| Authors : | 1- Birendra Chhotaray, Astronomy and Astrophysics Division, Physical Research Laboratory, Navrangpura, Ahmedabad - 380009, India
2- Neeraj Kumari, Astronomy and Astrophysics Division, Physical Research Laboratory, Navrangpura, Ahmedabad - 380009, India
3- Arghajit Jana, Institute of Astronomy, National Tsing Hua Univesity, No. 101號, Section 2, Guangfu Rd, East District, Hsinchu City, Taiwan 300
4- Gaurava K. Jaisawal, National Space Institute, Technical University of Denmark, Elektrovej 327-328, DK-2800 Lyngby, Denmark
5- Vipin Kumar, Astronomy and Astrophysics Division, Physical Research Laboratory, Navrangpura, Ahmedabad - 380009, India
6- Sachindra Naik, Astronomy and Astrophysics Division, Physical Research Laboratory, Navrangpura, Ahmedabad - 380009, India |
| Abstract : | In November 2020, the Be/X-ray binary pulsar 1A 0535+262 went into a giant X-ray outburst, reaching a peak luminosity of 11 Crab in the 15-50 keV range. During the giant outburst, the pulsar was observed with AstroSat and NuSTAR X-ray observatories, whereas the companion Be star was observed with the 1.2 m telescope at Mount Abu Infrared observatory in optical wavebands (4000-7500 \AA) at several epochs. Our work mainly focuses on the study of the properties of the pulsar during the outburst and corresponding effects in optical emission from the Be star. Using data from AstroSat, we detected X-ray pulsations at $\sim$103.5501 s in the light curves up to 150 keV. The pulse profile of the pulsar is found to show strong energy dependency. Energy resolved pulse profiles showed absorption dips below 7 keV and these dips vanish at higher energies. Beyond 30 keV strength of two peaks varies in the opposite manner. The 1-90 keV broadband spectral study is carried out using a model that consists of a blackbody emission, power-law with an exponential cutoff, a Gaussian component for iron emission line, and another Gaussian component for the cyclotron absorption line. The cyclotron line is found at $\sim$ 45 keV. In the optical waveband, there is a change in the shape and strength of the continuum found. The optical spectra exhibit emission lines at 4861\AA (HI), 6563\AA (HI), 6678\AA (HeI), and 7065 \AA (HeI) line. The strength of the H-alpha (H$\alpha$) line is found to be decreasing in correlation with X-ray flux from the peak of the outburst. |
