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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"

22113 results found.

  1. EP250223a: CrAO ZTSH optical observation
  2. GRB 250225B: VLT optical and near-infrared candidate counterpart
  3. GRB 250225B: VLT/FORS2 candidate optical afterglow
  4. GRB 250225B: SVOM/GRM observation of a long burst
  5. EP250226a/GRB 250226A: GSP detects optical counterpart
  6. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  7. EP250226a / GRB 250226A: TRT optical counterpart observation
  8. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  9. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  10. EP250223a: GMG Optical Observation
  11. EP250225a: Einstein Probe detected of a fast X-ray transient
  12. GRB 250225B: Swift detection of a burst
  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: AstroSat CZTI non-detection and upper limits
  17. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  18. EP250223a: Kinder optical follow-up observations
  19. GRB 250207a: ATCA Radio Upper Limits
  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. GRB 250222A: SVOM/GRM observation of a burst
  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. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  29. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
  30. EP250223a: OASDG optical observations
  31. EP250223a: NOT optical afterglow candidate
  32. EP250223a: Einstein Probe detection of an X-ray transient
  33. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  34. GRB 250221A: Optical counterpart detection by LCO.
  35. EP250220a: EP-FXT follow-up observations
  36. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  37. GRB 250221A: GRANDMA/TAROT Detection
  38. GRB 250221A: Swift-XRT refined Analysis
  39. GRB 250221A: 1.6m Mephisto optical detection
  40. GRB 250221A: AKO Optical Upper Limit
  41. GRB 250221A: Swift/UVOT Detection
  42. EP250220a: Liverpool Telescope upper limits
  43. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  44. GRB 250221A: REM optical/NIR afterglow detection
  45. GRB 250221A: Enhanced Swift-XRT position
  46. EP250220a: 1.6m Mephisto observations
  47. EP250220a: Liverpool Telescope optical upper limits
  48. EP250220a: Optical upper limit with Kinder observations
  49. SVOM trigger sb25022102 is not an astrophysical event
  50. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  51. GRB 250221A: Swift detection of a burst with an optical counterpart
  52. EP250220a: Xinglong optical upper limit
  53. GRB 250219A: Swift/UVOT Upper Limits
  54. GRB 250219A: OHP/T193 optical upper limit
  55. GRB 250219A: NOT optical observations
  56. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  57. GRB 250219A: 1.6m Mephisto optical upper limits
  58. GRB 250219A: Swift-XRT observations
  59. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  60. SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
  61. GRB 250217C: Swift-XRT observations
  62. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  63. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  64. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  65. GRB 250217C: SVOM/GRM observation
  66. GRB 250217C: Fermi GBM Observation
  67. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  68. IPN triangulation of GRB 250217C (short)
  69. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  70. GRB 250213A: Swift-XRT observations
  71. LIGO/Virgo/KAGRA S250206dm: AZT-33IK Target Optical Observations
  72. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  73. GRANDMA/OPD observations of GRB250215A
  74. GRB 250215A / EP250215a: LCO detection of the afterglow
  75. EP250212a: FTW optical and NIR upper limits
  76. GRB 250215A: Swift/UVOT Upper Limits
  77. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  78. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  79. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  80. GRB 250215A: SVOM/GRM observation
  81. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  82. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  83. EP250207b: Xinglong optical upper limit
  84. EP250212a: Xinglong optical upper limit
  85. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  86. GRB 250205A: VIRT Optical Upper Limit
  87. GRB 250205A: Leavitt Observatory optical upper limit
  88. EP250207B: Chandra localization of the X-ray counterpart
  89. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  90. EP250207b: VLA radio upper limits
  91. EP250212a: Liverpool Telescope optical upper limits
  92. GRB250101A: Radio upper limits from GMRT observations
  93. EP trigger 10202399251 (possibly EP250212a): NOT J-band upper limit
  94. EP250207B: GTC z-band Observations
  95. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Follow-up of AT2025ber
  96. GRB 250205A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  97. EP250207b: NOT optical counterpart candidate
  98. LIGO/Virgo/KAGRA S250206dm: GECKO Continued Observaiton with 7DT
  99. LIGO/Virgo/KAGRA S250206dm: AT 2025bbo observations with WFST
  100. GRB 250205A / EP250205A: radio detection with the VLA

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