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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"

20518 results found.

  1. EP250302A: 1.3m DFOT optical afterglow detection
  2. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  3. EP250304a: REM NIR upper limits
  4. EP250302a: Mondy Continued Optical Observations
  5. EP250304a: TRT optical counterpart detection
  6. EP250304a: Global MASTER-Net observations report
  7. EP250302a: SVOM/VT optical observation
  8. EP250302a: SAO RAS optical observations
  9. EP250225a: the candidate optical counterpart is an AGN
  10. EP250302a: Kinder optical follow-up observations
  11. EP250302a: NUTTelA-TAO Early Measurments
  12. EP250302a: REM NIR upper limits
  13. IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect
  14. EP250302a: Mondy Observations and Optical Light Curve
  15. EP250302a: VLT/MUSE optical redshift z = 1.131
  16. EP250302A: VLT near-infrared observations
  17. EP250302A: VLT/X-shooter tentative redshift
  18. EP250302a: OHP/T193 optical and spectroscopic observations
  19. EP250302a: Global MASTER-Net observations report
  20. EP250302a: Xinglong F60B optical observation
  21. EP250302a: Swift-XRT observations of a fading X-ray source
  22. EP250302a: Einstein Probe detection of an X-ray transient
  23. EP250302a: SVOM/C-GFT optical observations
  24. GRB 250226A: GRANDMA Optical Observations
  25. EP250302a: Montarrenti Observatory optical detection
  26. Fermi GRB 250302A: Global MASTER-Net observations report
  27. EP250302a: FTW optical and NIR detection
  28. EP250302a: Nanshan/HMT optical counterpart detection
  29. LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
  30. GRB 250225B: VLT near-infrared afterglow confirmation
  31. EP250228a: Optical observations with Kinder and Swift/UVOT
  32. GRB 250226A: KAO Optical Upper Limit
  33. GRB 250226A: AbAO AS-32 Optical Upper Limit
  34. EP250227a: Global MASTER-Net observations report
  35. EP250223A: Upper limits from Fermi-GBM Observations
  36. EP250227a: TRT optical upper limit
  37. GRB 250225B: VLT/HAWKI near-infrared observations
  38. EP250227a: Optical upper limits with Kinder observations
  39. EP250227a: NOT optical observations
  40. EP250228a: updates on the EP observations
  41. EP250223a: J band upper limit by SYSU 80cm telescope
  42. EP250228a: Global MASTER-Net observations report
  43. GRB 250226A / EP250226a: LCO detection of the afterglow
  44. GRB 250225B: VLT/Xshooter imaging
  45. GRB 250205A / EP250205A: further radio observations with the VLA
  46. GRB 250226B: INTEGRAL SPI-ACS and PICsIT detection
  47. EP250226a/GRB 250226A: INTEGRAL SPI-ACS and PICsIT detection
  48. GRB 250225B: INTEGRAL SPI-ACS detection
  49. EP250225a: NOT optical candidate counterpart
  50. EP250226a/GRB 250226A:Xinglong optical follow-up observations
  51. EP250226a / GRB 250226A: SVOM/VT optical observations
  52. EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations
  53. EP250225a: TRT optical upper limits
  54. EP250226a/GRB 250226A: 1.6m Mephisto observations
  55. LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations
  56. EP250226a/GRB 250226A: Kinder optical follow-up observations
  57. Fermi GRB 250226B: Global MASTER-Net observations report
  58. GRB 250221A: ATCA Detections and Upper Limits
  59. GRB 250225B: REM NIR upper limits
  60. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  61. GRB 250225B: VLT optical and near-infrared candidate counterpart
  62. GRB 250225B: VLT/FORS2 candidate optical afterglow
  63. GRB 250221A: EP-FXT detection of the X-ray afterglow
  64. EP250226a/GRB 250226A: GSP detects optical counterpart
  65. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  66. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  67. EP250226a: Global MASTER-Net observations report
  68. Swift GRB 250225B: Global MASTER-Net observations report
  69. Fermi GRB 250226A: Global MASTER-Net observations report
  70. Fermi trigger No 762205158: Global MASTER-Net observations report
  71. EP250225a: Global MASTER-Net observations report
  72. EP250225a: GSP optical upper limit
  73. EP250225a: Einstein Probe detected of a fast X-ray transient
  74. Fermi GRB 250225A: Global MASTER-Net observations report
  75. EP250223a: GROWTH-India Telescope optical observations
  76. EP250215A: J band upper limit by SYSU 80cm telescope
  77. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  78. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  79. EP250223a: Kinder optical follow-up observations
  80. GRB 250207a: ATCA Radio Upper Limits
  81. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  82. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  83. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  84. EP250223a: GOTO optical afterglow detections
  85. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  86. EP250223a: REM NIR upper limit
  87. EP250223a: TRT optical afterglow observation
  88. EP250223a: refined analysis of the EP-WXT and FXT observations
  89. EP250223a: 1.6m Mephisto and 50cm array observations
  90. EP250223a: SVOM/VT optical observation
  91. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  92. EP250223a: OASDG optical observations
  93. EP250223a: LCO detection of the afterglow
  94. EP250223a: NOT redshift z = 2.756
  95. EP250223a: NOT optical afterglow candidate
  96. EP250223a: Global MASTER-Net observations report
  97. GRB 250221A: VLA radio detection
  98. Fermi GRB 250223A: Global MASTER-Net observations report
  99. Fermi trigger No 762020305: Global MASTER-Net observations report
  100. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation

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