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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"

5516 results found.

  1. GRB 251002A: NIR observations with WINTER
  2. Fermi GBM Sub-Threshold Detection of GRB 250910A
  3. GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay
  4. GRB 251003A: COLIBRÍ photometric redshift
  5. GRB 251003A: GOTO detection of the optical counterpart
  6. GRB 251002A: GOTO detection of optical counterpart
  7. GRB 251003A: GTC/OSIRIS+ spectroscopic redshift z = 4.412
  8. GRB 251002A: AbAO optical observations
  9. GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
  10. GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
  11. GRB 251003A: LCOGT Optical Detection
  12. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  13. Swift GRB251003A: Global MASTER-Net observations report
  14. GRB 251001B: SVOM/VT optical observation
  15. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  16. GRB 250925A/EP250925a: EP-WXT detection
  17. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  18. GRB 250924A: Swift/UVOT Detection
  19. GRB 250924A: COLIBRÍ optical observations
  20. GRB 250924A: Swift detection of a burst with an optical counterpart
  21. Fermi GRB 250922B: Global MASTER-Net observations report
  22. Fermi trigger No 780156732: Global MASTER-Net observations report
  23. GRB 250922A: Fermi GBM Final Localization
  24. GRB 250920B: Enhanced Swift-XRT position
  25. GRB 250920C: GOTO optical counterpart candidate
  26. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  27. EP250919a: Global MASTER-Net observations report
  28. EP250916a: EP-FXT follow-up observation
  29. GRB 250916A: GOTO optical counterpart candidate
  30. GRB250912A: VLT/HAWK-I follow-up observations
  31. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  32. EP250910a: Global MASTER-Net observations report
  33. GRB 250910A: LCO optical upper limit
  34. EP250908c: Global MASTER-Net observations report
  35. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  36. EP250905a: Liverpool Telescope i-band upper limits
  37. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  38. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  39. IceCube Alert 250905.84: Global MASTER-Net observations report
  40. GRB 250905A: KAIT optical upper limit
  41. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  42. GRB 250904A: Prompt enhanced Swift-XRT position
  43. GRB 250904A: Swift detection of a burst
  44. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  45. GRB 250903A: LCO optical observation
  46. GRB 250903A: LCO optical afterglow detection
  47. EP250903a: LCO candidate counterpart discovery
  48. GRB 250903A: TRT optical counterpart detection
  49. EP250903a: Global MASTER-Net observations report
  50. EP250903a: TRT optical observations
  51. EP250903a: Einstein Probe detection of an X-ray transient
  52. EP 250827B: Detection of supernova counterpart by LCO.
  53. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  54. EP250827b: continued Liverpool Telescope observations
  55. Fermi GRB 250902B: Global MASTER-Net observations report
  56. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  57. GRB 250901A: EP-FXT follow-up observation
  58. EP250901a: Swift-XRT observations
  59. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  60. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  61. EP250901a: Mephisto optical upper limits
  62. EP250901a: Einstein Probe detection of an X-ray transient
  63. GRB 250831A: Swift-XRT counterpart detection
  64. GRB 250830B: MAXI/GSC detection
  65. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  66. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  67. Fermi GRB 250827A: Global MASTER-Net observations report
  68. EP250827a: Global MASTER-Net observations report
  69. Fermi GRB 250824B: Global MASTER-Net observations report
  70. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  71. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  72. GRB 250812A: SVOM/ECLAIRs refined analysis
  73. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  74. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  75. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  76. IPN triangulation of GRB 250814C (short)
  77. GRB 250818B: Liverpool Telescope optical detections
  78. GRB 250818B: Swift/UVOT Detection
  79. GRB 250818B: NOT optical observations
  80. Fermi trigger No 776849714: Global MASTER-Net observations report
  81. GRB 250818B: GOTO optical counterpart candidate
  82. sb25081602: Swift-XRT observations
  83. SVOM/sb25081602: detection of a likely X-ray transient
  84. GRB 250813B: Liverpool Telescope optical upper limits
  85. GRB 250814A: Further COLIBRÍ optical upper limit
  86. GRB 250814A: P200/WIRC observations of the afterglow candidate
  87. Fermi trigger No 776818276: Global MASTER-Net observations report
  88. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  89. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  90. EP250812a: Liverpool Telescope upper limits
  91. EP250812a: SVOM/VT optical counterpart
  92. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  93. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  94. IceCube Alert 250813.14: Global MASTER-Net observations report
  95. EP 250812a: GOTO optical upper limit
  96. EP250812a: Swift-XRT counterpart detection
  97. GRB 250812A: SVOM/VT optical afterglow confirmation
  98. GRB 250812A: SVOM detection of a faint long burst
  99. IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
  100. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry

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