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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"

45415 results found.

  1. EP250321A: J band upper limit by SYSU 80cm telescope
  2. EP250404a: BOOTES-4/JGT optical afterglow detection
  3. EP250404a: Nanshan/HMT optical counterpart detection
  4. EP250404a: Einstein Probe detection of an X-ray transient
  5. GRB 250404A: Fermi GBM Final Real-time Localization
  6. GRB 250402A: Mondy optical observations
  7. GRB 250403A: Swift/UVOT Detection
  8. GRB 250402A: Swift/UVOT Upper Limits
  9. EP250402a: Optical upper limit with Kinder observations
  10. GRB 250403A: SVOM/VT optical observation
  11. GRB 250403A: REM NIR afterglow detection
  12. GRB 250403A: LCO optical counterpart detection
  13. IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
  14. GRB 250403A: JinShan optical observations
  15. GRB 250402A: EP-FXT afterglow detection
  16. GRB 250403A: Optical counterpart detection by LCO.
  17. EP250402a: EP-FXT follow-up observations
  18. GRB 250403A: Swift-XRT observations
  19. GRB 250322A: 10 GHz VLA radio upper limits
  20. Fermi GRB 250403A: Global MASTER-Net observations report
  21. GRB 250403A: GOTO optical counterpart follow-up observations
  22. GRB 250402A: NUTTelA-TAO Early Optical Limits
  23. GRB 250403A: GMG Optical Observation
  24. GRB 250403A: 1.6m Mephisto multi-band optical detection
  25. GRB 250402A: Fermi GBM Observation
  26. GRB 250403A: SVOM/C-GFT optical observations
  27. GRB 250403A: GOTO detection of the optical afterglow
  28. GRB 250402A: Swift-XRT observations
  29. GRB 250403A : SVOM detection of a burst
  30. GRB 250403A: Fermi GBM Final Real-time Localization
  31. GRB 250225B: VLT host galaxy redshift z = 0.950
  32. GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  33. GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
  34. GRB 250402A: REM optical/NIR upper limits
  35. GRB 250402A: LCO optical counterpart detection
  36. GRB 250402A: refined SVOM/MXT data analysis
  37. The EP-WXT trigger 01709133862 is a flaring star
  38. EP250402a: Einstein Probe detection of a fast X-ray transient
  39. GRB 250402B: AstroSat CZTI detection of a short burst
  40. GRB 250402A: SVOM/VT optical counterpart
  41. GRB 250402A: SVOM detection of a burst
  42. GRB 250331C: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  43. GRB 250314A: ALMA detection
  44. GRB 250329B: Swift/UVOT Upper Limit
  45. GRB 250329A: Swift/UVOT Upper Limit
  46. GRB 250327B: Swift/UVOT Detection
  47. GRB 250327A: Swift/UVOT Upper Limits
  48. GRB 250331E: SVOM/GRM observation
  49. GRB 250327B: Kilonova-Catcher Observations
  50. GRB250331D: AbAO optical observations
  51. GRB 250331D: Fermi GBM observation
  52. GRB 250331C: Swift/UVOT Upper Limits
  53. GRB 250331B: Swift/UVOT Upper Limits
  54. GRB 250328A: AbAO AS-32 Optical Observations
  55. GRB 250219A: NOT candidate host galaxy detection
  56. GRB 250322B: GRBAlpha detection
  57. GRB 250331D: Swift-XRT observations
  58. GRB 250331C: Swift-XRT refined Analysis
  59. GRB 250331B: Swift-XRT refined Analysis
  60. GRB 250331B: Swift-XRT refined Analysis
  61. GRB 250322B possible detection by the AstroSat Satellite
  62. GRB 250330B: SVOM/GRM observation of a short burst
  63. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 2)
  64. Fermi GRB 250331E: Global MASTER-Net observations report
  65. Fermi GRB 250331D: Global MASTER-Net observations report
  66. GRB 250330B: EIRSAT-1 GMOD Detection
  67. GRB 250331E: Fermi GBM Final Real-time Localization
  68. GRB 250327A Swift-BAT refined analysis
  69. LIGO/Virgo/KAGRA S250331o: Updated Sky localization
  70. GRB 250329A: AbAO, Mondy and SAO RAS optical upper limits
  71. Fermi trigger No 765078057: Global MASTER-Net observations report
  72. GRB 250329B: CAHA 2.2m telescope optical limit
  73. GRB 250331D: Swift ToO observations
  74. Swift GRB 250331C: Global MASTER-Net observations report
  75. Swift GRB 250331B: Global MASTER-Net observations report
  76. GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
  77. Konus-Wind detection of GRB 250327B
  78. GRB 250331C: Enhanced Swift-XRT position
  79. IceCube-250330A: Upper limits from a search for additional neutrino events in IceCube
  80. LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
  81. GRB 250331B: Enhanced Swift-XRT position
  82. GRB 250320C : SVOM detection of a burst through offline search
  83. LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
  84. GRB 250329B: Swift-XRT confirmation of fading
  85. GRB 250330A: VLT/FORS2 Afterglow Detection
  86. GRB20250327B: 45th Parallel Observatory upper limit
  87. GRB 250328A: Swift/UVOT Detection
  88. GRB 250328A: Swift-XRT refined Analysis
  89. Fermi-LAT gamma-ray observations of IceCube-250330A
  90. SVOM/sb25033102 is a false trigger
  91. GRB 250330A: Fermi GBM Observation
  92. GRB 250331C: COLIBRÍ/DDRAGO optical upper limit
  93. GRB 250331B: COLIBRÍ/DDRAGO optical upper limit
  94. GRB 250331D: Fermi GBM Final Real-time Localization
  95. GRB 250331C: Prompt enhanced Swift-XRT position
  96. GRB 250331C: Swift detection of a burst
  97. GRB 250331B: Swift detection of a burst
  98. GRB 250330A: SVOM/VT optical upper limit
  99. GRB 250331A: MAXI/GSC detection
  100. SVOM/sb25033102: SVOM detection of an X-ray transient

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