreas, Ratheesh, Aswin, Raballo, Andrea, Yung, Alison, Berk, Michael, McKenna, Sarah, Hockey, Samuel, Hutcheon, Alexis, Scott, Elizabeth, McGorry, Pat, Shah, Jai, and Hickie, Ian B

Published
2024
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156. Thermal tolerance and environment adaptability of Indian pompano: Discovery of a resilient candidate species for sustainable mariculture production in a climate change scenario

Author

Divu, Damodaran Nair, Mojjada, Suresh Kumar, Anil, Mathavankonathu Kuttan, Gopidas, Ambarish Purackattu, Sundaram, Swathi Lekshmi Perumal, Mahalingam, Anbarasu, Menon, Muktha, Raveendran, Ratheesh Kumar, Mojjada, Ramesh Kumar, Tade, Mayur Shivdas, Shree, Jai, Subramanian, Aarsha, Raghavan, Suresh Vettath, and Gopalakrishnan, Achamveetil

Published
2024
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159. SAtellite-based Marine Process Understanding, Development, Research and Applications for Blue Economy (SAMUDRA): A Technology Demonstration Program in the Bay of Bengal

Author

Sharma, Rashmi, Agarwal, Neeraj, R, Ratheesh, Kumar, Surisetty VVArun, Rao, A. D., Prasad, KVSR, Seelam, Jaya Kumar, Murali, R. Mani, Suneel, V., K, Surendra Singh, Sarangi, R. K., Kizhakudan, Soba J., Kumar, A. Saravana, R.N.Samal, Das, Ansuman, Chaudhary, Aditya, M, Seemanth, M, Jishad, Mandal, Anup K., Shah, Shivani, Chakraborty, Abhisek, Bhowmick, Suchandra A., Ratheesh, Smitha, Mallick, Subrat K., Rao, V. Trinadha, Singh, Rimjhim B., Jain, Vibha S., Prakash, Chandra, Luhar, Rakeshkumar N., Nagababu, G., Patel, Ravi, Doshi, Ghanshyam J., Patel, YagneshKumar R., Jain, Nishkam, Bhalla, Saurabh, Prakash, Kumar Ravi, Pant, Vimlesh, Venkateswarlu, Ch, Gireesh, B., Sivaiah, B., Ali, Syed Moosa, Mali, Kiran, Mudumala, Vinod Kumar, Sinha, Mourani, Babu, K. N., Raman, Mini, Patel, J. G., Dube, Nitant, Kumar, Raj, Bahuguna, I. M., and Desai, Nilesh M.

Published
2023
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160. Sub-MeV spectroscopy with AstroSat-CZT Imager for Gamma Ray Bursts

Author

Chattopadhyay, Tanmoy, Gupta, Soumya, Sharma, Vidushi, Iyyani, Shabnam, Ratheesh, Ajay, Mithun, N. P. S., Aarthy, E., Palit, Sourav, Kumar, Abhay, Vadawale, Santosh V, Rao, A. R., Bhalerao, Varun, and Bhattacharya, Dipankar

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat has been a prolific Gamma-Ray Burst (GRB) monitor. While the 2-pixel Compton scattered events (100 - 300 keV) are used to extract sensitive spectroscopic information, the inclusion of the low-gain pixels (around 20% of the detector plane) after careful calibration extends the energy range of Compton energy spectra to 600 keV. The new feature also allows single-pixel spectroscopy of the GRBs to the sub-MeV range which is otherwise limited to 150 keV. We also introduced a new noise rejection algorithm in the analysis ('Compton noise'). These new additions not only enhances the spectroscopic sensitivity of CZTI, but the sub-MeV spectroscopy will also allow proper characterization of the GRBs not detected by Fermi. This article describes the methodology of single, Compton event and veto spectroscopy in 100 - 600 keV for the GRBs detected in the first year of operation. CZTI in last five years has detected around 20 bright GRBs. The new methodologies, when applied on the spectral analysis for this large sample of GRBs, has the potential to improve the results significantly and help in better understanding the prompt emission mechanism., Comment: Accepted for publication in Journal of Astrophysics and Astronomy, 5 years of AstroSat special issue

Published
2021
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161. A generalized event selection algorithm for AstroSat CZT Imager data

Author

Ratheesh, Ajay, Rao, A. R., Mithun, N. P. S, Vadawale, Santosh V., Vibhute, Ajay, Bhattacharya, Dipankar, Pradeep, Priya, Sreekumar, S., and Bhalerao, Varun

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

The Cadmium Zinc Telluride (CZT) Imager on board AstroSat is a hard X-ray imaging spectrometer operating in the energy range of 20 $-$ 100 keV. It also acts as an open hard X-ray monitor above 100 keV capable of detecting transient events like the Gamma-ray Bursts (GRBs). Additionally, the instrument has the sensitivity to measure hard X-ray polarization in the energy range of 100 $-$ 400 keV for bright on-axis sources like Crab and Cygnus X-1 and bright GRBs. As hard X-ray instruments like CZTI are sensitive to cosmic rays in addition to X-rays, it is required to identify and remove particle induced or other noise events and select events for scientific analysis of the data. The present CZTI data analysis pipeline includes algorithms for such event selection, but they have certain limitations. They were primarily designed for the analysis of data from persistent X-ray sources where the source flux is much less than the background and thus are not best suited for sources like GRBs. Here, we re-examine the characteristics of noise events in CZTI and present a generalized event selection method that caters to the analysis of data for all types of sources. The efficacy of the new method is reviewed by examining the Poissonian behavior of the selected events and the signal to noise ratio for GRBs., Comment: Accepted for publication in JAA

Published
2021
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162. IXPE View of BH XRBs during the First 2.5 Years of the Mission

Author

Michal Dovčiak, Jakub Podgorný, Jiří Svoboda, James F. Steiner, Philip Kaaret, Henric Krawczynski, Adam Ingram, Vadim Kravtsov, Lorenzo Marra, Fabio Muleri, Javier A. García, Guglielmo Mastroserio, Romana Mikušincová, Ajay Ratheesh, and Nicole Rodriguez Cavero

Subjects
X-ray polarisation, high-energy processes, black holes, X-ray binaries, Astronomy, QB1-991
Abstract

