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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. Swift GRB 250331B: Global MASTER-Net observations report
  2. GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
  3. Konus-Wind detection of GRB 250327B
  4. GRB 250331C: Enhanced Swift-XRT position
  5. IceCube-250330A: Upper limits from a search for additional neutrino events in IceCube
  6. LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
  7. GRB 250331B: Enhanced Swift-XRT position
  8. GRB 250320C : SVOM detection of a burst through offline search
  9. LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
  10. GRB 250329B: Swift-XRT confirmation of fading
  11. GRB 250330A: VLT/FORS2 Afterglow Detection
  12. GRB20250327B: 45th Parallel Observatory upper limit
  13. GRB 250328A: Swift/UVOT Detection
  14. GRB 250328A: Swift-XRT refined Analysis
  15. Fermi-LAT gamma-ray observations of IceCube-250330A
  16. SVOM/sb25033102 is a false trigger
  17. GRB 250330A: Fermi GBM Observation
  18. GRB 250331C: COLIBRÍ/DDRAGO optical upper limit
  19. GRB 250331B: COLIBRÍ/DDRAGO optical upper limit
  20. GRB 250331D: Fermi GBM Final Real-time Localization
  21. GRB 250331C: Prompt enhanced Swift-XRT position
  22. GRB 250331C: Swift detection of a burst
  23. GRB 250331B: Swift detection of a burst
  24. GRB 250330A: SVOM/VT optical upper limit
  25. GRB 250331A: MAXI/GSC detection
  26. SVOM/sb25033102: SVOM detection of an X-ray transient
  27. GRB 250314A: VLA detection
  28. LIGO/Virgo/KAGRA S250331o: Identification of a GW compact binary merger candidate
  29. Fermi GRB 250330B: Global MASTER-Net observations report
  30. GRB 250330B: Fermi GBM Final Real-time Localization
  31. Fermi GRB 250330A: Global MASTER-Net observations report
  32. GRB 250330A: BOOTES-7 early optical upper limit
  33. GRB 250330A: Swift/UVOT Upper Limits
  34. GRB 250330A: Swift-XRT afterglow detection
  35. GRB 250328A: 1.6m Mephisto optical observations
  36. GRB 250329B: SVOM/COLIBRÍ (F-GFT) optical upper limit
  37. GRB 250330A: Fermi GBM Final Localization
  38. IceCube-250330A - IceCube observation of a high-energy neutrino candidate track-like event
  39. IceCube Alert 250330.35: Global MASTER-Net observations report
  40. GRB 250330A: VLT/FORS2 Optical Observations
  41. GRB 250330A: Prompt Swift-XRT position
  42. GRB 250329B: Swift-XRT afterglow detection
  43. GRB 250330A: Swift detection of a burst
  44. Swift GRB250330.26: Global MASTER-Net observations report
  45. GRB 250328A: A fading optical afterglow confirmed by SVOM/VT
  46. GRB 250329B: SVOM/C-GFT optical upper limit
  47. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
  48. GRB 250327B: ALMA detection
  49. GRB 250327B: VLA detection
  50. GRB 250329B: SVOM/VT optical upper limit
  51. GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations
  52. GRB 250329B: 1.6m Mephisto Optical Upper Limits
  53. LIGO/Virgo/KAGRA S250329fl: 2 counterpart neutrino candidate events from an IceCube neutrino search
  54. GRB250329A: REM optical afterglow detection
  55. GRB 250329B: GWAC-F50A optical upper limit
  56. GRB 250329B: SVOM detection of a faint transient
  57. GRB 250329A: Swift-XRT afterglow detection
  58. GRB 250328A: SVOM/VT optical observation
  59. GRB 250329A: Fading optical counterpart detection by LCO.
  60. GRB 250328A: SVOM/C-GFT optical upper limit
  61. GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
  62. GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
  63. GRB 250329A: VLT/X-shooter redshift z = 2.921
  64. GRB 250329A: SVOM/VT optical counterpart confirmation
  65. GRB 250329A: SVOM detection of a burst
  66. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  67. GRB 250327B: J-band observations with WINTER
  68. GRB 250327B: MASTER detection of OT rebrightening
  69. GRB 250327B: LCO optical counterpart detection
  70. GRB 250328A: GWAC-F50A optical upper limit
  71. GRB 250328A: SVOM detection of a burst
  72. FRB 20250316A: FTW optical observations
  73. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  74. EP250302a: SPI-ACS/INTEGRAL Upper Limit
  75. GRB 250327B: CrAO and SAO RAS Optical Observations
  76. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  77. GRB 250327B: further optical observations by LCOGT
  78. EP250315a: Pan-STARRS r and i-band imaging and photometry
  79. GRB 250327b: Liverpool Telescope optical observations
  80. GRB 250322A: GRANDMA/TNOT optical upper limits
  81. LIGO/Virgo/KAGRA S250328ae: Updated Sky localization
  82. GRB 250327A: SVOM/VT upper limits on the XRT position
  83. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  84. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  85. GRB 250327B: Las Cumbres optical counterpart detection
  86. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  87. GRB 250327B: 1.6m Mephisto optical observations
  88. GRB 250327B: NOT spectroscopic redshift z = 3.035
  89. GRB 250327A: Swift-XRT refined Analysis
  90. GRB 250327B: GOTO optical counterpart detection
  91. GRB 250327B: SVOM/VT optically bright counterpart
  92. GRB 250327B: SAO RAS optical candidate
  93. GRB 250327B: SVOM detection of a burst
  94. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  95. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  96. GRB 250327A: J-band observations with WINTER
  97. GRB 250327A: SVOM/VT optical candidate
  98. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  99. GRB 250327A: Fermi GBM observation
  100. Fermi GRB 250327A: Global MASTER-Net observations report

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