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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"

44289 results found.

  1. IPN triangulation of GRB 260424B (short)
  2. GRB 260424B: SVOM/GRM detection of a short burst
  3. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  4. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  5. IceCube Alert 260425A: Global MASTER-Net observations report
  6. Fermi trigger No 798737427: Global MASTER-Net observations report
  7. GRB 260401A: cubesat Avion detection
  8. GRB 260424A: AstroSat CZTI detection of a long burst
  9. EP260321a: Upper limits from ATCA radio observations
  10. GRB 260421B: Kilonova-Catcher optical afterglow detection
  11. GRB 260421B: Insight-HXMT/HE detection
  12. The EP-WXT trigger 01709258652: Mondy optical observations
  13. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  14. EP260416a: Mondy optical observations
  15. GRB 260421B: SVOM/ECLAIRs refined analysis
  16. GRB 260421B: 3.6m DOT optical observation
  17. EP260416a: ZTSh R band observations
  18. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  19. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  20. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  21. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  22. GRB 260419A: AstroSat CZTI detection
  23. GRB 260421B: SVOM/GRM observation
  24. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  25. GRB 260421B: EP-FXT follow-up observation
  26. The EP-WXT trigger 01709260362 is likely a flaring star
  27. GOTO26djh/AT2026jpw: ATCA radio detection
  28. GRB 260421B: J-band upper limit with WINTER
  29. GRB 260421B: LCO optical counterpart detection
  30. GRB 260421B: Fermi GBM Observation
  31. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  32. GRB 260421A: AstroSat CZTI detection
  33. GOTO26djh/AT2026jpw: radio detection at 15GHz
  34. GRB 260412A: SVOM/ECLAIRs refined analysis
  35. GRB 260421B: SVOM/VT optical observations
  36. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  37. GRB 260310A: Late-time Chandra X-ray Detection
  38. GRB 260418A: Insight-HXMT/HE detection
  39. EP260416a: 1.3m DFOT optical observation
  40. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  41. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  42. Fermi GRB 260421C: Global MASTER-Net observations report
  43. GRB 260421C: Fermi GBM Final Real-time Localization
  44. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  45. Fermi GRB 260421B: Global MASTER-Net observations report
  46. GRB 260421B: BOOTES-7 early optical afterglow detection
  47. GRB 260421B: LCO optical afterglow confirmation
  48. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  49. GRB 260421B: TRT optical counterpart detection
  50. GRB 260421B: SVOM detection of a long burst
  51. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  52. GRB 260421B: Fermi GBM Final Real-time Localization
  53. Fermi GRB 260421A: Global MASTER-Net observations report
  54. GRB 260421A: Fermi GBM Final Real-time Localization
  55. EP260321a: VLA radio follow-up
  56. GRB 260412A: LCOGT Optical Upper Limits
  57. The EP-WXT trigger 01709260314 is likely a flaring star
  58. EP260416a: Optical follow-up observations with Kinder
  59. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  60. EP-WXT trigger 01709260303: KAIT optical observations
  61. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  62. The EP-WXT trigger 01709260303 is likely a flaring star
  63. GRB 260417A: SVOM/GRM observation
  64. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  65. GRB 260419B: Fermi GBM Final Real-time Localization
  66. GRB 260419A: Fermi GBM Final Real-time Localization
  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. GRB 260418B: Fermi GBM Final Real-time Localization
  73. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  74. EP260417a: Global MASTER-Net observations report
  75. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  76. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  77. GRB 260418A: Fermi GBM Final Real-time Localization
  78. EP260416a: GMG Optical Observation
  79. Fermi GRB 260417A: Global MASTER-Net observations report
  80. Konus-Wind detection of GRB 260411B
  81. GRB 260417B: Fermi GBM Final Real-time Localization
  82. GRB 260417A: AstroSat CZTI detection
  83. IPN triangulation of GRB 260411B
  84. EP260416a: LCO observations confirm end of flaring phase
  85. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  86. EP260417a: TRT optical counterpart detection
  87. EP260417a: Einstein Probe detection of an X-ray transient
  88. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  89. EP260417b: Einstein Probe detection of a fast X-ray transient
  90. EP-WXT trigger 01709259586: KAIT optical observations
  91. EP260416a: KAIT optical upper limit
  92. GRB 260414A: Insight-HXMT/HE detection
  93. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  94. EP260416a: WFST optical observations and rebrightening
  95. GRB 260417A: Fermi GBM Final Real-time Localization
  96. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  97. EP260416a: SVOM/VT optical observation
  98. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  99. GRB 260415B: Glowbug gamma-ray detection
  100. GRB 260411B: Glowbug gamma-ray detection

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