Accreting stellar-mass black holes represent unique laboratories for studying matter and radiation under the influence of extreme gravity. They are highly variable sources going through different accretion states, showing various components in their X-ray spectra from the thermal emission of the accretion disc dominating in the soft state to the up-scattered Comptonisation component from an X-ray corona in the hard state. X-ray polarisation measurements are particularly sensitive to the geometry of the X-ray scatterings and can thus constrain the orientation and relative positions of the innermost components of these systems. The IXPE mission has observed about a dozen stellar-mass black holes with masses up to 20 solar masses in X-ray binaries with different orientations and in various accretion states. The low-inclination sources in soft states have shown a low fraction of polarisation. On the other hand, several sources in soft and hard states have revealed X-ray polarisation higher than expected, which poses significant challenges for theoretical interpretation, with 4U 1630–47 being one of the most puzzling sources. IXPE has measured the spin of three black holes via the measurement of their polarisation properties in the soft emission state. In each of the three cases, the new results agree with the constraints from the spectral observations. The polarisation observations of the black hole X-ray transient Swift J1727.8–1613 across its entire outburst has revealed that the soft-state polarisation is much weaker than the hard-state polarisation. Remarkably, the observations furthermore show that the polarisation of the bright hard state and that of the 100 times less luminous dim hard state are identical within the accuracy of the measurement. For sources with a radio jet, the electric field polarisation tends to align with the radio jet, indicating the equatorial geometry of the X-ray corona, e.g., in the case of Cyg X–1. In the unique case of Cyg X–3, where the polarisation is perpendicular to the radio jet, the IXPE observations reveal the presence and geometry of obscuring material hiding this object from our direct view. The polarisation measurements acquired by the IXPE mission during its first 2.5 years have provided unprecedented insights into the geometry and physical processes of accreting stellar-mass black holes, challenging existing theoretical models and offering new avenues for understanding these extreme systems.

Published
2024
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163. Considerations on Possible Directions for a Wide Band Polarimetry X-ray Mission

Author

Paolo Soffitta, Enrico Costa, Nicolas De Angelis, Ettore Del Monte, Klaus Desch, Alessandro Di Marco, Giuseppe Di Persio, Sergio Fabiani, Riccardo Ferrazzoli, Markus Gruber, Takahashi Hiromitsu, Saba Imtiaz, Philip Kaaret, Jochen Kaminski, Dawoon E. Kim, Fabian Kislat, Henric Krawczynski, Fabio La Monaca, Carlo Lefevre, Hemanth Manikantan, Herman L. Marshall, Romana Mikusincova, Alfredo Morbidini, Fabio Muleri, Stephen L. O’Dell, Takashi Okajima, Mark Pearce, Vladislavs Plesanovs, Brian D. Ramsey, Ajay Ratheesh, Alda Rubini, Shravan Vengalil Menon, and Martin C. Weisskopf

Subjects
X-rays, astronomy, polarimetry, Astronomy, QB1-991
Abstract

The Imaging X-ray Polarimetry Explorer (IXPE) has confirmed that X-ray polarimetry is a valuable tool in astronomy, providing critical insights into the emission processes and the geometry of compact objects. IXPE was designed to be sensitive in the 2–8 keV energy range for three primary reasons: (1) celestial X-ray sources are bright within this range, (2) the optics are effective, and (3) most sources across various classes were expected to exhibit some level of polarization. Indeed, IXPE is a great success, and its discoveries are necessitating the revision of many theoretical models for numerous sources. However, one of IXPE’s main limitations is its relatively narrow energy band, coupled with rapidly declining efficiency. In this paper, we will demonstrate the benefits of devising a mission focused on a broader energy band (0.1–79 keV). This approach leverages current technologies that align well with theoretical expectations and builds on the successes of IXPE.

Published
2024
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169. STING—A User Governed Crime Alert App

Author

Menon, Athira B., Devipriya, Jyothika, S., Ratheesh, Karthika, Sudev, K. U., Anjali, T., Kacprzyk, Janusz, Series Editor, Gomide, Fernando, Advisory Editor, Kaynak, Okyay, Advisory Editor, Liu, Derong, Advisory Editor, Pedrycz, Witold, Advisory Editor, Polycarpou, Marios M., Advisory Editor, Rudas, Imre J., Advisory Editor, Wang, Jun, Advisory Editor, Senjyu, Tomonobu, editor, So–In, Chakchai, editor, and Joshi, Amit, editor

Published
2023
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170. Field-Oriented Control for Performance Improvement in Reaction Wheels and Implementation of Algorithm in FPGA

Author

Ratheesh, K., Sreejith, S., Haridas, T. R., Chaari, Fakher, Series Editor, Gherardini, Francesco, Series Editor, Ivanov, Vitalii, Series Editor, Cavas-Martínez, Francisco, Editorial Board Member, di Mare, Francesca, Editorial Board Member, Haddar, Mohamed, Editorial Board Member, Kwon, Young W., Editorial Board Member, Trojanowska, Justyna, Editorial Board Member, Priyadarsini, R.S., editor, and Sundararajan, T., editor

Published
2023
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171. Extraction of phase-based optoretinograms (ORG) from serial B-scans acquired over tens of seconds by mouse retinal raster scanning OCT system.

Author

Pijewska, Ewelina, Zhang, Pengfei, Meina, Michał, Meleppat, Ratheesh K, Szkulmowski, Maciej, and Zawadzki, Robert J

Subjects
Biomedical and Clinical Sciences, Ophthalmology and Optometry, Eye Disease and Disorders of Vision, Neurosciences, Bioengineering, Eye, Optical Physics, Materials Engineering, Ophthalmology and optometry, Biomedical engineering, Atomic, molecular and optical physics
Abstract

Several specialized retinal optical coherence tomography (OCT) acquisition and processing methods have been recently developed to allow in vivo probing of light-evoked photoreceptors function, focusing on measurements in individual photoreceptors (rods and cones). Recent OCT investigations in humans and experimental animals have shown that the outer segments in dark-adapted rods and cones elongate in response to the visible optical stimuli that bleach fractions of their visual photopigment. We have previously successfully contributed to these developments by implementing OCT intensity-based "optoretinograms" (ORG), the paradigm of using near-infrared OCT (NIR OCT) to measure bleaching-induced back-scattering and/or elongation changes of photoreceptors in the eye in vivo. In parallel, several groups have successfully implemented phase-based ORGs, mainly in human studies, exploiting changes in the phases of back-scattered light. This allowed more sensitive observations of tiny alterations of photoreceptors structures. Applications of the phase-based ORG have been implemented primarily in high speed and cellular resolution AO-OCT systems that can visualize photoreceptor mosaic, allowing phase measurements of path length changes in outer segments of individual photoreceptors. The phase-based ORG in standard resolution OCT systems is much more demanding to implement and has not been explored extensively. This manuscript describes our efforts to implement a phase analysis framework to retinal images acquired with a standard resolution and raster scanning OCT system, which offers much lower phase stability than line-field or full-field OCT detection schemes due to the relatively slower acquisition speed. Our initial results showcase the successful extraction of phase-based ORG signal from the B-scans acquired at ∼100 Hz rate and its favorable comparison with intensity-based ORG signal extracted from the same data sets. We implemented the calculation of phase-based ORG signals using Knox-Thompson paths and modified signal recovery by adding decorrelation weights. The phase-sensitive ORG signal analysis developed here for mouse retinal raster scanning OCT systems could be in principle extended to clinical retinal raster scanning OCT systems, potentially opening doors for clinically friendly ORG probing.

