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

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