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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"

32535 results found.

  1. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  2. Fermi GRB 260421B: Global MASTER-Net observations report
  3. GRB 260421B: BOOTES-7 early optical afterglow detection
  4. GRB 260421B: LCO optical afterglow confirmation
  5. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  6. GRB 260421B: TRT optical counterpart detection
  7. GRB 260421B: SVOM detection of a long burst
  8. Fermi GRB 260421A: Global MASTER-Net observations report
  9. EP260321a: VLA radio follow-up
  10. GRB 260412A: LCOGT Optical Upper Limits
  11. EP260416a: Optical follow-up observations with Kinder
  12. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  13. EP-WXT trigger 01709260303: KAIT optical observations
  14. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  15. GRB 260417A: SVOM/GRM observation
  16. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  17. EP260417a: GROWTH-India Telescope optical upper limit
  18. Fermi GRB 260417B: Global MASTER-Net observations report
  19. EP260417b: GROWTH-India Telescope optical upper limit
  20. EP260416a: Ondrejov D50 optical detection
  21. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  22. EP260417a: Global MASTER-Net observations report
  23. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  24. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  25. EP260416a: GMG Optical Observation
  26. Fermi GRB 260417A: Global MASTER-Net observations report
  27. Konus-Wind detection of GRB 260411B
  28. GRB 260417A: AstroSat CZTI detection
  29. IPN triangulation of GRB 260411B
  30. EP260416a: LCO observations confirm end of flaring phase
  31. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  32. EP260417a: TRT optical counterpart detection
  33. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  34. EP-WXT trigger 01709259586: KAIT optical observations
  35. EP260416a: KAIT optical upper limit
  36. GRB 260414A: Insight-HXMT/HE detection
  37. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  38. EP260416a: WFST optical observations and rebrightening
  39. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  40. EP260416a: SVOM/VT optical observation
  41. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  42. GRB 260415B: Glowbug gamma-ray detection
  43. GRB 260411B: Glowbug gamma-ray detection
  44. GRB 260415A: Insight-HXMT/HE detection
  45. EP260416a: COLIBRÍ optical counterpart candidate
  46. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  47. EP260416a: Global MASTER-Net observations report
  48. GOTO26djh/AT2026jpw : MASTER OT observation
  49. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  50. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  51. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  52. GRB 260415B: NuSTAR detection of long prompt emission
  53. GRB 260414A: Glowbug gamma-ray detection
  54. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  55. EP260321a: CMO SAI J,K observations
  56. GRB 260412A: Insight-HXMT/HE detection
  57. Fermi GRB 260413A: Global MASTER-Net observations report
  58. GRB 260410A: Glowbug gamma-ray detection of a short burst
  59. GRB 260410B: Insight-HXMT/HE detection
  60. GRB 260410A: Insight-HXMT/HE detection
  61. Konus-Wind detection of GRB 260410A (short/hard)
  62. GRB 260411B: GECAM-B observation of a long burst
  63. EP260321a: SVOM/VT optical observations and color changes around peak
  64. GRB 260410A: CALET Gamma-Ray Burst Monitor detection
  65. GRB 260412A: GECAM-B observation of a long burst
  66. Fermi GRB 260412A: Global MASTER-Net observations report
  67. GRB 260412A: Fermi GBM Observation
  68. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  69. GRB 260411B: Fermi-LAT detection
  70. GRB 260412A: SVOM detection of a long burst
  71. GRB 260411B: COLIBRÍ optical observations
  72. GRB 260410B: Fermi GBM Observation
  73. GRB 260411B: Ondrejov D50 optical afterglow detection
  74. GRB260411B: 3.6m DOT optical observation
  75. GRB 260411A: SVOM/GRM observation
  76. GRB 260411B: SVOM/GRM observation of a long burst
  77. GRB 260409A: Insight-HXMT/HE detection
  78. GRB 260411B: Fermi GBM Detection
  79. GRB 260411B: GOTO optical counterpart candidate
  80. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  81. GRB 260410A: COLIBRÍ optical upper limit
  82. EP-WXT01709259790: Optical Upper limits with kinder observations
  83. GRB 260410A: Fermi GBM Observation
  84. GRB 260410B: SVOM/GRM detection of a short faint burst
  85. GRB 260410A: Fermi-LAT detection
  86. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  87. EP260321a: Chandra X-ray Non-detection
  88. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  89. GRB 260407A: GECAM-A detection
  90. GRB 260407A: Insight-HXMT/HE detection
  91. EP260409a: SVOM/VT optical upper limits
  92. EP260409a: COLIBRÍ optical upper limits
  93. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  94. EP260409a: Global MASTER-Net observations report
  95. EP260321a: VLA radio detection
  96. GRB 260407A: Glowbug gamma-ray detection
  97. GRB 260402A: SVOM/ECLAIRs refined analysis
  98. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  99. GRB 260310A / AT2026fgk: X-ray rebrightening
  100. EP260402a / GRB 260402A: Mephisto optical upper limits

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