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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"

20956 results found.

  1. GRB 250221A: EP-FXT detection of the X-ray afterglow
  2. EP250226a/GRB 250226A: GSP detects optical counterpart
  3. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  4. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  5. EP250226a: Global MASTER-Net observations report
  6. Swift GRB 250225B: Global MASTER-Net observations report
  7. Fermi GRB 250226A: Global MASTER-Net observations report
  8. Fermi trigger No 762205158: Global MASTER-Net observations report
  9. EP250225a: Global MASTER-Net observations report
  10. EP250225a: GSP optical upper limit
  11. EP250225a: Einstein Probe detected of a fast X-ray transient
  12. Fermi GRB 250225A: Global MASTER-Net observations report
  13. EP250223a: GROWTH-India Telescope optical observations
  14. EP250215A: J band upper limit by SYSU 80cm telescope
  15. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  16. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  17. EP250223a: Kinder optical follow-up observations
  18. GRB 250207a: ATCA Radio Upper Limits
  19. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  20. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  21. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  22. EP250223a: GOTO optical afterglow detections
  23. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  24. EP250223a: REM NIR upper limit
  25. EP250223a: TRT optical afterglow observation
  26. EP250223a: refined analysis of the EP-WXT and FXT observations
  27. EP250223a: 1.6m Mephisto and 50cm array observations
  28. EP250223a: SVOM/VT optical observation
  29. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  30. EP250223a: OASDG optical observations
  31. EP250223a: LCO detection of the afterglow
  32. EP250223a: NOT redshift z = 2.756
  33. EP250223a: NOT optical afterglow candidate
  34. EP250223a: Global MASTER-Net observations report
  35. GRB 250221A: VLA radio detection
  36. Fermi GRB 250223A: Global MASTER-Net observations report
  37. Fermi trigger No 762020305: Global MASTER-Net observations report
  38. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  39. GRB 250221A: continued Mondy optical observations, brightening afterglow
  40. GRB 250221A: Optical counterpart detection by LCO.
  41. GRB 250221A: Mondy optical observations
  42. GRB 250221A: Assy optical observations
  43. EP250220a: FTW optical and NIR observations and upper limits
  44. EP250220a: EP-FXT follow-up observations
  45. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  46. Fermi trigger No 761805304: Global MASTER-Net observations report
  47. GRB 250221A: NOT optical observations
  48. GRB 250221A: 1.6m Mephisto optical detection
  49. GRB 250221A: Swift/UVOT Detection
  50. EP250220a: Liverpool Telescope upper limits
  51. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  52. GRB 250221A: REM optical/NIR afterglow detection
  53. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  54. EP250220a: 1.6m Mephisto observations
  55. EP250220a: Optical upper limit with Kinder observations
  56. Swift GRB250221.15: Global MASTER-Net observations report
  57. EP250220a: Global MASTER-Net observations report
  58. GRB 250219A: Swift/UVOT Upper Limits
  59. GRB 250219A: OHP/T193 optical upper limit
  60. GRB 250219A: NOT optical observations
  61. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  62. GRB 250219A: 1.6m Mephisto optical upper limits
  63. GRB 250219A: SVOM/VT optical counterpart
  64. GRB 250219A: Swift-XRT observations
  65. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  66. GRB 250219A: Swift ToO observations
  67. GRB 250217C: Swift-XRT observations
  68. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  69. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  70. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  71. GRB 250217C: Tiled Swift observations
  72. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  73. GRB 250213A: Swift-XRT observations
  74. LIGO/Virgo/KAGRA S250206dm: AZT-33IK Target Optical Observations
  75. Fermi GRB 250217C: Global MASTER-Net observations report
  76. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  77. Fermi GRB 250217A: Global MASTER-Net observations report
  78. GRANDMA/OPD observations of GRB250215A
  79. Fermi GRB 250216A: Global MASTER-Net observations report
  80. GRB 250215A / EP250215a: LCO detection of the afterglow
  81. EP250212a: FTW optical and NIR upper limits
  82. GRB 250215A: Swift/UVOT Upper Limits
  83. EP250215a / GRB 250215A : NOT optical observations
  84. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  85. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  86. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  87. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  88. EP250215a: Global MASTER-Net observations report
  89. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  90. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  91. Fermi GRB 250215A: Global MASTER-Net observations report
  92. Fermi trigger No 761206993: Global MASTER-Net observations report
  93. GRB 250213A：SVOM/VT optical candidate
  94. Fermi GRB 250214A: Global MASTER-Net observations report
  95. GRB 250213A: Swift ToO observations
  96. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  97. EP250212a: Global MASTER-Net observations report
  98. GRB 250205A: Leavitt Observatory optical upper limit
  99. EP250207B: Chandra localization of the X-ray counterpart
  100. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies

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