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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 250225B: GECAM-A detection
  2. GRB 250312A: GECAM-A detection
  3. GRB 250321B: Swift ToO observations
  4. EP250321a: WFST optical observations
  5. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  6. GRB 250321C: Fermi GBM Final Real-time Localization
  7. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  8. GRB 250320B: Fermi GBM Observation
  9. EP250321a: Xinglong 216 decaying optical observations
  10. GRB 250321A: Swift-BAT refined analysis
  11. GRB 250321A: Swift-XRT refined Analysis
  12. GRB 250320B: Fermi-LAT detection
  13. GRB 250321B: SVOM detection of a sub-threshold transient event
  14. EP250321a: SVOM/VT optical observation
  15. EP 250321A: Optical counterpart detection by LCO.
  16. EP250321a: Kinder optical follow-up observations
  17. GRB 250321A: Swift/UVOT Upper Limits
  18. GRB 250320B: SVOM/GRM observation of a long burst
  19. EP250321a: LCO optical counterpart detection
  20. EP250321a: Swift-XRT detection of an X-ray source
  21. EP250321A: COLIBRÍ Optical Observations
  22. EP250321a: VLT/X-shooter redshift z = 4.368
  23. GRB 250320B: AstroSat CZTI detection
  24. EP250321a: REM optical/NIR afterglow detection
  25. Fermi GRB 250320B: Global MASTER-Net observations report
  26. EP250321a: BOOTES-5/JGT optical afterglow detection
  27. EP250321a: TRT optical counterpart detection
  28. EP250321a: Global MASTER-Net observations report
  29. Swift GRB 250321A: Global MASTER-Net observations report
  30. Fermi GRB 250321A: Global MASTER-Net observations report
  31. EP250321a: Einstein Probe detection of an X-ray transient
  32. GRB 250321A: GOTO optical upper limits
  33. GRB 250321A: Swift-XRT localisation
  34. GRB 250314A: Keck/NIRC2 J-band upper limit
  35. EP250226a/GRB 250226A: KAIT optical observations
  36. GRB 250321A: Fermi GBM Observation
  37. GRB 250321A: Swift detection of a burst
  38. GRB 250321A: Fermi GBM Final Real-time Localization
  39. GRB 250320B: Fermi GBM Final Real-time Localization
  40. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  41. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  42. GRB 250320A: Fermi GBM Final Real-time Localization
  43. Fermi GRB 250319B: Global MASTER-Net observations report
  44. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  45. GRB 250313A: GRBAlpha detection
  46. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  47. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  48. GRB 250319B: Fermi GBM Final Localization
  49. GRB 250319A: Fermi GBM Final Localization
  50. GRB 250317D: EIRSAT-1 GMOD Detection
  51. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  52. GRB 250314A: ATCA radio upper limits
  53. EP250302a: VLA observations
  54. GRB 250317B: OHP/T193 continued follow-up
  55. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  56. GRB 250317C: SVOM/GRM observation of a long burst
  57. GRB 250317B: Leavitt Observatory optical upper limit
  58. GRB 250309B/AT2025dws: further ATCA observations
  59. GRB 250317B: Mondy AZT-33IK Optical Observations
  60. GRB 250317C: AstroSat CZTI detection
  61. GRB 250317B: NOT optical observations suggest an optical plateau phase
  62. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  63. GRB 250317C: GECAM-B detection
  64. GRB 250317B: OHP/T193 optical observations
  65. Fermi trigger No 763933627: Global MASTER-Net observations report
  66. GRB250312A: Swift/UVOT Upper Limits
  67. GRB 250317B: REM optical/NIR observations
  68. GRB 250317B: Swift-XRT observations
  69. GRB 250316A: Swift/UVOT Upper Limits
  70. GRB 250314A: REM optical/NIR upper limits
  71. GRB 250316A: AbAO AS-32 Optical Upper Limit
  72. EP 250317B: Fading optical counterpart detection by LCO
  73. GRB 250316A: Swift-XRT afterglow detection
  74. GRB 250317B: LCO detection of the fading optical afterglow
  75. GRB 250317B: refined SVOM/MXT analysis
  76. GRB250317B: SVOM/VT detection of an optical candidate from VHF data
  77. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  78. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  79. GRB 250317B: SVOM detection of a burst
  80. GRB 250316A: Fermi GBM Observation
  81. GRB 250316A: Swift-XRT observations
  82. Fermi trigger No 763862734: Global MASTER-Net observations report
  83. GRB 250317A: Fermi GBM Final Real-time Localization
  84. Fermi GRB 250316A: Global MASTER-Net observations report
  85. GRB 250314A: SVOM/GRM analysis
  86. GRB 250316A: Swift ToO observations
  87. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  88. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  89. The EP-WXT trigger 01709132801 is likely a flaring star
  90. GRB 250316A: Fermi GBM Final Real-time Localization
  91. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  92. GRB 250314A: EP-FXT afterglow detection
  93. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  94. GRB 250314A: Swift/UVOT Upper Limits
  95. GRB 250312B: GRBAlpha detection
  96. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  97. GRB 250314A: Swift XRT Detection
  98. EP250315a: optical counterpart candidate detected by Gemini North
  99. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  100. EP250315a: Einstein Probe detection of an X-ray transient

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