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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"

32495 results found.

  1. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  2. GRB 260429B / EP260429a: AstroSat CZTI detection
  3. EP260502a: BOOTES-7: early optical upper limit
  4. EP260502a: Las Cumbres upper limit
  5. GRB 260429A: SVOM/GRM observation of a short burst
  6. EP260429a: Global MASTER-Net observations report
  7. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  8. GRB 260424B: AstroSat CZTI detection
  9. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  10. EP260429a: LCO optical upper limits
  11. EP260430a: LCO optical upper limits
  12. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  13. Fermi GRB 260429A: Global MASTER-Net observations report
  14. EP260430a: Global MASTER-Net observations report
  15. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  16. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  17. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  18. GRB 260428A: AstroSat CZTI detection
  19. Fermi GRB 260428A: Global MASTER-Net observations report
  20. EP260416a: Mondy and Terskol optical upper limits
  21. GRB 260424B: Glowbug gamma-ray detection of a short burst
  22. GRB 260424B: COLIBRÍ optical upper limit
  23. Konus-Wind detection of GRB 260424B
  24. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  25. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  26. IPN triangulation of GRB 260424B (short)
  27. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  28. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  29. GRB 260401A: cubesat Avion detection
  30. EP260321a: Upper limits from ATCA radio observations
  31. GRB 260421B: Kilonova-Catcher optical afterglow detection
  32. GRB 260421B: Insight-HXMT/HE detection
  33. The EP-WXT trigger 01709258652: Mondy optical observations
  34. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  35. EP260416a: Mondy optical observations
  36. GRB 260421B: SVOM/ECLAIRs refined analysis
  37. GRB 260421B: 3.6m DOT optical observation
  38. EP260416a: ZTSh R band observations
  39. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  40. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  41. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  42. GRB 260419A: AstroSat CZTI detection
  43. GRB 260421B: SVOM/GRM observation
  44. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  45. GRB 260421B: EP-FXT follow-up observation
  46. GOTO26djh/AT2026jpw: ATCA radio detection
  47. GRB 260421B: J-band upper limit with WINTER
  48. GRB 260421B: LCO optical counterpart detection
  49. GRB 260421B: Fermi GBM Observation
  50. GRB 260421A: AstroSat CZTI detection
  51. GOTO26djh/AT2026jpw: radio detection at 15GHz
  52. GRB 260412A: SVOM/ECLAIRs refined analysis
  53. GRB 260421B: SVOM/VT optical observations
  54. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  55. GRB 260310A: Late-time Chandra X-ray Detection
  56. GRB 260418A: Insight-HXMT/HE detection
  57. EP260416a: 1.3m DFOT optical observation
  58. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  59. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  60. Fermi GRB 260421C: Global MASTER-Net observations report
  61. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  62. Fermi GRB 260421B: Global MASTER-Net observations report
  63. GRB 260421B: BOOTES-7 early optical afterglow detection
  64. GRB 260421B: LCO optical afterglow confirmation
  65. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  66. GRB 260421B: TRT optical counterpart detection
  67. GRB 260421B: SVOM detection of a long burst
  68. Fermi GRB 260421A: Global MASTER-Net observations report
  69. EP260321a: VLA radio follow-up
  70. GRB 260412A: LCOGT Optical Upper Limits
  71. EP260416a: Optical follow-up observations with Kinder
  72. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  73. EP-WXT trigger 01709260303: KAIT optical observations
  74. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  75. GRB 260417A: SVOM/GRM observation
  76. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  77. EP260417a: GROWTH-India Telescope optical upper limit
  78. Fermi GRB 260417B: Global MASTER-Net observations report
  79. EP260417b: GROWTH-India Telescope optical upper limit
  80. EP260416a: Ondrejov D50 optical detection
  81. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  82. EP260417a: Global MASTER-Net observations report
  83. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  84. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  85. EP260416a: GMG Optical Observation
  86. Fermi GRB 260417A: Global MASTER-Net observations report
  87. Konus-Wind detection of GRB 260411B
  88. GRB 260417A: AstroSat CZTI detection
  89. IPN triangulation of GRB 260411B
  90. EP260416a: LCO observations confirm end of flaring phase
  91. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  92. EP260417a: TRT optical counterpart detection
  93. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  94. EP-WXT trigger 01709259586: KAIT optical observations
  95. EP260416a: KAIT optical upper limit
  96. GRB 260414A: Insight-HXMT/HE detection
  97. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  98. EP260416a: WFST optical observations and rebrightening
  99. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  100. EP260416a: SVOM/VT optical observation

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