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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"

5514 results found.

  1. GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay
  2. GRB 251003A: COLIBRÍ photometric redshift
  3. GRB 251003A: GOTO detection of the optical counterpart
  4. GRB 251002A: GOTO detection of optical counterpart
  5. GRB 251003A: GTC/OSIRIS+ spectroscopic redshift z = 4.412
  6. GRB 251002A: AbAO optical observations
  7. GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
  8. GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
  9. GRB 251003A: LCOGT Optical Detection
  10. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  11. Swift GRB251003A: Global MASTER-Net observations report
  12. GRB 251001B: SVOM/VT optical observation
  13. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  14. GRB 250925A/EP250925a: EP-WXT detection
  15. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  16. GRB 250924A: Swift/UVOT Detection
  17. GRB 250924A: COLIBRÍ optical observations
  18. GRB 250924A: Swift detection of a burst with an optical counterpart
  19. Fermi GRB 250922B: Global MASTER-Net observations report
  20. Fermi trigger No 780156732: Global MASTER-Net observations report
  21. GRB 250922A: Fermi GBM Final Localization
  22. GRB 250920B: Enhanced Swift-XRT position
  23. GRB 250920C: GOTO optical counterpart candidate
  24. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  25. EP250919a: Global MASTER-Net observations report
  26. EP250916a: EP-FXT follow-up observation
  27. GRB 250916A: GOTO optical counterpart candidate
  28. GRB250912A: VLT/HAWK-I follow-up observations
  29. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  30. EP250910a: Global MASTER-Net observations report
  31. GRB 250910A: LCO optical upper limit
  32. EP250908c: Global MASTER-Net observations report
  33. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  34. EP250905a: Liverpool Telescope i-band upper limits
  35. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  36. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  37. IceCube Alert 250905.84: Global MASTER-Net observations report
  38. GRB 250905A: KAIT optical upper limit
  39. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  40. GRB 250904A: Prompt enhanced Swift-XRT position
  41. GRB 250904A: Swift detection of a burst
  42. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  43. GRB 250903A: LCO optical observation
  44. GRB 250903A: LCO optical afterglow detection
  45. EP250903a: LCO candidate counterpart discovery
  46. GRB 250903A: TRT optical counterpart detection
  47. EP250903a: Global MASTER-Net observations report
  48. EP250903a: TRT optical observations
  49. EP250903a: Einstein Probe detection of an X-ray transient
  50. EP 250827B: Detection of supernova counterpart by LCO.
  51. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  52. EP250827b: continued Liverpool Telescope observations
  53. Fermi GRB 250902B: Global MASTER-Net observations report
  54. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  55. GRB 250901A: EP-FXT follow-up observation
  56. EP250901a: Swift-XRT observations
  57. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  58. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  59. EP250901a: Mephisto optical upper limits
  60. EP250901a: Einstein Probe detection of an X-ray transient
  61. GRB 250831A: Swift-XRT counterpart detection
  62. GRB 250830B: MAXI/GSC detection
  63. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  64. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  65. Fermi GRB 250827A: Global MASTER-Net observations report
  66. EP250827a: Global MASTER-Net observations report
  67. Fermi GRB 250824B: Global MASTER-Net observations report
  68. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  69. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  70. GRB 250812A: SVOM/ECLAIRs refined analysis
  71. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  72. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  73. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  74. IPN triangulation of GRB 250814C (short)
  75. GRB 250818B: Liverpool Telescope optical detections
  76. GRB 250818B: Swift/UVOT Detection
  77. GRB 250818B: NOT optical observations
  78. Fermi trigger No 776849714: Global MASTER-Net observations report
  79. GRB 250818B: GOTO optical counterpart candidate
  80. sb25081602: Swift-XRT observations
  81. SVOM/sb25081602: detection of a likely X-ray transient
  82. GRB 250813B: Liverpool Telescope optical upper limits
  83. GRB 250814A: Further COLIBRÍ optical upper limit
  84. GRB 250814A: P200/WIRC observations of the afterglow candidate
  85. Fermi trigger No 776818276: Global MASTER-Net observations report
  86. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  87. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  88. EP250812a: Liverpool Telescope upper limits
  89. EP250812a: SVOM/VT optical counterpart
  90. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  91. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  92. IceCube Alert 250813.14: Global MASTER-Net observations report
  93. EP 250812a: GOTO optical upper limit
  94. EP250812a: Swift-XRT counterpart detection
  95. GRB 250812A: SVOM/VT optical afterglow confirmation
  96. GRB 250812A: SVOM detection of a faint long burst
  97. IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
  98. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  99. IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
  100. EP250806a: Liverpool telescope optical upper limit

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