Published
2021

174. The Addition of Fish Oil to Cognitive Behavioral Case Management for Youth Depression: A Randomized, Double-Blind, Placebo-Controlled, Multicenter Clinical Trial

Author

Amminger, G. Paul, Rice, Simon, Davey, Christopher G., Quinn, Amelia L., Hermens, Daniel F., Zmicerevska, Natalia, Nichles, Alissa, Hickie, Ian, Incerti, Lisa, Weller, Amber, Joseph, Sarah, Hilton, Zarah, Pugh, Charlotte, Rayner, Madeline, Reid, Nate, Ratheesh, Aswin, Yung, Alison R., Yuen, Hok Pan, Mackinnon, Andrew, Hetrick, Sarah, Parker, Alexandra, Street, Rebekah, Berger, Maximus, Berk, Michael, McGorry, Patrick D., and Lin, Ashleigh

Published
2024
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176. The first X-ray polarimetric observation of the black hole binary LMC X-1

Author

J Podgorný, L Marra, F Muleri, N Rodriguez Cavero, A Ratheesh, M Dovčiak, R Mikušincová, M Brigitte, J F Steiner, A Veledina, S Bianchi, H Krawczynski, J Svoboda, P Kaaret, G Matt, J A García, P-O Petrucci, A Lutovinov, A Semena, A Di Marco, M Negro, M C Weisskopf, A Ingram, J Poutanen, B Beheshtipour, S Chun, K Hu, T Mizuno, Z Sixuan, F Tombesi, S Zane, I Agudo, L A Antonelli, M Bachetti, L Baldini, W H Baumgartner, R Bellazzini, S D Bongiorno, R Bonino, A Brez, N Bucciantini, F Capitanio, S Castellano, E Cavazzuti, C Chen, S Ciprini, E Costa, A De Rosa, E Del Monte, L Di Gesu, N Di Lalla, I Donnarumma, V Doroshenko, S R Ehlert, T Enoto, Y Evangelista, S Fabiani, R Ferrazzoli, S Gunji, K Hayashida, J Heyl, W Iwakiri, S G Jorstad, V Karas, F Kislat, T Kitaguchi, J J Kolodziejczak, F La Monaca, L Latronico, I Liodakis, S Maldera, A Manfreda, F Marin, A Marinucci, A P Marscher, H L Marshall, F Massaro, I Mitsuishi, C-Y Ng, S L O’Dell, N Omodei, C Oppedisano, A Papitto, G G Pavlov, A L Peirson, M Perri, M Pesce-Rollins, M Pilia, A Possenti, S Puccetti, B D Ramsey, J Rankin, O J Roberts, R W Romani, C Sgrò, P Slane, P Soffitta, G Spandre, D A Swartz, T Tamagawa, F Tavecchio, R Taverna, Y Tawara, A F Tennant, N E Thomas, A Trois, S S Tsygankov, R Turolla, J Vink, K Wu, and F Xie

Published
2023
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177. Simultaneous space and phase resolved X-ray polarimetry of the Crab pulsar and nebula

Author

Bucciantini, Niccolò, Ferrazzoli, Riccardo, Bachetti, Matteo, Rankin, John, Di Lalla, Niccolò, Sgrò, Carmelo, Omodei, Nicola, Kitaguchi, Takao, Mizuno, Tsunefumi, Gunji, Shuichi, Watanabe, Eri, Baldini, Luca, Slane, Patrick, Weisskopf, Martin C., Romani, Roger W., Possenti, Andrea, Marshall, Herman L., Silvestri, Stefano, Pacciani, Luigi, Negro, Michela, Muleri, Fabio, de Oña Wilhelmi, Emma, Xie, Fei, Heyl, Jeremy, Pesce-Rollins, Melissa, Wong, Josephine, Pilia, Maura, Agudo, Iván, Antonelli, Lucio A., Baumgartner, Wayne H., Bellazzini, Ronaldo, Bianchi, Stefano, Bongiorno, Stephen D., Bonino, Raffaella, Brez, Alessandro, Capitanio, Fiamma, Castellano, Simone, Cavazzuti, Elisabetta, Chen, Chien-Ting, Ciprini, Stefano, Costa, Enrico, De Rosa, Alessandra, Del Monte, Ettore, Di Gesu, Laura, Di Marco, Alessandro, Donnarumma, Immacolata, Doroshenko, Victor, Dovčiak, Michal, Ehlert, Steven R., Enoto, Teruaki, Evangelista, Yuri, Fabiani, Sergio, Garcia, Javier A., Hayashida, Kiyoshi, Iwakiri, Wataru, Jorstad, Svetlana G., Kaaret, Philip, Karas, Vladimir, Kislat, Fabian, Kolodziejczak, Jeffery J., Krawczynski, Henric, La Monaca, Fabio, Latronico, Luca, Liodakis, Ioannis, Maldera, Simone, Manfreda, Alberto, Marin, Frédéric, Marinucci, Andrea, Marscher, Alan P., Massaro, Francesco, Matt, Giorgio, Mitsuishi, Ikuyuki, Ng, C.-Y., O’Dell, Stephen L., Oppedisano, Chiara, Papitto, Alessandro, Pavlov, George G., Peirson, Abel L., Perri, Matteo, Petrucci, Pierre-Olivier, Poutanen, Juri, Puccetti, Simonetta, Ramsey, Brian D., Ratheesh, Ajay, Roberts, Oliver J., Soffitta, Paolo, Spandre, Gloria, Swartz, Doug, Tamagawa, Toru, Tavecchio, Fabrizio, Taverna, Roberto, Tawara, Yuzuru, Tennant, Allyn F., Thomas, Nicolas E., Tombesi, Francesco, Trois, Alessio, Tsygankov, Sergey, Turolla, Roberto, Vink, Jacco, Wu, Kinwah, and Zane, Silvia

Published
2023
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180. An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

