WALƘIYAR HASKEN GAMMA TA 1991 TANA KAƊA KAMAR MAGNETAR

A ranar 11 ga Yuli 1991, na’urar BATSE da ke cikin tashar kallon hasken gamma ta Compton (Compton Gamma Ray Observatory) ta naɗi walƙiyar hasken gamma. An ruwaito GRB 910711 a matsayin fashewa mafi gajarta da aikin ya taɓa gani: kololuwa mai haske ta kusan millisecond 10, sannan wutsiya mai rauni ta millisecond 100 zuwa 200. A 2023, nazarin gajerun fashewa 724 ya mayar da ita ɗan takara mafi ƙarfi ga girgizar kilohertz (kilohertz oscillations) — haske da ke hawa da sauka sau dubbai a kowane daƙiƙa — wadda aka fassara a matsayin motsin tauraron neutron “mai nauyi fiye da kima” (hypermassive) da haɗuwar taurari ta bari.

Waɗanda ake zargi biyu ga walƙiya gajera ɗaya

Gajerun fashewar hasken gamma suna da tushe biyu masu yiwuwa: haɗuwar taurari masu matsewa, ko babbar fashewar magnetar (magnetar giant flare), tauraron neutron mai filin maganaɗisu mai ƙarfin gaske. Wasu manyan fashewa daga wasu galaxy suna kama da fashewar haɗuwa a tsawon lokaci da makamashin haskensu; ba tare da madaidaicin matsayi a sararin sama ba, yana da wuya a bambanta su. Matsayin GRB 910711 yana da rashin tabbas na kusan digiri 6.

Run-Chao Chen da Bin-Bin Zhang (Jami’ar Nanjing), Ore Gottlieb (Cibiyar Fasaha ta Massachusetts, MIT) da abokan aiki biyar sun fara ne daga wani saɓani a cikin fassarar haɗuwa.

Haske mai tsauri da ba zai ɗauki bugu ba

Bakan hasken (spectrum) GRB 910711 yana dacewa kusan da kyau da baƙin jiki (blackbody) — hasken jiki mai zafi wanda haske ba ya ratsa shi — kamar yadda yake dacewa da siffar da aka saba amfani da ita ga fashewar haɗuwa. Da wannan siffa ta biyu, yana fitowa “mai tsauri” (hard) fiye da yadda aka saba — mai karkata ga photon masu makamashi mai yawa — a ƙarshen iyakar fashewar da BATSE ta auna.

Gyaran da ya dace: hasken da ke fitowa daga photosphere, layin da gajimaren da haske ba ya ratsa shi ke sakin haskensa. Amma a can, hasken yana fitowa nesa da injin tsakiya, bayan watsuwa da yawa. Bugun kilohertz da tauraron neutron a tsakiya ya saita zai buƙaci ƙarin hanya don tsira daga tafiyar, ko a sake gina shi a hanyar fita.

Tagwaye mafi rauni na fashewa da aka sani

Ma’aunin kwatancensu shi ne GRB 200415A, da aka naɗa a ranar 15 ga Afrilu 2020: babbar fashewar magnetar daga galaxy na kusa NGC 253, mai nisan megaparsec 3.5 — megaparsec shi ne ma’aunin da masana falaki ke amfani da shi don nisa tsakanin galaxy.

Idan aka daidaita su a kan kololuwarsu, lanƙwasan hasken biyu suna kama da juna: kololuwa iri ɗaya ta millisecond 10, wutsiya mafi rauni iri ɗaya, siffofi masu gajarta kamar kusan microsecond 90 — kashi ɗaya cikin miliyan na daƙiƙa — a 1991, da 65 a 2020. Samfurin fashewar 2020 da aka sa ta rage haske kawai, kamar ta tashi a wuri mafi nisa, yana sake samar da siffar fashewar 1991. Misali ne kawai, marubutan sun jaddada, ba auna nisa ba.

Ƙarin sautukan kusan hertz 360

A cikin kololuwar, ƙungiyar ta sami ɗan tudu a hertz 360 — sau 360 a kowane daƙiƙa — a fashewar 1991, da kuma a hertz 350 a 2020. A cikin millisecond 10, ba za a iya bambanta mitocin da ke kusa da juna fiye da kusan hertz 100 ba: tudun biyu ba sa bambanta.

Taswirorin ƙari gwargwadon lokaci suna nuna ƙololuwa da ke haskakawa a cikakkun ninkin hertz 360, kamar ƙarin sautukan nota ɗaya: sau 1, 3, 5, 6 da 11 na 360 a GRB 910711; sau 2, 4, 6 da 12 a GRB 200415A. Dukansu suna raba na shida, kusan hertz 2,160, kusa da wata girgiza da aka riga aka ruwaito a fashewar 2020.

