Is a mourner allowed to participate in a Purim party?[1]

A mourner within Shiva:[2] A mourner within Shiva may not leave his house on Purim, even to participate in an annual and communal Purim party. This applies even if music will not be played at the party.

A mourner within Shloshim: A mourner within Shloshim of his father or mother may not participate in an annual and communal Purim party. This applies even if music will not be played at the party. [Some[3] write that other mourners that are within Shloshim may participate in a Purim party that they attend annually, so long as they do not dance, and music will not be played at the party. However other Poskim[4] are stringent even in such a case.]

A mourner within 12 months: All mourners of a parent that are within the year of mourning may participate in a Purim party that they attend annually, so long as they do not dance, and music will not be played at the party.[5] However there are Poskim[6] that are stringent even in such a case.

Seuda in home of Avel:[7] An Avel may hold a Purim feast in his home and invite family and friends to join. If music is played each year by the feast, it is permitted for the music to be played even in the attendance of the Avel.[8]

[1] See Rama Yoreh Deah 391:2; Piskeiy Teshuvos 696:7; Nitei Gavriel Aveilus 31:5; Purim 78:13

[2] See Previous Q&A; Piskeiy Teshuvos 696:7

[3] Piskeiy Teshuvos ibid; Vetzrauch Iyun as from where he received this difference between an Avel over a parent or other relative if in Rama 391:2 all Aveilim are included in the prohibition!

[4] Igros Moshe 3:161; See Nitei Gavriel Aveilus 31:5; Purim 78:13

[5] Piskeiy Teshuvos ibid in name of Minchas Yitzchak; and the practical directive of Rabbanim.

The reason: As if he does not attend it will appear like public mourning. Vetzaruch Iyun as according to this it should be permitted to attend even if music is played. [See Nimukei Orach Chaim 696:3]

[6] Igros Moshe 3:161

[7] Rama 391:2; Nitei Gavriel Aveilus 2 31:4

[8] Nimukei Orach Chaim 696:1