Abstract
The Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat, an open detector above \(\sim \)100 keV, is a promising tool for the investigation of hard X-ray characteristics of \(\gamma \)-ray pulsars. A custom algorithm has been developed to detect pulsars from long integration (\(\sim \)years) of archival data, as reported by us earlier. Here, we extend this method in the analysis to include additional \(\sim \)20% of the CZTI pixels that were earlier ignored due to their lower gain values. Recent efforts have provided better and more secure calibration of these pixels, demonstrating their higher thresholds and extended energy range up to \(\sim \)1 MeV. Here, we use the additional information provided by these pixels, enabling the construction of pulse profiles over a larger energy range. We compare the profiles of the Crab pulsar at different sub-bands and show that the behavior is consistent with the extended energy coverage. As detailed spectroscopy over this full band remains difficult due to the limited count rate, we construct hardness ratios which, together with AstroSat mass model simulations, are able to constrain the power-law index of the radiation spectrum. We present our results for the phase-resolved spectrum of PSR J0534\(+\)2200 and for the total pulsed emission of PSR J1513−5908. The recovered photon indices are found to be accurate within \({\sim }20\)%.
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Acknowledgements
We thank the anonymous referee for comments and suggestions that significantly improved the paper. This work uses data from the Indian astronomy mission AstroSat, archived at the Indian Space Science Data Centre (ISSDC). The instrument CZTI was built by a TIFR-led consortium of institutes across India, including VSSC, IUCAA, URSC, PRL and SAC. The Indian Space Research Organization funded, facilitated and managed the project. We extend our acknowledgement to the team members of the CZTI POC at IUCAA for helping with the aggregation of data. We also thank Fermi timing observers, Paul Ray and Matthew Kerr for their timely and favorable response in providing LAT ephemeris for the pulsars. We thank the HPC facility at IUCAA, where we carried out all the data analysis. Anusree acknowledges support for this work from the DST-INSPIRE Fellowship grant, IF170239, under the Ministry of Science and Technology, India.
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Anusree, K.G., Bhattacharya, D., Bhalerao, V. et al. Pulsars in AstroSat-CZTI: detection in sub-MeV bands and estimation of spectral index from hardness ratios. J Astrophys Astron 43, 91 (2022). https://doi.org/10.1007/s12036-022-09886-9
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DOI: https://doi.org/10.1007/s12036-022-09886-9