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MAXI J1820+070 is a newly discovered transient black hole X-ray binary, whichshowed several spectral and temporal features. In this work, we analyse thebroadband X-ray spectra from all three simultaneously observing X-rayinstruments onboard AstroSat, as well as contemporaneous X-ray spectra fromNuSTAR, observed during the hard state of MAXI J1820+070 in March 2018.Implementing a combination of multi-colour disc model, relativistic blurredreflection model relxilllpCp and a distant reflection in the form of xillverCp,we achieve reasonable and consistent fits for AstroSat and NuSTAR spectra. Thebest-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 coronaheight ($h \lesssim 8 R_{\rm g}$), and a high corona temperature ($kT_{\rm e}\sim 115-150$ keV). Addition of a second Comptonisation component leads to asignificantly better fit, with the $kT_{\rm e}$ of the second Comptonisationcomponent being $\sim 14-18$ keV. Our results from independent observationswith two different satellites in a similar source state indicate aninhomogeneous corona, with decreasing temperature attributed to increasingheight. Besides, utilising the broader energy coverage of AstroSat, we estimatethe black hole mass to be $6.7-13.9 \ M_{\odot}$, consistent with independentmeasurements reported in the literature.

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