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

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