Author

James F. Steiner, Edward Nathan, Kun Hu, Henric Krawczynski, Michal Dovčiak, Alexandra Veledina, Fabio Muleri, Jiri Svoboda, Kevin Alabarta, Maxime Parra, Yash Bhargava, Giorgio Matt, Juri Poutanen, Pierre-Olivier Petrucci, Allyn F. Tennant, M. Cristina Baglio, Luca Baldini, Samuel Barnier, Sudip Bhattacharyya, Stefano Bianchi, Maimouna Brigitte, Mauricio Cabezas, Floriane Cangemi, Fiamma Capitanio, Jacob Casey, Nicole Rodriguez Cavero, Simone Castellano, Elisabetta Cavazzuti, Sohee Chun, Eugene Churazov, Enrico Costa, Niccolò Di Lalla, Alessandro Di Marco, Elise Egron, Melissa Ewing, Sergio Fabiani, Javier A. García, David A. Green, Victoria Grinberg, Petr Hadrava, Adam Ingram, Philip Kaaret, Fabian Kislat, Takao Kitaguchi, Vadim Kravtsov, Brankica Kubátová, Fabio La Monaca, Luca Latronico, Vladislav Loktev, Christian Malacaria, Frédéric Marin, Andrea Marinucci, Olga Maryeva, Guglielmo Mastroserio, Tsunefumi Mizuno, Michela Negro, Nicola Omodei, Jakub Podgorný, John Rankin, Ajay Ratheesh, Lauren Rhodes, David M. Russell, Miroslav Šlechta, Paolo Soffitta, Sean Spooner, Valery Suleimanov, Francesco Tombesi, Sergei A. Trushkin, Martin C. Weisskopf, Silvia Zane, Andrzej A. Zdziarski, Sixuan Zhang, Wenda Zhang, Menglei Zhou, Iván Agudo, Lucio A. Antonelli, Matteo Bachetti, Wayne H. Baumgartner, Ronaldo Bellazzini, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolò Bucciantini, Chien-Ting Chen, Stefano Ciprini, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Immacolata Donnarumma, Victor Doroshenko, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Riccardo Ferrazzoli, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, Wataru Iwakiri, Svetlana G. Jorstad, Vladimir Karas, Jeffery J. Kolodziejczak, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Alan P. Marscher, Herman L. Marshall, Francesco Massaro, Ikuyuki Mitsuishi, Chi-Yung Ng, Stephen L. O’Dell, Chiara Oppedisano, Alessandro Papitto, George G. Pavlov, Abel L. Peirson, Matteo Perri, Melissa Pesce-Rollins, Maura Pilia, Andrea Possenti, Simonetta Puccetti, Brian D. Ramsey, Oliver J. Roberts, Roger W. Romani, Carmelo Sgrò, Patrick Slane, Gloria Spandre, Douglas A. Swartz, Toru Tamagawa, Fabrizio Tavecchio, Roberto Taverna, Yuzuru Tawara, Nicholas E. Thomas, Alessio Trois, Sergey S. Tsygankov, Roberto Turolla, Jacco Vink, Kinwah Wu, and Fei Xie

Subjects
Accretion, Polarimetry, X-ray astronomy, Stellar mass black holes, Astrophysics, QB460-466
Abstract

We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer’s (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = −25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1’s au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1’s spin is likely high ( a _* ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE’s bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.

Published
2024
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181. Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1

Author

Fabio La Monaca, Alessandro Di Marco, Juri Poutanen, Matteo Bachetti, Sara Elisa Motta, Alessandro Papitto, Maura Pilia, Fei Xie, Stefano Bianchi, Anna Bobrikova, Enrico Costa, Wei Deng, Ming-Yu Ge, Giulia Illiano, Shu-Mei Jia, Henric Krawczynski, Eleonora Veronica Lai, Kuan Liu, Guglielmo Mastroserio, Fabio Muleri, John Rankin, Paolo Soffitta, Alexandra Veledina, Filippo Ambrosino, Melania Del Santo, Wei Chen, Javier A. Garcia, Philip Kaaret, Thomas D. Russell, Wen-Hao Wei, Shuang-Nan Zhang, Chao Zuo, Zaven Arzoumanian, Massimo Cocchi, Andrea Gnarini, Ruben Farinelli, Keith Gendreau, Francesco Ursini, Martin C. Weisskopf, Silvia Zane, Iván Agudo, Lucio A. Antonelli, Luca Baldini, Wayne H. Baumgartner, Ronaldo Bellazzini, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolò Bucciantini, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting Chen, Stefano Ciprini, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Niccolò Di Lalla, Immacolata Donnarumma, Victor Doroshenko, Michal Dovčiak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, Wataru Iwakiri, Svetlana G. Jorstad, Vladimir Karas, Fabian Kislat, Takao Kitaguchi, Jeffery J. Kolodziejczak, Luca Latronico, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Frédéric Marin, Andrea Marinucci, Alan P. Marscher, Herman L. Marshall, Francesco Massaro, Giorgio Matt, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Michela Negro, Chi-Yung Ng, Stephen L. O’Dell, Nicola Omodei, Chiara Oppedisano, George G. Pavlov, Abel L. Peirson, Matteo Perri, Melissa Pesce-Rollins, Pierre-Olivier Petrucci, Andrea Possenti, Simonetta Puccetti, Brian D. Ramsey, Ajay Ratheesh, Oliver J. Roberts, Roger W. Romani, Carmelo Sgrò, Patrick Slane, Gloria Spandre, Douglas A. Swartz, Toru Tamagawa, Fabrizio Tavecchio, Roberto Taverna, Yuzuru Tawara, Allyn F. Tennant, Nicholas E. Thomas, Francesco Tombesi, Alessio Trois, Sergey S. Tsygankov, Roberto Turolla, Jacco Vink, Kinwah Wu, and IXPE Collaboration

Subjects
Polarimetry, Spectropolarimetry, Neutron stars, Accretion, Stellar accretion disks, Low-mass x-ray binary stars, Astrophysics, QB460-466
Abstract

The Imaging X-ray Polarimetry Explorer measured with high significance the X-ray polarization of the brightest Z-source, Sco X-1, resulting in the nominal 2–8 keV energy band in a polarization degree of 1.0% ± 0.2% and a polarization angle of 8° ± 6° at a 90% confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broadband spectrum from soft to hard X-rays. The source has been observed mainly in its soft state, with short periods of flaring. We also observed low-frequency quasiperiodic oscillations. From a spectropolarimetric analysis, we associate a polarization to the accretion disk at

Published
2024
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182. Discovery of a Shock-compressed Magnetic Field in the Northwestern Rim of the Young Supernova Remnant RX J1713.7–3946 with X-Ray Polarimetry

