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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. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  2. IceCube Alert 260425A: Global MASTER-Net observations report
  3. Fermi trigger No 798737427: Global MASTER-Net observations report
  4. GRB 260401A: cubesat Avion detection
  5. GRB 260424A: AstroSat CZTI detection of a long burst
  6. EP260321a: Upper limits from ATCA radio observations
  7. GRB 260421B: Kilonova-Catcher optical afterglow detection
  8. GRB 260421B: Insight-HXMT/HE detection
  9. The EP-WXT trigger 01709258652: Mondy optical observations
  10. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  11. EP260416a: Mondy optical observations
  12. GRB 260421B: SVOM/ECLAIRs refined analysis
  13. GRB 260421B: 3.6m DOT optical observation
  14. EP260416a: ZTSh R band observations
  15. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  16. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  17. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  18. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  19. GRB 260419A: AstroSat CZTI detection
  20. GRB 260421B: SVOM/GRM observation
  21. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  22. GRB 260421B: EP-FXT follow-up observation
  23. The EP-WXT trigger 01709260362 is likely a flaring star
  24. GOTO26djh/AT2026jpw: ATCA radio detection
  25. GRB 260421B: J-band upper limit with WINTER
  26. GRB 260421B: LCO optical counterpart detection
  27. GRB 260421B: Fermi GBM Observation
  28. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  29. GRB 260421A: AstroSat CZTI detection
  30. GOTO26djh/AT2026jpw: radio detection at 15GHz
  31. GRB 260412A: SVOM/ECLAIRs refined analysis
  32. GRB 260421B: SVOM/VT optical observations
  33. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  34. GRB 260310A: Late-time Chandra X-ray Detection
  35. GRB 260418A: Insight-HXMT/HE detection
  36. EP260416a: 1.3m DFOT optical observation
  37. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  38. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  39. Fermi GRB 260421C: Global MASTER-Net observations report
  40. GRB 260421C: Fermi GBM Final Real-time Localization
  41. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  42. Fermi GRB 260421B: Global MASTER-Net observations report
  43. GRB 260421B: BOOTES-7 early optical afterglow detection
  44. GRB 260421B: LCO optical afterglow confirmation
  45. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  46. GRB 260421B: TRT optical counterpart detection
  47. GRB 260421B: SVOM detection of a long burst
  48. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  49. GRB 260421B: Fermi GBM Final Real-time Localization
  50. Fermi GRB 260421A: Global MASTER-Net observations report
  51. GRB 260421A: Fermi GBM Final Real-time Localization
  52. EP260321a: VLA radio follow-up
  53. GRB 260412A: LCOGT Optical Upper Limits
  54. The EP-WXT trigger 01709260314 is likely a flaring star
  55. EP260416a: Optical follow-up observations with Kinder
  56. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  57. EP-WXT trigger 01709260303: KAIT optical observations
  58. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  59. The EP-WXT trigger 01709260303 is likely a flaring star
  60. GRB 260417A: SVOM/GRM observation
  61. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  62. GRB 260419B: Fermi GBM Final Real-time Localization
  63. GRB 260419A: Fermi GBM Final Real-time Localization
  64. Fermi trigger No 798275385: Global MASTER-Net observations report
  65. EP260417a: GROWTH-India Telescope optical upper limit
  66. Fermi GRB 260417B: Global MASTER-Net observations report
  67. EP260417b: GROWTH-India Telescope optical upper limit
  68. EP260416a: Ondrejov D50 optical detection
  69. GRB 260418B: Fermi GBM Final Real-time Localization
  70. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  71. EP260417a: Global MASTER-Net observations report
  72. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  73. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  74. GRB 260418A: Fermi GBM Final Real-time Localization
  75. EP260416a: GMG Optical Observation
  76. Fermi GRB 260417A: Global MASTER-Net observations report
  77. Konus-Wind detection of GRB 260411B
  78. GRB 260417B: Fermi GBM Final Real-time Localization
  79. GRB 260417A: AstroSat CZTI detection
  80. IPN triangulation of GRB 260411B
  81. EP260416a: LCO observations confirm end of flaring phase
  82. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  83. EP260417a: TRT optical counterpart detection
  84. EP260417a: Einstein Probe detection of an X-ray transient
  85. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  86. EP260417b: Einstein Probe detection of a fast X-ray transient
  87. EP-WXT trigger 01709259586: KAIT optical observations
  88. EP260416a: KAIT optical upper limit
  89. GRB 260414A: Insight-HXMT/HE detection
  90. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  91. EP260416a: WFST optical observations and rebrightening
  92. GRB 260417A: Fermi GBM Final Real-time Localization
  93. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  94. EP260416a: SVOM/VT optical observation
  95. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  96. GRB 260415B: Glowbug gamma-ray detection
  97. GRB 260411B: Glowbug gamma-ray detection
  98. GRB 260415A: Insight-HXMT/HE detection
  99. EP260416a: COLIBRÍ optical counterpart candidate
  100. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw

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