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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

27319 results found.

  1. GRB 260504B: LCO z-band upper limit
  2. SVOM GRB 260504B: MASTER-OAFA optical observations
  3. GRB 260504B: SVOM detection of a short burst
  4. Fermi GRB 260504A: Global MASTER-Net observations report
  5. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  6. GRB 260429B / EP260429a: EP-FXT follow-up observation
  7. EP260502a: Einstein Probe detection of an X-ray transient
  8. GRB 260429A: SVOM/GRM observation of a short burst
  9. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  10. EP260429a: Global MASTER-Net observations report
  11. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  12. GRB 260424B: AstroSat CZTI detection
  13. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  14. EP260429a: LCO optical upper limits
  15. EP260430a: LCO optical upper limits
  16. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  17. GRB 260429A: Fermi GBM Detection
  18. Fermi GRB 260429A: Global MASTER-Net observations report
  19. EP260430a: Global MASTER-Net observations report
  20. EP260430a: Einstein Probe detection of an X-ray transient
  21. EP260429a: EP-WXT detection of a fast X-ray transient
  22. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  23. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  24. Fermi GRB 260428A: Global MASTER-Net observations report
  25. EP260416a: Mondy and Terskol optical upper limits
  26. GRB 260424B: Glowbug gamma-ray detection of a short burst
  27. GRB 260424B: COLIBRÍ optical upper limit
  28. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  29. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  30. IceCube Alert 260425A: Global MASTER-Net observations report
  31. Fermi trigger No 798737427: Global MASTER-Net observations report
  32. GRB 260401A: cubesat Avion detection
  33. EP260321a: Upper limits from ATCA radio observations
  34. GRB 260421B: Kilonova-Catcher optical afterglow detection
  35. The EP-WXT trigger 01709258652: Mondy optical observations
  36. EP260416a: Mondy optical observations
  37. GRB 260421B: 3.6m DOT optical observation
  38. EP260416a: ZTSh R band observations
  39. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  40. GRB 260421B: SVOM/GRM observation
  41. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  42. GRB 260421B: EP-FXT follow-up observation
  43. GOTO26djh/AT2026jpw: ATCA radio detection
  44. GRB 260421B: J-band upper limit with WINTER
  45. GRB 260421B: LCO optical counterpart detection
  46. GRB 260421B: Fermi GBM Observation
  47. GOTO26djh/AT2026jpw: radio detection at 15GHz
  48. GRB 260421B: SVOM/VT optical observations
  49. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  50. GRB 260310A: Late-time Chandra X-ray Detection
  51. EP260416a: 1.3m DFOT optical observation
  52. Fermi GRB 260421C: Global MASTER-Net observations report
  53. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  54. Fermi GRB 260421B: Global MASTER-Net observations report
  55. GRB 260421B: LCO optical afterglow confirmation
  56. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  57. GRB 260421B: TRT optical counterpart detection
  58. GRB 260421B: SVOM detection of a long burst
  59. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  60. Fermi GRB 260421A: Global MASTER-Net observations report
  61. EP260321a: VLA radio follow-up
  62. GRB 260412A: LCOGT Optical Upper Limits
  63. EP260416a: Optical follow-up observations with Kinder
  64. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  65. GRB 260417A: SVOM/GRM observation
  66. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  67. Fermi trigger No 798275385: Global MASTER-Net observations report
  68. EP260417a: GROWTH-India Telescope optical upper limit
  69. Fermi GRB 260417B: Global MASTER-Net observations report
  70. EP260417b: GROWTH-India Telescope optical upper limit
  71. EP260416a: Ondrejov D50 optical detection
  72. EP260417a: Global MASTER-Net observations report
  73. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  74. EP260416a: GMG Optical Observation
  75. Fermi GRB 260417A: Global MASTER-Net observations report
  76. EP260416a: LCO observations confirm end of flaring phase
  77. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  78. EP260417a: TRT optical counterpart detection
  79. EP260417a: Einstein Probe detection of an X-ray transient
  80. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  81. EP260417b: Einstein Probe detection of a fast X-ray transient
  82. EP260416a: KAIT optical upper limit
  83. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  84. EP260416a: WFST optical observations and rebrightening
  85. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  86. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  87. GRB 260415B: Glowbug gamma-ray detection
  88. GRB 260411B: Glowbug gamma-ray detection
  89. EP260416a: COLIBRÍ optical counterpart candidate
  90. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  91. EP260416a: Global MASTER-Net observations report
  92. EP260416a: Einstein Probe detection of an X-ray transient
  93. GOTO26djh/AT2026jpw : MASTER OT observation
  94. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  95. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  96. GRB 260415B: NuSTAR detection of long prompt emission
  97. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  98. Fermi trigger No 797912738: Global MASTER-Net observations report
  99. GRB 260414A: Glowbug gamma-ray detection
  100. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope

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