Author

Riccardo Ferrazzoli, Dmitry Prokhorov, Niccolò Bucciantini, Patrick Slane, Jacco Vink, Martina Cardillo, Yi-Jung Yang, Stefano Silvestri, Ping Zhou, Enrico Costa, Nicola Omodei, C.-Y. Ng, Paolo Soffitta, Martin C. Weisskopf, Luca Baldini, Alessandro Di Marco, Victor Doroshenko, Jeremy Heyl, Philip Kaaret, Dawoon E. Kim, Frédéric Marin, Tsunefumi Mizuno, Melissa Pesce-Rollins, Carmelo Sgrò, Douglas A. Swartz, Toru Tamagawa, Fei Xie, Iván Agudo, Lucio A. Antonelli, Matteo Bachetti, Wayne H. Baumgartner, Ronaldo Bellazzini, Stefano Bianchi, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting Chen, Stefano Ciprini, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Niccolò Di Lalla, Immacolata Donnarumma, Michal Dovčiak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Javier A. Garcia, Shuichi Gunji, Kiyoshi Hayashida, Wataru Iwakiri, Svetlana G. Jorstad, Vladimir Karas, Fabian Kislat, Takao Kitaguchi, Jeffery J. Kolodziejczak, Henric Krawczynski, Fabio La Monaca, Luca Latronico, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Andrea Marinucci, Alan P. Marscher, Herman L. Marshall, Francesco Massaro, Giorgio Matt, Ikuyuki Mitsuishi, Fabio Muleri, Michela Negro, Stephen L. O’Dell, Chiara Oppedisano, Alessandro Papitto, George G. Pavlov, Abel L. Peirson, Matteo Perri, Pierre-Olivier Petrucci, Maura Pilia, Andrea Possenti, Juri Poutanen, Simonetta Puccetti, Brian D. Ramsey, John Rankin, Ajay Ratheesh, Oliver J. Roberts, Roger W. Romani, Gloria Spandre, Fabrizio Tavecchio, Roberto Taverna, Yuzuru Tawara, Allyn F. Tennant, Nicholas E. Thomas, Francesco Tombesi, Alessio Trois, Sergey S. Tsygankov, Roberto Turolla, Kinwah Wu, and Silvia Zane

Subjects
X-ray astronomy, Polarimetry, Supernova remnants, Astrophysics, QB460-466
Abstract

Supernova remnants (SNRs) provide insights into cosmic-ray acceleration and magnetic field dynamics at shock fronts. Recent X-ray polarimetric measurements by the Imaging X-ray Polarimetry Explorer (IXPE) have revealed radial magnetic fields near particle acceleration sites in young SNRs, including Cassiopeia A, Tycho, and SN 1006. We present here the spatially resolved IXPE X-ray polarimetric observation of the northwestern rim of SNR RX J1713.7–3946. For the first time, our analysis shows that the magnetic field in the particle acceleration sites of this SNR is oriented tangentially with respect to the shock front. Because of the lack of precise Faraday rotation measurements in the radio band, this was not possible before. The average measured polarization degree (PD) of the synchrotron emission is 12.5% ± 3.3%, lower than the one measured by IXPE in SN 1006, comparable to the Tycho one, but notably higher than the one in Cassiopeia A. On subparsec scales, localized patches within RX J1713.7–3946 display a PD of up to 41.5% ± 9.5%. These results are compatible with a shock-compressed magnetic field. However, in order to explain the observed PD, either the presence of a radial net magnetic field upstream of the shock or partial reisotropization of the turbulence downstream by radial magnetohydrodynamical instabilities can be invoked. From comparison of PD and magnetic field distribution with γ -rays and ^12 CO data, our results provide new inputs in favor of a leptonic origin of the γ -ray emission.

Published
2024
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183. Dramatic Drop in the X-Ray Polarization of Swift J1727.8–1613 in the Soft Spectral State

Author

Jiří Svoboda, Michal Dovčiak, James F. Steiner, Philip Kaaret, Jakub Podgorný, Juri Poutanen, Alexandra Veledina, Fabio Muleri, Roberto Taverna, Henric Krawczynski, Maïmouna Brigitte, Sudeb Ranjan Datta, Stefano Bianchi, Teo Muñoz-Darias, Michela Negro, Nicole Rodriguez Cavero, Noel Castro Segura, Niek Bollemeijer, Javier A. García, Adam Ingram, Giorgio Matt, Edward Nathan, Martin C. Weisskopf, Diego Altamirano, Luca Baldini, Fiamma Capitanio, Elise Egron, Razieh Emami, Kun Hu, Lorenzo Marra, Guglielmo Mastroserio, Pierre-Olivier Petrucci, Ajay Ratheesh, Paolo Soffitta, Francesco Tombesi, Yi-Jung Yang, and Yuexin Zhang

Subjects
Black hole physics, X-ray astronomy, Polarimetry, Stellar mass black holes, Astrophysics, QB460-466
Abstract

Black hole X-ray binaries exhibit different spectral and timing properties in different accretion states. The X-ray outburst of a recently discovered and extraordinarily bright source, Swift J1727.8–1613, has enabled the first investigation of how the X-ray polarization properties of a source evolve with spectral state. The 2–8 keV polarization degree was previously measured by the Imaging X-ray Polarimetry Explorer (IXPE) to be ≈4% in the hard and hard intermediate states. Here we present new IXPE results taken in the soft state, with the X-ray flux dominated by the thermal accretion disk emission. We find that the polarization degree has dropped dramatically to ≲1%. This result indicates that the measured X-ray polarization is largely sensitive to the accretion state and the polarization fraction is significantly higher in the hard state when the X-ray emission is dominated by upscattered radiation in the X-ray corona. The combined polarization measurements in the soft and hard states disfavor a very high or low inclination of the system.

Published
2024
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184. X-Ray Polarization of the Eastern Lobe of SS 433

Author

Philip Kaaret, Riccardo Ferrazzoli, Stefano Silvestri, Michela Negro, Alberto Manfreda, Kinwah Wu, Enrico Costa, Paolo Soffitta, Samar Safi-Harb, Juri Poutanen, Alexandra Veledina, Alessandro Di Marco, Patrick Slane, Stefano Bianchi, Adam Ingram, Roger W. Romani, Nicolò Cibrario, Brydyn Mac Intyre, Romana Mikus̆incová, Ajay Ratheesh, James F. Steiner, Jiri Svoboda, Stefano Tugliani, Iván Agudo, Lucio A. Antonelli, Matteo Bachetti, Luca Baldini, Wayne H. Baumgartner, Ronaldo Bellazzini, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolò Bucciantini, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting Chen, Stefano Ciprini, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Niccolò Di Lalla, Immacolata Donnarumma, Victor Doroshenko, Michal Dovčiak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Javier A. García, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, Wataru Iwakiri, Svetlana G. Jorstad, Vladimir Karas, Fabian Kislat, Takao Kitaguchi, Jeffery J. Kolodziejczak, Henric Krawczynski, Fabio La Monaca, Luca Latronico, Ioannis Liodakis, Simone Maldera, Frédéric Marin, Andrea Marinucci, Alan P. Marscher, Herman L. Marshall, Francesco Massaro, Giorgio Matt, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Fabio Muleri, Chi-Yung Ng, Stephen L. O’Dell, Nicola Omodei, Chiara Oppedisano, Alessandro Papitto, George G. Pavlov, Abel L. Peirson, Matteo Perri, Melissa Pesce-Rollins, Pierre-Olivier Petrucci, Maura Pilia, Andrea Possenti, Simonetta Puccetti, Brian D. Ramsey, John Rankin, Oliver J. Roberts, Carmelo Sgrò, Gloria Spandre, Douglas A. Swartz, Toru Tamagawa, Fabrizio Tavecchio, Roberto Taverna, Yuzuru Tawara, Allyn F. Tennant, Nicholas E. Thomas, Francesco Tombesi, Alessio Trois, Sergey S. Tsygankov, Roberto Turolla, Jacco Vink, Martin C. Weisskopf, Fei Xie, and Silvia Zane

