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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"

32445 results found.

  1. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  2. GRB 250320B: Fermi GBM Observation
  3. GRB 250321A: Swift-BAT refined analysis
  4. GRB 250321A: Swift-XRT refined Analysis
  5. GRB 250320B: Fermi-LAT detection
  6. GRB 250321B: SVOM detection of a sub-threshold transient event
  7. EP 250321A: Optical counterpart detection by LCO.
  8. GRB 250321A: Swift/UVOT Upper Limits
  9. GRB 250320B: SVOM/GRM observation of a long burst
  10. GRB 250320B: AstroSat CZTI detection
  11. Fermi GRB 250320B: Global MASTER-Net observations report
  12. Swift GRB 250321A: Global MASTER-Net observations report
  13. Fermi GRB 250321A: Global MASTER-Net observations report
  14. GRB 250321A: GOTO optical upper limits
  15. GRB 250321A: Swift-XRT localisation
  16. GRB 250314A: Keck/NIRC2 J-band upper limit
  17. EP250226a/GRB 250226A: KAIT optical observations
  18. GRB 250321A: Fermi GBM Observation
  19. GRB 250321A: Swift detection of a burst
  20. GRB 250321A: Fermi GBM Final Real-time Localization
  21. GRB 250320B: Fermi GBM Final Real-time Localization
  22. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  23. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  24. GRB 250320A: Fermi GBM Final Real-time Localization
  25. Fermi GRB 250319B: Global MASTER-Net observations report
  26. GRB 250313A: GRBAlpha detection
  27. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  28. GRB 250319B: Fermi GBM Final Localization
  29. GRB 250319A: Fermi GBM Final Localization
  30. GRB 250317D: EIRSAT-1 GMOD Detection
  31. GRB 250314A: ATCA radio upper limits
  32. GRB 250317B: OHP/T193 continued follow-up
  33. GRB 250317C: SVOM/GRM observation of a long burst
  34. GRB 250317B: Leavitt Observatory optical upper limit
  35. GRB 250309B/AT2025dws: further ATCA observations
  36. GRB 250317B: Mondy AZT-33IK Optical Observations
  37. GRB 250317C: AstroSat CZTI detection
  38. GRB 250317B: NOT optical observations suggest an optical plateau phase
  39. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  40. GRB 250317C: GECAM-B detection
  41. GRB 250317B: OHP/T193 optical observations
  42. GRB250312A: Swift/UVOT Upper Limits
  43. GRB 250317B: REM optical/NIR observations
  44. GRB 250317B: Swift-XRT observations
  45. GRB 250316A: Swift/UVOT Upper Limits
  46. GRB 250314A: REM optical/NIR upper limits
  47. GRB 250316A: AbAO AS-32 Optical Upper Limit
  48. EP 250317B: Fading optical counterpart detection by LCO
  49. GRB 250316A: Swift-XRT afterglow detection
  50. GRB 250317B: LCO detection of the fading optical afterglow
  51. GRB 250317B: refined SVOM/MXT analysis
  52. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  53. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  54. GRB 250317B: SVOM detection of a burst
  55. GRB 250316A: Fermi GBM Observation
  56. GRB 250316A: Swift-XRT observations
  57. GRB 250317A: Fermi GBM Final Real-time Localization
  58. Fermi GRB 250316A: Global MASTER-Net observations report
  59. GRB 250314A: SVOM/GRM analysis
  60. GRB 250316A: Swift ToO observations
  61. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  62. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  63. GRB 250316A: Fermi GBM Final Real-time Localization
  64. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  65. GRB 250314A: EP-FXT afterglow detection
  66. GRB 250314A: Swift/UVOT Upper Limits
  67. GRB 250312B: GRBAlpha detection
  68. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  69. GRB 250314A: Swift XRT Detection
  70. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  71. GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
  72. SVOM/MXT upper limit on GRB 250314A
  73. GRB 250314A: SVOM/VT upper limit
  74. GRB 250314A: NOT near-infrared candidate counterpart
  75. GRB 250313A: Fermi GBM Detection
  76. GRB 250313A: CALET Gamma-Ray Burst Monitor detection
  77. GRB 250312B: Fermi GBM Observation
  78. GRB 250313A: Swift-XRT observations
  79. Konus-Wind detection of GRB 250313A
  80. Konus-Wind detection of GRB 250308A
  81. GRB 250314A: SVOM detection of a burst
  82. EP250311a/GRB 250311A: Correction to EP-WXT detection time
  83. GRB 250313B: SVOM/GRM observation of a soft bright short burst
  84. GRB 250313A: SVOM/GRM observation of a bright long burst
  85. GRB 250313A: AstroSat CZTI detection of a bright long burst
  86. GRB 250313A: Fermi-LAT detection
  87. GRB 250313A: Swift ToO observations
  88. GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
  89. EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
  90. Fermi GRB 250313A: Global MASTER-Net observations report
  91. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  92. GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
  93. GRB 250313A: Fermi GBM Final Real-time Localization
  94. EP250311a/GRB 250311A: EP-FXT follow-up observation
  95. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  96. GRB 250312A: Swift-XRT refined Analysis
  97. Fermi Gamma-ray Burst Monitor trigger 763509110/250312911 is not a GRB
  98. Fermi GRB 250312B: Global MASTER-Net observations report
  99. GRB 250312A: Enhanced Swift-XRT position
  100. GRB 250312B: Fermi GBM Final Localization

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