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Identification of candidate millisecond pulsars from Fermi LAT observations

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Research in Astronomy and Astrophysics 2016年第6期16卷 113-122页

作者： Xue-Jie Dai Zhong-Xiang Wang jithesh vadakkumthani Yi Xing Shanghai Astronomical Observatory Chinese Academy of SciencesShanghai 200030China University of Chinese Academy of Sciences Beijing 100049China

We report our detailed data analysis of 39 γ-ray sources selected from the 992 unassociated sources in the third Fermi Large Area Telescope Third Source Catalog. The selection criteria, which were set for finding candidate millisecond pulsars （MSPs）, are non-variables with curved spectra and 〉5° Galactic latitudes. From our analysis, 24 sources were found to be point-like sources not contaminated by back- ground or nearby unknown sources. Three of them, Jl544.6-1125, J1625.1-0021 and J1653.6-0158, have been previously studied, indicating that they are likely MSPs. The spectra of J0318.1＋0252 and J2053.9＋2922 do not have properties similar to known γ-ray MSPs, and we thus suggest that they are not MSPs. Analysis of archival X-ray data for most of the 24 sources was also conducted. Four sources were found with X-ray objects in their error circles, and 16 with no detection. The ratios between the γ-ray fluxes and X-ray fluxes or flux upper limits are generally lower than those of known γ-ray MSPs, suggesting that if the γ-ray sources are MSPs, none of the X-ray objects are their counterparts. Deep X-ray or radio observations of these sources are needed in order to identify their MSP nature.

关键词： stars pulsars -- stars binaries -- gamma rays stars

High energy properties of the flat spectrum radio quasar 4C 50.11

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Research in Astronomy and Astrophysics 2018年第1期18卷 69-82页

作者： Jia-Neng Zhou vadakkumthani jithesh Liang Chen Zhong-Xiang Wang Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai 200030 China Inter-University Centre for Astronomy and Astrophysics Post Bag 4 Ganeshkhind Pune 411007 India University of Chinese Academy of Sciences Beijing 100049 China

We investigate theγ-ray and X-ray properties of the flat spectrum radio quasar（FSRQ）4C 50.11 at redshift z=*** Fermi-LAT data indicate that this source was in an active state since July *** this active period,the source’s emission appeared harder inγ-rays,with the flux having increased by more than a factor of *** analyze two distinct flares seen in the active state and find that the variability is as short as several *** Swift-XRT data show that the source was variable at X-ray energies,but no evidence is found for flux or spectral changes related to theγ-ray *** broad-band X-ray spectrum obtained with Swift-XRT and Nu STAR is described well by a broken power law model,with an extremely flat spectrum（Γ_1~0.1）below the break energy,E_（break）~2.1 keV,and Γ_2~1.5 above the break *** spectral flattening below^3 keV is likely due to the low energy cut-off in the energy distribution of the photon-emitting electron *** fit the broad-band spectral energy distribution of the source during both the active and quiescent *** X-ray andγ-ray emission from the jet is mainly due to the inverse-Compton scattering process,with seed photons provided from the broad line region,and the jet is estimated to be larger than the accretion power if the jet is mainly composed of electron-proton pairs.

关键词： galaxies:jets gamma rays:galaxies quasars:individual(4C 50.11) radiation mechanisms:non-thermal

Identification of candidate millisecond pulsars from Fermi LAT observations Ⅱ

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Research in Astronomy and Astrophysics 2017年第7期17卷 89-98页

作者： Xue-Jie Dai Zhong-Xiang Wang jithesh vadakkumthani Yi Xing Shanghai Astronomical Observatory Chinese Academy of Sciences University of Chinese Academy of Sciences

On the basis of the properties of known γ-ray millisecond pulsars（MSPs）, we have selected 77un-associated sources from the Fermi Large Area Telescope（LAT） third source catalog for the purpose of finding likely candidate MSPs. Previously, detailed LAT data analysis for 39 of them was reported,and here we report the analysis for the remaining 38 sources. We identify that among the 38 sources, 28 of them are single point-like sources with clean background and their spectra show significant *** also conduct an analysis of archival X-ray data available for 24 of the 28 sources. In the fields of10 sources, there is at least one X-ray object, and in those of the other 14 sources, no X-ray object is detected but this is probably due to the X-ray observations being short. We discuss the possible MSP nature for these sources. Six of them（J0514.6-4406, J1035.7-6720, J1624.2-4041, J1744.1-7619,J1946.4-5403 and J2039.6-5618） are most likely associated with pulsars because of multi-wavelength identifications including direct radio or γ-ray detection of pulsations. To firmly establish the associations or verify the MSP nature for other sources, deep X-ray and/or optical observations are needed.

关键词： stars pulsars - stars binaries - gamma rays stars

Broadband Spectral Properties of MAXI J1348-630 using AstroSat Observations

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Research in Astronomy and Astrophysics 2023年第1期23卷 161-170页

作者： Gitika Mall jithesh vadakkumthani Ranjeev Misra Center for Field Theory and Particle Physics and Department of Physics Fudan UniversityShanghai 200438China Department of Physics and Electronics CHRIST(Deemed to be University)Hosur Main RoadBengaluru 560029India Inter-University Centre for Astronomy and Astrophysics(IUCAA) PB No.4GaneshkhindPune 411007India

We present broadband X-ray spectral analysis of the black hole X-ray binary MAXI J1348-630,performed using five AstroSat *** source was in the soft spectral state for the first three observations and in the hard state for the last *** three soft state spectra were modeled using a relativistic thin accretion disk with reflection features and thermal *** fitting of the soft state spectra constrained the spin parameter of the black hole a_(*)>0.97 and the disk inclination angle i=32.9_(-0.6)^(+4.1)*** bright and faint hard states had bolometric flux a factor of~6 and~10 less than that of the soft state *** spectra were fitted using the same model except that the inner disk radius was not assumed to be at the last stable ***,the estimated values do not indicate large truncation radii and the inferred accretion rate in the disk was an order of magnitude lower than that of the soft *** with earlier reported temporal analysis,AstroS at data provide a comprehensive picture of the evolution of the source.

关键词： black hole physics-X-rays binaries-accretion-accretion disks-X-rays individual(MAXI J1348-630)