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

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