Subjects
High mass x-ray binary stars, Jets, High energy astrophysics, Supernova remnants, Astrophysical black holes, Astrophysics, QB460-466
Abstract

How astrophysical systems translate the kinetic energy of bulk motion into the acceleration of particles to very high energies is a pressing question. SS 433 is a microquasar that emits TeV γ -rays indicating the presence of high-energy particles. A region of hard X-ray emission in the eastern lobe of SS 433 was recently identified as an acceleration site. We observed this region with the Imaging X-ray Polarimetry Explorer and measured a polarization degree in the range 38%–77%. The high polarization degree indicates the magnetic field has a well-ordered component if the X-rays are due to synchrotron emission. The polarization angle is in the range −12° to +10° (east of north), which indicates that the magnetic field is parallel to the jet. Magnetic fields parallel to the bulk flow have also been found in supernova remnants and the jets of powerful radio galaxies. This may be caused by interaction of the flow with the ambient medium.

Published
2024
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185. X-Ray Polarized View of the Accretion Geometry in the X-Ray Binary Circinus X-1

Author

John Rankin, Fabio La Monaca, Alessandro Di Marco, Juri Poutanen, Anna Bobrikova, Vadim Kravtsov, Fabio Muleri, Maura Pilia, Alexandra Veledina, Rob Fender, Philip Kaaret, Dawoon E. Kim, Andrea Marinucci, Herman L. Marshall, Alessandro Papitto, Allyn F. Tennant, Sergey S. Tsygankov, Martin C. Weisskopf, Kinwah Wu, Silvia Zane, Filippo Ambrosino, Ruben Farinelli, Andrea Gnarini, Iván Agudo, Lucio A. Antonelli, Matteo Bachetti, Luca Baldini, Wayne H. Baumgartner, Ronaldo Bellazzini, Stefano Bianchi, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolò Bucciantini, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting Chen, Stefano Ciprini, Enrico Costa, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Niccolò Di Lalla, Immacolata Donnarumma, Victor Doroshenko, Michal Dovčiak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, Javier A. Garcia, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, Wataru Iwakiri, Svetlana G. Jorstad, Vladimir Karas, Fabian Kislat, Takao Kitaguchi, Jeffery J. Kolodziejczak, Henric Krawczynski, Luca Latronico, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Frédéric Marin, Alan P. Marscher, Francesco Massaro, Giorgio Matt, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Michela Negro, Chi-Yung Ng, Stephen L. O’Dell, Nicola Omodei, Chiara Oppedisano, George G. Pavlov, Abel L. Peirson, Matteo Perri, Melissa Pesce-Rollins, Pierre-Olivier Petrucci, Andrea Possenti, Simonetta Puccetti, Brian D. Ramsey, Ajay Ratheesh, Oliver J. Roberts, Roger W. Romani, Carmelo Sgrò, Patrick Slane, Paolo Soffitta, Gloria Spandre, Douglas A. Swartz, Toru Tamagawa, Fabrizio Tavecchio, Roberto Taverna, Yuzuru Tawara, Nicholas E. Thomas, Francesco Tombesi, Alessio Trois, Roberto Turolla, Jacco Vink, and Fei Xie

Subjects
X-ray binary stars, Polarimetry, X-ray astronomy, X-ray sources, Astrophysics, QB460-466
Abstract

Cir X-1 is a neutron star X-ray binary characterized by strong variations in flux during its eccentric ∼16.6 day orbit. There are also strong variations in the spectral state, and it has historically shown both atoll and Z state properties. We observed the source with the Imaging X-ray Polarimetry Explorer during two orbital segments, 6 days apart, for a total of 263 ks. We find an X-ray polarization degree in these segments of 1.6% ± 0.3% and 1.4% ± 0.3% at polarization angles of 37° ± 5° and −12° ± 7°, respectively. Thus, we observed a rotation of the polarization angle by 49° ± 8° along the orbit. Because variations of accretion flow, and then of the hardness ratio, are expected during the orbit, we also studied the polarization binned in hardness ratio and found the polarization angle differing by 67° ± 11° between the lowest and highest values of the hardness ratio. We discuss possible interpretations of this result that could indicate a possible misalignment between the symmetry axes of the accretion disk and the Comptonizing region caused by the misalignment of the neutron star’s angular momentum with respect to the orbital one.

Published
2024
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186. Remineralization potential of strontium-doped nano-hydroxyapatite dentifrice and casein phosphopeptide-amorphous calcium phosphate cream on white spot lesions in enamel following orthodontic debonding – a randomized controlled trial

Author

Ratheesh Rajendran, Delphine Priscilla Antony S, Mohammed Ashik P, Subin Bharath, Arun Jacob Thomas, and Artak Heboyan

Subjects
Medicine (General), R5-920
Abstract

Aim and Objective: This study was intended to compare and determine the potency of strontium-doped nano-hydroxyapatite paste against a topical cream containing casein phosphopeptide-amorphous calcium phosphate and a regular dentifrice for remineralization of white spot lesions of enamel following orthodontic debonding. Methods: Ninety individuals with white spot lesions on their enamel who visited the orthodontic department for de-bonding were selected for the research. Patients were randomly assigned to three distinct groups with each group consisting of 30 patients. Group 1 served as the control and received regular dentifrice, Group 2 received strontium-doped nano-hydroxyapatite paste, and Group 3 received casein phosphopeptide-amorphous calcium phosphate topical cream. Patients were instructed to locally apply a specified amount of the prescribed preparation twice daily for six weeks. The data were analysed using the statistical programme SPSS 22.0 (SPSS Inc., Chicago, IL, USA), and the level of significance had been set at p

Published
2024
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187. A variable magnetic disc wind in the black hole X-ray binary GRS 1915+105?

