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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"

28084 results found.

  1. GRB 260421B: 3.6m DOT optical observation
  2. EP260416a: ZTSh R band observations
  3. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  4. GRB 260421B: SVOM/GRM observation
  5. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  6. GRB 260421B: EP-FXT follow-up observation
  7. GOTO26djh/AT2026jpw: ATCA radio detection
  8. GRB 260421B: J-band upper limit with WINTER
  9. GRB 260421B: LCO optical counterpart detection
  10. GRB 260421B: Fermi GBM Observation
  11. GOTO26djh/AT2026jpw: radio detection at 15GHz
  12. GRB 260421B: SVOM/VT optical observations
  13. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  14. GRB 260310A: Late-time Chandra X-ray Detection
  15. EP260416a: 1.3m DFOT optical observation
  16. Fermi GRB 260421C: Global MASTER-Net observations report
  17. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  18. Fermi GRB 260421B: Global MASTER-Net observations report
  19. GRB 260421B: LCO optical afterglow confirmation
  20. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  21. GRB 260421B: TRT optical counterpart detection
  22. GRB 260421B: SVOM detection of a long burst
  23. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  24. Fermi GRB 260421A: Global MASTER-Net observations report
  25. EP260321a: VLA radio follow-up
  26. GRB 260412A: LCOGT Optical Upper Limits
  27. EP260416a: Optical follow-up observations with Kinder
  28. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  29. GRB 260417A: SVOM/GRM observation
  30. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  31. Fermi trigger No 798275385: Global MASTER-Net observations report
  32. EP260417a: GROWTH-India Telescope optical upper limit
  33. Fermi GRB 260417B: Global MASTER-Net observations report
  34. EP260417b: GROWTH-India Telescope optical upper limit
  35. EP260416a: Ondrejov D50 optical detection
  36. EP260417a: Global MASTER-Net observations report
  37. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  38. EP260416a: GMG Optical Observation
  39. Fermi GRB 260417A: Global MASTER-Net observations report
  40. EP260416a: LCO observations confirm end of flaring phase
  41. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  42. EP260417a: TRT optical counterpart detection
  43. EP260417a: Einstein Probe detection of an X-ray transient
  44. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  45. EP260417b: Einstein Probe detection of a fast X-ray transient
  46. EP260416a: KAIT optical upper limit
  47. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  48. EP260416a: WFST optical observations and rebrightening
  49. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  50. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  51. GRB 260415B: Glowbug gamma-ray detection
  52. GRB 260411B: Glowbug gamma-ray detection
  53. EP260416a: COLIBRÍ optical counterpart candidate
  54. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  55. EP260416a: Global MASTER-Net observations report
  56. EP260416a: Einstein Probe detection of an X-ray transient
  57. GOTO26djh/AT2026jpw : MASTER OT observation
  58. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  59. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  60. GRB 260415B: NuSTAR detection of long prompt emission
  61. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  62. Fermi trigger No 797912738: Global MASTER-Net observations report
  63. GRB 260414A: Glowbug gamma-ray detection
  64. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  65. EP260321a: CMO SAI J,K observations
  66. Fermi GRB 260413A: Global MASTER-Net observations report
  67. GRB 260410A: Glowbug gamma-ray detection of a short burst
  68. Fermi GRB 260412A: Global MASTER-Net observations report
  69. GRB 260412A: Fermi GBM Observation
  70. GRB 260411B: Fermi-LAT detection
  71. GRB 260411B: COLIBRÍ optical observations
  72. GRB 260410B: Fermi GBM Observation
  73. GRB260411B: 3.6m DOT optical observation
  74. GRB 260411A: SVOM/GRM observation
  75. GRB 260411B: SVOM/GRM observation of a long burst
  76. GRB 260409A: Insight-HXMT/HE detection
  77. GRB 260411B: Fermi GBM Detection
  78. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  79. GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  80. GRB 260410A: COLIBRÍ optical upper limit
  81. EP-WXT01709259790: Optical Upper limits with kinder observations
  82. GRB 260410A: Fermi GBM Observation
  83. GRB 260410B: SVOM/GRM detection of a short faint burst
  84. EP-WXT01709259790: Xinglong optical upper limit
  85. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  86. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  87. EP260409a: COLIBRÍ optical upper limits
  88. EP260409a: Global MASTER-Net observations report
  89. EP260409a: Einstein Probe detection of an X-ray transient
  90. EP260321a: VLA radio detection
  91. GRB 260407A: Glowbug gamma-ray detection
  92. GRB 260402A: SVOM/ECLAIRs refined analysis
  93. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  94. EP260402a / GRB 260402A: Mephisto optical upper limits
  95. EP-WXT01709259586: Xinglong optical upper limit
  96. EP260403a: Mephisto optical upper limits
  97. EP260402a/GRB 260402A: Xinglong optical upper limit
  98. EP260405a: GMOS-N optical upper limits
  99. EP260405a: Global MASTER-Net observations report
  100. EP260405a: Einstein Probe detection of a fast X-ray transient

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