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

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