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

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