Follow up observations of 4U 1543-47 with AstroSat

ATel #14749; Akash Garg (JMIU),N. P.S. Mithun (PRL), Nazma Husain (JMIU), Sneha Prakash Mudambi (CHRIST University),Yash Bhargava (IUCAA), Ranjeev Misra (IUCAA), M. C. Ramadevi (ISRO), Anuj Nandi (ISRO) and Somasri Sen (JMIU)
on 3 Jul 2021; 14:55 UT
Credential Certification: SNEHA PRAKASH MUDAMBI (mudambisnehaprakash@gmail.com)

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We triggered ToO observations of the black hole X-ray binary 4U 1543-47 with AstroSat as a follow up to the reports by NICER(Atel #14725), SWIFT(ATel #14715), MAXI(ATel #14708,#14701) indicating an onset of its outburst after nearly two decades. AstroSat observed 4U 1543-47 on 2021-07-01(MJD 59396) starting from 00:59:32 to 11:53:10 (UTC) with 40 arcmin offset pointing for 20 ks. LAXPC spectrum could be well described by a combination of disk emission(diskbb) and Comptonization models (simpl) in the energy range 4.0-25.0 keV. Inner disc temperature was found to be around KT_in=0.91+/-0.01 keV. Spectrum also showed the presence of a broad Fe K line feature at 6.4 keV. Asymptotic power index was estimated to be 3.3+/-0.3. Disk flux was found to contribute 95 percent of the total flux in the 4.0-25.0 keV band which was estimated to be 2.5E-8 ergs^(-1)cm^(-2)(with an error of about 30 percent due to uncertainties in the off-axis effective area). From CZTI observations, we estimated the upper limit of the flux in the 25.0-50.0 keV band to be 1.5E-10 ergs^(-1)cm^(-2), which is consistent with the LAXPC spectral model. Following this, we carried out a timing analysis in the energy range 4.0-25.0 keV. The source shows little rapid variation with the variability of 1.0+/-0.5 percent in the 4.0-8.0 keV and less than 4 percent in the 8.0-25.0 keV band in the frequency range 0.1-10 Hz. Further, follow up observations are encouraged. We thank the AstroSat Time Allocation team and operations team for the quick response to the ToO proposal.