Bispectrum yana duba ko girgizai suna da alaƙa: girgizai masu alaƙa suna samar da ƙarfi a jimillar mitocinsu. A fashewar 2020, ɓangaren hertz 4,320 ya yi daidai da ɓangarori biyu masu alaƙa a hertz 2,160, waɗanda su kansu suka yi daidai da hertz 720 da 1,440 masu alaƙa.

Fashewar ƙarya 100,000

Don gwada ko daidaituwa ce, ga kowace fashewa ƙungiyar ta yi lanƙwasan haske na ƙarya 100,000 masu siffar kololuwa iri ɗaya da hayaniyar ƙirga photon, amma babu girgiza. Tudun hertz 360 ya fito da ƙarfi iri ɗaya ko fiye a kusan kashi 5% daga cikinsu ga GRB 910711, da 0.1% ga GRB 200415A. Lokacin da na ƙaryar su ma suka ɗauki girgizar kilohertz da aka riga aka ruwaito da hayaniyar baya mafi kama da gaskiya, waɗannan alƙaluman sun tashi zuwa 15.5% da 33.4%: shi kaɗai, ƙaramin tudun ya rage zama abin mamaki.

An gwada ƙarin sautukan ne kawai da na ƙarya marasa girgiza, kuma a can sun tsaya daram. Ƙaramin bambanci a mitar tushe yana ninkuwa a kowane ƙarin sauti, don haka tsarin yana gwada shi da kyau fiye da tudun shi kaɗai. Yayin bincike daga hertz 260 zuwa 460, fashewar biyu sun fi son kusan hertz 360; na ƙaryar ba su yi haka ba. Idan aka kwatanta da na ƙarya marasa girgiza, an kai ga haɗaɗɗen ƙarfin alaƙar sau 1.3 kawai cikin 10,000 ga GRB 910711, da sau 4.5 ga GRB 200415A.

Galaxy goma sha bakwai masu yiwuwa

A kowane nisa, GRB 910711 zai yi rauni sosai ga makamashin haskensa, idan aka kwatanta da sanannun fashewar haɗuwa. A matsayin babbar fashewa ya dace, idan yana cikin kusan megaparsec 55, kusan ninki 16 nesa da NGC 253. A wannan zangon da yankinsa na sararin sama, ƙungiyar ta lissafa galaxy 17, mafi kusa a kusan megaparsec 9.1, dukansu an rarraba su a matsayin galibi masu samar da taurari. Idan wannan fassarar ta tsaya, BATSE ta kama babbar fashewarta ta farko daga wani galaxy a 1991.

Me zai iya kaɗa a hertz 360

A manyan fashewa daga Galaxy ɗinmu, girgizai masu sauri sun bayyana a wutsiyoyin da ke dushewa, ba a kololuwar ba; ɗaya, a kusan hertz 625, an danganta ta da girgizar ɓawon tauraron. A ƙarƙashin wasu zato za ta iya faɗuwa kusa da hertz 360, amma tana dogara ne ga cikin kowane tauraro da filin maganaɗisunsa: magnetar biyu su raba ta zai zama daidaituwa. Mafi zama hasashe shi ne girgiza a iyakar inda abin nukiliya ke juyawa zuwa abin quark (quark matter) a can cikin tsakiya: mitarta, tsakanin hertz 100 da 1,000, tana dogara ne galibi ga ilimin kimiyyar nukiliya, kaɗan ga nauyin tauraron. Yadda kowace irin wannan girgiza za ta tsara hasken kololuwar har yanzu ba a tabbatar ba.

Bugu da aka ji a hasken gamma kaɗai

Sakamakon “ba su tabbatar da” asalin magnetar “shi kaɗai ba”, marubutan sun rubuta, amma sun mayar da shi “fassara mafi tattali”: haɗuwar taurari dole ta bayyana bakan haske mai tsauri, bugu da ya ratsa photosphere, kamanni da fashewar 2020 da ƙarin sautuka da aka raba duka a lokaci guda. Idan irin waɗannan ƙarin sautuka suka bayyana a gajerun fashewa na gaba, hasken gamma kaɗai zai iya taimakawa wajen bambanta fashewar magnetar da haɗuwar taurari, a kan lokaci don shirya ƙarin kallo. GRB 910711 tana riƙe da yankin sararin sama na digiri 6, galaxy 17 masu yiwuwa, da bugu kusa da hertz 360.