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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"
  1. IceCube Alert 260425A: Global MASTER-Net observations report
  2. Fermi trigger No 798737427: Global MASTER-Net observations report
  3. GRB 260401A: cubesat Avion detection
  4. GRB 260424A: AstroSat CZTI detection of a long burst
  5. EP260321a: Upper limits from ATCA radio observations
  6. GRB 260421B: Kilonova-Catcher optical afterglow detection
  7. GRB 260421B: Insight-HXMT/HE detection
  8. The EP-WXT trigger 01709258652: Mondy optical observations
  9. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  10. EP260416a: Mondy optical observations
  11. GRB 260421B: SVOM/ECLAIRs refined analysis
  12. GRB 260421B: 3.6m DOT optical observation
  13. EP260416a: ZTSh R band observations
  14. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  15. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  16. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  17. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  18. GRB 260419A: AstroSat CZTI detection
  19. GRB 260421B: SVOM/GRM observation
  20. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  21. GRB 260421B: EP-FXT follow-up observation
  22. The EP-WXT trigger 01709260362 is likely a flaring star
  23. GOTO26djh/AT2026jpw: ATCA radio detection
  24. GRB 260421B: J-band upper limit with WINTER
  25. GRB 260421B: LCO optical counterpart detection
  26. GRB 260421B: Fermi GBM Observation
  27. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  28. GRB 260421A: AstroSat CZTI detection
  29. GOTO26djh/AT2026jpw: radio detection at 15GHz
  30. GRB 260412A: SVOM/ECLAIRs refined analysis
  31. GRB 260421B: SVOM/VT optical observations
  32. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  33. GRB 260310A: Late-time Chandra X-ray Detection
  34. GRB 260418A: Insight-HXMT/HE detection
  35. EP260416a: 1.3m DFOT optical observation
  36. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  37. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  38. Fermi GRB 260421C: Global MASTER-Net observations report
  39. GRB 260421C: Fermi GBM Final Real-time Localization
  40. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  41. Fermi GRB 260421B: Global MASTER-Net observations report
  42. GRB 260421B: BOOTES-7 early optical afterglow detection
  43. GRB 260421B: LCO optical afterglow confirmation
  44. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  45. GRB 260421B: TRT optical counterpart detection
  46. GRB 260421B: SVOM detection of a long burst
  47. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  48. GRB 260421B: Fermi GBM Final Real-time Localization
  49. Fermi GRB 260421A: Global MASTER-Net observations report
  50. GRB 260421A: Fermi GBM Final Real-time Localization
  51. EP260321a: VLA radio follow-up
  52. GRB 260412A: LCOGT Optical Upper Limits
  53. The EP-WXT trigger 01709260314 is likely a flaring star
  54. EP260416a: Optical follow-up observations with Kinder
  55. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  56. EP-WXT trigger 01709260303: KAIT optical observations
  57. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  58. The EP-WXT trigger 01709260303 is likely a flaring star
  59. GRB 260417A: SVOM/GRM observation
  60. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  61. GRB 260419B: Fermi GBM Final Real-time Localization
  62. GRB 260419A: Fermi GBM Final Real-time Localization
  63. Fermi trigger No 798275385: Global MASTER-Net observations report
  64. EP260417a: GROWTH-India Telescope optical upper limit
  65. Fermi GRB 260417B: Global MASTER-Net observations report
  66. EP260417b: GROWTH-India Telescope optical upper limit
  67. EP260416a: Ondrejov D50 optical detection
  68. GRB 260418B: Fermi GBM Final Real-time Localization
  69. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  70. EP260417a: Global MASTER-Net observations report
  71. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  72. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  73. GRB 260418A: Fermi GBM Final Real-time Localization
  74. EP260416a: GMG Optical Observation
  75. Fermi GRB 260417A: Global MASTER-Net observations report
  76. Konus-Wind detection of GRB 260411B
  77. GRB 260417B: Fermi GBM Final Real-time Localization
  78. GRB 260417A: AstroSat CZTI detection
  79. IPN triangulation of GRB 260411B
  80. EP260416a: LCO observations confirm end of flaring phase
  81. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  82. EP260417a: TRT optical counterpart detection
  83. EP260417a: Einstein Probe detection of an X-ray transient
  84. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  85. EP260417b: Einstein Probe detection of a fast X-ray transient
  86. EP-WXT trigger 01709259586: KAIT optical observations
  87. EP260416a: KAIT optical upper limit
  88. GRB 260414A: Insight-HXMT/HE detection
  89. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  90. EP260416a: WFST optical observations and rebrightening
  91. GRB 260417A: Fermi GBM Final Real-time Localization
  92. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  93. EP260416a: SVOM/VT optical observation
  94. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  95. GRB 260415B: Glowbug gamma-ray detection
  96. GRB 260411B: Glowbug gamma-ray detection
  97. GRB 260415A: Insight-HXMT/HE detection
  98. EP260416a: COLIBRÍ optical counterpart candidate
  99. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  100. EP260416a: Global MASTER-Net observations report

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