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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"

20951 results found.

  1. EP250402a: EP-FXT follow-up observations
  2. GRB 250403A: Swift-XRT observations
  3. GRB 250322A: 10 GHz VLA radio upper limits
  4. Fermi GRB 250403A: Global MASTER-Net observations report
  5. GRB 250403A: GOTO optical counterpart follow-up observations
  6. GRB 250402A: NUTTelA-TAO Early Optical Limits
  7. GRB 250403A: 1.6m Mephisto multi-band optical detection
  8. GRB 250403A: SVOM/C-GFT optical observations
  9. GRB 250403A: GOTO detection of the optical afterglow
  10. GRB 250402A: Swift-XRT observations
  11. GRB 250225B: VLT host galaxy redshift z = 0.950
  12. GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  13. GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
  14. GRB 250402A: REM optical/NIR upper limits
  15. GRB 250402A: LCO optical counterpart detection
  16. GRB 250402A: refined SVOM/MXT data analysis
  17. EP250402a: Einstein Probe detection of a fast X-ray transient
  18. GRB 250331C: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  19. GRB 250314A: ALMA detection
  20. GRB 250329B: Swift/UVOT Upper Limit
  21. GRB 250329A: Swift/UVOT Upper Limit
  22. GRB 250327B: Swift/UVOT Detection
  23. GRB 250327A: Swift/UVOT Upper Limits
  24. GRB 250327B: Kilonova-Catcher Observations
  25. GRB250331D: AbAO optical observations
  26. GRB 250331C: Swift/UVOT Upper Limits
  27. GRB 250331B: Swift/UVOT Upper Limits
  28. GRB 250328A: AbAO AS-32 Optical Observations
  29. GRB 250219A: NOT candidate host galaxy detection
  30. GRB 250331D: Swift-XRT observations
  31. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 2)
  32. Fermi GRB 250331E: Global MASTER-Net observations report
  33. Fermi GRB 250331D: Global MASTER-Net observations report
  34. Fermi trigger No 765078057: Global MASTER-Net observations report
  35. GRB 250331D: Swift ToO observations
  36. Swift GRB 250331C: Global MASTER-Net observations report
  37. Swift GRB 250331B: Global MASTER-Net observations report
  38. GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
  39. LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
  40. LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
  41. GRB 250330A: VLT/FORS2 Afterglow Detection
  42. GRB20250327B: 45th Parallel Observatory upper limit
  43. GRB 250328A: Swift/UVOT Detection
  44. Fermi-LAT gamma-ray observations of IceCube-250330A
  45. GRB 250330A: SVOM/VT optical upper limit
  46. GRB 250314A: VLA detection
  47. Fermi GRB 250330B: Global MASTER-Net observations report
  48. Fermi GRB 250330A: Global MASTER-Net observations report
  49. GRB 250330A: BOOTES-7 early optical upper limit
  50. GRB 250330A: Swift/UVOT Upper Limits
  51. GRB 250330A: Swift-XRT afterglow detection
  52. GRB 250328A: 1.6m Mephisto optical observations
  53. IceCube Alert 250330.35: Global MASTER-Net observations report
  54. GRB 250330A: VLT/FORS2 Optical Observations
  55. Swift GRB250330.26: Global MASTER-Net observations report
  56. GRB 250329B: SVOM/C-GFT optical upper limit
  57. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
  58. GRB 250327B: ALMA detection
  59. GRB 250327B: VLA detection
  60. GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations
  61. GRB 250329B: 1.6m Mephisto Optical Upper Limits
  62. GRB250329A: REM optical afterglow detection
  63. GRB 250329B: GWAC-F50A optical upper limit
  64. GRB 250328A: SVOM/VT optical observation
  65. GRB 250329A: Fading optical counterpart detection by LCO.
  66. GRB 250328A: SVOM/C-GFT optical upper limit
  67. GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
  68. GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
  69. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  70. GRB 250327B: J-band observations with WINTER
  71. GRB 250327B: LCO optical counterpart detection
  72. GRB 250328A: GWAC-F50A optical upper limit
  73. FRB 20250316A: FTW optical observations
  74. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  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. GRB 250327b: Liverpool Telescope optical observations
  79. GRB 250327A: SVOM/VT upper limits on the XRT position
  80. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  81. GRB 250327B: 1.6m Mephisto optical observations
  82. GRB 250327B: GOTO optical counterpart detection
  83. GRB 250327B: SAO RAS optical candidate
  84. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  85. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  86. GRB 250327A: J-band observations with WINTER
  87. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  88. Fermi GRB 250327A: Global MASTER-Net observations report
  89. Swift GRB 250327A: Global MASTER-Net observations report
  90. GRB 250327A: DDOTI Optical Observations
  91. GRB 250327A: COLIBRÍ optical upper limit
  92. Fermi trigger No 764700395: Global MASTER-Net observations report
  93. EP250321a: Mondy AZT-33IK Continued Optical Observations
  94. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  95. GRB 250322A: third epoch of NOT optical observations
  96. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  97. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  98. GRB 250322A: further NOT optical observations
  99. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  100. GRB 250322A: Swift/UVOT Upper Limits

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