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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"

20968 results found.

  1. GRB 250818B: Kilonova-Catcher optical afterglow detection
  2. GRB 250818B: Liverpool Telescope optical detections
  3. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  4. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  5. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  6. GRB 250818B: Swift/UVOT Detection
  7. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  8. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  9. GRB 250818B: TRT Optical Observation
  10. Fermi GRB 250816A: Global MASTER-Net observations report
  11. GRB 250818B: SAO RAS optical observations
  12. Swift GRB 250818A: Global MASTER-Net observations report
  13. GRB 250818B: NOT optical observations
  14. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  15. Fermi trigger No 776849714: Global MASTER-Net observations report
  16. GRB 250818B: KAIT optical observations
  17. GRB 250818A: Swift/UVOT Upper Limits
  18. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  19. GRB 250813B: SVOM/ECLAIRs refined analysis
  20. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  21. GRB 250818B: SVOM/VT optical observation
  22. GRB 250814A: Further GRAWITA TNG NIR observations
  23. GRB 250818B: Swift-XRT afterglow detection
  24. GRB 250818B: GOTO optical counterpart candidate
  25. sb25081602: Swift-XRT observations
  26. Fermi GRB 250814B: Global MASTER-Net observations report
  27. GRB 250813B: Liverpool Telescope optical upper limits
  28. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  29. GRB 250814A: GRAWITA TNG NIR observations
  30. GRB 250812A: SVOM/VT optical continued observation
  31. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  32. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  33. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  34. GRB 250814A: P200/WIRC observations of the afterglow candidate
  35. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  36. GRB 250814A: Possible afterglow candidate from P200/WIRC
  37. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  38. Fermi trigger No 776818276: Global MASTER-Net observations report
  39. Swift GRB250814.32: Global MASTER-Net observations report
  40. GRB 250814A: J-band upper limit from WINTER
  41. GRB 250813B: NOT observations of the optical afterglow
  42. GRB 250813B: SVOM/VT optical observations
  43. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  44. GRB 250814A: DDOTI Optical Upper Limit
  45. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  46. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  47. GRB 250813B: Ondrejov D50 fast decay
  48. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  49. EP250812a: Nickel optical upper limit
  50. GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
  51. GRB250812a: STEP/T80S Indication of slow decay of afterglow
  52. EP250812a: NOT, NTT, and GS observations
  53. GRB 250812A: Swift/UVOT Detection
  54. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  55. EP250812a: SVOM/VT optical counterpart
  56. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  57. IceCube Alert 250813.14: Global MASTER-Net observations report
  58. GRB 250812A: Swift ToO observations
  59. EP 250812a: GOTO optical upper limit
  60. GRB 250812A: Kilonova-Catcher optical afterglow detection
  61. EP250812a: Swift-XRT counterpart detection
  62. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  63. GRB 250812A: SVOM/VT optical afterglow confirmation
  64. GRB 250812A: Swift-XRT afterglow detection
  65. GRB 250812A: TRT likely optical counterpart detection
  66. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  67. GRB 250809A: Swift/UVOT Detection
  68. GRB 250702B: Chandra X-ray Detection
  69. EP250807a: Global MASTER-Net observations report
  70. Fermi GRB 250808A: Global MASTER-Net observations report
  71. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  72. GRB 250808A: Swift-XRT candidate counterpart detection
  73. GRB 250807A: SVOM/VT optical continued observation
  74. EP-WXT trigger 01709195487: KAIT confirmation of the stellar flare
  75. GRB 250807B: Swift/UVOT Detection
  76. GRB 250807B: Kilonova-Catcher optical afterglow detection
  77. GRB 250807A: Swift/UVOT Detection
  78. EP250807a: NTT z-band optical upper limit
  79. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  80. Swift GRB250807.45: Global MASTER-Net observations report
  81. GRB 250807B: NTT optical observations
  82. EP250807a: EP-WXT detection of a fast X-ray transient
  83. EP 250807.979: GOTO optical upper limit
  84. GRB 250807A: SVOM/VT optical observation
  85. EP250806a: Upper limit from Fermi-GBM Observations
  86. Swift GRB250807.65: Global MASTER-Net observations report
  87. GRB 250805A: Kilonova-Catcher optical upper limits
  88. GRB 250805A: Swift/UVOT Upper Limits
  89. GRB 250806A: Swift/UVOT U-band detection
  90. IceCube Alert 250804.84: Global MASTER-Net observations report
  91. EP#01709198415/EP250806a: Swift-XRT observations
  92. EP250806a: Global MASTER-Net observations report
  93. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  94. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  95. GRB 250806A: J-band upper limit from WINTER
  96. GRB 250806A: KAIT optical upper limit
  97. GRB 250806A: Kilonova-Catcher optical upper limits
  98. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  99. GRB 250805A: ESO/VLT observations
  100. GRB 250804B: Swift-XRT observations

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