The Sara-Sirajgonj Railway Company Ltd opened this line in 1915-16; it was worked by Eastern Bengal Railway(EBR). The broad gauge(BG) line takes off from Ishurdi , where it connected to the main line, in an easterly direction to Sirajganj on the banks of the Jamuna river, a length of 53 miles(85km). The line was woked by EBR as part of its network. 
The railway was finally purchased by EBR
Refer to FIBIS Fact File #4: “Research sources for Indian Railways, 1845-1947” - available from the Fibis shop. This Fact File contains invaluable advice on 'Researching ancestors in the UK records of Indian Railways' with particular reference to the India Office Records (IOR) held at the British Library
An on-line search of the IOR records relating to this railway  gives the following: -
- L/F/8/18/1400 “Sara-Sirajganj Railway Company Limited, Indenture, Secretary of State; 1916"