Author

Ratheesh, Ajay, Tombesi, Francesco, Fukumura, Kiego, Soffitta, Paolo, Costa, Enrico, and Kazanas, Demosthenes

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

GRS 1915+105 being one of the brightest transient black hole binary (BHB) in the X-rays, offers a unique test-bed for the study of the connection between accretion and ejection mechanisms in BHBs. In particular, this source can be used to study the accretion disc wind and how it depends on the state changes in BHBs. Our aim is to investigate the origin and geometry of the accretion disc wind in GRS 1915+105. We analysed the spectra of GRS 1915+105 in the soft $\phi$ and hard $\chi$ classes, using the high resolution spectroscopy offered by Chandra HETGS. In the soft state, we find a series of wind absorption lines that follow a non linear dependence of velocity width, velocity shift and equivalent width with respect to ionisation, indicating a multiple component or stratified outflow. In the hard state we find only a faint Fe XXVI absorption line. We model the absorption lines in both the states using a dedicated MHD wind model to investigate a magnetic origin of the wind and to probe the cause of variability in the observed lines flux between the two states. The MHD disc wind model provides a good fit for both states, indicating the possibility of a magnetic origin of the wind. The multiple ionisation components of the wind are well characterised as a stratification of the same magnetic outflow. We find that the observed variability in the lines flux between soft and hard states cannot be explained by photo-ionisation alone but it is most likely due to a large (three orders of magnitude) increase in the wind density. We find the mass outflow rate of the wind to be comparable to the accretion rate, suggesting a intimate link between accretion and ejection processes that lead to state changes in BHBs., Comment: 11 pages, 9 figures. Shortened abstract. Accepted for publication in A&A

Published
2020
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188. In-flight calibration system of Imaging X-ray Polarimetry Explorer

Author

Ferrazzoli, Riccardo, Muleri, Fabio, Lefevre, Carlo, Morbidini, Alfredo, Amici, Fabrizio, Brienza, Daniele, Costa, Enrico, Del Monte, Ettore, Di Marco, Alessandro, Di Persio, Giuseppe, Donnarumma, Immacolata, Fabiani, Sergio, La Monaca, Fabio, Loffredo, Pasqualino, Maiolo, Luca, Maita, Francesco, Piazzolla, Raffaele, Ramsey, Brian, Rankin, John, Ratheesh, Ajay, Rubini, Alda, Sarra, Paolo, Soffitta, Paolo, Tobia, Antonino, and Xie, Fei

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract

The NASA/ASI Imaging X-ray Polarimetry Explorer, which will be launched in 2021, will be the first instrument to perform spatially resolved X-ray polarimetry on several astronomical sources in the 2-8 keV energy band. These measurements are made possible owing to the use of a gas pixel detector (GPD) at the focus of three X-ray telescopes. The GPD allows simultaneous measurements of the interaction point, energy, arrival time, and polarization angle of detected X-ray photons. The increase in sensitivity, achieved 40 years ago, for imaging and spectroscopy with the Einstein satellite will thus be extended to X-ray polarimetry for the first time. The characteristics of gas multiplication detectors are subject to changes over time. Because the GPD is a novel instrument, it is particularly important to verify its performance and stability during its mission lifetime. For this purpose, the spacecraft hosts a filter and calibration set (FCS), which includes both polarized and unpolarized calibration sources for performing in-flight calibration of the instruments. In this study, we present the design of the flight models of the FCS and the first measurements obtained using silicon drift detectors and CCD cameras, as well as those obtained in thermal vacuum with the flight units of the GPD. We show that the calibration sources successfully assess and verify the functionality of the GPD and validate its scientific results in orbit; this improves our knowledge of the behavior of these detectors in X-ray polarimetry., Comment: 22 pages, 16 figures, published on Journal of Astronomical Telescopes, Instruments, and Systems

Published
2020
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189. Full-Duplex and Dynamic-TDD: Pushing the Limits of Spectrum Reuse in Multi-Cell Communications

Author

Silva Jr., José Mairton B. da, Wikström, Gustav, Mungara, Ratheesh K., and Fischione, Carlo

Subjects
Computer Science - Information Theory, Computer Science - Networking and Internet Architecture, Electrical Engineering and Systems Science - Signal Processing
Abstract

Although in cellular networks full-duplex and dynamic time-division duplexing promise increased spectrum efficiency, their potential is so far challenged by increased interference. While previous studies have shown that self-interference can be suppressed to a sufficient level, we show that the cross-link interference for both duplexing modes, especially from base station to base station, is the remaining challenge in multi-cell networks, restricting the uplink performance. Using beamforming techniques of low-complexity, we show that this interference can be mitigated, and that full-duplex and dynamic time-division duplexing can substantially increase the capacity of multi-cell networks. Our results suggest that if we can control the cross link interference in full-duplex, then we can almost double the multi cell network capacity as well as user throughput. Therefore, the techniques in this paper have the potentiality to enable a smooth introduction of full-duplex into cellular systems., Comment: 15 pages, 6 figures. Accepted to IEEE Wireless Communications - Special Issue on Full Duplex Communications Theory, Standardization and Practice

Published
2020

190. A spectral study of the black hole X-ray binary MAXI J1820+070 with AstroSat and NuSTAR

Author

Chakraborty, Sudip, Navale, Nilam, Ratheesh, Ajay, and Bhattacharyya, Sudip

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

MAXI J1820+070 is a newly discovered transient black hole X-ray binary, which showed several spectral and temporal features. In this work, we analyse the broadband X-ray spectra from all three simultaneously observing X-ray instruments onboard AstroSat, as well as contemporaneous X-ray spectra from NuSTAR, observed during the hard state of MAXI J1820+070 in March 2018. Implementing a combination of multi-colour disc model, relativistic blurred reflection model relxilllpCp and a distant reflection in the form of xillverCp, we achieve reasonable and consistent fits for AstroSat and NuSTAR spectra. The best-fit model suggests a low temperature disc ($kT_{\rm in} \sim 0.3$ keV), iron overabundance ($A_{\rm Fe} \sim 4-5$ solar), a short lamp-post corona height ($h \lesssim 8 R_{\rm g}$), and a high corona temperature ($kT_{\rm e} \sim 115-150$ keV). Addition of a second Comptonisation component leads to a significantly better fit, with the $kT_{\rm e}$ of the second Comptonisation component being $\sim 14-18$ keV. Our results from independent observations with two different satellites in a similar source state indicate an inhomogeneous corona, with decreasing temperature attributed to increasing height. Besides, utilising the broader energy coverage of AstroSat, we estimate the black hole mass to be $6.7-13.9 \ M_{\odot}$, consistent with independent measurements reported in the literature.

Published
2020
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191. Effects of risperidone/paliperidone versus placebo on cognitive functioning over the first 6 months of treatment for psychotic disorder: secondary analysis of a triple-blind randomised clinical trial

Author

Allott, Kelly, Yuen, Hok Pan, Baldwin, Lara, O’Donoghue, Brian, Fornito, Alex, Chopra, Sidhant, Nelson, Barnaby, Graham, Jessica, Kerr, Melissa J., Proffitt, Tina-Marie, Ratheesh, Aswin, Alvarez-Jimenez, Mario, Harrigan, Susy, Brown, Ellie, Thompson, Andrew D., Pantelis, Christos, Berk, Michael, McGorry, Patrick D., Francey, Shona M., and Wood, Stephen J.

Published
2023
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194. In vivo multimodal retinal imaging of disease-related pigmentary changes in retinal pigment epithelium.

