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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 250327A Swift-BAT refined analysis
  2. LIGO/Virgo/KAGRA S250331o: Updated Sky localization
  3. GRB 250329A: AbAO, Mondy and SAO RAS optical upper limits
  4. Fermi trigger No 765078057: Global MASTER-Net observations report
  5. GRB 250329B: CAHA 2.2m telescope optical limit
  6. GRB 250331D: Swift ToO observations
  7. Swift GRB 250331C: Global MASTER-Net observations report
  8. Swift GRB 250331B: Global MASTER-Net observations report
  9. GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
  10. Konus-Wind detection of GRB 250327B
  11. GRB 250331C: Enhanced Swift-XRT position
  12. IceCube-250330A: Upper limits from a search for additional neutrino events in IceCube
  13. LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
  14. GRB 250331B: Enhanced Swift-XRT position
  15. GRB 250320C : SVOM detection of a burst through offline search
  16. LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
  17. GRB 250329B: Swift-XRT confirmation of fading
  18. GRB 250330A: VLT/FORS2 Afterglow Detection
  19. GRB20250327B: 45th Parallel Observatory upper limit
  20. GRB 250328A: Swift/UVOT Detection
  21. GRB 250328A: Swift-XRT refined Analysis
  22. Fermi-LAT gamma-ray observations of IceCube-250330A
  23. SVOM/sb25033102 is a false trigger
  24. GRB 250330A: Fermi GBM Observation
  25. GRB 250331C: COLIBRÍ/DDRAGO optical upper limit
  26. GRB 250331B: COLIBRÍ/DDRAGO optical upper limit
  27. GRB 250331D: Fermi GBM Final Real-time Localization
  28. GRB 250331C: Prompt enhanced Swift-XRT position
  29. GRB 250331C: Swift detection of a burst
  30. GRB 250331B: Swift detection of a burst
  31. GRB 250330A: SVOM/VT optical upper limit
  32. GRB 250331A: MAXI/GSC detection
  33. SVOM/sb25033102: SVOM detection of an X-ray transient
  34. GRB 250314A: VLA detection
  35. LIGO/Virgo/KAGRA S250331o: Identification of a GW compact binary merger candidate
  36. Fermi GRB 250330B: Global MASTER-Net observations report
  37. GRB 250330B: Fermi GBM Final Real-time Localization
  38. Fermi GRB 250330A: Global MASTER-Net observations report
  39. GRB 250330A: BOOTES-7 early optical upper limit
  40. GRB 250330A: Swift/UVOT Upper Limits
  41. GRB 250330A: Swift-XRT afterglow detection
  42. GRB 250328A: 1.6m Mephisto optical observations
  43. GRB 250329B: SVOM/COLIBRÍ (F-GFT) optical upper limit
  44. GRB 250330A: Fermi GBM Final Localization
  45. IceCube-250330A - IceCube observation of a high-energy neutrino candidate track-like event
  46. IceCube Alert 250330.35: Global MASTER-Net observations report
  47. GRB 250330A: VLT/FORS2 Optical Observations
  48. GRB 250330A: Prompt Swift-XRT position
  49. GRB 250329B: Swift-XRT afterglow detection
  50. GRB 250330A: Swift detection of a burst
  51. Swift GRB250330.26: Global MASTER-Net observations report
  52. GRB 250328A: A fading optical afterglow confirmed by SVOM/VT
  53. GRB 250329B: SVOM/C-GFT optical upper limit
  54. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
  55. GRB 250327B: ALMA detection
  56. GRB 250327B: VLA detection
  57. GRB 250329B: SVOM/VT optical upper limit
  58. GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations
  59. GRB 250329B: 1.6m Mephisto Optical Upper Limits
  60. LIGO/Virgo/KAGRA S250329fl: 2 counterpart neutrino candidate events from an IceCube neutrino search
  61. GRB250329A: REM optical afterglow detection
  62. GRB 250329B: GWAC-F50A optical upper limit
  63. GRB 250329B: SVOM detection of a faint transient
  64. GRB 250329A: Swift-XRT afterglow detection
  65. GRB 250328A: SVOM/VT optical observation
  66. GRB 250329A: Fading optical counterpart detection by LCO.
  67. GRB 250328A: SVOM/C-GFT optical upper limit
  68. GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
  69. GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
  70. GRB 250329A: VLT/X-shooter redshift z = 2.921
  71. GRB 250329A: SVOM/VT optical counterpart confirmation
  72. GRB 250329A: SVOM detection of a burst
  73. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  74. GRB 250327B: J-band observations with WINTER
  75. GRB 250327B: MASTER detection of OT rebrightening
  76. GRB 250327B: LCO optical counterpart detection
  77. GRB 250328A: GWAC-F50A optical upper limit
  78. GRB 250328A: SVOM detection of a burst
  79. FRB 20250316A: FTW optical observations
  80. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  81. EP250302a: SPI-ACS/INTEGRAL Upper Limit
  82. GRB 250327B: CrAO and SAO RAS Optical Observations
  83. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  84. GRB 250327B: further optical observations by LCOGT
  85. EP250315a: Pan-STARRS r and i-band imaging and photometry
  86. GRB 250327b: Liverpool Telescope optical observations
  87. GRB 250322A: GRANDMA/TNOT optical upper limits
  88. LIGO/Virgo/KAGRA S250328ae: Updated Sky localization
  89. GRB 250327A: SVOM/VT upper limits on the XRT position
  90. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  91. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  92. GRB 250327B: Las Cumbres optical counterpart detection
  93. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  94. GRB 250327B: 1.6m Mephisto optical observations
  95. GRB 250327B: NOT spectroscopic redshift z = 3.035
  96. GRB 250327A: Swift-XRT refined Analysis
  97. GRB 250327B: GOTO optical counterpart detection
  98. GRB 250327B: SVOM/VT optically bright counterpart
  99. GRB 250327B: SAO RAS optical candidate
  100. GRB 250327B: SVOM detection of a burst

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