Believed to be a nuclear device being lowered into its Shakti test position.
See Interactive map India's nuclear industry locations http://www.nti.org/gmap/?country=india&layers=biological,chemical,missile,nuclear&layers=nuclear
Based on my independent open source research I maintain that India desires/has a thermonuclear capability. This is in order to maintain full or partial parity with China's thermo arsenal (for MAD) and to maintain a wide margin of superiority over Pakistan.
India like all other nations (except North Korea) is aware that hot nuclear testing (ie. with actual fission and/or fusion explosions) would cause international isolation and a range of Western and Chinese sanctions. Furthermore computer simulations of such explosions enjoy greater accuracy/assurance that, to a limited extent, reduces the need to hot test one's actual devices.
It is likely India would seek (has received) cold and hot test results - most probably from Russia and perhaps from France and Israel (noting Indo-Israeli joint tests of nuclear (intended) missiles).
Such thermonuclear hot test information doesn't come cheap. India's perserverence in paying billions for an as yet long-delayed, undelivered aircraft carrier from Russia would seem an extraordinary waste if it weren't for some of that money also going into thermonuclear test results and perhaps designs. Russia, after all has never used carriers in battle or seen a major naval action since it lost to Japan in 1905 (Battle of Tsushima). This makes the value of a Russian made carrier (even to copy or as a testbed) intrinsically dubious. However Russian aid in thermonuclear development is (or has been) vastly more important to India.
Observation of tests by P5 countries since 1940s as well as intel collection by covert means would also yield hot and cold test data and designs etc. Dual use components and processes from cooperative countries and companies would have also helped.
Can Indian boosted fission shots (at the 1998 Operation Shakti (Pokhran-II) multitest - see below) be considered to collectively amount to a two stage thermonuclear (thermo) test? http://nuclearweaponarchive.org/India/IndiaShakti.html
Is the trend that all P5 countries (except France) that have built submarine reactors have historically already built thermonuclear weapons - be seen as sufficiently indicative? As a side issue Brazil's current development of a submarine reactor may suggest that Brazil has not lost its very significant nuclear weapons development capacity.
In what ways might India's thermo devices derived from, differ from or be similar to, those of India's providing ally Russia? and perhaps from France and Israel?
Russian nuclear tests http://scholar.googleusercontent.com/scholar?q=cache:yefIzEzuzFAJ:scholar.google.com/+Pokhran+thermonuclear+strategy+-reactor&hl=en&as_sdt=0,5&as_ylo=2008