Author

Meleppat, Ratheesh K, Ronning, Kaitryn E, Karlen, Sarah J, Burns, Marie E, Pugh, Edward N, and Zawadzki, Robert J

Abstract

Melanosomes, lipofuscin, and melanolipofuscin are the three principal types of pigmented granules found in retinal pigment epithelium (RPE) cells. Changes in the density of melanosomes and lipofuscin in RPE cells are considered hallmarks of various retinal diseases, including Stargardt disease and age-related macular degeneration (AMD). Herein, we report the potential of an in vivo multimodal imaging technique based on directional back-scattering and short-wavelength fundus autofluorescence (SW-FAF) to study disease-related changes in the density of melanosomes and lipofuscin granules in RPE cells. Changes in the concentration of these granules in Abca4-/- mice (a model of Stargardt disease) relative to age-matched wild-type (WT) controls were investigated. Directional optical coherence tomography (dOCT) was used to assess melanosome density in vivo, whereas the autofluorescence (AF) images and emission spectra acquired with a spectrometer-integrated scanning laser ophthalmoscope (SLO) were used to characterize lipofuscin and melanolipofuscin granules in the same RPE region. Subcellular-resolution ex vivo imaging using confocal fluorescence microscopy and electron microscopy was performed on the same tissue region to visualize and quantify melanosomes, lipofuscin, and melanolipofuscin granules. Comparisons between in vivo and ex vivo results confirmed an increased concentration of lipofuscin granules and decreased concentration of melanosomes in the RPE of Abca4-/- mice, and provided an explanation for the differences in fluorescence and directionality of RPE scattering observed in vivo between the two mouse strains.

Published
2021

195. The macroecology of Indian pollinators : patterns, processes and future implications

Author

Kallivalappil, Ratheesh

Subjects
C181 Biodiversity, C100 Biology
Abstract

Pollination is a key ecosystem service and vital step in the reproduction of most angiosperms. Therefore, the endangerment and extinction of pollinator species collapse the complex ecological networks and hence threaten both agriculture and biodiversity. A large proportion of the human diet depends directly or indirectly on animal pollination. Both invertebrates and vertebrates pollinate a variety of angiosperms. While much research has been focused on insect pollinators, the role of vertebrate pollinators is not as widely recognized. Vertebrates pollinate a variety of plants including economically important crop species in tropical countries and many of these plants are either completely or partially dependent on pollinators for fruit/seed production. Therefore, declining pollination services in these tropical cultivated goods may result in substantial losses in revenue. Here, my project investigates the extinction risk of global and Indian vertebrate pollinator species using the IUCN extinction risk assessment method. The potential pollinator species have been identified from various primary, peer-reviewed literature sources. I compiled a dataset consisting of 1,554 and 99 vertebrate pollinator species for the globe and India respectively. Additionally, the project explores the economic value of pollination services for Indian vertebrate pollinators. The results for the global extinction risk show asymmetric patterns of threat within the vertebrate groups. Globally, mammal pollinators were more highly threatened than the bird and reptile pollinators, though there were large-scale population declines experienced across all pollinator groups. The narrow ranged pollinators experienced large-scale threat and population decline relative to broad ranged pollinators. Hotspots of threat for vertebrate pollinators are shown in the Andes of South America, Madagascar, and south-eastern Australia. The interactive effect of body mass and body length and significant phylogenetic signal along with various external anthropogenic factors show the extinction risk in global pollinators are a combined effect of both intrinsic biological traits and extrinsic anthropogenic factors across multiple scales. The extinction risk assessment for Indian pollinators show mammals are the only pollinator group threatened with extinction. But both bird and mammal pollinators face population decline, a similar trend reported for the global pollinators. Like global pollinators, the population decline is higher in narrow ranged pollinators than the broad ranged pollinators. Body size does not predict threat and population decline in Indian pollinators, a contradictory result to the global pattern. Absence of phylogenetic signal in threat and population decline show they are evolutionarily not predisposed to extinction. Like global pollinators, most Indian pollinators appear to be threatened by agriculture and biological activities. The value of vertebrate pollination services is estimated to be £2.85 million (₹28.2 crores) and the contribution of bird pollinators are higher than mammal pollinators. The study also highlights the beneficial role of bat pollinators to the Indian economy and biodiversity. Thus, it emphasizes the need for the Government of India to revoke the status of fruit bats as vermin and list them as protected in the Schedules of Indian Wildlife Protection Act, 1972.

Published
2021

196. Effects of risperidone/paliperidone versus placebo on cognitive functioning over the first 6 months of treatment for psychotic disorder: secondary analysis of a triple-blind randomised clinical trial

Author

Kelly Allott, Hok Pan Yuen, Lara Baldwin, Brian O’Donoghue, Alex Fornito, Sidhant Chopra, Barnaby Nelson, Jessica Graham, Melissa J. Kerr, Tina-Marie Proffitt, Aswin Ratheesh, Mario Alvarez-Jimenez, Susy Harrigan, Ellie Brown, Andrew D. Thompson, Christos Pantelis, Michael Berk, Patrick D. McGorry, Shona M. Francey, and Stephen J. Wood

Subjects
Neurosciences. Biological psychiatry. Neuropsychiatry, RC321-571
Abstract

Abstract The drivers of cognitive change following first-episode psychosis remain poorly understood. Evidence regarding the role of antipsychotic medication is primarily based on naturalistic studies or clinical trials without a placebo arm, making it difficult to disentangle illness from medication effects. A secondary analysis of a randomised, triple-blind, placebo-controlled trial, where antipsychotic-naive patients with first-episode psychotic disorder were allocated to receive risperidone/paliperidone or matched placebo plus intensive psychosocial therapy for 6 months was conducted. A healthy control group was also recruited. A cognitive battery was administered at baseline and 6 months. Intention-to-treat analysis involved 76 patients (antipsychotic medication group: 37; 18.6Mage [2.9] years; 21 women; placebo group: 39; 18.3Mage [2.7]; 22 women); and 42 healthy controls (19.2Mage [3.0] years; 28 women). Cognitive performance predominantly remained stable (working memory, verbal fluency) or improved (attention, processing speed, cognitive control), with no group-by-time interaction evident. However, a significant group-by-time interaction was observed for immediate recall (p = 0.023), verbal learning (p = 0.024) and delayed recall (p = 0.005). The medication group declined whereas the placebo group improved on each measure (immediate recall: p = 0.024; η p 2 = 0.062; verbal learning: p = 0.015; η p 2 = 0.072 both medium effects; delayed recall: p = 0.001; η p 2 = 0.123 large effect). The rate of change for the placebo and healthy control groups was similar. Per protocol analysis (placebo n = 16, medication n = 11) produced similar findings. Risperidone/paliperidone may worsen verbal learning and memory in the early months of psychosis treatment. Replication of this finding and examination of various antipsychotic agents are needed in confirmatory trials. Antipsychotic effects should be considered in longitudinal studies of cognition in psychosis. Trial registration: Australian New Zealand Clinical Trials Registry ( http://www.anzctr.org.au/ ; ACTRN12607000608460).

Published
2023
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