A brief reference in the text that indicates the source of the idea or quotation consulted by the author is:

The correct option is In-text citation.

In academic writing, when an author refers to, summarizes, paraphrases, or quotes another source, they must acknowledge that source. A brief reference placed directly within the body of the text to identify the source of the idea or quotation is called an in-text citation. This typically includes details like the author's last name and the year of publication (e.g., Smith, 2020), which allows readers to find the full reference details in the bibliography or reference list at the end of the document.

Let's look at why the other choices do not fit the description:
- Sectional heading: This is a title or label used to organize sections within a document to guide the reader through the structure, not to cite a source.
- Hypothetical statement: This is a proposed explanation or assumption made for the sake of argument or testing (a hypothesis), rather than a reference to a source.
- Objective: This states the purpose or goal of a study or document, not the source of information.